Sync from Piper @425656941

PROTOBUF_SYNC_PIPER
2022-02-01 18:24:53 +00:00 · 2022-02-01 18:24:53 +00:00 · ab4585a695
parent 1f66b1b032 d0a2c395e9
commit ab4585a695
644 changed files with 31898 additions and 25241 deletions
--- a/.github/mergeable.yml
+++ b/.github/mergeable.yml
@ -9,10 +9,10 @@ mergeable:
          - and:
            - must_include:
                regex: 'release notes: yes'
-                message: 'Please include release notes: yes'
+                message: 'Include release notes: yes'
            - must_include:
                regex: '^(autotools|bazel|c#|c\+\+|cleanup|cmake|conformance tests|integration|go|java|javascript|objective-c|php|protoc|python|ruby|kotlin)'
-                message: 'Please include at least a language label (e.g., c++, java, python). Or apply one of the following labels: autotools, bazel, cmake, cleanup, conformance tests, integration, protoc.'
+                message: 'at least a language label (e.g., c++, java, python). Or apply one of the following labels: autotools, bazel, cmake, cleanup, conformance tests, integration, protoc.'
          - must_include:
              regex: 'release notes: no'
-              message: 'Please include release notes: no'
+              message: 'Include release notes: no'
--- a/265
+++ b/265
@ -2,11 +2,13 @@

 load("@bazel_skylib//rules:common_settings.bzl", "string_flag")
 load("@rules_cc//cc:defs.bzl", "cc_binary", "cc_library", "cc_test", "objc_library", native_cc_proto_library = "cc_proto_library")
+load("@rules_pkg//:pkg.bzl", "pkg_zip")
+load("@rules_pkg//:mappings.bzl", "pkg_attributes", "pkg_files")
 load("@rules_proto//proto:defs.bzl", "proto_lang_toolchain", "proto_library")
 load("@rules_python//python:defs.bzl", "py_library")
 load("@rules_java//java:defs.bzl", "java_binary", "java_lite_proto_library", "java_proto_library")
 load(":cc_proto_blacklist_test.bzl", "cc_proto_blacklist_test")
-
+load(":protobuf_release.bzl", "package_naming")
 licenses(["notice"])

 exports_files(["LICENSE"])
@ -26,7 +28,6 @@ ZLIB_DEPS = ["@zlib//:zlib"]
 ################################################################################

 MSVC_COPTS = [
-    "/DHAVE_PTHREAD",
    "/wd4018",  # -Wno-sign-compare
    "/wd4065",  # switch statement contains 'default' but no 'case' labels
    "/wd4146",  # unary minus operator applied to unsigned type, result still unsigned
@ -46,7 +47,6 @@ MSVC_COPTS = [
 COPTS = select({
    ":msvc": MSVC_COPTS,
    "//conditions:default": [
-        "-DHAVE_PTHREAD",
        "-DHAVE_ZLIB",
        "-Wmissing-field-initializers",
        "-Woverloaded-virtual",
@ -65,6 +65,13 @@ create_compiler_config_setting(
    ],
 )

+# Android NDK builds can specify different crosstool_top flags to choose which
+# STL they use for C++. We need these multiple variants to catch all of those
+# versions of crosstool_top and reliably detect Android.
+#
+# For more info on the various crosstool_tops used by NDK Bazel builds, see:
+# https://docs.bazel.build/versions/master/android-ndk.html#configuring-the-stl
+
 config_setting(
    name = "android",
    values = {
@ -76,6 +83,17 @@ config_setting(
    ],
 )

+config_setting(
+    name = "android-stlport",
+    values = {
+        "crosstool_top": "@androidndk//:toolchain-stlport",
+    },
+    visibility = [
+        # Public, but Protobuf only visibility.
+        "//:__subpackages__",
+    ],
+)
+
 config_setting(
    name = "android-libcpp",
    values = {
@ -98,11 +116,24 @@ config_setting(
    ],
 )

+config_setting(
+    name = "android-default",
+    values = {
+        "crosstool_top": "@androidndk//:default_crosstool",
+    },
+    visibility = [
+        # Public, but Protobuf only visibility.
+        "//:__subpackages__",
+    ],
+)
+
 # Android and MSVC builds do not need to link in a separate pthread library.
 LINK_OPTS = select({
    ":android": [],
+    ":android-stlport": [],
    ":android-libcpp": [],
    ":android-gnu-libstdcpp": [],
+    ":android-default": [],
    ":msvc": [
        # Suppress linker warnings about files with no symbols defined.
        "-ignore:4221",
@ -147,6 +178,7 @@ cc_library(
        "src/google/protobuf/message_lite.cc",
        "src/google/protobuf/parse_context.cc",
        "src/google/protobuf/repeated_field.cc",
+        "src/google/protobuf/repeated_ptr_field.cc",
        "src/google/protobuf/stubs/bytestream.cc",
        "src/google/protobuf/stubs/common.cc",
        "src/google/protobuf/stubs/int128.cc",
@ -488,6 +520,70 @@ cc_binary(
    deps = [":protoc_lib"],
 )

+
+################################################################################
+# Generates protoc release artifacts.
+################################################################################
+
+genrule(
+    name = "protoc_readme",
+    visibility = ["//visibility:private"],
+    cmd = """
+echo "Protocol Buffers - Google's data interchange format
+Copyright 2008 Google Inc.
+https://developers.google.com/protocol-buffers/
+This package contains a precompiled binary version of the protocol buffer
+compiler (protoc). This binary is intended for users who want to use Protocol
+Buffers in languages other than C++ but do not want to compile protoc
+themselves. To install, simply place this binary somewhere in your PATH.
+If you intend to use the included well known types then don't forget to
+copy the contents of the 'include' directory somewhere as well, for example
+into '/usr/local/include/'.
+Please refer to our official github site for more installation instructions:
+  https://github.com/protocolbuffers/protobuf" > $@
+    """,
+    outs = ["readme.txt"],
+)
+
+# plugin.proto is excluded from this list because it belongs in a nested folder (protobuf/compiler/plugin.proto)
+pkg_files(
+    name = "wkt_protos_files",
+    srcs =  [value[0] for value in WELL_KNOWN_PROTO_MAP.values() if not value[0].endswith("plugin.proto")],
+    visibility = ["//visibility:private"],
+    prefix = "include/google/protobuf",
+)
+
+pkg_files(
+    name = "compiler_plugin_protos_files",
+    srcs =  ["src/google/protobuf/compiler/plugin.proto"],
+    visibility = ["//visibility:private"],
+    prefix = "include/google/protobuf/compiler",
+)
+
+pkg_files(
+    name = "protoc_files",
+    srcs =  [":protoc"],
+    attributes = pkg_attributes(mode = "0555"),
+    visibility = ["//visibility:private"],
+    prefix = "bin/",
+)
+
+package_naming(
+    name = "protoc_pkg_naming",
+)
+
+pkg_zip(
+    name = "protoc_release",
+    package_file_name = "protoc-{version}-{platform}.zip",
+    package_variables = ":protoc_pkg_naming",
+    srcs = [
+        ":protoc_files",
+        ":wkt_protos_files",
+        ":compiler_plugin_protos_files",
+        "readme.txt",
+    ],
+)
+
 ################################################################################
 # Tests
 ################################################################################
@ -560,6 +656,8 @@ RELATIVE_TEST_PROTOS = [
 TEST_PROTOS = ["src/" + s for s in RELATIVE_TEST_PROTOS]

 GENERIC_RELATIVE_TEST_PROTOS = [
+    "google/protobuf/map_proto2_unittest.proto",
+    "google/protobuf/map_unittest.proto",
    "google/protobuf/unittest.proto",
    "google/protobuf/unittest_arena.proto",
    "google/protobuf/unittest_custom_options.proto",
@ -953,7 +1051,6 @@ py_proto_library(
    protoc = ":protoc",
    py_libs = [
        ":python_srcs",
-        "@six//:six",
    ],
    srcs_version = "PY2AND3",
    visibility = ["//visibility:public"],
@ -1087,7 +1184,7 @@ proto_library(
    name = "generated_protos_proto",
    srcs = [
        "src/google/protobuf/unittest_import_public.proto",
-        "unittest_gen.proto",
+        "unittest_gen_import.proto",
    ],
 )

@ -1095,7 +1192,7 @@ py_proto_library(
    name = "generated_protos_py",
    srcs = [
        "src/google/protobuf/unittest_import_public.proto",
-        "unittest_gen.proto",
+        "unittest_gen_import.proto",
    ],
    default_runtime = "",
    protoc = ":protoc",
@ -1225,6 +1322,19 @@ cc_binary(
 #     ],
 # )

+
+java_proto_library(
+    name = "java_test_protos",
+    deps = [":generic_test_protos"],
+    visibility = ["//java:__subpackages__"],
+)
+
+java_lite_proto_library(
+    name = "java_lite_test_protos",
+    deps = [":generic_test_protos"],
+    visibility = ["//java:__subpackages__"],
+)
+
 java_proto_library(
    name = "test_messages_proto2_java_proto",
    visibility = [
@ -1318,3 +1428,146 @@ filegroup(
    srcs = glob(["**/*.bzl"]),
    visibility = ["//visibility:public"],
 )
+
+# Kotlin proto rules
+
+genrule(
+    name = "gen_kotlin_unittest_lite",
+    srcs = [
+        "src/google/protobuf/unittest_lite.proto",
+        "src/google/protobuf/unittest_import_lite.proto",
+        "src/google/protobuf/unittest_import_public_lite.proto",
+        "src/google/protobuf/map_lite_unittest.proto",
+    ],
+    outs = [
+        "TestAllTypesLiteKt.kt",
+        "ForeignMessageLiteKt.kt",
+        "TestAllExtensionsLiteKt.kt",
+        "TestEmptyMessageLiteKt.kt",
+        "TestEmptyMessageWithExtensionsLiteKt.kt",
+        "TestMapLiteKt.kt",
+        "OptionalGroup_extension_liteKt.kt",
+        "RepeatedGroup_extension_liteKt.kt",
+    ],
+    visibility = ["//java:__subpackages__"],
+    cmd = "$(location //:protoc) " +
+          "--kotlin_out=lite:$(@D) -Isrc/ " +
+          "$(locations src/google/protobuf/unittest_lite.proto) && " +
+          "$(location //:protoc) " +
+          "--kotlin_out=lite:$(@D) -Isrc/ " +
+          "$(locations src/google/protobuf/map_lite_unittest.proto) && " +
+          "cp $(@D)/com/google/protobuf/TestAllTypesLiteKt.kt " +
+          "$(location TestAllTypesLiteKt.kt) && " +
+          "cp $(@D)/com/google/protobuf/ForeignMessageLiteKt.kt " +
+          "$(location ForeignMessageLiteKt.kt) && " +
+          "cp $(@D)/com/google/protobuf/TestAllExtensionsLiteKt.kt " +
+          "$(location TestAllExtensionsLiteKt.kt) && " +
+          "cp $(@D)/com/google/protobuf/TestAllTypesLiteKt.kt " +
+          "$(location TestAllTypesLiteKt.kt) && " +
+          "cp $(@D)/com/google/protobuf/TestEmptyMessageLiteKt.kt " +
+          "$(location TestEmptyMessageLiteKt.kt) && " +
+          "cp $(@D)/com/google/protobuf/TestEmptyMessageWithExtensionsLiteKt.kt " +
+          "$(location TestEmptyMessageWithExtensionsLiteKt.kt) && " +
+          "cp $(@D)/protobuf_unittest/TestMapLiteKt.kt " +
+          "$(location TestMapLiteKt.kt) && " +
+          "cp $(@D)/com/google/protobuf/OptionalGroup_extension_liteKt.kt " +
+          "$(location OptionalGroup_extension_liteKt.kt) && " +
+          "cp $(@D)/com/google/protobuf/RepeatedGroup_extension_liteKt.kt " +
+          "$(location RepeatedGroup_extension_liteKt.kt)",
+    tools = [":protoc"],
+)
+
+genrule(
+    name = "gen_kotlin_unittest",
+    srcs = [
+        "src/google/protobuf/unittest.proto",
+        "src/google/protobuf/unittest_import.proto",
+        "src/google/protobuf/unittest_import_public.proto",
+        "src/google/protobuf/map_proto2_unittest.proto",
+    ],
+    outs = [
+        "TestAllTypesKt.kt",
+        "ForeignMessageKt.kt",
+        "TestAllExtensionsKt.kt",
+        "TestEmptyMessageKt.kt",
+        "TestEmptyMessageWithExtensionsKt.kt",
+        "TestIntIntMapKt.kt",
+        "TestEnumMapKt.kt",
+        "TestMapsKt.kt",
+        "OptionalGroup_extensionKt.kt",
+        "RepeatedGroup_extensionKt.kt",
+    ],
+    visibility = ["//java:__subpackages__"],
+    cmd = "$(location //:protoc) " +
+          "--kotlin_out=shared,immutable:$(@D) -Isrc/ " +
+          "$(location src/google/protobuf/unittest.proto) && " +
+          "$(location //:protoc) " +
+          "--kotlin_out=shared,immutable:$(@D) -Isrc/ " + 
+          "$(location src/google/protobuf/map_proto2_unittest.proto) && " +
+          "cp $(@D)/protobuf_unittest/TestAllTypesKt.kt " +
+          "$(location TestAllTypesKt.kt) && " +
+          "cp $(@D)/protobuf_unittest/ForeignMessageKt.kt " +
+          "$(location ForeignMessageKt.kt) && " +
+          "cp $(@D)/protobuf_unittest/TestAllExtensionsKt.kt " +
+          "$(location TestAllExtensionsKt.kt) && " +
+          "cp $(@D)/protobuf_unittest/TestEmptyMessageKt.kt " +
+          "$(location TestEmptyMessageKt.kt) && " +
+          "cp $(@D)/protobuf_unittest/TestEmptyMessageWithExtensionsKt.kt " +
+          "$(location TestEmptyMessageWithExtensionsKt.kt) && " +
+          "cp $(@D)/protobuf_unittest/TestIntIntMapKt.kt " +
+          "$(location TestIntIntMapKt.kt) && " +
+          "cp $(@D)/protobuf_unittest/TestEnumMapKt.kt " +
+          "$(location TestEnumMapKt.kt) && " +
+          "cp $(@D)/protobuf_unittest/TestMapsKt.kt " +
+          "$(location TestMapsKt.kt) && " +
+          "cp $(@D)/protobuf_unittest/OptionalGroup_extensionKt.kt " +
+          "$(location OptionalGroup_extensionKt.kt) && " +
+          "cp $(@D)/protobuf_unittest/RepeatedGroup_extensionKt.kt " +
+          "$(location RepeatedGroup_extensionKt.kt)",
+    tools = ["//:protoc"],
+)
+
+genrule(
+    name = "gen_kotlin_proto3_unittest_lite",
+    srcs = [
+        "src/google/protobuf/unittest_proto3_lite.proto",
+        "src/google/protobuf/unittest_import.proto",
+        "src/google/protobuf/unittest_import_public.proto",
+    ],
+    outs = [
+        "TestAllTypesProto3LiteKt.kt",
+        "TestEmptyMessageProto3LiteKt.kt",
+    ],
+    visibility = ["//java:__subpackages__"],
+    cmd = "$(location //:protoc) " +
+          "--kotlin_out=lite:$(@D) -Isrc/ " +
+          "$(location src/google/protobuf/unittest_proto3_lite.proto) && " +
+          "cp $(@D)/proto3_lite_unittest/TestAllTypesKt.kt " +
+          "$(location TestAllTypesProto3LiteKt.kt) && " +
+          "cp $(@D)/proto3_lite_unittest/TestEmptyMessageKt.kt " +
+          "$(location TestEmptyMessageProto3LiteKt.kt)",
+    tools = ["//:protoc"],
+)
+
+genrule(
+    name = "gen_kotlin_proto3_unittest",
+    srcs = [
+        "src/google/protobuf/unittest_proto3.proto",
+        "src/google/protobuf/unittest_import.proto",
+        "src/google/protobuf/unittest_import_public.proto",
+    ],
+    outs = [
+        "TestAllTypesProto3Kt.kt",
+        "TestEmptyMessageProto3Kt.kt",
+    ],
+    visibility = ["//java:__subpackages__"],
+    cmd = "$(location //:protoc) " +
+          "--kotlin_out=shared,immutable:$(@D) -Isrc/ " +
+          "$(location src/google/protobuf/unittest_proto3.proto) && " +
+          "cp $(@D)/proto3_unittest/TestAllTypesKt.kt " +
+          "$(location TestAllTypesProto3Kt.kt) && " +
+          "cp $(@D)/proto3_unittest/TestEmptyMessageKt.kt " +
+          "$(location TestEmptyMessageProto3Kt.kt)",
+    tools = ["//:protoc"],
+)
+
--- a/CHANGES.txt
+++ b/CHANGES.txt
@ -1,6 +1,110 @@
 Unreleased Changes (C++/Java/Python/PHP/Objective-C/C#/Ruby/JavaScript)
-  Protocol Compiler
+
+  Ruby
+  * JSON will now output shorter strings for double and float fields when possible
+    without losing precision.
+  * Encoding and decoding of binary format will now work properly on big-endian
+    systems.
+  * UTF-8 verification was fixed to properly reject surrogate code points.
+  * Unknown enums for proto2 protos now properly implement proto2's behavior of
+    putting such values in unknown fields.
+
+2022-01-28 version 3.19.4 (C++/Java/Python/PHP/Objective-C/C#/Ruby/JavaScript)
+
+  Python
+  * Make libprotobuf symbols local on OSX to fix issue #9395 (#9435)
+
+  Ruby
+  * Fixed a data loss bug that could occur when the number of `optional`
+    fields in a message is an exact multiple of 32. (#9440).
+
+  PHP
+  * Fixed a data loss bug that could occur when the number of `optional`
+    fields in a message is an exact multiple of 32. (#9440).
+
+2022-01-10 version 3.19.3 (C++/Java/Python/PHP/Objective-C/C#/Ruby/JavaScript)
+
+  Python
+  * Fix missing Windows wheel for Python 3.10 on PyPI
+
+2022-01-05 version 3.19.2 (C++/Java/Python/PHP/Objective-C/C#/Ruby/JavaScript)
+
+  Java
+  * Improve performance characteristics of UnknownFieldSet parsing (#9371)
+  * This release addresses a Security Advisory for Java users
+   (https://github.com/protocolbuffers/protobuf/security/advisories/GHSA-wrvw-hg22-4m67)
+
+2022-01-05 version 3.18.2 (C++/Java/Python/PHP/Objective-C/C#/Ruby/JavaScript)
+
+  Java
+  * Improve performance characteristics of UnknownFieldSet parsing (#9371)
+  * This release addresses a Security Advisory for Java users
+   (https://github.com/protocolbuffers/protobuf/security/advisories/GHSA-wrvw-hg22-4m67)
+
+2022-01-05 version 3.16.1 (Java)
+
+  Java
+  * Improve performance characteristics of UnknownFieldSet parsing (#9371)
+  * This release addresses a Security Advisory for Java users
+   (https://github.com/protocolbuffers/protobuf/security/advisories/GHSA-wrvw-hg22-4m67)
+
+2021-10-28 version 3.19.1 (C++/Java/Python/PHP/Objective-C/C#/Ruby/JavaScript)
+
+  Bazel
+  * Ensure that release archives contain everything needed for Bazel (#9131)
+  * Align dependency handling with Bazel best practices (#9165)
+
+  JavaScript
+  * Fix `ReferenceError: window is not defined` when getting the global object (#9156)
+
+  Ruby
+  * Fix memory leak in MessageClass.encode (#9150)
+
+2021-10-15 version 3.19.0 (C++/Java/Python/PHP/Objective-C/C#/Ruby/JavaScript)
+
+  C++
  * Make proto2::Message::DiscardUnknownFields() non-virtual
+  * Separate RepeatedPtrField into its own header file
+  * For default floating point values of 0, consider all bits significant
+  * cmake: support `MSVC_RUNTIME_LIBRARY` property (#8851)
+  * Fix shadowing warnings (#8926)
+  * Fix for issue #8484, constant initialization doesn't compile in msvc clang-cl environment (#8993)
+  * Fix build on AIX and SunOS (#8373) (#9065)
+  * Add Android stlport and default toolchains to BUILD. (#8290)
+
+  Java
+  * For default floating point values of 0, consider all bits significant
+  * Annotate `//java/com/google/protobuf/util/...` with nullness annotations
+  * Use ArrayList copy constructor (#7853)
+
+  Kotlin
+  * Switch Kotlin proto DSLs to be implemented with inline value classes
+  * Fix inlining and deprecation for repeated string fields in kotlin (#9120)
+
+  Python
+  * Proto2 DecodeError now includes message name in error message
+  * Make MessageToDict convert map keys to strings (#8122)
+  * Add python-requires in setup.py (#8989)
+  * Add python 3.10 (#9034)
+
+  JavaScript
+  * Skip exports if not available by CommonJS (#8856)
+  * JS: Comply with CSP no-unsafe-eval. (#8864)
+
+  PHP
+  * Added "object" as a reserved name for PHP (#8962)
+
+  Ruby
+  * Override Map.clone to use Map's dup method (#7938)
+  * Ruby: build extensions for arm64-darwin (#8232)
+  * Add class method Timestamp.from_time to ruby well known types (#8562)
+  * Adopt pure ruby DSL implementation for JRuby (#9047)
+  * Add size to Map class (#8068)
+  * Fix for descriptor_pb.rb: google/protobuf should be required first (#9121)
+
+  C#
+  * Correctly set ExtensionRegistry when parsing with MessageParser, but using an already existing CodedInputStream (#7246)
+  * [C#] Make FieldDescriptor propertyName public (#7642)

 2021-10-04 version 3.18.1 (C++/Java/Python/PHP/Objective-C/C#/Ruby/JavaScript)

--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@ -1,9 +1,31 @@
 # Contributing to Protocol Buffers

-We welcome your contributions to protocol buffers. This doc describes the
+We welcome some types of contributions to protocol buffers. This doc describes the
 process to contribute patches to protobuf and the general guidelines we
 expect contributors to follow.

+## What We Accept
+
+* Bug fixes with unit tests demonstrating the problem are very welcome.
+  We also appreciate bug reports, even when they don't come with a patch.
+  Bug fixes without tests are usually not accepted.
+* New APIs and features with adequate test coverage and documentation
+  may be accepted if they do not compromise backwards 
+  compatibility. However there's a fairly high bar of usefulness a new public
+  method must clear before it will be accepted. Features that are fine in 
+  isolation are often rejected because they don't have enough impact to justify the 
+  conceptual burden and ongoing maintenance cost. It's best to file an issue 
+  and get agreement from maintainers on the value of a new feature before
+  working on a PR.
+* Performance optimizations may be accepted if they have convincing benchmarks that demonstrate 
+  an improvement and they do not significantly increase complexity.  
+* Changes to existing APIs are almost never accepted. Stability and
+  backwards compatibility are paramount. In the unlikely event a breaking change 
+  is required, it must usually be implemented in google3 first. 
+* Changes to the wire and text formats are never accepted. Any breaking change
+  to these formats would have to be implemented as a completely new format.
+  We cannot begin generating protos that cannot be parsed by existing code.
+
 ## Before You Start

 We accept patches in the form of github pull requests. If you are new to
@ -58,7 +80,7 @@ the final release.
 * Create small PRs that are narrowly focused on addressing a single concern.
  We often receive PRs that are trying to fix several things at a time, but if
  only one fix is considered acceptable, nothing gets merged and both author's
-  & review's time is wasted. Create more PRs to address different concerns and
+  & reviewer's time is wasted. Create more PRs to address different concerns and
  everyone will be happy.
 * For speculative changes, consider opening an issue and discussing it first.
  If you are suggesting a behavioral or API change, make sure you get explicit
--- a/Makefile.am
+++ b/Makefile.am
@ -1011,6 +1011,7 @@ python_EXTRA_DIST=                                                           \
  python/google/protobuf/internal/any_test.proto                             \
  python/google/protobuf/internal/api_implementation.cc                      \
  python/google/protobuf/internal/api_implementation.py                      \
+  python/google/protobuf/internal/builder.py                                 \
  python/google/protobuf/internal/containers.py                              \
  python/google/protobuf/internal/decoder.py                                 \
  python/google/protobuf/internal/descriptor_database_test.py                \
@ -1426,7 +1427,6 @@ EXTRA_DIST = $(@DIST_LANG@_EXTRA_DIST)   \
  examples/pubspec.yaml                  \
  protobuf.bzl                           \
  protobuf_deps.bzl                      \
-  third_party/six.BUILD                  \
  third_party/zlib.BUILD                 \
  util/python/BUILD                      \
  internal.bzl
--- a/Protobuf-C++.podspec
+++ b/Protobuf-C++.podspec
@ -35,9 +35,6 @@ Pod::Spec.new do |s|
    # Do not let src/google/protobuf/stubs/time.h override system API
    'USE_HEADERMAP' => 'NO',
    'ALWAYS_SEARCH_USER_PATHS' => 'NO',
-
-    # Configure tool is not being used for Xcode. When building, assume pthread is supported.
-    'GCC_PREPROCESSOR_DEFINITIONS' => '"$(inherited)" "HAVE_PTHREAD=1"',
  }

 end
--- a/Protobuf.podspec
+++ b/Protobuf.podspec
@ -5,10 +5,10 @@
 # dependent projects use the :git notation to refer to the library.
 Pod::Spec.new do |s|
  s.name     = 'Protobuf'
-  s.version  = '3.18.1'
+  s.version  = '3.19.4'
  s.summary  = 'Protocol Buffers v.3 runtime library for Objective-C.'
  s.homepage = 'https://github.com/protocolbuffers/protobuf'
-  s.license  = '3-Clause BSD License'
+  s.license  = 'BSD-3-Clause'
  s.authors  = { 'The Protocol Buffers contributors' => 'protobuf@googlegroups.com' }
  s.cocoapods_version = '>= 1.0'

--- a/71
+++ b/71
@ -27,7 +27,7 @@ http_archive(
 )

 # Load common dependencies.
-load("//:protobuf_deps.bzl", "protobuf_deps")
+load("//:protobuf_deps.bzl", "PROTOBUF_MAVEN_ARTIFACTS", "protobuf_deps")
 protobuf_deps()

 bind(
@ -36,68 +36,33 @@ bind(
 )

 load("@rules_jvm_external//:defs.bzl", "maven_install")
+
 maven_install(
-    artifacts = [
-        "com.google.code.gson:gson:2.8.6",
-        "com.google.errorprone:error_prone_annotations:2.3.2",
-        "com.google.j2objc:j2obj_annotations:1.3",
-        "com.google.guava:guava:30.1.1-jre",
-        "com.google.truth:truth:1.1.2",
-        "junit:junit:4.12",
-        "org.easymock:easymock:3.2",
-    ],
+    artifacts = PROTOBUF_MAVEN_ARTIFACTS,
+    # For updating instructions, see:
+    # https://github.com/bazelbuild/rules_jvm_external#updating-maven_installjson
+    maven_install_json = "//:maven_install.json",
    repositories = [
        "https://repo1.maven.org/maven2",
        "https://repo.maven.apache.org/maven2",
    ],
-    # For updating instructions, see: 
-    # https://github.com/bazelbuild/rules_jvm_external#updating-maven_installjson
-    maven_install_json = "//:maven_install.json",
 )

 load("@maven//:defs.bzl", "pinned_maven_install")
+
 pinned_maven_install()

-bind(
-    name = "guava",
-    actual = "@maven//:com_google_guava_guava",
-)
-
-bind(
-    name = "gson",
-    actual = "@maven//:com_google_code_gson_gson",
-)
-
-bind(
-    name = "error_prone_annotations",
-    actual = "@maven//:com_google_errorprone_error_prone_annotations",
-)
-
-bind(
-    name = "j2objc_annotations",
-    actual = "@maven//:com_google_j2objc_j2objc_annotations",
-)
-
-bind(
-    name = "junit",
-    actual = "@maven//:junit_junit",
-)
-
-bind(
-    name = "easymock",
-    actual = "@maven//:org_easymock_easymock",
-)
-
-bind(
-    name = "easymock_classextension",
-    actual = "@maven//:org_easymock_easymockclassextension",
-)
-
-bind(
-    name = "truth",
-    actual = "@maven//:com_google_truth_truth",
-)
-
 # For `cc_proto_blacklist_test` and `build_test`.
 load("@bazel_skylib//:workspace.bzl", "bazel_skylib_workspace")
+
 bazel_skylib_workspace()
+
+load("@rules_pkg//:deps.bzl", "rules_pkg_dependencies")
+rules_pkg_dependencies()
+
+# For `kt_jvm_library`
+load("@io_bazel_rules_kotlin//kotlin:repositories.bzl", "kotlin_repositories")
+kotlin_repositories()
+
+load("@io_bazel_rules_kotlin//kotlin:core.bzl", "kt_register_toolchains")
+kt_register_toolchains()
--- a/appveyor.bat
+++ b/appveyor.bat
@ -38,7 +38,7 @@ dotnet restore
 dotnet build -c %configuration% || goto error

 echo Testing C#
-dotnet test -c %configuration% -f netcoreapp2.1 Google.Protobuf.Test\Google.Protobuf.Test.csproj || goto error
+dotnet test -c %configuration% -f netcoreapp3.1 Google.Protobuf.Test\Google.Protobuf.Test.csproj || goto error
 dotnet test -c %configuration% -f net451 Google.Protobuf.Test\Google.Protobuf.Test.csproj || goto error

 goto :EOF
--- a/benchmarks/README.md
+++ b/benchmarks/README.md
@ -4,8 +4,8 @@
 This directory contains benchmarking schemas and data sets that you
 can use to test a variety of performance scenarios against your
 protobuf language runtime. If you are looking for performance
-numbers of officially support languages, see [here](
-https://github.com/protocolbuffers/protobuf/blob/master/docs/performance.md)
+numbers of officially supported languages, see [Protobuf Performance](
+https://github.com/protocolbuffers/protobuf/blob/master/docs/performance.md).

 ## Prerequisite

--- a/cmake/CMakeLists.txt
+++ b/cmake/CMakeLists.txt
@ -127,9 +127,6 @@ if (protobuf_DISABLE_RTTI)
 endif()

 find_package(Threads REQUIRED)
-if (CMAKE_USE_PTHREADS_INIT)
-  add_definitions(-DHAVE_PTHREAD)
-endif (CMAKE_USE_PTHREADS_INIT)

 set(_protobuf_FIND_ZLIB)
 if (protobuf_WITH_ZLIB)
@ -209,6 +206,8 @@ if (MSVC)
    # Build with multiple processes
    add_definitions(/MP)
  endif()
+  # Set source file and execution character sets to UTF-8
+  add_definitions(/utf-8)
  # MSVC warning suppressions
  add_definitions(
    /wd4018 # 'expression' : signed/unsigned mismatch
--- a/cmake/extract_includes.bat.in
+++ b/cmake/extract_includes.bat.in
@ -41,6 +41,8 @@ copy "${PROTOBUF_SOURCE_WIN32_PATH}\..\src\google\protobuf\compiler\php\php_gene
 copy "${PROTOBUF_SOURCE_WIN32_PATH}\..\src\google\protobuf\compiler\plugin.h" include\google\protobuf\compiler\plugin.h
 copy "${PROTOBUF_SOURCE_WIN32_PATH}\..\src\google\protobuf\compiler\plugin.pb.h" include\google\protobuf\compiler\plugin.pb.h
 copy "${PROTOBUF_SOURCE_WIN32_PATH}\..\src\google\protobuf\compiler\python\python_generator.h" include\google\protobuf\compiler\python\python_generator.h
+copy "${PROTOBUF_SOURCE_WIN32_PATH}\..\src\google\protobuf\compiler\python\python_pyi_generator.h" include\google\protobuf\compiler\python\python_pyi_generator.h
+copy "${PROTOBUF_SOURCE_WIN32_PATH}\..\src\google\protobuf\compiler\python\python_helpers.h" include\google\protobuf\compiler\python\python_helpers.h
 copy "${PROTOBUF_SOURCE_WIN32_PATH}\..\src\google\protobuf\compiler\ruby\ruby_generator.h" include\google\protobuf\compiler\ruby\ruby_generator.h
 copy "${PROTOBUF_SOURCE_WIN32_PATH}\..\src\google\protobuf\descriptor.h" include\google\protobuf\descriptor.h
 copy "${PROTOBUF_SOURCE_WIN32_PATH}\..\src\google\protobuf\descriptor.pb.h" include\google\protobuf\descriptor.pb.h
@ -48,6 +50,7 @@ copy "${PROTOBUF_SOURCE_WIN32_PATH}\..\src\google\protobuf\descriptor_database.h
 copy "${PROTOBUF_SOURCE_WIN32_PATH}\..\src\google\protobuf\duration.pb.h" include\google\protobuf\duration.pb.h
 copy "${PROTOBUF_SOURCE_WIN32_PATH}\..\src\google\protobuf\dynamic_message.h" include\google\protobuf\dynamic_message.h
 copy "${PROTOBUF_SOURCE_WIN32_PATH}\..\src\google\protobuf\empty.pb.h" include\google\protobuf\empty.pb.h
+copy "${PROTOBUF_SOURCE_WIN32_PATH}\..\src\google\protobuf\explicitly_constructed.h" include\google\protobuf\explicitly_constructed.h
 copy "${PROTOBUF_SOURCE_WIN32_PATH}\..\src\google\protobuf\extension_set.h" include\google\protobuf\extension_set.h
 copy "${PROTOBUF_SOURCE_WIN32_PATH}\..\src\google\protobuf\extension_set_inl.h" include\google\protobuf\extension_set_inl.h
 copy "${PROTOBUF_SOURCE_WIN32_PATH}\..\src\google\protobuf\field_access_listener.h" include\google\protobuf\field_access_listener.h
@ -92,6 +95,7 @@ copy "${PROTOBUF_SOURCE_WIN32_PATH}\..\src\google\protobuf\port_undef.inc" inclu
 copy "${PROTOBUF_SOURCE_WIN32_PATH}\..\src\google\protobuf\reflection.h" include\google\protobuf\reflection.h
 copy "${PROTOBUF_SOURCE_WIN32_PATH}\..\src\google\protobuf\reflection_ops.h" include\google\protobuf\reflection_ops.h
 copy "${PROTOBUF_SOURCE_WIN32_PATH}\..\src\google\protobuf\repeated_field.h" include\google\protobuf\repeated_field.h
+copy "${PROTOBUF_SOURCE_WIN32_PATH}\..\src\google\protobuf\repeated_ptr_field.h" include\google\protobuf\repeated_ptr_field.h
 copy "${PROTOBUF_SOURCE_WIN32_PATH}\..\src\google\protobuf\service.h" include\google\protobuf\service.h
 copy "${PROTOBUF_SOURCE_WIN32_PATH}\..\src\google\protobuf\source_context.pb.h" include\google\protobuf\source_context.pb.h
 copy "${PROTOBUF_SOURCE_WIN32_PATH}\..\src\google\protobuf\struct.pb.h" include\google\protobuf\struct.pb.h
--- a/cmake/libprotobuf-lite.cmake
+++ b/cmake/libprotobuf-lite.cmake
@ -2,9 +2,9 @@ set(libprotobuf_lite_files
  ${protobuf_source_dir}/src/google/protobuf/any_lite.cc
  ${protobuf_source_dir}/src/google/protobuf/arena.cc
  ${protobuf_source_dir}/src/google/protobuf/arenastring.cc
+  ${protobuf_source_dir}/src/google/protobuf/arenaz_sampler.cc
  ${protobuf_source_dir}/src/google/protobuf/extension_set.cc
  ${protobuf_source_dir}/src/google/protobuf/generated_enum_util.cc
-  ${protobuf_source_dir}/src/google/protobuf/generated_message_table_driven_lite.cc
  ${protobuf_source_dir}/src/google/protobuf/generated_message_tctable_lite.cc
  ${protobuf_source_dir}/src/google/protobuf/generated_message_util.cc
  ${protobuf_source_dir}/src/google/protobuf/implicit_weak_message.cc
@ -38,15 +38,13 @@ set(libprotobuf_lite_includes
  ${protobuf_source_dir}/src/google/protobuf/arena.h
  ${protobuf_source_dir}/src/google/protobuf/arena_impl.h
  ${protobuf_source_dir}/src/google/protobuf/arenastring.h
+  ${protobuf_source_dir}/src/google/protobuf/arenaz_sampler.h
  ${protobuf_source_dir}/src/google/protobuf/explicitly_constructed.h
  ${protobuf_source_dir}/src/google/protobuf/extension_set.h
  ${protobuf_source_dir}/src/google/protobuf/extension_set_inl.h
  ${protobuf_source_dir}/src/google/protobuf/generated_enum_util.h
-  ${protobuf_source_dir}/src/google/protobuf/generated_message_table_driven.h
-  ${protobuf_source_dir}/src/google/protobuf/generated_message_table_driven_lite.h
  ${protobuf_source_dir}/src/google/protobuf/generated_message_tctable_decl.h
  ${protobuf_source_dir}/src/google/protobuf/generated_message_tctable_impl.h
-  ${protobuf_source_dir}/src/google/protobuf/generated_message_tctable_impl.inc
  ${protobuf_source_dir}/src/google/protobuf/generated_message_util.h
  ${protobuf_source_dir}/src/google/protobuf/has_bits.h
  ${protobuf_source_dir}/src/google/protobuf/implicit_weak_message.h
--- a/cmake/libprotobuf.cmake
+++ b/cmake/libprotobuf.cmake
@ -14,7 +14,6 @@ set(libprotobuf_files
  ${protobuf_source_dir}/src/google/protobuf/field_mask.pb.cc
  ${protobuf_source_dir}/src/google/protobuf/generated_message_bases.cc
  ${protobuf_source_dir}/src/google/protobuf/generated_message_reflection.cc
-  ${protobuf_source_dir}/src/google/protobuf/generated_message_table_driven.cc
  ${protobuf_source_dir}/src/google/protobuf/generated_message_tctable_full.cc
  ${protobuf_source_dir}/src/google/protobuf/io/gzip_stream.cc
  ${protobuf_source_dir}/src/google/protobuf/io/printer.cc
--- a/cmake/libprotoc.cmake
+++ b/cmake/libprotoc.cmake
@ -91,6 +91,8 @@ set(libprotoc_files
  ${protobuf_source_dir}/src/google/protobuf/compiler/plugin.cc
  ${protobuf_source_dir}/src/google/protobuf/compiler/plugin.pb.cc
  ${protobuf_source_dir}/src/google/protobuf/compiler/python/python_generator.cc
+  ${protobuf_source_dir}/src/google/protobuf/compiler/python/python_helpers.cc
+  ${protobuf_source_dir}/src/google/protobuf/compiler/python/python_pyi_generator.cc
  ${protobuf_source_dir}/src/google/protobuf/compiler/ruby/ruby_generator.cc
  ${protobuf_source_dir}/src/google/protobuf/compiler/subprocess.cc
  ${protobuf_source_dir}/src/google/protobuf/compiler/zip_writer.cc
@ -117,6 +119,7 @@ set(libprotoc_headers
  ${protobuf_source_dir}/src/google/protobuf/compiler/php/php_generator.h
  ${protobuf_source_dir}/src/google/protobuf/compiler/plugin.h
  ${protobuf_source_dir}/src/google/protobuf/compiler/python/python_generator.h
+  ${protobuf_source_dir}/src/google/protobuf/compiler/python/python_pyi_generator.h
  ${protobuf_source_dir}/src/google/protobuf/compiler/ruby/ruby_generator.h
 )

--- a/cmake/protobuf-module.cmake.in
+++ b/cmake/protobuf-module.cmake.in
@ -110,16 +110,6 @@ function(_protobuf_find_libraries name filename)
  endif()
 endfunction()

-# Internal function: find threads library
-function(_protobuf_find_threads)
-    set(CMAKE_THREAD_PREFER_PTHREAD TRUE)
-    find_package(Threads)
-    if(Threads_FOUND)
-        list(APPEND PROTOBUF_LIBRARIES ${CMAKE_THREAD_LIBS_INIT})
-        set(PROTOBUF_LIBRARIES "${PROTOBUF_LIBRARIES}" PARENT_SCOPE)
-    endif()
-endfunction()
-
 #
 # Main.
 #
@ -139,10 +129,6 @@ _protobuf_find_libraries(Protobuf_LITE protobuf-lite)
 # The Protobuf Protoc Library
 _protobuf_find_libraries(Protobuf_PROTOC protoc)

-if(UNIX)
-  _protobuf_find_threads()
-endif()
-
 # Set the include directory
 get_target_property(Protobuf_INCLUDE_DIRS protobuf::libprotobuf
  INTERFACE_INCLUDE_DIRECTORIES)
--- a/cmake/tests.cmake
+++ b/cmake/tests.cmake
@ -131,6 +131,7 @@ set(tests_files
  ${protobuf_source_dir}/src/google/protobuf/any_test.cc
  ${protobuf_source_dir}/src/google/protobuf/arena_unittest.cc
  ${protobuf_source_dir}/src/google/protobuf/arenastring_unittest.cc
+  ${protobuf_source_dir}/src/google/protobuf/arenaz_sampler_test.cc
  ${protobuf_source_dir}/src/google/protobuf/compiler/annotation_test_util.cc
  ${protobuf_source_dir}/src/google/protobuf/compiler/annotation_test_util.h
  ${protobuf_source_dir}/src/google/protobuf/compiler/command_line_interface_unittest.cc
@ -155,6 +156,7 @@ set(tests_files
  ${protobuf_source_dir}/src/google/protobuf/dynamic_message_unittest.cc
  ${protobuf_source_dir}/src/google/protobuf/extension_set_unittest.cc
  ${protobuf_source_dir}/src/google/protobuf/generated_message_reflection_unittest.cc
+  ${protobuf_source_dir}/src/google/protobuf/generated_message_tctable_lite_test.cc
  ${protobuf_source_dir}/src/google/protobuf/inlined_string_field_unittest.cc
  ${protobuf_source_dir}/src/google/protobuf/io/coded_stream_unittest.cc
  ${protobuf_source_dir}/src/google/protobuf/io/io_win32_unittest.cc
--- a/conformance/ConformanceJava.java
+++ b/conformance/ConformanceJava.java
@ -361,7 +361,7 @@ class ConformanceJava {

      case TEXT_FORMAT:
        return Conformance.ConformanceResponse.newBuilder()
-            .setTextPayload(TextFormat.printToString(testMessage))
+            .setTextPayload(TextFormat.printer().printToString(testMessage))
            .build();

      default:
--- a/conformance/conformance_python.py
+++ b/conformance/conformance_python.py
@ -39,8 +39,8 @@ import sys
 import os
 from google.protobuf import json_format
 from google.protobuf import message
-from google.protobuf import test_messages_proto3_pb2
-from google.protobuf import test_messages_proto2_pb2
+from google3.third_party.protobuf import test_messages_proto3_pb2
+from google3.third_party.protobuf import test_messages_proto2_pb2
 from google.protobuf import text_format
 import conformance_pb2

--- a/conformance/conformance_test_runner.cc
+++ b/conformance/conformance_test_runner.cc
@ -162,7 +162,7 @@ void ForkPipeRunner::RunTest(
    // We failed to read from the child, assume a crash and try to reap.
    GOOGLE_LOG(INFO) << "Trying to reap child, pid=" << child_pid_;

-    int status;
+    int status = 0;
    waitpid(child_pid_, &status, WEXITED);

    string error_msg;
--- a/csharp/Google.Protobuf.Tools.nuspec
+++ b/csharp/Google.Protobuf.Tools.nuspec
@ -5,7 +5,7 @@
    <title>Google Protocol Buffers tools</title>
    <summary>Tools for Protocol Buffers - Google's data interchange format.</summary>
    <description>See project site for more info.</description>
-    <version>3.18.1</version>
+    <version>3.19.4</version>
    <authors>Google Inc.</authors>
    <owners>protobuf-packages</owners>
    <licenseUrl>https://github.com/protocolbuffers/protobuf/blob/master/LICENSE</licenseUrl>
--- a/csharp/NuGet.Config
+++ b/csharp/NuGet.Config
@ -0,0 +1,8 @@
+<?xml version="1.0" encoding="utf-8"?>
+<configuration>
+  <packageSources>
+    <!--To inherit the global NuGet package sources remove the <clear/> line below -->
+    <clear />
+    <add key="NuGet.org (v3)" value="https://api.nuget.org/v3/index.json" />
+  </packageSources>
+</configuration>
--- a/csharp/build_packages.bat
+++ b/csharp/build_packages.bat
@ -1,7 +1,7 @@
@rem Builds Google.Protobuf NuGet packages

 dotnet restore src/Google.Protobuf.sln
-dotnet pack -c Release src/Google.Protobuf.sln || goto :error
+dotnet pack -c Release src/Google.Protobuf.sln -p:ContinuousIntegrationBuild=true || goto :error

 goto :EOF

--- a/csharp/buildall.sh
+++ b/csharp/buildall.sh
@ -10,8 +10,8 @@ dotnet restore $SRC/Google.Protobuf.sln
 dotnet build -c $CONFIG $SRC/Google.Protobuf.sln

 echo Running tests.
-# Only test netcoreapp2.1, which uses the .NET Core runtime.
+# Only test netcoreapp3.1, which uses the .NET Core runtime.
 # If we want to test the .NET 4.5 version separately, we could
 # run Mono explicitly. However, we don't have any differences between
 # the .NET 4.5 and netstandard2.1 assemblies.
-dotnet test -c $CONFIG -f netcoreapp2.1 $SRC/Google.Protobuf.Test/Google.Protobuf.Test.csproj
+dotnet test -c $CONFIG -f netcoreapp3.1 $SRC/Google.Protobuf.Test/Google.Protobuf.Test.csproj
--- a/csharp/compatibility_tests/v3.0.0/src/Google.Protobuf.Test/Google.Protobuf.Test.csproj
+++ b/csharp/compatibility_tests/v3.0.0/src/Google.Protobuf.Test/Google.Protobuf.Test.csproj
@ -2,7 +2,7 @@

  <PropertyGroup>
    <OutputType>Exe</OutputType>
-    <TargetFrameworks>net451;netcoreapp2.1</TargetFrameworks>
+    <TargetFrameworks>net451;netcoreapp3.1</TargetFrameworks>
    <AssemblyOriginatorKeyFile>../../keys/Google.Protobuf.snk</AssemblyOriginatorKeyFile>
    <SignAssembly>true</SignAssembly>
    <IsPackable>False</IsPackable>
--- a/csharp/compatibility_tests/v3.0.0/test.sh
+++ b/csharp/compatibility_tests/v3.0.0/test.sh
@ -22,7 +22,7 @@ function run_test() {
  dotnet restore src/Google.Protobuf.Test/Google.Protobuf.Test.csproj
  dotnet build -c Release src/Google.Protobuf/Google.Protobuf.csproj
  dotnet build -c Release src/Google.Protobuf.Test/Google.Protobuf.Test.csproj
-  dotnet run -c Release -f netcoreapp2.1 -p src/Google.Protobuf.Test/Google.Protobuf.Test.csproj
+  dotnet run -c Release -f netcoreapp3.1 -p src/Google.Protobuf.Test/Google.Protobuf.Test.csproj
 }

 set -ex
--- a/csharp/install_dotnet_sdk.ps1
+++ b/csharp/install_dotnet_sdk.ps1
@ -16,5 +16,5 @@ Invoke-WebRequest -Uri $InstallScriptUrl -OutFile $InstallScriptPath

 # The SDK versions to install should be kept in sync with versions
 # installed by kokoro/linux/dockerfile/test/csharp/Dockerfile
-&$InstallScriptPath -Version 2.1.802
-&$InstallScriptPath -Version 5.0.102
+&$InstallScriptPath -Version 3.1.415
+&$InstallScriptPath -Version 6.0.100
--- a/csharp/src/AddressBook/AddressBook.csproj
+++ b/csharp/src/AddressBook/AddressBook.csproj
@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">

  <PropertyGroup>
-    <TargetFramework>netcoreapp2.1</TargetFramework>
+    <TargetFramework>netcoreapp3.1</TargetFramework>
    <OutputType>Exe</OutputType>
    <StartupObject>Google.Protobuf.Examples.AddressBook.Program</StartupObject>
    <IsPackable>False</IsPackable>
--- a/csharp/src/AddressBook/Addressbook.cs
+++ b/csharp/src/AddressBook/Addressbook.cs
@ -32,9 +32,10 @@ namespace Google.Protobuf.Examples.AddressBook {
            "Eg4KBm51bWJlchgBIAEoCRIoCgR0eXBlGAIgASgOMhoudHV0b3JpYWwuUGVy",
            "c29uLlBob25lVHlwZSIrCglQaG9uZVR5cGUSCgoGTU9CSUxFEAASCAoESE9N",
            "RRABEggKBFdPUksQAiIvCgtBZGRyZXNzQm9vaxIgCgZwZW9wbGUYASADKAsy",
-            "EC50dXRvcmlhbC5QZXJzb25CZgobY29tLmV4YW1wbGUudHV0b3JpYWwucHJv",
-            "dG9zQhFBZGRyZXNzQm9va1Byb3Rvc1ABWgsuLi90dXRvcmlhbKoCJEdvb2ds",
-            "ZS5Qcm90b2J1Zi5FeGFtcGxlcy5BZGRyZXNzQm9va2IGcHJvdG8z"));
+            "EC50dXRvcmlhbC5QZXJzb25ClQEKG2NvbS5leGFtcGxlLnR1dG9yaWFsLnBy",
+            "b3Rvc0IRQWRkcmVzc0Jvb2tQcm90b3NQAVo6Z2l0aHViLmNvbS9wcm90b2Nv",
+            "bGJ1ZmZlcnMvcHJvdG9idWYvZXhhbXBsZXMvZ28vdHV0b3JpYWxwYqoCJEdv",
+            "b2dsZS5Qcm90b2J1Zi5FeGFtcGxlcy5BZGRyZXNzQm9va2IGcHJvdG8z"));
      descriptor = pbr::FileDescriptor.FromGeneratedCode(descriptorData,
          new pbr::FileDescriptor[] { global::Google.Protobuf.WellKnownTypes.TimestampReflection.Descriptor, },
          new pbr::GeneratedClrTypeInfo(null, null, new pbr::GeneratedClrTypeInfo[] {
--- a/csharp/src/Google.Protobuf.Benchmarks/Program.cs
+++ b/csharp/src/Google.Protobuf.Benchmarks/Program.cs
@ -36,7 +36,7 @@ namespace Google.Protobuf.Benchmarks
 {
    class Program
    {
-        // typical usage: dotnet run -c Release -f netcoreapp2.1
+        // typical usage: dotnet run -c Release -f netcoreapp3.1
        // (this can profile both .net core and .net framework; for some reason
        // if you start from "-f net461", it goes horribly wrong)
        public static void Main(string[] args)
--- a/csharp/src/Google.Protobuf.Conformance/Google.Protobuf.Conformance.csproj
+++ b/csharp/src/Google.Protobuf.Conformance/Google.Protobuf.Conformance.csproj
@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">

  <PropertyGroup>
-    <TargetFramework>netcoreapp2.1</TargetFramework>
+    <TargetFramework>netcoreapp3.1</TargetFramework>
    <OutputType>Exe</OutputType>
    <IsPackable>False</IsPackable>
  </PropertyGroup>
--- a/csharp/src/Google.Protobuf.JsonDump/Google.Protobuf.JsonDump.csproj
+++ b/csharp/src/Google.Protobuf.JsonDump/Google.Protobuf.JsonDump.csproj
@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">

  <PropertyGroup>
-    <TargetFramework>netcoreapp2.1</TargetFramework>
+    <TargetFramework>netcoreapp3.1</TargetFramework>
    <OutputType>Exe</OutputType>
    <IsPackable>False</IsPackable>
  </PropertyGroup>
--- a/csharp/src/Google.Protobuf.Test.TestProtos/Google.Protobuf.Test.TestProtos.csproj
+++ b/csharp/src/Google.Protobuf.Test.TestProtos/Google.Protobuf.Test.TestProtos.csproj
@ -1,4 +1,4 @@
-<Project Sdk="Microsoft.NET.Sdk">
+<Project Sdk="Microsoft.NET.Sdk">

  <!--
    This TestProtos project is kept separate from the original test project for many reasons.
@ -15,7 +15,7 @@

  <!-- Needed for the net45 build to work on Unix. See https://github.com/dotnet/designs/pull/33 -->
  <ItemGroup>
-    <PackageReference Include="Microsoft.NETFramework.ReferenceAssemblies" Version="1.0.0-preview.2" PrivateAssets="All" />
+    <PackageReference Include="Microsoft.NETFramework.ReferenceAssemblies" Version="1.0.0" PrivateAssets="All" />
  </ItemGroup>
  
  <ItemGroup>
--- a/csharp/src/Google.Protobuf.Test.TestProtos/TestMessagesProto2.cs
+++ b/csharp/src/Google.Protobuf.Test.TestProtos/TestMessagesProto2.cs
@ -25,7 +25,7 @@ namespace ProtobufTestMessages.Proto2 {
      byte[] descriptorData = global::System.Convert.FromBase64String(
          string.Concat(
            "Cipnb29nbGUvcHJvdG9idWYvdGVzdF9tZXNzYWdlc19wcm90bzIucHJvdG8S",
-            "HXByb3RvYnVmX3Rlc3RfbWVzc2FnZXMucHJvdG8yIqQ+ChJUZXN0QWxsVHlw",
+            "HXByb3RvYnVmX3Rlc3RfbWVzc2FnZXMucHJvdG8yIsQ+ChJUZXN0QWxsVHlw",
            "ZXNQcm90bzISFgoOb3B0aW9uYWxfaW50MzIYASABKAUSFgoOb3B0aW9uYWxf",
            "aW50NjQYAiABKAMSFwoPb3B0aW9uYWxfdWludDMyGAMgASgNEhcKD29wdGlv",
            "bmFsX3VpbnQ2NBgEIAEoBBIXCg9vcHRpb25hbF9zaW50MzIYBSABKBESFwoP",
@ -148,79 +148,81 @@ namespace ProtobufTestMessages.Proto2 {
            "NTY3ODkxMjM0NTY3ODkSHQoNZGVmYXVsdF9mbG9hdBj7ASABKAI6BTllKzA5",
            "Eh4KDmRlZmF1bHRfZG91YmxlGPwBIAEoAToFN2UrMjISGwoMZGVmYXVsdF9i",
            "b29sGP0BIAEoCDoEdHJ1ZRIgCg5kZWZhdWx0X3N0cmluZxj+ASABKAk6B1Jv",
-            "c2VidWQSEwoKZmllbGRuYW1lMRiRAyABKAUSFAoLZmllbGRfbmFtZTIYkgMg",
-            "ASgFEhUKDF9maWVsZF9uYW1lMxiTAyABKAUSFgoNZmllbGRfX25hbWU0XxiU",
-            "AyABKAUSFAoLZmllbGQwbmFtZTUYlQMgASgFEhYKDWZpZWxkXzBfbmFtZTYY",
-            "lgMgASgFEhMKCmZpZWxkTmFtZTcYlwMgASgFEhMKCkZpZWxkTmFtZTgYmAMg",
-            "ASgFEhQKC2ZpZWxkX05hbWU5GJkDIAEoBRIVCgxGaWVsZF9OYW1lMTAYmgMg",
-            "ASgFEhUKDEZJRUxEX05BTUUxMRibAyABKAUSFQoMRklFTERfbmFtZTEyGJwD",
-            "IAEoBRIXCg5fX2ZpZWxkX25hbWUxMxidAyABKAUSFwoOX19GaWVsZF9uYW1l",
-            "MTQYngMgASgFEhYKDWZpZWxkX19uYW1lMTUYnwMgASgFEhYKDWZpZWxkX19O",
-            "YW1lMTYYoAMgASgFEhcKDmZpZWxkX25hbWUxN19fGKEDIAEoBRIXCg5GaWVs",
-            "ZF9uYW1lMThfXxiiAyABKAUaYgoNTmVzdGVkTWVzc2FnZRIJCgFhGAEgASgF",
-            "EkYKC2NvcmVjdXJzaXZlGAIgASgLMjEucHJvdG9idWZfdGVzdF9tZXNzYWdl",
-            "cy5wcm90bzIuVGVzdEFsbFR5cGVzUHJvdG8yGjQKEk1hcEludDMySW50MzJF",
-            "bnRyeRILCgNrZXkYASABKAUSDQoFdmFsdWUYAiABKAU6AjgBGjQKEk1hcElu",
-            "dDY0SW50NjRFbnRyeRILCgNrZXkYASABKAMSDQoFdmFsdWUYAiABKAM6AjgB",
-            "GjYKFE1hcFVpbnQzMlVpbnQzMkVudHJ5EgsKA2tleRgBIAEoDRINCgV2YWx1",
-            "ZRgCIAEoDToCOAEaNgoUTWFwVWludDY0VWludDY0RW50cnkSCwoDa2V5GAEg",
-            "ASgEEg0KBXZhbHVlGAIgASgEOgI4ARo2ChRNYXBTaW50MzJTaW50MzJFbnRy",
-            "eRILCgNrZXkYASABKBESDQoFdmFsdWUYAiABKBE6AjgBGjYKFE1hcFNpbnQ2",
-            "NFNpbnQ2NEVudHJ5EgsKA2tleRgBIAEoEhINCgV2YWx1ZRgCIAEoEjoCOAEa",
-            "OAoWTWFwRml4ZWQzMkZpeGVkMzJFbnRyeRILCgNrZXkYASABKAcSDQoFdmFs",
-            "dWUYAiABKAc6AjgBGjgKFk1hcEZpeGVkNjRGaXhlZDY0RW50cnkSCwoDa2V5",
-            "GAEgASgGEg0KBXZhbHVlGAIgASgGOgI4ARo6ChhNYXBTZml4ZWQzMlNmaXhl",
-            "ZDMyRW50cnkSCwoDa2V5GAEgASgPEg0KBXZhbHVlGAIgASgPOgI4ARo6ChhN",
-            "YXBTZml4ZWQ2NFNmaXhlZDY0RW50cnkSCwoDa2V5GAEgASgQEg0KBXZhbHVl",
-            "GAIgASgQOgI4ARo0ChJNYXBJbnQzMkZsb2F0RW50cnkSCwoDa2V5GAEgASgF",
-            "Eg0KBXZhbHVlGAIgASgCOgI4ARo1ChNNYXBJbnQzMkRvdWJsZUVudHJ5EgsK",
-            "A2tleRgBIAEoBRINCgV2YWx1ZRgCIAEoAToCOAEaMgoQTWFwQm9vbEJvb2xF",
-            "bnRyeRILCgNrZXkYASABKAgSDQoFdmFsdWUYAiABKAg6AjgBGjYKFE1hcFN0",
-            "cmluZ1N0cmluZ0VudHJ5EgsKA2tleRgBIAEoCRINCgV2YWx1ZRgCIAEoCToC",
-            "OAEaNQoTTWFwU3RyaW5nQnl0ZXNFbnRyeRILCgNrZXkYASABKAkSDQoFdmFs",
-            "dWUYAiABKAw6AjgBGn4KG01hcFN0cmluZ05lc3RlZE1lc3NhZ2VFbnRyeRIL",
-            "CgNrZXkYASABKAkSTgoFdmFsdWUYAiABKAsyPy5wcm90b2J1Zl90ZXN0X21l",
-            "c3NhZ2VzLnByb3RvMi5UZXN0QWxsVHlwZXNQcm90bzIuTmVzdGVkTWVzc2Fn",
-            "ZToCOAEacwocTWFwU3RyaW5nRm9yZWlnbk1lc3NhZ2VFbnRyeRILCgNrZXkY",
-            "ASABKAkSQgoFdmFsdWUYAiABKAsyMy5wcm90b2J1Zl90ZXN0X21lc3NhZ2Vz",
-            "LnByb3RvMi5Gb3JlaWduTWVzc2FnZVByb3RvMjoCOAEaeAoYTWFwU3RyaW5n",
-            "TmVzdGVkRW51bUVudHJ5EgsKA2tleRgBIAEoCRJLCgV2YWx1ZRgCIAEoDjI8",
+            "c2VidWQSHgoNZGVmYXVsdF9ieXRlcxj/ASABKAw6Bmpvc2h1YRITCgpmaWVs",
+            "ZG5hbWUxGJEDIAEoBRIUCgtmaWVsZF9uYW1lMhiSAyABKAUSFQoMX2ZpZWxk",
+            "X25hbWUzGJMDIAEoBRIWCg1maWVsZF9fbmFtZTRfGJQDIAEoBRIUCgtmaWVs",
+            "ZDBuYW1lNRiVAyABKAUSFgoNZmllbGRfMF9uYW1lNhiWAyABKAUSEwoKZmll",
+            "bGROYW1lNxiXAyABKAUSEwoKRmllbGROYW1lOBiYAyABKAUSFAoLZmllbGRf",
+            "TmFtZTkYmQMgASgFEhUKDEZpZWxkX05hbWUxMBiaAyABKAUSFQoMRklFTERf",
+            "TkFNRTExGJsDIAEoBRIVCgxGSUVMRF9uYW1lMTIYnAMgASgFEhcKDl9fZmll",
+            "bGRfbmFtZTEzGJ0DIAEoBRIXCg5fX0ZpZWxkX25hbWUxNBieAyABKAUSFgoN",
+            "ZmllbGRfX25hbWUxNRifAyABKAUSFgoNZmllbGRfX05hbWUxNhigAyABKAUS",
+            "FwoOZmllbGRfbmFtZTE3X18YoQMgASgFEhcKDkZpZWxkX25hbWUxOF9fGKID",
+            "IAEoBRpiCg1OZXN0ZWRNZXNzYWdlEgkKAWEYASABKAUSRgoLY29yZWN1cnNp",
+            "dmUYAiABKAsyMS5wcm90b2J1Zl90ZXN0X21lc3NhZ2VzLnByb3RvMi5UZXN0",
+            "QWxsVHlwZXNQcm90bzIaNAoSTWFwSW50MzJJbnQzMkVudHJ5EgsKA2tleRgB",
+            "IAEoBRINCgV2YWx1ZRgCIAEoBToCOAEaNAoSTWFwSW50NjRJbnQ2NEVudHJ5",
+            "EgsKA2tleRgBIAEoAxINCgV2YWx1ZRgCIAEoAzoCOAEaNgoUTWFwVWludDMy",
+            "VWludDMyRW50cnkSCwoDa2V5GAEgASgNEg0KBXZhbHVlGAIgASgNOgI4ARo2",
+            "ChRNYXBVaW50NjRVaW50NjRFbnRyeRILCgNrZXkYASABKAQSDQoFdmFsdWUY",
+            "AiABKAQ6AjgBGjYKFE1hcFNpbnQzMlNpbnQzMkVudHJ5EgsKA2tleRgBIAEo",
+            "ERINCgV2YWx1ZRgCIAEoEToCOAEaNgoUTWFwU2ludDY0U2ludDY0RW50cnkS",
+            "CwoDa2V5GAEgASgSEg0KBXZhbHVlGAIgASgSOgI4ARo4ChZNYXBGaXhlZDMy",
+            "Rml4ZWQzMkVudHJ5EgsKA2tleRgBIAEoBxINCgV2YWx1ZRgCIAEoBzoCOAEa",
+            "OAoWTWFwRml4ZWQ2NEZpeGVkNjRFbnRyeRILCgNrZXkYASABKAYSDQoFdmFs",
+            "dWUYAiABKAY6AjgBGjoKGE1hcFNmaXhlZDMyU2ZpeGVkMzJFbnRyeRILCgNr",
+            "ZXkYASABKA8SDQoFdmFsdWUYAiABKA86AjgBGjoKGE1hcFNmaXhlZDY0U2Zp",
+            "eGVkNjRFbnRyeRILCgNrZXkYASABKBASDQoFdmFsdWUYAiABKBA6AjgBGjQK",
+            "Ek1hcEludDMyRmxvYXRFbnRyeRILCgNrZXkYASABKAUSDQoFdmFsdWUYAiAB",
+            "KAI6AjgBGjUKE01hcEludDMyRG91YmxlRW50cnkSCwoDa2V5GAEgASgFEg0K",
+            "BXZhbHVlGAIgASgBOgI4ARoyChBNYXBCb29sQm9vbEVudHJ5EgsKA2tleRgB",
+            "IAEoCBINCgV2YWx1ZRgCIAEoCDoCOAEaNgoUTWFwU3RyaW5nU3RyaW5nRW50",
+            "cnkSCwoDa2V5GAEgASgJEg0KBXZhbHVlGAIgASgJOgI4ARo1ChNNYXBTdHJp",
+            "bmdCeXRlc0VudHJ5EgsKA2tleRgBIAEoCRINCgV2YWx1ZRgCIAEoDDoCOAEa",
+            "fgobTWFwU3RyaW5nTmVzdGVkTWVzc2FnZUVudHJ5EgsKA2tleRgBIAEoCRJO",
+            "CgV2YWx1ZRgCIAEoCzI/LnByb3RvYnVmX3Rlc3RfbWVzc2FnZXMucHJvdG8y",
+            "LlRlc3RBbGxUeXBlc1Byb3RvMi5OZXN0ZWRNZXNzYWdlOgI4ARpzChxNYXBT",
+            "dHJpbmdGb3JlaWduTWVzc2FnZUVudHJ5EgsKA2tleRgBIAEoCRJCCgV2YWx1",
+            "ZRgCIAEoCzIzLnByb3RvYnVmX3Rlc3RfbWVzc2FnZXMucHJvdG8yLkZvcmVp",
+            "Z25NZXNzYWdlUHJvdG8yOgI4ARp4ChhNYXBTdHJpbmdOZXN0ZWRFbnVtRW50",
+            "cnkSCwoDa2V5GAEgASgJEksKBXZhbHVlGAIgASgOMjwucHJvdG9idWZfdGVz",
+            "dF9tZXNzYWdlcy5wcm90bzIuVGVzdEFsbFR5cGVzUHJvdG8yLk5lc3RlZEVu",
+            "dW06AjgBGm0KGU1hcFN0cmluZ0ZvcmVpZ25FbnVtRW50cnkSCwoDa2V5GAEg",
+            "ASgJEj8KBXZhbHVlGAIgASgOMjAucHJvdG9idWZfdGVzdF9tZXNzYWdlcy5w",
+            "cm90bzIuRm9yZWlnbkVudW1Qcm90bzI6AjgBGjMKBERhdGESFAoLZ3JvdXBf",
+            "aW50MzIYygEgASgFEhUKDGdyb3VwX3VpbnQzMhjLASABKA0aIQoRTWVzc2Fn",
+            "ZVNldENvcnJlY3QqCAgEEP////8HOgIIARrgAQobTWVzc2FnZVNldENvcnJl",
+            "Y3RFeHRlbnNpb24xEgsKA3N0chgZIAEoCTKzAQoVbWVzc2FnZV9zZXRfZXh0",
+            "ZW5zaW9uEkMucHJvdG9idWZfdGVzdF9tZXNzYWdlcy5wcm90bzIuVGVzdEFs",
+            "bFR5cGVzUHJvdG8yLk1lc3NhZ2VTZXRDb3JyZWN0GPm7XiABKAsyTS5wcm90",
+            "b2J1Zl90ZXN0X21lc3NhZ2VzLnByb3RvMi5UZXN0QWxsVHlwZXNQcm90bzIu",
+            "TWVzc2FnZVNldENvcnJlY3RFeHRlbnNpb24xGt8BChtNZXNzYWdlU2V0Q29y",
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+            "bFR5cGVzUHJvdG8yLk1lc3NhZ2VTZXRDb3JyZWN0GJCz/AEgASgLMk0ucHJv",
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            "LnByb3RvYnVmX3Rlc3RfbWVzc2FnZXMucHJvdG8yLlRlc3RBbGxUeXBlc1By",
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-            "cHJvdG8yLlRlc3RBbGxUeXBlc1Byb3RvMi5NZXNzYWdlU2V0Q29ycmVjdBj5",
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-            "bFR5cGVzUHJvdG8yLk1lc3NhZ2VTZXRDb3JyZWN0RXh0ZW5zaW9uMRrfAQob",
-            "TWVzc2FnZVNldENvcnJlY3RFeHRlbnNpb24yEgkKAWkYCSABKAUytAEKFW1l",
-            "c3NhZ2Vfc2V0X2V4dGVuc2lvbhJDLnByb3RvYnVmX3Rlc3RfbWVzc2FnZXMu",
-            "cHJvdG8yLlRlc3RBbGxUeXBlc1Byb3RvMi5NZXNzYWdlU2V0Q29ycmVjdBiQ",
-            "s/wBIAEoCzJNLnByb3RvYnVmX3Rlc3RfbWVzc2FnZXMucHJvdG8yLlRlc3RB",
-            "bGxUeXBlc1Byb3RvMi5NZXNzYWdlU2V0Q29ycmVjdEV4dGVuc2lvbjIiOQoK",
-            "TmVzdGVkRW51bRIHCgNGT08QABIHCgNCQVIQARIHCgNCQVoQAhIQCgNORUcQ",
-            "////////////ASoFCHgQyQFCDQoLb25lb2ZfZmllbGRKBgjoBxCQTiIhChRG",
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-            "cm90bzISWgoNb3B0aW9uYWxncm91cBjsByABKAoyQi5wcm90b2J1Zl90ZXN0",
-            "X21lc3NhZ2VzLnByb3RvMi5Vbmtub3duVG9UZXN0QWxsVHlwZXMuT3B0aW9u",
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-            "bnQzMhjzByADKAUaGgoNT3B0aW9uYWxHcm91cBIJCgFhGAEgASgFIhYKFE51",
-            "bGxIeXBvdGhlc2lzUHJvdG8yIi8KDkVudW1Pbmx5UHJvdG8yIh0KBEJvb2wS",
-            "CgoGa0ZhbHNlEAASCQoFa1RydWUQASpGChFGb3JlaWduRW51bVByb3RvMhIP",
-            "CgtGT1JFSUdOX0ZPTxAAEg8KC0ZPUkVJR05fQkFSEAESDwoLRk9SRUlHTl9C",
-            "QVoQAjpKCg9leHRlbnNpb25faW50MzISMS5wcm90b2J1Zl90ZXN0X21lc3Nh",
-            "Z2VzLnByb3RvMi5UZXN0QWxsVHlwZXNQcm90bzIYeCABKAVCLwooY29tLmdv",
-            "b2dsZS5wcm90b2J1Zl90ZXN0X21lc3NhZ2VzLnByb3RvMkgB+AEB"));
+            "b3RvMhh4IAEoBUIvCihjb20uZ29vZ2xlLnByb3RvYnVmX3Rlc3RfbWVzc2Fn",
+            "ZXMucHJvdG8ySAH4AQE="));
      descriptor = pbr::FileDescriptor.FromGeneratedCode(descriptorData,
          new pbr::FileDescriptor[] { },
          new pbr::GeneratedClrTypeInfo(new[] {typeof(global::ProtobufTestMessages.Proto2.ForeignEnumProto2), }, new pb::Extension[] { TestMessagesProto2Extensions.ExtensionInt32 }, new pbr::GeneratedClrTypeInfo[] {
-            new pbr::GeneratedClrTypeInfo(typeof(global::ProtobufTestMessages.Proto2.TestAllTypesProto2), global::ProtobufTestMessages.Proto2.TestAllTypesProto2.Parser, new[]{ "OptionalInt32", "OptionalInt64", "OptionalUint32", "OptionalUint64", "OptionalSint32", "OptionalSint64", "OptionalFixed32", "OptionalFixed64", "OptionalSfixed32", "OptionalSfixed64", "OptionalFloat", "OptionalDouble", "OptionalBool", "OptionalString", "OptionalBytes", "OptionalNestedMessage", "OptionalForeignMessage", "OptionalNestedEnum", "OptionalForeignEnum", "OptionalStringPiece", "OptionalCord", "RecursiveMessage", "RepeatedInt32", "RepeatedInt64", "RepeatedUint32", "RepeatedUint64", "RepeatedSint32", "RepeatedSint64", "RepeatedFixed32", "RepeatedFixed64", "RepeatedSfixed32", "RepeatedSfixed64", "RepeatedFloat", "RepeatedDouble", "RepeatedBool", "RepeatedString", "RepeatedBytes", "RepeatedNestedMessage", "RepeatedForeignMessage", "RepeatedNestedEnum", "RepeatedForeignEnum", "RepeatedStringPiece", "RepeatedCord", "PackedInt32", "PackedInt64", "PackedUint32", "PackedUint64", "PackedSint32", "PackedSint64", "PackedFixed32", "PackedFixed64", "PackedSfixed32", "PackedSfixed64", "PackedFloat", "PackedDouble", "PackedBool", "PackedNestedEnum", "UnpackedInt32", "UnpackedInt64", "UnpackedUint32", "UnpackedUint64", "UnpackedSint32", "UnpackedSint64", "UnpackedFixed32", "UnpackedFixed64", "UnpackedSfixed32", "UnpackedSfixed64", "UnpackedFloat", "UnpackedDouble", "UnpackedBool", "UnpackedNestedEnum", "MapInt32Int32", "MapInt64Int64", "MapUint32Uint32", "MapUint64Uint64", "MapSint32Sint32", "MapSint64Sint64", "MapFixed32Fixed32", "MapFixed64Fixed64", "MapSfixed32Sfixed32", "MapSfixed64Sfixed64", "MapInt32Float", "MapInt32Double", "MapBoolBool", "MapStringString", "MapStringBytes", "MapStringNestedMessage", "MapStringForeignMessage", "MapStringNestedEnum", "MapStringForeignEnum", "OneofUint32", "OneofNestedMessage", "OneofString", "OneofBytes", "OneofBool", "OneofUint64", "OneofFloat", "OneofDouble", "OneofEnum", "Data", "DefaultInt32", "DefaultInt64", "DefaultUint32", "DefaultUint64", "DefaultSint32", "DefaultSint64", "DefaultFixed32", "DefaultFixed64", "DefaultSfixed32", "DefaultSfixed64", "DefaultFloat", "DefaultDouble", "DefaultBool", "DefaultString", "Fieldname1", "FieldName2", "FieldName3", "FieldName4", "Field0Name5", "Field0Name6", "FieldName7", "FieldName8", "FieldName9", "FieldName10", "FIELDNAME11", "FIELDName12", "FieldName13", "FieldName14", "FieldName15", "FieldName16", "FieldName17", "FieldName18" }, new[]{ "OneofField" }, new[]{ typeof(global::ProtobufTestMessages.Proto2.TestAllTypesProto2.Types.NestedEnum) }, null, new pbr::GeneratedClrTypeInfo[] { new pbr::GeneratedClrTypeInfo(typeof(global::ProtobufTestMessages.Proto2.TestAllTypesProto2.Types.NestedMessage), global::ProtobufTestMessages.Proto2.TestAllTypesProto2.Types.NestedMessage.Parser, new[]{ "A", "Corecursive" }, null, null, null, null),
+            new pbr::GeneratedClrTypeInfo(typeof(global::ProtobufTestMessages.Proto2.TestAllTypesProto2), global::ProtobufTestMessages.Proto2.TestAllTypesProto2.Parser, new[]{ "OptionalInt32", "OptionalInt64", "OptionalUint32", "OptionalUint64", "OptionalSint32", "OptionalSint64", "OptionalFixed32", "OptionalFixed64", "OptionalSfixed32", "OptionalSfixed64", "OptionalFloat", "OptionalDouble", "OptionalBool", "OptionalString", "OptionalBytes", "OptionalNestedMessage", "OptionalForeignMessage", "OptionalNestedEnum", "OptionalForeignEnum", "OptionalStringPiece", "OptionalCord", "RecursiveMessage", "RepeatedInt32", "RepeatedInt64", "RepeatedUint32", "RepeatedUint64", "RepeatedSint32", "RepeatedSint64", "RepeatedFixed32", "RepeatedFixed64", "RepeatedSfixed32", "RepeatedSfixed64", "RepeatedFloat", "RepeatedDouble", "RepeatedBool", "RepeatedString", "RepeatedBytes", "RepeatedNestedMessage", "RepeatedForeignMessage", "RepeatedNestedEnum", "RepeatedForeignEnum", "RepeatedStringPiece", "RepeatedCord", "PackedInt32", "PackedInt64", "PackedUint32", "PackedUint64", "PackedSint32", "PackedSint64", "PackedFixed32", "PackedFixed64", "PackedSfixed32", "PackedSfixed64", "PackedFloat", "PackedDouble", "PackedBool", "PackedNestedEnum", "UnpackedInt32", "UnpackedInt64", "UnpackedUint32", "UnpackedUint64", "UnpackedSint32", "UnpackedSint64", "UnpackedFixed32", "UnpackedFixed64", "UnpackedSfixed32", "UnpackedSfixed64", "UnpackedFloat", "UnpackedDouble", "UnpackedBool", "UnpackedNestedEnum", "MapInt32Int32", "MapInt64Int64", "MapUint32Uint32", "MapUint64Uint64", "MapSint32Sint32", "MapSint64Sint64", "MapFixed32Fixed32", "MapFixed64Fixed64", "MapSfixed32Sfixed32", "MapSfixed64Sfixed64", "MapInt32Float", "MapInt32Double", "MapBoolBool", "MapStringString", "MapStringBytes", "MapStringNestedMessage", "MapStringForeignMessage", "MapStringNestedEnum", "MapStringForeignEnum", "OneofUint32", "OneofNestedMessage", "OneofString", "OneofBytes", "OneofBool", "OneofUint64", "OneofFloat", "OneofDouble", "OneofEnum", "Data", "DefaultInt32", "DefaultInt64", "DefaultUint32", "DefaultUint64", "DefaultSint32", "DefaultSint64", "DefaultFixed32", "DefaultFixed64", "DefaultSfixed32", "DefaultSfixed64", "DefaultFloat", "DefaultDouble", "DefaultBool", "DefaultString", "DefaultBytes", "Fieldname1", "FieldName2", "FieldName3", "FieldName4", "Field0Name5", "Field0Name6", "FieldName7", "FieldName8", "FieldName9", "FieldName10", "FIELDNAME11", "FIELDName12", "FieldName13", "FieldName14", "FieldName15", "FieldName16", "FieldName17", "FieldName18" }, new[]{ "OneofField" }, new[]{ typeof(global::ProtobufTestMessages.Proto2.TestAllTypesProto2.Types.NestedEnum) }, null, new pbr::GeneratedClrTypeInfo[] { new pbr::GeneratedClrTypeInfo(typeof(global::ProtobufTestMessages.Proto2.TestAllTypesProto2.Types.NestedMessage), global::ProtobufTestMessages.Proto2.TestAllTypesProto2.Types.NestedMessage.Parser, new[]{ "A", "Corecursive" }, null, null, null, null),
            null, null, null, null, null, null, null, null, null, null, null, null, null, null, null, null, null, null, null, new pbr::GeneratedClrTypeInfo(typeof(global::ProtobufTestMessages.Proto2.TestAllTypesProto2.Types.Data), global::ProtobufTestMessages.Proto2.TestAllTypesProto2.Types.Data.Parser, new[]{ "GroupInt32", "GroupUint32" }, null, null, null, null),
            new pbr::GeneratedClrTypeInfo(typeof(global::ProtobufTestMessages.Proto2.TestAllTypesProto2.Types.MessageSetCorrect), global::ProtobufTestMessages.Proto2.TestAllTypesProto2.Types.MessageSetCorrect.Parser, null, null, null, null, null),
            new pbr::GeneratedClrTypeInfo(typeof(global::ProtobufTestMessages.Proto2.TestAllTypesProto2.Types.MessageSetCorrectExtension1), global::ProtobufTestMessages.Proto2.TestAllTypesProto2.Types.MessageSetCorrectExtension1.Parser, new[]{ "Str" }, null, null, new pb::Extension[] { global::ProtobufTestMessages.Proto2.TestAllTypesProto2.Types.MessageSetCorrectExtension1.Extensions.MessageSetExtension }, null),
@ -228,7 +230,8 @@ namespace ProtobufTestMessages.Proto2 {
            new pbr::GeneratedClrTypeInfo(typeof(global::ProtobufTestMessages.Proto2.ForeignMessageProto2), global::ProtobufTestMessages.Proto2.ForeignMessageProto2.Parser, new[]{ "C" }, null, null, null, null),
            new pbr::GeneratedClrTypeInfo(typeof(global::ProtobufTestMessages.Proto2.UnknownToTestAllTypes), global::ProtobufTestMessages.Proto2.UnknownToTestAllTypes.Parser, new[]{ "OptionalInt32", "OptionalString", "NestedMessage", "OptionalGroup", "OptionalBool", "RepeatedInt32" }, null, null, null, new pbr::GeneratedClrTypeInfo[] { new pbr::GeneratedClrTypeInfo(typeof(global::ProtobufTestMessages.Proto2.UnknownToTestAllTypes.Types.OptionalGroup), global::ProtobufTestMessages.Proto2.UnknownToTestAllTypes.Types.OptionalGroup.Parser, new[]{ "A" }, null, null, null, null)}),
            new pbr::GeneratedClrTypeInfo(typeof(global::ProtobufTestMessages.Proto2.NullHypothesisProto2), global::ProtobufTestMessages.Proto2.NullHypothesisProto2.Parser, null, null, null, null, null),
-            new pbr::GeneratedClrTypeInfo(typeof(global::ProtobufTestMessages.Proto2.EnumOnlyProto2), global::ProtobufTestMessages.Proto2.EnumOnlyProto2.Parser, null, null, new[]{ typeof(global::ProtobufTestMessages.Proto2.EnumOnlyProto2.Types.Bool) }, null, null)
+            new pbr::GeneratedClrTypeInfo(typeof(global::ProtobufTestMessages.Proto2.EnumOnlyProto2), global::ProtobufTestMessages.Proto2.EnumOnlyProto2.Parser, null, null, new[]{ typeof(global::ProtobufTestMessages.Proto2.EnumOnlyProto2.Types.Bool) }, null, null),
+            new pbr::GeneratedClrTypeInfo(typeof(global::ProtobufTestMessages.Proto2.OneStringProto2), global::ProtobufTestMessages.Proto2.OneStringProto2.Parser, new[]{ "Data" }, null, null, null, null)
          }));
    }
    #endregion
@ -404,6 +407,7 @@ namespace ProtobufTestMessages.Proto2 {
      defaultDouble_ = other.defaultDouble_;
      defaultBool_ = other.defaultBool_;
      defaultString_ = other.defaultString_;
+      defaultBytes_ = other.defaultBytes_;
      fieldname1_ = other.fieldname1_;
      fieldName2_ = other.fieldName2_;
      FieldName3_ = other.FieldName3_;
@ -2394,6 +2398,32 @@ namespace ProtobufTestMessages.Proto2 {
      defaultString_ = null;
    }

+    /// <summary>Field number for the "default_bytes" field.</summary>
+    public const int DefaultBytesFieldNumber = 255;
+    private readonly static pb::ByteString DefaultBytesDefaultValue = pb::ByteString.FromBase64("am9zaHVh");
+
+    private pb::ByteString defaultBytes_;
+    [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
+    [global::System.CodeDom.Compiler.GeneratedCode("protoc", null)]
+    public pb::ByteString DefaultBytes {
+      get { return defaultBytes_ ?? DefaultBytesDefaultValue; }
+      set {
+        defaultBytes_ = pb::ProtoPreconditions.CheckNotNull(value, "value");
+      }
+    }
+    /// <summary>Gets whether the "default_bytes" field is set</summary>
+    [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
+    [global::System.CodeDom.Compiler.GeneratedCode("protoc", null)]
+    public bool HasDefaultBytes {
+      get { return defaultBytes_ != null; }
+    }
+    /// <summary>Clears the value of the "default_bytes" field</summary>
+    [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
+    [global::System.CodeDom.Compiler.GeneratedCode("protoc", null)]
+    public void ClearDefaultBytes() {
+      defaultBytes_ = null;
+    }
+
    /// <summary>Field number for the "fieldname1" field.</summary>
    public const int Fieldname1FieldNumber = 401;
    private readonly static int Fieldname1DefaultValue = 0;
@ -3041,6 +3071,7 @@ namespace ProtobufTestMessages.Proto2 {
      if (!pbc::ProtobufEqualityComparers.BitwiseDoubleEqualityComparer.Equals(DefaultDouble, other.DefaultDouble)) return false;
      if (DefaultBool != other.DefaultBool) return false;
      if (DefaultString != other.DefaultString) return false;
+      if (DefaultBytes != other.DefaultBytes) return false;
      if (Fieldname1 != other.Fieldname1) return false;
      if (FieldName2 != other.FieldName2) return false;
      if (FieldName3 != other.FieldName3) return false;
@ -3184,6 +3215,7 @@ namespace ProtobufTestMessages.Proto2 {
      if (HasDefaultDouble) hash ^= pbc::ProtobufEqualityComparers.BitwiseDoubleEqualityComparer.GetHashCode(DefaultDouble);
      if (HasDefaultBool) hash ^= DefaultBool.GetHashCode();
      if (HasDefaultString) hash ^= DefaultString.GetHashCode();
+      if (HasDefaultBytes) hash ^= DefaultBytes.GetHashCode();
      if (HasFieldname1) hash ^= Fieldname1.GetHashCode();
      if (HasFieldName2) hash ^= FieldName2.GetHashCode();
      if (HasFieldName3) hash ^= FieldName3.GetHashCode();
@ -3477,6 +3509,10 @@ namespace ProtobufTestMessages.Proto2 {
        output.WriteRawTag(242, 15);
        output.WriteString(DefaultString);
      }
+      if (HasDefaultBytes) {
+        output.WriteRawTag(250, 15);
+        output.WriteBytes(DefaultBytes);
+      }
      if (HasFieldname1) {
        output.WriteRawTag(136, 25);
        output.WriteInt32(Fieldname1);
@ -3815,6 +3851,10 @@ namespace ProtobufTestMessages.Proto2 {
        output.WriteRawTag(242, 15);
        output.WriteString(DefaultString);
      }
+      if (HasDefaultBytes) {
+        output.WriteRawTag(250, 15);
+        output.WriteBytes(DefaultBytes);
+      }
      if (HasFieldname1) {
        output.WriteRawTag(136, 25);
        output.WriteInt32(Fieldname1);
@ -4106,6 +4146,9 @@ namespace ProtobufTestMessages.Proto2 {
      if (HasDefaultString) {
        size += 2 + pb::CodedOutputStream.ComputeStringSize(DefaultString);
      }
+      if (HasDefaultBytes) {
+        size += 2 + pb::CodedOutputStream.ComputeBytesSize(DefaultBytes);
+      }
      if (HasFieldname1) {
        size += 2 + pb::CodedOutputStream.ComputeInt32Size(Fieldname1);
      }
@ -4366,6 +4409,9 @@ namespace ProtobufTestMessages.Proto2 {
      if (other.HasDefaultString) {
        DefaultString = other.DefaultString;
      }
+      if (other.HasDefaultBytes) {
+        DefaultBytes = other.DefaultBytes;
+      }
      if (other.HasFieldname1) {
        Fieldname1 = other.Fieldname1;
      }
@ -4988,6 +5034,10 @@ namespace ProtobufTestMessages.Proto2 {
            DefaultString = input.ReadString();
            break;
          }
+          case 2042: {
+            DefaultBytes = input.ReadBytes();
+            break;
+          }
          case 3208: {
            Fieldname1 = input.ReadInt32();
            break;
@ -5594,6 +5644,10 @@ namespace ProtobufTestMessages.Proto2 {
            DefaultString = input.ReadString();
            break;
          }
+          case 2042: {
+            DefaultBytes = input.ReadBytes();
+            break;
+          }
          case 3208: {
            Fieldname1 = input.ReadInt32();
            break;
@ -8043,6 +8097,209 @@ namespace ProtobufTestMessages.Proto2 {

  }

+  public sealed partial class OneStringProto2 : pb::IMessage<OneStringProto2>
+  #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
+      , pb::IBufferMessage
+  #endif
+  {
+    private static readonly pb::MessageParser<OneStringProto2> _parser = new pb::MessageParser<OneStringProto2>(() => new OneStringProto2());
+    private pb::UnknownFieldSet _unknownFields;
+    [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
+    [global::System.CodeDom.Compiler.GeneratedCode("protoc", null)]
+    public static pb::MessageParser<OneStringProto2> Parser { get { return _parser; } }
+
+    [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
+    [global::System.CodeDom.Compiler.GeneratedCode("protoc", null)]
+    public static pbr::MessageDescriptor Descriptor {
+      get { return global::ProtobufTestMessages.Proto2.TestMessagesProto2Reflection.Descriptor.MessageTypes[5]; }
+    }
+
+    [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
+    [global::System.CodeDom.Compiler.GeneratedCode("protoc", null)]
+    pbr::MessageDescriptor pb::IMessage.Descriptor {
+      get { return Descriptor; }
+    }
+
+    [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
+    [global::System.CodeDom.Compiler.GeneratedCode("protoc", null)]
+    public OneStringProto2() {
+      OnConstruction();
+    }
+
+    partial void OnConstruction();
+
+    [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
+    [global::System.CodeDom.Compiler.GeneratedCode("protoc", null)]
+    public OneStringProto2(OneStringProto2 other) : this() {
+      data_ = other.data_;
+      _unknownFields = pb::UnknownFieldSet.Clone(other._unknownFields);
+    }
+
+    [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
+    [global::System.CodeDom.Compiler.GeneratedCode("protoc", null)]
+    public OneStringProto2 Clone() {
+      return new OneStringProto2(this);
+    }
+
+    /// <summary>Field number for the "data" field.</summary>
+    public const int DataFieldNumber = 1;
+    private readonly static string DataDefaultValue = "";
+
+    private string data_;
+    [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
+    [global::System.CodeDom.Compiler.GeneratedCode("protoc", null)]
+    public string Data {
+      get { return data_ ?? DataDefaultValue; }
+      set {
+        data_ = pb::ProtoPreconditions.CheckNotNull(value, "value");
+      }
+    }
+    /// <summary>Gets whether the "data" field is set</summary>
+    [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
+    [global::System.CodeDom.Compiler.GeneratedCode("protoc", null)]
+    public bool HasData {
+      get { return data_ != null; }
+    }
+    /// <summary>Clears the value of the "data" field</summary>
+    [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
+    [global::System.CodeDom.Compiler.GeneratedCode("protoc", null)]
+    public void ClearData() {
+      data_ = null;
+    }
+
+    [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
+    [global::System.CodeDom.Compiler.GeneratedCode("protoc", null)]
+    public override bool Equals(object other) {
+      return Equals(other as OneStringProto2);
+    }
+
+    [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
+    [global::System.CodeDom.Compiler.GeneratedCode("protoc", null)]
+    public bool Equals(OneStringProto2 other) {
+      if (ReferenceEquals(other, null)) {
+        return false;
+      }
+      if (ReferenceEquals(other, this)) {
+        return true;
+      }
+      if (Data != other.Data) return false;
+      return Equals(_unknownFields, other._unknownFields);
+    }
+
+    [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
+    [global::System.CodeDom.Compiler.GeneratedCode("protoc", null)]
+    public override int GetHashCode() {
+      int hash = 1;
+      if (HasData) hash ^= Data.GetHashCode();
+      if (_unknownFields != null) {
+        hash ^= _unknownFields.GetHashCode();
+      }
+      return hash;
+    }
+
+    [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
+    [global::System.CodeDom.Compiler.GeneratedCode("protoc", null)]
+    public override string ToString() {
+      return pb::JsonFormatter.ToDiagnosticString(this);
+    }
+
+    [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
+    [global::System.CodeDom.Compiler.GeneratedCode("protoc", null)]
+    public void WriteTo(pb::CodedOutputStream output) {
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
+      output.WriteRawMessage(this);
+    #else
+      if (HasData) {
+        output.WriteRawTag(10);
+        output.WriteString(Data);
+      }
+      if (_unknownFields != null) {
+        _unknownFields.WriteTo(output);
+      }
+    #endif
+    }
+
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
+    [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
+    [global::System.CodeDom.Compiler.GeneratedCode("protoc", null)]
+    void pb::IBufferMessage.InternalWriteTo(ref pb::WriteContext output) {
+      if (HasData) {
+        output.WriteRawTag(10);
+        output.WriteString(Data);
+      }
+      if (_unknownFields != null) {
+        _unknownFields.WriteTo(ref output);
+      }
+    }
+    #endif
+
+    [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
+    [global::System.CodeDom.Compiler.GeneratedCode("protoc", null)]
+    public int CalculateSize() {
+      int size = 0;
+      if (HasData) {
+        size += 1 + pb::CodedOutputStream.ComputeStringSize(Data);
+      }
+      if (_unknownFields != null) {
+        size += _unknownFields.CalculateSize();
+      }
+      return size;
+    }
+
+    [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
+    [global::System.CodeDom.Compiler.GeneratedCode("protoc", null)]
+    public void MergeFrom(OneStringProto2 other) {
+      if (other == null) {
+        return;
+      }
+      if (other.HasData) {
+        Data = other.Data;
+      }
+      _unknownFields = pb::UnknownFieldSet.MergeFrom(_unknownFields, other._unknownFields);
+    }
+
+    [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
+    [global::System.CodeDom.Compiler.GeneratedCode("protoc", null)]
+    public void MergeFrom(pb::CodedInputStream input) {
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
+      input.ReadRawMessage(this);
+    #else
+      uint tag;
+      while ((tag = input.ReadTag()) != 0) {
+        switch(tag) {
+          default:
+            _unknownFields = pb::UnknownFieldSet.MergeFieldFrom(_unknownFields, input);
+            break;
+          case 10: {
+            Data = input.ReadString();
+            break;
+          }
+        }
+      }
+    #endif
+    }
+
+    #if !GOOGLE_PROTOBUF_REFSTRUCT_COMPATIBILITY_MODE
+    [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
+    [global::System.CodeDom.Compiler.GeneratedCode("protoc", null)]
+    void pb::IBufferMessage.InternalMergeFrom(ref pb::ParseContext input) {
+      uint tag;
+      while ((tag = input.ReadTag()) != 0) {
+        switch(tag) {
+          default:
+            _unknownFields = pb::UnknownFieldSet.MergeFieldFrom(_unknownFields, ref input);
+            break;
+          case 10: {
+            Data = input.ReadString();
+            break;
+          }
+        }
+      }
+    }
+    #endif
+
+  }
+
  #endregion

 }
--- a/csharp/src/Google.Protobuf.Test/Collections/RepeatedFieldTest.cs
+++ b/csharp/src/Google.Protobuf.Test/Collections/RepeatedFieldTest.cs
@ -840,7 +840,7 @@ namespace Google.Protobuf.Collections
            var list2 = new RepeatedField<double> { SampleNaNs.Regular, SampleNaNs.PayloadFlipped };
            var list3 = new RepeatedField<double> { SampleNaNs.Regular, SampleNaNs.SignallingFlipped };

-            // All SampleNaNs have the same hashcode under certain targets (e.g. netcoreapp2.1)
+            // All SampleNaNs have the same hashcode under certain targets (e.g. netcoreapp3.1)
            EqualityTester.AssertInequality(list1, list2, checkHashcode: false);
            EqualityTester.AssertEquality(list1, list3);
            Assert.True(list1.Contains(SampleNaNs.SignallingFlipped));
--- a/csharp/src/Google.Protobuf.Test/GeneratedMessageTest.Proto2.cs
+++ b/csharp/src/Google.Protobuf.Test/GeneratedMessageTest.Proto2.cs
@ -380,5 +380,18 @@ namespace Google.Protobuf
                TestGroupExtension.Parser.WithExtensionRegistry(new ExtensionRegistry() { TestNestedExtension.Extensions.OptionalGroupExtension }),
                message);
        }
+
+        [Test]
+        public void RoundTrip_ParseUsingCodedInput()
+        {
+            var message = new TestAllExtensions();
+            message.SetExtension(UnittestExtensions.OptionalBoolExtension, true);
+            byte[] bytes = message.ToByteArray();
+            using (CodedInputStream input = new CodedInputStream(bytes))
+            {
+                var parsed = TestAllExtensions.Parser.WithExtensionRegistry(new ExtensionRegistry() { UnittestExtensions.OptionalBoolExtension }).ParseFrom(input);
+                Assert.AreEqual(message, parsed);
+            }
+        }
    }
 }
--- a/csharp/src/Google.Protobuf.Test/Google.Protobuf.Test.csproj
+++ b/csharp/src/Google.Protobuf.Test/Google.Protobuf.Test.csproj
@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">

  <PropertyGroup>
-    <TargetFrameworks>net451;netcoreapp2.1;net50</TargetFrameworks>
+    <TargetFrameworks>net451;netcoreapp3.1;net60</TargetFrameworks>
    <AssemblyOriginatorKeyFile>../../keys/Google.Protobuf.snk</AssemblyOriginatorKeyFile>
    <SignAssembly>true</SignAssembly>
    <IsPackable>False</IsPackable>
@ -21,7 +21,7 @@

  <!-- Needed for the net45 build to work on Unix. See https://github.com/dotnet/designs/pull/33 -->
  <ItemGroup>
-    <PackageReference Include="Microsoft.NETFramework.ReferenceAssemblies" Version="1.0.0-preview.2" PrivateAssets="All" />
+    <PackageReference Include="Microsoft.NETFramework.ReferenceAssemblies" Version="1.0.0" PrivateAssets="All" />
  </ItemGroup>

  <ItemGroup>
--- a/csharp/src/Google.Protobuf.Test/JsonParserTest.cs
+++ b/csharp/src/Google.Protobuf.Test/JsonParserTest.cs
@ -35,6 +35,7 @@ using Google.Protobuf.TestProtos;
 using Google.Protobuf.WellKnownTypes;
 using NUnit.Framework;
 using ProtobufTestMessages.Proto2;
+using ProtobufTestMessages.Proto3;
 using System;
 using UnitTest.Issues.TestProtos;

@ -551,13 +552,9 @@ namespace Google.Protobuf
        }

        [Test]
-        // Skip these test cases in .NET 5 because floating point parsing supports bigger values.
-        // These big values won't throw an error in the test.
-#if !NET5_0
        [TestCase("1.7977e308")]
        [TestCase("-1.7977e308")]
        [TestCase("1e309")]
-#endif
        [TestCase("1,0")]
        [TestCase("1.0.0")]
        [TestCase("+1")]
@ -922,10 +919,10 @@ namespace Google.Protobuf
        }

        [Test]
-        [TestCase("\"FOREIGN_BAR\"", ForeignEnum.ForeignBar)]
-        [TestCase("5", ForeignEnum.ForeignBar)]
-        [TestCase("100", (ForeignEnum)100)]
-        public void EnumValid(string value, ForeignEnum expectedValue)
+        [TestCase("\"FOREIGN_BAR\"", TestProtos.ForeignEnum.ForeignBar)]
+        [TestCase("5", TestProtos.ForeignEnum.ForeignBar)]
+        [TestCase("100", (TestProtos.ForeignEnum)100)]
+        public void EnumValid(string value, TestProtos.ForeignEnum expectedValue)
        {
            string json = "{ \"singleForeignEnum\": " + value + " }";
            var parsed = TestAllTypes.Parser.ParseJson(json);
@ -1025,5 +1022,128 @@ namespace Google.Protobuf
        {
            return '"' + text + '"';
        }
+
+        [Test]
+        public void ParseAllNullValues()
+        {
+            string json = @"{
+  ""optionalInt32"": null,
+  ""optionalInt64"": null,
+  ""optionalUint32"": null,
+  ""optionalUint64"": null,
+  ""optionalSint32"": null,
+  ""optionalSint64"": null,
+  ""optionalFixed32"": null,
+  ""optionalFixed64"": null,
+  ""optionalSfixed32"": null,
+  ""optionalSfixed64"": null,
+  ""optionalFloat"": null,
+  ""optionalDouble"": null,
+  ""optionalBool"": null,
+  ""optionalString"": null,
+  ""optionalBytes"": null,
+  ""optionalNestedEnum"": null,
+  ""optionalNestedMessage"": null,
+  ""repeatedInt32"": null,
+  ""repeatedInt64"": null,
+  ""repeatedUint32"": null,
+  ""repeatedUint64"": null,
+  ""repeatedSint32"": null,
+  ""repeatedSint64"": null,
+  ""repeatedFixed32"": null,
+  ""repeatedFixed64"": null,
+  ""repeatedSfixed32"": null,
+  ""repeatedSfixed64"": null,
+  ""repeatedFloat"": null,
+  ""repeatedDouble"": null,
+  ""repeatedBool"": null,
+  ""repeatedString"": null,
+  ""repeatedBytes"": null,
+  ""repeatedNestedEnum"": null,
+  ""repeatedNestedMessage"": null,
+  ""mapInt32Int32"": null,
+  ""mapBoolBool"": null,
+  ""mapStringNestedMessage"": null
+}";
+
+            TestAllTypesProto3 message = new TestAllTypesProto3();
+
+            message.OptionalInt32 = 1;
+            message.OptionalInt64 = 1;
+            message.OptionalUint32 = 1;
+            message.OptionalUint64 = 1;
+            message.OptionalSint32 = 1;
+            message.OptionalSint64 = 1;
+            message.OptionalFixed32 = 1;
+            message.OptionalFixed64 = 1;
+            message.OptionalSfixed32 = 1;
+            message.OptionalSfixed64 = 1;
+            message.OptionalFloat = 1;
+            message.OptionalDouble = 1;
+            message.OptionalBool = true;
+            message.OptionalString = "1";
+            message.OptionalBytes = ByteString.CopyFrom(new byte[] { 1 });
+            message.OptionalNestedEnum = TestAllTypesProto3.Types.NestedEnum.Bar;
+            message.OptionalNestedMessage = new TestAllTypesProto3.Types.NestedMessage();
+            message.RepeatedInt32.Add(1);
+            message.RepeatedInt64.Add(1);
+            message.RepeatedUint32.Add(1);
+            message.RepeatedUint64.Add(1);
+            message.RepeatedSint32.Add(1);
+            message.RepeatedSint64.Add(1);
+            message.RepeatedFixed32.Add(1);
+            message.RepeatedFixed64.Add(1);
+            message.RepeatedSfixed32.Add(1);
+            message.RepeatedSfixed64.Add(1);
+            message.RepeatedFloat.Add(1);
+            message.RepeatedDouble.Add(1);
+            message.RepeatedBool.Add(true);
+            message.RepeatedString.Add("1");
+            message.RepeatedBytes.Add(ByteString.CopyFrom(new byte[] { 1 }));
+            message.RepeatedNestedEnum.Add(TestAllTypesProto3.Types.NestedEnum.Bar);
+            message.RepeatedNestedMessage.Add(new TestAllTypesProto3.Types.NestedMessage());
+            message.MapInt32Int32.Add(1, 1);
+            message.MapBoolBool.Add(true, true);
+            message.MapStringNestedMessage.Add(" ", new TestAllTypesProto3.Types.NestedMessage());
+
+            JsonParser.Default.Merge(message, json);
+
+            Assert.AreEqual(0, message.OptionalInt32);
+            Assert.AreEqual(0, message.OptionalInt64);
+            Assert.AreEqual(0, message.OptionalUint32);
+            Assert.AreEqual(0, message.OptionalUint64);
+            Assert.AreEqual(0, message.OptionalSint32);
+            Assert.AreEqual(0, message.OptionalSint64);
+            Assert.AreEqual(0, message.OptionalFixed32);
+            Assert.AreEqual(0, message.OptionalFixed64);
+            Assert.AreEqual(0, message.OptionalSfixed32);
+            Assert.AreEqual(0, message.OptionalSfixed64);
+            Assert.AreEqual(0, message.OptionalFloat);
+            Assert.AreEqual(0, message.OptionalDouble);
+            Assert.AreEqual(false, message.OptionalBool);
+            Assert.AreEqual("", message.OptionalString);
+            Assert.AreEqual(ByteString.Empty, message.OptionalBytes);
+            Assert.AreEqual(TestAllTypesProto3.Types.NestedEnum.Foo, message.OptionalNestedEnum);
+            Assert.AreEqual(null, message.OptionalNestedMessage);
+            Assert.AreEqual(0, message.RepeatedInt32.Count);
+            Assert.AreEqual(0, message.RepeatedInt64.Count);
+            Assert.AreEqual(0, message.RepeatedUint32.Count);
+            Assert.AreEqual(0, message.RepeatedUint64.Count);
+            Assert.AreEqual(0, message.RepeatedSint32.Count);
+            Assert.AreEqual(0, message.RepeatedSint64.Count);
+            Assert.AreEqual(0, message.RepeatedFixed32.Count);
+            Assert.AreEqual(0, message.RepeatedFixed64.Count);
+            Assert.AreEqual(0, message.RepeatedSfixed32.Count);
+            Assert.AreEqual(0, message.RepeatedFloat.Count);
+            Assert.AreEqual(0, message.RepeatedDouble.Count);
+            Assert.AreEqual(0, message.RepeatedBool.Count);
+            Assert.AreEqual(0, message.RepeatedString.Count);
+            Assert.AreEqual(0, message.RepeatedBytes.Count);
+            Assert.AreEqual(0, message.RepeatedNestedEnum.Count);
+            Assert.AreEqual(0, message.RepeatedNestedMessage.Count);
+            Assert.AreEqual(0, message.MapInt32Int32.Count);
+            Assert.AreEqual(0, message.MapBoolBool.Count);
+            Assert.AreEqual(0, message.MapStringNestedMessage.Count);
+        }
    }
 }
--- a/csharp/src/Google.Protobuf.Test/JsonTokenizerTest.cs
+++ b/csharp/src/Google.Protobuf.Test/JsonTokenizerTest.cs
@ -199,12 +199,8 @@ namespace Google.Protobuf
        [TestCase("1e-")]
        [TestCase("--")]
        [TestCase("--1")]
-        // Skip these test cases in .NET 5 because floating point parsing supports bigger values.
-        // These big values won't throw an error in the test.
-#if !NET5_0
        [TestCase("-1.7977e308")]
        [TestCase("1.7977e308")]
-#endif
        public void InvalidNumberValue(string json)
        {
            AssertThrowsAfter(json);
--- a/csharp/src/Google.Protobuf.Test/Reflection/DescriptorsTest.cs
+++ b/csharp/src/Google.Protobuf.Test/Reflection/DescriptorsTest.cs
@ -124,6 +124,7 @@ namespace Google.Protobuf.Reflection
            }

            Assert.AreEqual(10, file.SerializedData[0]);
+            TestDescriptorToProto(file.ToProto, file.Proto);
        }

        [Test]
@ -231,6 +232,7 @@ namespace Google.Protobuf.Reflection
            {
                Assert.AreEqual(i, messageType.EnumTypes[i].Index);
            }
+            TestDescriptorToProto(messageType.ToProto, messageType.Proto);
        }

        [Test]
@ -294,6 +296,11 @@ namespace Google.Protobuf.Reflection
            // For a field in a regular onoef, ContainingOneof and RealContainingOneof should be the same.
            Assert.AreEqual("oneof_field", fieldInOneof.ContainingOneof.Name);
            Assert.AreSame(fieldInOneof.ContainingOneof, fieldInOneof.RealContainingOneof);
+
+            TestDescriptorToProto(primitiveField.ToProto, primitiveField.Proto);
+            TestDescriptorToProto(enumField.ToProto, enumField.Proto);
+            TestDescriptorToProto(foreignMessageField.ToProto, foreignMessageField.Proto);
+            TestDescriptorToProto(fieldInOneof.ToProto, fieldInOneof.Proto);
        }

        [Test]
@ -338,6 +345,8 @@ namespace Google.Protobuf.Reflection
            {
                Assert.AreEqual(i, enumType.Values[i].Index);
            }
+            TestDescriptorToProto(enumType.ToProto, enumType.Proto);
+            TestDescriptorToProto(nestedType.ToProto, nestedType.Proto);
        }

        [Test]
@ -361,6 +370,7 @@ namespace Google.Protobuf.Reflection
            }

            CollectionAssert.AreEquivalent(expectedFields, descriptor.Fields);
+            TestDescriptorToProto(descriptor.ToProto, descriptor.Proto);
        }

        [Test]
@ -370,6 +380,7 @@ namespace Google.Protobuf.Reflection
            Assert.IsNull(descriptor.Parser);
            Assert.IsNull(descriptor.ClrType);
            Assert.IsNull(descriptor.Fields[1].Accessor);
+            TestDescriptorToProto(descriptor.ToProto, descriptor.Proto);
        }

        // From TestFieldOrdering:
@ -391,6 +402,7 @@ namespace Google.Protobuf.Reflection
        {
            var descriptor = Google.Protobuf.Reflection.FileDescriptor.DescriptorProtoFileDescriptor;
            Assert.AreEqual("google/protobuf/descriptor.proto", descriptor.Name);
+            TestDescriptorToProto(descriptor.ToProto, descriptor.Proto);
        }

        [Test]
@ -453,5 +465,17 @@ namespace Google.Protobuf.Reflection
                }
            }
        }
+
+        private static void TestDescriptorToProto(Func<IMessage> toProtoFunction, IMessage expectedProto)
+        {
+            var clone1 = toProtoFunction();
+            var clone2 = toProtoFunction();
+            Assert.AreNotSame(clone1, clone2);
+            Assert.AreNotSame(clone1, expectedProto);
+            Assert.AreNotSame(clone2, expectedProto);
+
+            Assert.AreEqual(clone1, clone2);
+            Assert.AreEqual(clone1, expectedProto);
+        }
    }
 }
--- a/csharp/src/Google.Protobuf.Test/testprotos.pb
+++ b/csharp/src/Google.Protobuf.Test/testprotos.pb
--- a/csharp/src/Google.Protobuf/Compatibility/DynamicallyAccessedMemberTypes.cs
+++ b/csharp/src/Google.Protobuf/Compatibility/DynamicallyAccessedMemberTypes.cs
@ -0,0 +1,127 @@
+#region Copyright notice and license
+// Protocol Buffers - Google's data interchange format
+// Copyright 2015 Google Inc.  All rights reserved.
+// https://developers.google.com/protocol-buffers/
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+#endregion
+
+#if !NET5_0_OR_GREATER
+// Copied with permission from https://github.com/dotnet/runtime/tree/8fbf206d0e518b45ca855832e8bfb391afa85972/src/libraries/System.Private.CoreLib/src/System/Diagnostics/CodeAnalysis
+namespace System.Diagnostics.CodeAnalysis
+{
+    /// <summary>
+    /// Specifies the types of members that are dynamically accessed.
+    ///
+    /// This enumeration has a <see cref="FlagsAttribute"/> attribute that allows a
+    /// bitwise combination of its member values.
+    /// </summary>
+    [Flags]
+    internal enum DynamicallyAccessedMemberTypes
+    {
+        /// <summary>
+        /// Specifies no members.
+        /// </summary>
+        None = 0,
+
+        /// <summary>
+        /// Specifies the default, parameterless public constructor.
+        /// </summary>
+        PublicParameterlessConstructor = 0x0001,
+
+        /// <summary>
+        /// Specifies all public constructors.
+        /// </summary>
+        PublicConstructors = 0x0002 | PublicParameterlessConstructor,
+
+        /// <summary>
+        /// Specifies all non-public constructors.
+        /// </summary>
+        NonPublicConstructors = 0x0004,
+
+        /// <summary>
+        /// Specifies all public methods.
+        /// </summary>
+        PublicMethods = 0x0008,
+
+        /// <summary>
+        /// Specifies all non-public methods.
+        /// </summary>
+        NonPublicMethods = 0x0010,
+
+        /// <summary>
+        /// Specifies all public fields.
+        /// </summary>
+        PublicFields = 0x0020,
+
+        /// <summary>
+        /// Specifies all non-public fields.
+        /// </summary>
+        NonPublicFields = 0x0040,
+
+        /// <summary>
+        /// Specifies all public nested types.
+        /// </summary>
+        PublicNestedTypes = 0x0080,
+
+        /// <summary>
+        /// Specifies all non-public nested types.
+        /// </summary>
+        NonPublicNestedTypes = 0x0100,
+
+        /// <summary>
+        /// Specifies all public properties.
+        /// </summary>
+        PublicProperties = 0x0200,
+
+        /// <summary>
+        /// Specifies all non-public properties.
+        /// </summary>
+        NonPublicProperties = 0x0400,
+
+        /// <summary>
+        /// Specifies all public events.
+        /// </summary>
+        PublicEvents = 0x0800,
+
+        /// <summary>
+        /// Specifies all non-public events.
+        /// </summary>
+        NonPublicEvents = 0x1000,
+
+        /// <summary>
+        /// Specifies all interfaces implemented by the type.
+        /// </summary>
+        Interfaces = 0x2000,
+
+        /// <summary>
+        /// Specifies all members.
+        /// </summary>
+        All = ~None
+    }
+}
+#endif
--- a/csharp/src/Google.Protobuf/Compatibility/DynamicallyAccessedMembersAttribute.cs
+++ b/csharp/src/Google.Protobuf/Compatibility/DynamicallyAccessedMembersAttribute.cs
@ -0,0 +1,83 @@
+#region Copyright notice and license
+// Protocol Buffers - Google's data interchange format
+// Copyright 2015 Google Inc.  All rights reserved.
+// https://developers.google.com/protocol-buffers/
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+#endregion
+
+#if !NET5_0_OR_GREATER
+// Copied with permission from https://github.com/dotnet/runtime/tree/8fbf206d0e518b45ca855832e8bfb391afa85972/src/libraries/System.Private.CoreLib/src/System/Diagnostics/CodeAnalysis
+namespace System.Diagnostics.CodeAnalysis
+{
+    /// <summary>
+    /// Indicates that certain members on a specified <see cref="Type"/> are accessed dynamically,
+    /// for example through <see cref="System.Reflection"/>.
+    /// </summary>
+    /// <remarks>
+    /// This allows tools to understand which members are being accessed during the execution
+    /// of a program.
+    ///
+    /// This attribute is valid on members whose type is <see cref="Type"/> or <see cref="string"/>.
+    ///
+    /// When this attribute is applied to a location of type <see cref="string"/>, the assumption is
+    /// that the string represents a fully qualified type name.
+    ///
+    /// When this attribute is applied to a class, interface, or struct, the members specified
+    /// can be accessed dynamically on <see cref="Type"/> instances returned from calling
+    /// <see cref="object.GetType"/> on instances of that class, interface, or struct.
+    ///
+    /// If the attribute is applied to a method it's treated as a special case and it implies
+    /// the attribute should be applied to the "this" parameter of the method. As such the attribute
+    /// should only be used on instance methods of types assignable to System.Type (or string, but no methods
+    /// will use it there).
+    /// </remarks>
+    [AttributeUsage(
+        AttributeTargets.Field | AttributeTargets.ReturnValue | AttributeTargets.GenericParameter |
+        AttributeTargets.Parameter | AttributeTargets.Property | AttributeTargets.Method |
+        AttributeTargets.Class | AttributeTargets.Interface | AttributeTargets.Struct,
+        Inherited = false)]
+    internal sealed class DynamicallyAccessedMembersAttribute : Attribute
+    {
+        /// <summary>
+        /// Initializes a new instance of the <see cref="DynamicallyAccessedMembersAttribute"/> class
+        /// with the specified member types.
+        /// </summary>
+        /// <param name="memberTypes">The types of members dynamically accessed.</param>
+        public DynamicallyAccessedMembersAttribute(DynamicallyAccessedMemberTypes memberTypes)
+        {
+            MemberTypes = memberTypes;
+        }
+
+        /// <summary>
+        /// Gets the <see cref="DynamicallyAccessedMemberTypes"/> which specifies the type
+        /// of members dynamically accessed.
+        /// </summary>
+        public DynamicallyAccessedMemberTypes MemberTypes { get; }
+    }
+}
+#endif
--- a/csharp/src/Google.Protobuf/Compatibility/RequiresUnreferencedCodeAttribute.cs
+++ b/csharp/src/Google.Protobuf/Compatibility/RequiresUnreferencedCodeAttribute.cs
@ -0,0 +1,72 @@
+#region Copyright notice and license
+// Protocol Buffers - Google's data interchange format
+// Copyright 2015 Google Inc.  All rights reserved.
+// https://developers.google.com/protocol-buffers/
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+#endregion
+
+#if !NET5_0_OR_GREATER
+// Copied with permission from https://github.com/dotnet/runtime/tree/8fbf206d0e518b45ca855832e8bfb391afa85972/src/libraries/System.Private.CoreLib/src/System/Diagnostics/CodeAnalysis
+namespace System.Diagnostics.CodeAnalysis
+{
+    /// <summary>
+    /// Indicates that the specified method requires dynamic access to code that is not referenced
+    /// statically, for example through <see cref="System.Reflection"/>.
+    /// </summary>
+    /// <remarks>
+    /// This allows tools to understand which methods are unsafe to call when removing unreferenced
+    /// code from an application.
+    /// </remarks>
+    [AttributeUsage(AttributeTargets.Method | AttributeTargets.Constructor | AttributeTargets.Class, Inherited = false)]
+    internal sealed class RequiresUnreferencedCodeAttribute : Attribute
+    {
+        /// <summary>
+        /// Initializes a new instance of the <see cref="RequiresUnreferencedCodeAttribute"/> class
+        /// with the specified message.
+        /// </summary>
+        /// <param name="message">
+        /// A message that contains information about the usage of unreferenced code.
+        /// </param>
+        public RequiresUnreferencedCodeAttribute(string message)
+        {
+            Message = message;
+        }
+
+        /// <summary>
+        /// Gets a message that contains information about the usage of unreferenced code.
+        /// </summary>
+        public string Message { get; }
+
+        /// <summary>
+        /// Gets or sets an optional URL that contains more information about the method,
+        /// why it requires unreferenced code, and what options a consumer has to deal with it.
+        /// </summary>
+        public string Url { get; set; }
+    }
+}
+#endif
--- a/csharp/src/Google.Protobuf/Compatibility/TypeExtensions.cs
+++ b/csharp/src/Google.Protobuf/Compatibility/TypeExtensions.cs
@ -31,6 +31,7 @@
 #endregion

 using System;
+using System.Diagnostics.CodeAnalysis;
 using System.Reflection;

 #if !NET35
@ -59,7 +60,11 @@ namespace Google.Protobuf.Compatibility
        /// including inherited properties or null if there is no such public property.
        /// Here, "public property" means a property where either the getter, or the setter, or both, is public.
        /// </summary>
-        internal static PropertyInfo GetProperty(this Type target, string name)
+        [UnconditionalSuppressMessage("Trimming", "IL2072",
+            Justification = "The BaseType of the target will have all properties because of the annotation.")]
+        internal static PropertyInfo GetProperty(
+            [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicProperties | DynamicallyAccessedMemberTypes.NonPublicProperties)]
+            this Type target, string name)
        {
            // GetDeclaredProperty only returns properties declared in the given type, so we need to recurse.
            while (target != null)
@ -86,7 +91,11 @@ namespace Google.Protobuf.Compatibility
        /// class Child : Base declares public void Foo(long)).
        /// </remarks>
        /// <exception cref="AmbiguousMatchException">One type in the hierarchy declared more than one method with the same name</exception>
-        internal static MethodInfo GetMethod(this Type target, string name)
+        [UnconditionalSuppressMessage("Trimming", "IL2072",
+            Justification = "The BaseType of the target will have all properties because of the annotation.")]
+        internal static MethodInfo GetMethod(
+            [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicMethods | DynamicallyAccessedMemberTypes.NonPublicMethods)]
+            this Type target, string name)
        {
            // GetDeclaredMethod only returns methods declared in the given type, so we need to recurse.
            while (target != null)
--- a/csharp/src/Google.Protobuf/Compatibility/UnconditionalSuppressMessageAttribute.cs
+++ b/csharp/src/Google.Protobuf/Compatibility/UnconditionalSuppressMessageAttribute.cs
@ -0,0 +1,117 @@
+#region Copyright notice and license
+// Protocol Buffers - Google's data interchange format
+// Copyright 2015 Google Inc.  All rights reserved.
+// https://developers.google.com/protocol-buffers/
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//     * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+#endregion
+
+#if !NET5_0_OR_GREATER
+// Copied with permission from https://github.com/dotnet/runtime/tree/8fbf206d0e518b45ca855832e8bfb391afa85972/src/libraries/System.Private.CoreLib/src/System/Diagnostics/CodeAnalysis
+namespace System.Diagnostics.CodeAnalysis
+{
+    /// <summary>
+    /// Suppresses reporting of a specific rule violation, allowing multiple suppressions on a
+    /// single code artifact.
+    /// </summary>
+    /// <remarks>
+    /// <see cref="UnconditionalSuppressMessageAttribute"/> is different than
+    /// <see cref="SuppressMessageAttribute"/> in that it doesn't have a
+    /// <see cref="ConditionalAttribute"/>. So it is always preserved in the compiled assembly.
+    /// </remarks>
+    [AttributeUsage(AttributeTargets.All, Inherited = false, AllowMultiple = true)]
+    internal sealed class UnconditionalSuppressMessageAttribute : Attribute
+    {
+        /// <summary>
+        /// Initializes a new instance of the <see cref="UnconditionalSuppressMessageAttribute"/>
+        /// class, specifying the category of the tool and the identifier for an analysis rule.
+        /// </summary>
+        /// <param name="category">The category for the attribute.</param>
+        /// <param name="checkId">The identifier of the analysis rule the attribute applies to.</param>
+        public UnconditionalSuppressMessageAttribute(string category, string checkId)
+        {
+            Category = category;
+            CheckId = checkId;
+        }
+
+        /// <summary>
+        /// Gets the category identifying the classification of the attribute.
+        /// </summary>
+        /// <remarks>
+        /// The <see cref="Category"/> property describes the tool or tool analysis category
+        /// for which a message suppression attribute applies.
+        /// </remarks>
+        public string Category { get; }
+
+        /// <summary>
+        /// Gets the identifier of the analysis tool rule to be suppressed.
+        /// </summary>
+        /// <remarks>
+        /// Concatenated together, the <see cref="Category"/> and <see cref="CheckId"/>
+        /// properties form a unique check identifier.
+        /// </remarks>
+        public string CheckId { get; }
+
+        /// <summary>
+        /// Gets or sets the scope of the code that is relevant for the attribute.
+        /// </summary>
+        /// <remarks>
+        /// The Scope property is an optional argument that specifies the metadata scope for which
+        /// the attribute is relevant.
+        /// </remarks>
+        public string Scope { get; set; }
+
+        /// <summary>
+        /// Gets or sets a fully qualified path that represents the target of the attribute.
+        /// </summary>
+        /// <remarks>
+        /// The <see cref="Target"/> property is an optional argument identifying the analysis target
+        /// of the attribute. An example value is "System.IO.Stream.ctor():System.Void".
+        /// Because it is fully qualified, it can be long, particularly for targets such as parameters.
+        /// The analysis tool user interface should be capable of automatically formatting the parameter.
+        /// </remarks>
+        public string Target { get; set; }
+
+        /// <summary>
+        /// Gets or sets an optional argument expanding on exclusion criteria.
+        /// </summary>
+        /// <remarks>
+        /// The <see cref="MessageId "/> property is an optional argument that specifies additional
+        /// exclusion where the literal metadata target is not sufficiently precise. For example,
+        /// the <see cref="UnconditionalSuppressMessageAttribute"/> cannot be applied within a method,
+        /// and it may be desirable to suppress a violation against a statement in the method that will
+        /// give a rule violation, but not against all statements in the method.
+        /// </remarks>
+        public string MessageId { get; set; }
+
+        /// <summary>
+        /// Gets or sets the justification for suppressing the code analysis message.
+        /// </summary>
+        public string Justification { get; set; }
+    }
+}
+#endif
--- a/csharp/src/Google.Protobuf/Google.Protobuf.csproj
+++ b/csharp/src/Google.Protobuf/Google.Protobuf.csproj
@ -1,10 +1,10 @@
-<Project Sdk="Microsoft.NET.Sdk">
+<Project Sdk="Microsoft.NET.Sdk">

  <PropertyGroup>
    <Description>C# runtime library for Protocol Buffers - Google's data interchange format.</Description>
    <Copyright>Copyright 2015, Google Inc.</Copyright>
    <AssemblyTitle>Google Protocol Buffers</AssemblyTitle>
-    <VersionPrefix>3.18.1</VersionPrefix>
+    <VersionPrefix>3.19.4</VersionPrefix>
    <!-- C# 7.2 is required for Span/BufferWriter/ReadOnlySequence -->
    <LangVersion>7.2</LangVersion>
    <Authors>Google Inc.</Authors>
@ -15,12 +15,14 @@
    <PackageTags>Protocol;Buffers;Binary;Serialization;Format;Google;proto;proto3</PackageTags>
    <PackageReleaseNotes>C# proto3 support</PackageReleaseNotes>
    <PackageProjectUrl>https://github.com/protocolbuffers/protobuf</PackageProjectUrl>
-    <PackageLicenseUrl>https://github.com/protocolbuffers/protobuf/blob/master/LICENSE</PackageLicenseUrl>
+    <PackageLicenseExpression>BSD-3-Clause</PackageLicenseExpression>
    <RepositoryType>git</RepositoryType>
    <RepositoryUrl>https://github.com/protocolbuffers/protobuf.git</RepositoryUrl>
-    <AllowUnsafeBlocks>True</AllowUnsafeBlocks>
+    <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
+    <EmbedUntrackedSources>true</EmbedUntrackedSources>
    <!-- Include PDB in the built .nupkg -->
    <AllowedOutputExtensionsInPackageBuildOutputFolder>$(AllowedOutputExtensionsInPackageBuildOutputFolder);.pdb</AllowedOutputExtensionsInPackageBuildOutputFolder>
+    <IsTrimmable>true</IsTrimmable>
  </PropertyGroup>

  <PropertyGroup Condition=" '$(TargetFramework)' == 'netstandard2.0' ">
@ -43,7 +45,7 @@

  <ItemGroup Condition=" '$(TargetFramework)' == 'netstandard2.0' ">
    <PackageReference Include="System.Memory" Version="4.5.3"/>
-    <!-- Needed for netcoreapp2.1 to work correctly. .NET is not able to load the assembly without this -->
+    <!-- Needed for netcoreapp3.1 to work correctly. .NET is not able to load the assembly without this -->
    <PackageReference Include="System.Runtime.CompilerServices.Unsafe" Version="4.5.2"/>
  </ItemGroup>

--- a/csharp/src/Google.Protobuf/JsonFormatter.cs
+++ b/csharp/src/Google.Protobuf/JsonFormatter.cs
@ -40,6 +40,7 @@ using System.IO;
 using System.Linq;
 using System.Collections.Generic;
 using System.Reflection;
+using System.Diagnostics.CodeAnalysis;

 namespace Google.Protobuf
 {
@ -879,6 +880,8 @@ namespace Google.Protobuf
            private static readonly Dictionary<System.Type, Dictionary<object, string>> dictionaries
                = new Dictionary<System.Type, Dictionary<object, string>>();

+            [UnconditionalSuppressMessage("Trimming", "IL2072",
+                Justification = "The field for the value must still be present. It will be returned by reflection, will be in this collection, and its name can be resolved.")]
            internal static string GetOriginalName(object value)
            {
                var enumType = value.GetType();
@ -898,21 +901,13 @@ namespace Google.Protobuf
                return originalName;
            }

-#if NET35
-            // TODO: Consider adding functionality to TypeExtensions to avoid this difference.
-            private static Dictionary<object, string> GetNameMapping(System.Type enumType) =>
-                enumType.GetFields(BindingFlags.NonPublic | BindingFlags.Public | BindingFlags.Static)
-                    .Where(f => (f.GetCustomAttributes(typeof(OriginalNameAttribute), false)
-                                 .FirstOrDefault() as OriginalNameAttribute)
-                                 ?.PreferredAlias ?? true)
-                    .ToDictionary(f => f.GetValue(null),
-                                  f => (f.GetCustomAttributes(typeof(OriginalNameAttribute), false)
-                                        .FirstOrDefault() as OriginalNameAttribute)
-                                        // If the attribute hasn't been applied, fall back to the name of the field.
-                                        ?.Name ?? f.Name);
-#else
-            private static Dictionary<object, string> GetNameMapping(System.Type enumType) =>
-                enumType.GetTypeInfo().DeclaredFields
+            private static Dictionary<object, string> GetNameMapping(
+                [DynamicallyAccessedMembers(
+                    DynamicallyAccessedMemberTypes.PublicFields |
+                    DynamicallyAccessedMemberTypes.NonPublicFields)]
+                System.Type enumType)
+            {
+                return enumType.GetTypeInfo().DeclaredFields
                    .Where(f => f.IsStatic)
                    .Where(f => f.GetCustomAttributes<OriginalNameAttribute>()
                                 .FirstOrDefault()?.PreferredAlias ?? true)
@ -921,7 +916,7 @@ namespace Google.Protobuf
                                        .FirstOrDefault()
                                        // If the attribute hasn't been applied, fall back to the name of the field.
                                        ?.Name ?? f.Name);
-#endif
+            }
        }
    }
 }
--- a/csharp/src/Google.Protobuf/JsonTokenizer.cs
+++ b/csharp/src/Google.Protobuf/JsonTokenizer.cs
@ -471,9 +471,18 @@ namespace Google.Protobuf
                // TODO: What exception should we throw if the value can't be represented as a double?
                try
                {
-                    return double.Parse(builder.ToString(),
+                    double result = double.Parse(builder.ToString(),
                        NumberStyles.AllowLeadingSign | NumberStyles.AllowDecimalPoint | NumberStyles.AllowExponent,
                        CultureInfo.InvariantCulture);
+
+                    // .NET Core 3.0 and later returns infinity if the number is too large or small to be represented.
+                    // For compatibility with other Protobuf implementations the tokenizer should still throw.
+                    if (double.IsInfinity(result))
+                    {
+                        throw reader.CreateException("Numeric value out of range: " + builder);
+                    }
+
+                    return result;
                }
                catch (OverflowException)
                {
--- a/csharp/src/Google.Protobuf/MessageParser.cs
+++ b/csharp/src/Google.Protobuf/MessageParser.cs
@ -187,14 +187,17 @@ namespace Google.Protobuf
        internal void MergeFrom(IMessage message, CodedInputStream codedInput)
        {
            bool originalDiscard = codedInput.DiscardUnknownFields;
+            ExtensionRegistry originalRegistry = codedInput.ExtensionRegistry;
            try
            {
                codedInput.DiscardUnknownFields = DiscardUnknownFields;
+                codedInput.ExtensionRegistry = Extensions;
                message.MergeFrom(codedInput);
            }
            finally
            {
                codedInput.DiscardUnknownFields = originalDiscard;
+                codedInput.ExtensionRegistry = originalRegistry;
            }
        }

--- a/csharp/src/Google.Protobuf/Reflection/CustomOptions.cs
+++ b/csharp/src/Google.Protobuf/Reflection/CustomOptions.cs
@ -34,6 +34,7 @@ using Google.Protobuf.Collections;
 using System;
 using System.Collections;
 using System.Collections.Generic;
+using System.Diagnostics.CodeAnalysis;
 using System.Linq;
 using System.Reflection;

@ -63,6 +64,8 @@ namespace Google.Protobuf.Reflection
    /// </remarks>
    public sealed class CustomOptions
    {
+        private const string UnreferencedCodeMessage = "CustomOptions is incompatible with trimming.";
+
        private static readonly object[] EmptyParameters = new object[0];
        private readonly IDictionary<int, IExtensionValue> values;

@ -77,6 +80,7 @@ namespace Google.Protobuf.Reflection
        /// <param name="field">The field to fetch the value for.</param>
        /// <param name="value">The output variable to populate.</param>
        /// <returns><c>true</c> if a suitable value for the field was found; <c>false</c> otherwise.</returns>
+        [RequiresUnreferencedCode(UnreferencedCodeMessage)]
        public bool TryGetBool(int field, out bool value) => TryGetPrimitiveValue(field, out value);

        /// <summary>
@ -85,6 +89,7 @@ namespace Google.Protobuf.Reflection
        /// <param name="field">The field to fetch the value for.</param>
        /// <param name="value">The output variable to populate.</param>
        /// <returns><c>true</c> if a suitable value for the field was found; <c>false</c> otherwise.</returns>
+        [RequiresUnreferencedCode(UnreferencedCodeMessage)]
        public bool TryGetInt32(int field, out int value) => TryGetPrimitiveValue(field, out value);

        /// <summary>
@ -93,6 +98,7 @@ namespace Google.Protobuf.Reflection
        /// <param name="field">The field to fetch the value for.</param>
        /// <param name="value">The output variable to populate.</param>
        /// <returns><c>true</c> if a suitable value for the field was found; <c>false</c> otherwise.</returns>
+        [RequiresUnreferencedCode(UnreferencedCodeMessage)]
        public bool TryGetInt64(int field, out long value) => TryGetPrimitiveValue(field, out value);

        /// <summary>
@ -102,6 +108,7 @@ namespace Google.Protobuf.Reflection
        /// <param name="field">The field to fetch the value for.</param>
        /// <param name="value">The output variable to populate.</param>
        /// <returns><c>true</c> if a suitable value for the field was found; <c>false</c> otherwise.</returns>
+        [RequiresUnreferencedCode(UnreferencedCodeMessage)]
        public bool TryGetFixed32(int field, out uint value) => TryGetUInt32(field, out value);

        /// <summary>
@ -111,6 +118,7 @@ namespace Google.Protobuf.Reflection
        /// <param name="field">The field to fetch the value for.</param>
        /// <param name="value">The output variable to populate.</param>
        /// <returns><c>true</c> if a suitable value for the field was found; <c>false</c> otherwise.</returns>
+        [RequiresUnreferencedCode(UnreferencedCodeMessage)]
        public bool TryGetFixed64(int field, out ulong value) => TryGetUInt64(field, out value);

        /// <summary>
@ -120,6 +128,7 @@ namespace Google.Protobuf.Reflection
        /// <param name="field">The field to fetch the value for.</param>
        /// <param name="value">The output variable to populate.</param>
        /// <returns><c>true</c> if a suitable value for the field was found; <c>false</c> otherwise.</returns>
+        [RequiresUnreferencedCode(UnreferencedCodeMessage)]
        public bool TryGetSFixed32(int field, out int value) => TryGetInt32(field, out value);

        /// <summary>
@ -129,6 +138,7 @@ namespace Google.Protobuf.Reflection
        /// <param name="field">The field to fetch the value for.</param>
        /// <param name="value">The output variable to populate.</param>
        /// <returns><c>true</c> if a suitable value for the field was found; <c>false</c> otherwise.</returns>
+        [RequiresUnreferencedCode(UnreferencedCodeMessage)]
        public bool TryGetSFixed64(int field, out long value) => TryGetInt64(field, out value);

        /// <summary>
@ -138,6 +148,7 @@ namespace Google.Protobuf.Reflection
        /// <param name="field">The field to fetch the value for.</param>
        /// <param name="value">The output variable to populate.</param>
        /// <returns><c>true</c> if a suitable value for the field was found; <c>false</c> otherwise.</returns>
+        [RequiresUnreferencedCode(UnreferencedCodeMessage)]
        public bool TryGetSInt32(int field, out int value) => TryGetPrimitiveValue(field, out value);

        /// <summary>
@ -147,6 +158,7 @@ namespace Google.Protobuf.Reflection
        /// <param name="field">The field to fetch the value for.</param>
        /// <param name="value">The output variable to populate.</param>
        /// <returns><c>true</c> if a suitable value for the field was found; <c>false</c> otherwise.</returns>
+        [RequiresUnreferencedCode(UnreferencedCodeMessage)]
        public bool TryGetSInt64(int field, out long value) => TryGetPrimitiveValue(field, out value);

        /// <summary>
@ -155,6 +167,7 @@ namespace Google.Protobuf.Reflection
        /// <param name="field">The field to fetch the value for.</param>
        /// <param name="value">The output variable to populate.</param>
        /// <returns><c>true</c> if a suitable value for the field was found; <c>false</c> otherwise.</returns>
+        [RequiresUnreferencedCode(UnreferencedCodeMessage)]
        public bool TryGetUInt32(int field, out uint value) => TryGetPrimitiveValue(field, out value);

        /// <summary>
@ -163,6 +176,7 @@ namespace Google.Protobuf.Reflection
        /// <param name="field">The field to fetch the value for.</param>
        /// <param name="value">The output variable to populate.</param>
        /// <returns><c>true</c> if a suitable value for the field was found; <c>false</c> otherwise.</returns>
+        [RequiresUnreferencedCode(UnreferencedCodeMessage)]
        public bool TryGetUInt64(int field, out ulong value) => TryGetPrimitiveValue(field, out value);

        /// <summary>
@ -171,6 +185,7 @@ namespace Google.Protobuf.Reflection
        /// <param name="field">The field to fetch the value for.</param>
        /// <param name="value">The output variable to populate.</param>
        /// <returns><c>true</c> if a suitable value for the field was found; <c>false</c> otherwise.</returns>
+        [RequiresUnreferencedCode(UnreferencedCodeMessage)]
        public bool TryGetFloat(int field, out float value) => TryGetPrimitiveValue(field, out value);

        /// <summary>
@ -179,6 +194,7 @@ namespace Google.Protobuf.Reflection
        /// <param name="field">The field to fetch the value for.</param>
        /// <param name="value">The output variable to populate.</param>
        /// <returns><c>true</c> if a suitable value for the field was found; <c>false</c> otherwise.</returns>
+        [RequiresUnreferencedCode(UnreferencedCodeMessage)]
        public bool TryGetDouble(int field, out double value) => TryGetPrimitiveValue(field, out value);

        /// <summary>
@ -187,6 +203,7 @@ namespace Google.Protobuf.Reflection
        /// <param name="field">The field to fetch the value for.</param>
        /// <param name="value">The output variable to populate.</param>
        /// <returns><c>true</c> if a suitable value for the field was found; <c>false</c> otherwise.</returns>
+        [RequiresUnreferencedCode(UnreferencedCodeMessage)]
        public bool TryGetString(int field, out string value) => TryGetPrimitiveValue(field, out value);

        /// <summary>
@ -195,6 +212,7 @@ namespace Google.Protobuf.Reflection
        /// <param name="field">The field to fetch the value for.</param>
        /// <param name="value">The output variable to populate.</param>
        /// <returns><c>true</c> if a suitable value for the field was found; <c>false</c> otherwise.</returns>
+        [RequiresUnreferencedCode(UnreferencedCodeMessage)]
        public bool TryGetBytes(int field, out ByteString value) => TryGetPrimitiveValue(field, out value);

        /// <summary>
@ -203,6 +221,7 @@ namespace Google.Protobuf.Reflection
        /// <param name="field">The field to fetch the value for.</param>
        /// <param name="value">The output variable to populate.</param>
        /// <returns><c>true</c> if a suitable value for the field was found; <c>false</c> otherwise.</returns>
+        [RequiresUnreferencedCode(UnreferencedCodeMessage)]
        public bool TryGetMessage<T>(int field, out T value) where T : class, IMessage, new()
        {
            if (values == null)
@ -240,6 +259,7 @@ namespace Google.Protobuf.Reflection
            return false;
        }

+        [RequiresUnreferencedCode(UnreferencedCodeMessage)]
        private bool TryGetPrimitiveValue<T>(int field, out T value)
        {
            if (values == null)
--- a/csharp/src/Google.Protobuf/Reflection/Descriptor.cs
+++ b/csharp/src/Google.Protobuf/Reflection/Descriptor.cs
@ -113,52 +113,53 @@ namespace Google.Protobuf.Reflection {
            "CgpkZXByZWNhdGVkGAMgASgIOgVmYWxzZRIRCgltYXBfZW50cnkYByABKAgS",
            "QwoUdW5pbnRlcnByZXRlZF9vcHRpb24Y5wcgAygLMiQuZ29vZ2xlLnByb3Rv",
            "YnVmLlVuaW50ZXJwcmV0ZWRPcHRpb24qCQjoBxCAgICAAkoECAQQBUoECAUQ",
-            "BkoECAYQB0oECAgQCUoECAkQCiKeAwoMRmllbGRPcHRpb25zEjoKBWN0eXBl",
+            "BkoECAYQB0oECAgQCUoECAkQCiK+AwoMRmllbGRPcHRpb25zEjoKBWN0eXBl",
            "GAEgASgOMiMuZ29vZ2xlLnByb3RvYnVmLkZpZWxkT3B0aW9ucy5DVHlwZToG",
            "U1RSSU5HEg4KBnBhY2tlZBgCIAEoCBI/CgZqc3R5cGUYBiABKA4yJC5nb29n",
            "bGUucHJvdG9idWYuRmllbGRPcHRpb25zLkpTVHlwZToJSlNfTk9STUFMEhMK",
-            "BGxhenkYBSABKAg6BWZhbHNlEhkKCmRlcHJlY2F0ZWQYAyABKAg6BWZhbHNl",
-            "EhMKBHdlYWsYCiABKAg6BWZhbHNlEkMKFHVuaW50ZXJwcmV0ZWRfb3B0aW9u",
-            "GOcHIAMoCzIkLmdvb2dsZS5wcm90b2J1Zi5VbmludGVycHJldGVkT3B0aW9u",
-            "Ii8KBUNUeXBlEgoKBlNUUklORxAAEggKBENPUkQQARIQCgxTVFJJTkdfUElF",
-            "Q0UQAiI1CgZKU1R5cGUSDQoJSlNfTk9STUFMEAASDQoJSlNfU1RSSU5HEAES",
-            "DQoJSlNfTlVNQkVSEAIqCQjoBxCAgICAAkoECAQQBSJeCgxPbmVvZk9wdGlv",
-            "bnMSQwoUdW5pbnRlcnByZXRlZF9vcHRpb24Y5wcgAygLMiQuZ29vZ2xlLnBy",
-            "b3RvYnVmLlVuaW50ZXJwcmV0ZWRPcHRpb24qCQjoBxCAgICAAiKTAQoLRW51",
-            "bU9wdGlvbnMSEwoLYWxsb3dfYWxpYXMYAiABKAgSGQoKZGVwcmVjYXRlZBgD",
-            "IAEoCDoFZmFsc2USQwoUdW5pbnRlcnByZXRlZF9vcHRpb24Y5wcgAygLMiQu",
-            "Z29vZ2xlLnByb3RvYnVmLlVuaW50ZXJwcmV0ZWRPcHRpb24qCQjoBxCAgICA",
-            "AkoECAUQBiJ9ChBFbnVtVmFsdWVPcHRpb25zEhkKCmRlcHJlY2F0ZWQYASAB",
-            "KAg6BWZhbHNlEkMKFHVuaW50ZXJwcmV0ZWRfb3B0aW9uGOcHIAMoCzIkLmdv",
-            "b2dsZS5wcm90b2J1Zi5VbmludGVycHJldGVkT3B0aW9uKgkI6AcQgICAgAIi",
-            "ewoOU2VydmljZU9wdGlvbnMSGQoKZGVwcmVjYXRlZBghIAEoCDoFZmFsc2US",
-            "QwoUdW5pbnRlcnByZXRlZF9vcHRpb24Y5wcgAygLMiQuZ29vZ2xlLnByb3Rv",
-            "YnVmLlVuaW50ZXJwcmV0ZWRPcHRpb24qCQjoBxCAgICAAiKtAgoNTWV0aG9k",
-            "T3B0aW9ucxIZCgpkZXByZWNhdGVkGCEgASgIOgVmYWxzZRJfChFpZGVtcG90",
-            "ZW5jeV9sZXZlbBgiIAEoDjIvLmdvb2dsZS5wcm90b2J1Zi5NZXRob2RPcHRp",
-            "b25zLklkZW1wb3RlbmN5TGV2ZWw6E0lERU1QT1RFTkNZX1VOS05PV04SQwoU",
+            "BGxhenkYBSABKAg6BWZhbHNlEh4KD3VudmVyaWZpZWRfbGF6eRgPIAEoCDoF",
+            "ZmFsc2USGQoKZGVwcmVjYXRlZBgDIAEoCDoFZmFsc2USEwoEd2VhaxgKIAEo",
+            "CDoFZmFsc2USQwoUdW5pbnRlcnByZXRlZF9vcHRpb24Y5wcgAygLMiQuZ29v",
+            "Z2xlLnByb3RvYnVmLlVuaW50ZXJwcmV0ZWRPcHRpb24iLwoFQ1R5cGUSCgoG",
+            "U1RSSU5HEAASCAoEQ09SRBABEhAKDFNUUklOR19QSUVDRRACIjUKBkpTVHlw",
+            "ZRINCglKU19OT1JNQUwQABINCglKU19TVFJJTkcQARINCglKU19OVU1CRVIQ",
+            "AioJCOgHEICAgIACSgQIBBAFIl4KDE9uZW9mT3B0aW9ucxJDChR1bmludGVy",
+            "cHJldGVkX29wdGlvbhjnByADKAsyJC5nb29nbGUucHJvdG9idWYuVW5pbnRl",
+            "cnByZXRlZE9wdGlvbioJCOgHEICAgIACIpMBCgtFbnVtT3B0aW9ucxITCgth",
+            "bGxvd19hbGlhcxgCIAEoCBIZCgpkZXByZWNhdGVkGAMgASgIOgVmYWxzZRJD",
+            "ChR1bmludGVycHJldGVkX29wdGlvbhjnByADKAsyJC5nb29nbGUucHJvdG9i",
+            "dWYuVW5pbnRlcnByZXRlZE9wdGlvbioJCOgHEICAgIACSgQIBRAGIn0KEEVu",
+            "dW1WYWx1ZU9wdGlvbnMSGQoKZGVwcmVjYXRlZBgBIAEoCDoFZmFsc2USQwoU",
            "dW5pbnRlcnByZXRlZF9vcHRpb24Y5wcgAygLMiQuZ29vZ2xlLnByb3RvYnVm",
-            "LlVuaW50ZXJwcmV0ZWRPcHRpb24iUAoQSWRlbXBvdGVuY3lMZXZlbBIXChNJ",
-            "REVNUE9URU5DWV9VTktOT1dOEAASEwoPTk9fU0lERV9FRkZFQ1RTEAESDgoK",
-            "SURFTVBPVEVOVBACKgkI6AcQgICAgAIingIKE1VuaW50ZXJwcmV0ZWRPcHRp",
-            "b24SOwoEbmFtZRgCIAMoCzItLmdvb2dsZS5wcm90b2J1Zi5VbmludGVycHJl",
-            "dGVkT3B0aW9uLk5hbWVQYXJ0EhgKEGlkZW50aWZpZXJfdmFsdWUYAyABKAkS",
-            "GgoScG9zaXRpdmVfaW50X3ZhbHVlGAQgASgEEhoKEm5lZ2F0aXZlX2ludF92",
-            "YWx1ZRgFIAEoAxIUCgxkb3VibGVfdmFsdWUYBiABKAESFAoMc3RyaW5nX3Zh",
-            "bHVlGAcgASgMEhcKD2FnZ3JlZ2F0ZV92YWx1ZRgIIAEoCRozCghOYW1lUGFy",
-            "dBIRCgluYW1lX3BhcnQYASACKAkSFAoMaXNfZXh0ZW5zaW9uGAIgAigIItUB",
-            "Cg5Tb3VyY2VDb2RlSW5mbxI6Cghsb2NhdGlvbhgBIAMoCzIoLmdvb2dsZS5w",
-            "cm90b2J1Zi5Tb3VyY2VDb2RlSW5mby5Mb2NhdGlvbhqGAQoITG9jYXRpb24S",
-            "EAoEcGF0aBgBIAMoBUICEAESEAoEc3BhbhgCIAMoBUICEAESGAoQbGVhZGlu",
-            "Z19jb21tZW50cxgDIAEoCRIZChF0cmFpbGluZ19jb21tZW50cxgEIAEoCRIh",
-            "ChlsZWFkaW5nX2RldGFjaGVkX2NvbW1lbnRzGAYgAygJIqcBChFHZW5lcmF0",
-            "ZWRDb2RlSW5mbxJBCgphbm5vdGF0aW9uGAEgAygLMi0uZ29vZ2xlLnByb3Rv",
-            "YnVmLkdlbmVyYXRlZENvZGVJbmZvLkFubm90YXRpb24aTwoKQW5ub3RhdGlv",
-            "bhIQCgRwYXRoGAEgAygFQgIQARITCgtzb3VyY2VfZmlsZRgCIAEoCRINCgVi",
-            "ZWdpbhgDIAEoBRILCgNlbmQYBCABKAVCfgoTY29tLmdvb2dsZS5wcm90b2J1",
-            "ZkIQRGVzY3JpcHRvclByb3Rvc0gBWi1nb29nbGUuZ29sYW5nLm9yZy9wcm90",
-            "b2J1Zi90eXBlcy9kZXNjcmlwdG9ycGL4AQGiAgNHUEKqAhpHb29nbGUuUHJv",
-            "dG9idWYuUmVmbGVjdGlvbg=="));
+            "LlVuaW50ZXJwcmV0ZWRPcHRpb24qCQjoBxCAgICAAiJ7Cg5TZXJ2aWNlT3B0",
+            "aW9ucxIZCgpkZXByZWNhdGVkGCEgASgIOgVmYWxzZRJDChR1bmludGVycHJl",
+            "dGVkX29wdGlvbhjnByADKAsyJC5nb29nbGUucHJvdG9idWYuVW5pbnRlcnBy",
+            "ZXRlZE9wdGlvbioJCOgHEICAgIACIq0CCg1NZXRob2RPcHRpb25zEhkKCmRl",
+            "cHJlY2F0ZWQYISABKAg6BWZhbHNlEl8KEWlkZW1wb3RlbmN5X2xldmVsGCIg",
+            "ASgOMi8uZ29vZ2xlLnByb3RvYnVmLk1ldGhvZE9wdGlvbnMuSWRlbXBvdGVu",
+            "Y3lMZXZlbDoTSURFTVBPVEVOQ1lfVU5LTk9XThJDChR1bmludGVycHJldGVk",
+            "X29wdGlvbhjnByADKAsyJC5nb29nbGUucHJvdG9idWYuVW5pbnRlcnByZXRl",
+            "ZE9wdGlvbiJQChBJZGVtcG90ZW5jeUxldmVsEhcKE0lERU1QT1RFTkNZX1VO",
+            "S05PV04QABITCg9OT19TSURFX0VGRkVDVFMQARIOCgpJREVNUE9URU5UEAIq",
+            "CQjoBxCAgICAAiKeAgoTVW5pbnRlcnByZXRlZE9wdGlvbhI7CgRuYW1lGAIg",
+            "AygLMi0uZ29vZ2xlLnByb3RvYnVmLlVuaW50ZXJwcmV0ZWRPcHRpb24uTmFt",
+            "ZVBhcnQSGAoQaWRlbnRpZmllcl92YWx1ZRgDIAEoCRIaChJwb3NpdGl2ZV9p",
+            "bnRfdmFsdWUYBCABKAQSGgoSbmVnYXRpdmVfaW50X3ZhbHVlGAUgASgDEhQK",
+            "DGRvdWJsZV92YWx1ZRgGIAEoARIUCgxzdHJpbmdfdmFsdWUYByABKAwSFwoP",
+            "YWdncmVnYXRlX3ZhbHVlGAggASgJGjMKCE5hbWVQYXJ0EhEKCW5hbWVfcGFy",
+            "dBgBIAIoCRIUCgxpc19leHRlbnNpb24YAiACKAgi1QEKDlNvdXJjZUNvZGVJ",
+            "bmZvEjoKCGxvY2F0aW9uGAEgAygLMiguZ29vZ2xlLnByb3RvYnVmLlNvdXJj",
+            "ZUNvZGVJbmZvLkxvY2F0aW9uGoYBCghMb2NhdGlvbhIQCgRwYXRoGAEgAygF",
+            "QgIQARIQCgRzcGFuGAIgAygFQgIQARIYChBsZWFkaW5nX2NvbW1lbnRzGAMg",
+            "ASgJEhkKEXRyYWlsaW5nX2NvbW1lbnRzGAQgASgJEiEKGWxlYWRpbmdfZGV0",
+            "YWNoZWRfY29tbWVudHMYBiADKAkipwEKEUdlbmVyYXRlZENvZGVJbmZvEkEK",
+            "CmFubm90YXRpb24YASADKAsyLS5nb29nbGUucHJvdG9idWYuR2VuZXJhdGVk",
+            "Q29kZUluZm8uQW5ub3RhdGlvbhpPCgpBbm5vdGF0aW9uEhAKBHBhdGgYASAD",
+            "KAVCAhABEhMKC3NvdXJjZV9maWxlGAIgASgJEg0KBWJlZ2luGAMgASgFEgsK",
+            "A2VuZBgEIAEoBUJ+ChNjb20uZ29vZ2xlLnByb3RvYnVmQhBEZXNjcmlwdG9y",
+            "UHJvdG9zSAFaLWdvb2dsZS5nb2xhbmcub3JnL3Byb3RvYnVmL3R5cGVzL2Rl",
+            "c2NyaXB0b3JwYvgBAaICA0dQQqoCGkdvb2dsZS5Qcm90b2J1Zi5SZWZsZWN0",
+            "aW9u"));
      descriptor = pbr::FileDescriptor.FromGeneratedCode(descriptorData,
          new pbr::FileDescriptor[] { },
          new pbr::GeneratedClrTypeInfo(null, null, new pbr::GeneratedClrTypeInfo[] {
@ -175,7 +176,7 @@ namespace Google.Protobuf.Reflection {
            new pbr::GeneratedClrTypeInfo(typeof(global::Google.Protobuf.Reflection.MethodDescriptorProto), global::Google.Protobuf.Reflection.MethodDescriptorProto.Parser, new[]{ "Name", "InputType", "OutputType", "Options", "ClientStreaming", "ServerStreaming" }, null, null, null, null),
            new pbr::GeneratedClrTypeInfo(typeof(global::Google.Protobuf.Reflection.FileOptions), global::Google.Protobuf.Reflection.FileOptions.Parser, new[]{ "JavaPackage", "JavaOuterClassname", "JavaMultipleFiles", "JavaGenerateEqualsAndHash", "JavaStringCheckUtf8", "OptimizeFor", "GoPackage", "CcGenericServices", "JavaGenericServices", "PyGenericServices", "PhpGenericServices", "Deprecated", "CcEnableArenas", "ObjcClassPrefix", "CsharpNamespace", "SwiftPrefix", "PhpClassPrefix", "PhpNamespace", "PhpMetadataNamespace", "RubyPackage", "UninterpretedOption" }, null, new[]{ typeof(global::Google.Protobuf.Reflection.FileOptions.Types.OptimizeMode) }, null, null),
            new pbr::GeneratedClrTypeInfo(typeof(global::Google.Protobuf.Reflection.MessageOptions), global::Google.Protobuf.Reflection.MessageOptions.Parser, new[]{ "MessageSetWireFormat", "NoStandardDescriptorAccessor", "Deprecated", "MapEntry", "UninterpretedOption" }, null, null, null, null),
-            new pbr::GeneratedClrTypeInfo(typeof(global::Google.Protobuf.Reflection.FieldOptions), global::Google.Protobuf.Reflection.FieldOptions.Parser, new[]{ "Ctype", "Packed", "Jstype", "Lazy", "Deprecated", "Weak", "UninterpretedOption" }, null, new[]{ typeof(global::Google.Protobuf.Reflection.FieldOptions.Types.CType), typeof(global::Google.Protobuf.Reflection.FieldOptions.Types.JSType) }, null, null),
+            new pbr::GeneratedClrTypeInfo(typeof(global::Google.Protobuf.Reflection.FieldOptions), global::Google.Protobuf.Reflection.FieldOptions.Parser, new[]{ "Ctype", "Packed", "Jstype", "Lazy", "UnverifiedLazy", "Deprecated", "Weak", "UninterpretedOption" }, null, new[]{ typeof(global::Google.Protobuf.Reflection.FieldOptions.Types.CType), typeof(global::Google.Protobuf.Reflection.FieldOptions.Types.JSType) }, null, null),
            new pbr::GeneratedClrTypeInfo(typeof(global::Google.Protobuf.Reflection.OneofOptions), global::Google.Protobuf.Reflection.OneofOptions.Parser, new[]{ "UninterpretedOption" }, null, null, null, null),
            new pbr::GeneratedClrTypeInfo(typeof(global::Google.Protobuf.Reflection.EnumOptions), global::Google.Protobuf.Reflection.EnumOptions.Parser, new[]{ "AllowAlias", "Deprecated", "UninterpretedOption" }, null, null, null, null),
            new pbr::GeneratedClrTypeInfo(typeof(global::Google.Protobuf.Reflection.EnumValueOptions), global::Google.Protobuf.Reflection.EnumValueOptions.Parser, new[]{ "Deprecated", "UninterpretedOption" }, null, null, null, null),
@ -2507,7 +2508,6 @@ namespace Google.Protobuf.Reflection {
    /// For booleans, "true" or "false".
    /// For strings, contains the default text contents (not escaped in any way).
    /// For bytes, contains the C escaped value.  All bytes >= 128 are escaped.
-    /// TODO(kenton):  Base-64 encode?
    /// </summary>
    [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
    [global::System.CodeDom.Compiler.GeneratedCode("protoc", null)]
@ -6943,6 +6943,7 @@ namespace Google.Protobuf.Reflection {
      packed_ = other.packed_;
      jstype_ = other.jstype_;
      lazy_ = other.lazy_;
+      unverifiedLazy_ = other.unverifiedLazy_;
      deprecated_ = other.deprecated_;
      weak_ = other.weak_;
      uninterpretedOption_ = other.uninterpretedOption_.Clone();
@ -7096,6 +7097,12 @@ namespace Google.Protobuf.Reflection {
    /// implementation must either *always* check its required fields, or *never*
    /// check its required fields, regardless of whether or not the message has
    /// been parsed.
+    ///
+    /// As of 2021, lazy does no correctness checks on the byte stream during
+    /// parsing.  This may lead to crashes if and when an invalid byte stream is
+    /// finally parsed upon access.
+    ///
+    /// TODO(b/211906113):  Enable validation on lazy fields.
    /// </summary>
    [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
    [global::System.CodeDom.Compiler.GeneratedCode("protoc", null)]
@ -7119,6 +7126,38 @@ namespace Google.Protobuf.Reflection {
      _hasBits0 &= ~8;
    }

+    /// <summary>Field number for the "unverified_lazy" field.</summary>
+    public const int UnverifiedLazyFieldNumber = 15;
+    private readonly static bool UnverifiedLazyDefaultValue = false;
+
+    private bool unverifiedLazy_;
+    /// <summary>
+    /// unverified_lazy does no correctness checks on the byte stream. This should
+    /// only be used where lazy with verification is prohibitive for performance
+    /// reasons.
+    /// </summary>
+    [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
+    [global::System.CodeDom.Compiler.GeneratedCode("protoc", null)]
+    public bool UnverifiedLazy {
+      get { if ((_hasBits0 & 64) != 0) { return unverifiedLazy_; } else { return UnverifiedLazyDefaultValue; } }
+      set {
+        _hasBits0 |= 64;
+        unverifiedLazy_ = value;
+      }
+    }
+    /// <summary>Gets whether the "unverified_lazy" field is set</summary>
+    [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
+    [global::System.CodeDom.Compiler.GeneratedCode("protoc", null)]
+    public bool HasUnverifiedLazy {
+      get { return (_hasBits0 & 64) != 0; }
+    }
+    /// <summary>Clears the value of the "unverified_lazy" field</summary>
+    [global::System.Diagnostics.DebuggerNonUserCodeAttribute]
+    [global::System.CodeDom.Compiler.GeneratedCode("protoc", null)]
+    public void ClearUnverifiedLazy() {
+      _hasBits0 &= ~64;
+    }
+
    /// <summary>Field number for the "deprecated" field.</summary>
    public const int DeprecatedFieldNumber = 3;
    private readonly static bool DeprecatedDefaultValue = false;
@ -7215,6 +7254,7 @@ namespace Google.Protobuf.Reflection {
      if (Packed != other.Packed) return false;
      if (Jstype != other.Jstype) return false;
      if (Lazy != other.Lazy) return false;
+      if (UnverifiedLazy != other.UnverifiedLazy) return false;
      if (Deprecated != other.Deprecated) return false;
      if (Weak != other.Weak) return false;
      if(!uninterpretedOption_.Equals(other.uninterpretedOption_)) return false;
@ -7232,6 +7272,7 @@ namespace Google.Protobuf.Reflection {
      if (HasPacked) hash ^= Packed.GetHashCode();
      if (HasJstype) hash ^= Jstype.GetHashCode();
      if (HasLazy) hash ^= Lazy.GetHashCode();
+      if (HasUnverifiedLazy) hash ^= UnverifiedLazy.GetHashCode();
      if (HasDeprecated) hash ^= Deprecated.GetHashCode();
      if (HasWeak) hash ^= Weak.GetHashCode();
      hash ^= uninterpretedOption_.GetHashCode();
@ -7280,6 +7321,10 @@ namespace Google.Protobuf.Reflection {
        output.WriteRawTag(80);
        output.WriteBool(Weak);
      }
+      if (HasUnverifiedLazy) {
+        output.WriteRawTag(120);
+        output.WriteBool(UnverifiedLazy);
+      }
      uninterpretedOption_.WriteTo(output, _repeated_uninterpretedOption_codec);
      if (_extensions != null) {
        _extensions.WriteTo(output);
@ -7318,6 +7363,10 @@ namespace Google.Protobuf.Reflection {
        output.WriteRawTag(80);
        output.WriteBool(Weak);
      }
+      if (HasUnverifiedLazy) {
+        output.WriteRawTag(120);
+        output.WriteBool(UnverifiedLazy);
+      }
      uninterpretedOption_.WriteTo(ref output, _repeated_uninterpretedOption_codec);
      if (_extensions != null) {
        _extensions.WriteTo(ref output);
@ -7344,6 +7393,9 @@ namespace Google.Protobuf.Reflection {
      if (HasLazy) {
        size += 1 + 1;
      }
+      if (HasUnverifiedLazy) {
+        size += 1 + 1;
+      }
      if (HasDeprecated) {
        size += 1 + 1;
      }
@ -7378,6 +7430,9 @@ namespace Google.Protobuf.Reflection {
      if (other.HasLazy) {
        Lazy = other.Lazy;
      }
+      if (other.HasUnverifiedLazy) {
+        UnverifiedLazy = other.UnverifiedLazy;
+      }
      if (other.HasDeprecated) {
        Deprecated = other.Deprecated;
      }
@ -7427,6 +7482,10 @@ namespace Google.Protobuf.Reflection {
            Weak = input.ReadBool();
            break;
          }
+          case 120: {
+            UnverifiedLazy = input.ReadBool();
+            break;
+          }
          case 7994: {
            uninterpretedOption_.AddEntriesFrom(input, _repeated_uninterpretedOption_codec);
            break;
@ -7472,6 +7531,10 @@ namespace Google.Protobuf.Reflection {
            Weak = input.ReadBool();
            break;
          }
+          case 120: {
+            UnverifiedLazy = input.ReadBool();
+            break;
+          }
          case 7994: {
            uninterpretedOption_.AddEntriesFrom(ref input, _repeated_uninterpretedOption_codec);
            break;
--- a/csharp/src/Google.Protobuf/Reflection/EnumDescriptor.cs
+++ b/csharp/src/Google.Protobuf/Reflection/EnumDescriptor.cs
@ -68,6 +68,14 @@ namespace Google.Protobuf.Reflection

        internal EnumDescriptorProto Proto { get { return proto; } }

+        /// <summary>
+        /// Returns a clone of the underlying <see cref="EnumDescriptorProto"/> describing this enum.
+        /// Note that a copy is taken every time this method is called, so clients using it frequently
+        /// (and not modifying it) may want to cache the returned value.
+        /// </summary>
+        /// <returns>A protobuf representation of this enum descriptor.</returns>
+        public EnumDescriptorProto ToProto() => Proto.Clone();
+
        /// <summary>
        /// The brief name of the descriptor's target.
        /// </summary>
--- a/csharp/src/Google.Protobuf/Reflection/EnumValueDescriptor.cs
+++ b/csharp/src/Google.Protobuf/Reflection/EnumValueDescriptor.cs
@ -55,6 +55,14 @@ namespace Google.Protobuf.Reflection

        internal EnumValueDescriptorProto Proto { get { return proto; } }

+        /// <summary>
+        /// Returns a clone of the underlying <see cref="EnumValueDescriptorProto"/> describing this enum value.
+        /// Note that a copy is taken every time this method is called, so clients using it frequently
+        /// (and not modifying it) may want to cache the returned value.
+        /// </summary>
+        /// <returns>A protobuf representation of this enum value descriptor.</returns>
+        public EnumValueDescriptorProto ToProto() => Proto.Clone();
+
        /// <summary>
        /// Returns the name of the enum value described by this object.
        /// </summary>
--- a/csharp/src/Google.Protobuf/Reflection/FieldDescriptor.cs
+++ b/csharp/src/Google.Protobuf/Reflection/FieldDescriptor.cs
@ -45,7 +45,6 @@ namespace Google.Protobuf.Reflection
        private MessageDescriptor extendeeType;
        private MessageDescriptor messageType;
        private FieldType fieldType;
-        private readonly string propertyName; // Annoyingly, needed in Crosslink.
        private IFieldAccessor accessor;

        /// <summary>
@ -70,6 +69,11 @@ namespace Google.Protobuf.Reflection
        /// </summary>
        public string JsonName { get; }

+        /// <summary>
+        /// The name of the property in the <c>ContainingType.ClrType</c> class.
+        /// </summary>
+        public string PropertyName { get; }
+
        /// <summary>
        /// Indicates whether this field supports presence, either implicitly (e.g. due to it being a message
        /// type field) or explicitly via Has/Clear members. If this returns true, it is safe to call
@ -87,6 +91,14 @@ namespace Google.Protobuf.Reflection

        internal FieldDescriptorProto Proto { get; }

+        /// <summary>
+        /// Returns a clone of the underlying <see cref="FieldDescriptorProto"/> describing this field.
+        /// Note that a copy is taken every time this method is called, so clients using it frequently
+        /// (and not modifying it) may want to cache the returned value.
+        /// </summary>
+        /// <returns>A protobuf representation of this field descriptor.</returns>
+        public FieldDescriptorProto ToProto() => Proto.Clone();
+
        /// <summary>
        /// An extension identifier for this field, or <c>null</c> if this field isn't an extension.
        /// </summary>
@ -123,7 +135,7 @@ namespace Google.Protobuf.Reflection
            // for later.
            // We could trust the generated code and check whether the type of the property is
            // a MapField, but that feels a tad nasty.
-            this.propertyName = propertyName;
+            PropertyName = propertyName;
            Extension = extension;
            JsonName =  Proto.JsonName == "" ? JsonFormatter.ToJsonName(Proto.Name) : Proto.JsonName;
        }
@ -235,7 +247,8 @@ namespace Google.Protobuf.Reflection
                }
                else
                {
-                    return !Proto.Options.HasPacked || Proto.Options.Packed;
+                    // Packed by default with proto3
+                    return Proto.Options == null || !Proto.Options.HasPacked || Proto.Options.Packed;
                }
            }
        }
@ -436,19 +449,19 @@ namespace Google.Protobuf.Reflection
            // If we're given no property name, that's because we really don't want an accessor.
            // This could be because it's a map message, or it could be that we're loading a FileDescriptor dynamically.
            // TODO: Support dynamic messages.
-            if (propertyName == null)
+            if (PropertyName == null)
            {
                return null;
            }

-            var property = ContainingType.ClrType.GetProperty(propertyName);
+            var property = ContainingType.ClrType.GetProperty(PropertyName);
            if (property == null)
            {
-                throw new DescriptorValidationException(this, $"Property {propertyName} not found in {ContainingType.ClrType}");
+                throw new DescriptorValidationException(this, $"Property {PropertyName} not found in {ContainingType.ClrType}");
            }
            return IsMap ? new MapFieldAccessor(property, this)
                : IsRepeated ? new RepeatedFieldAccessor(property, this)
-                : (IFieldAccessor) new SingleFieldAccessor(property, this);
+                : (IFieldAccessor) new SingleFieldAccessor(ContainingType.ClrType, property, this);
        }
    }
 }
--- a/csharp/src/Google.Protobuf/Reflection/FileDescriptor.cs
+++ b/csharp/src/Google.Protobuf/Reflection/FileDescriptor.cs
@ -249,6 +249,14 @@ namespace Google.Protobuf.Reflection
        /// </value>
        internal FileDescriptorProto Proto { get; }

+        /// <summary>
+        /// Returns a clone of the underlying <see cref="FileDescriptorProto"/> describing this file.
+        /// Note that a copy is taken every time this method is called, so clients using it frequently
+        /// (and not modifying it) may want to cache the returned value.
+        /// </summary>
+        /// <returns>A protobuf representation of this file descriptor.</returns>
+        public FileDescriptorProto ToProto() => Proto.Clone();
+
        /// <summary>
        /// The syntax of the file
        /// </summary>
--- a/csharp/src/Google.Protobuf/Reflection/GeneratedClrTypeInfo.cs
+++ b/csharp/src/Google.Protobuf/Reflection/GeneratedClrTypeInfo.cs
@ -30,6 +30,7 @@
 // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 #endregion
 using System;
+using System.Diagnostics.CodeAnalysis;

 namespace Google.Protobuf.Reflection
 {
@ -43,10 +44,19 @@ namespace Google.Protobuf.Reflection
        private static readonly string[] EmptyNames = new string[0];
        private static readonly GeneratedClrTypeInfo[] EmptyCodeInfo = new GeneratedClrTypeInfo[0];
        private static readonly Extension[] EmptyExtensions = new Extension[0];
+        internal const DynamicallyAccessedMemberTypes MessageAccessibility =
+            // Creating types
+            DynamicallyAccessedMemberTypes.PublicConstructors |
+            // Getting and setting properties
+            DynamicallyAccessedMemberTypes.PublicProperties |
+            DynamicallyAccessedMemberTypes.NonPublicProperties |
+            // Calling presence methods
+            DynamicallyAccessedMemberTypes.PublicMethods;

        /// <summary>
        /// Irrelevant for file descriptors; the CLR type for the message for message descriptors.
        /// </summary>
+        [DynamicallyAccessedMembers(MessageAccessibility)]
        public Type ClrType { get; private set; }

        /// <summary>
@ -88,7 +98,11 @@ namespace Google.Protobuf.Reflection
        /// Each array parameter may be null, to indicate a lack of values.
        /// The parameter order is designed to make it feasible to format the generated code readably.
        /// </summary>
-        public GeneratedClrTypeInfo(Type clrType, MessageParser parser, string[] propertyNames, string[] oneofNames, Type[] nestedEnums, Extension[] extensions, GeneratedClrTypeInfo[] nestedTypes)
+        public GeneratedClrTypeInfo(
+            // Preserve all public members on message types when trimming is enabled.
+            // This ensures that members used by reflection, e.g. JSON serialization, are preserved.
+            [DynamicallyAccessedMembers(MessageAccessibility)]
+            Type clrType, MessageParser parser, string[] propertyNames, string[] oneofNames, Type[] nestedEnums, Extension[] extensions, GeneratedClrTypeInfo[] nestedTypes)
        {
            NestedTypes = nestedTypes ?? EmptyCodeInfo;
            NestedEnums = nestedEnums ?? ReflectionUtil.EmptyTypes;
@ -104,7 +118,11 @@ namespace Google.Protobuf.Reflection
        /// Each array parameter may be null, to indicate a lack of values.
        /// The parameter order is designed to make it feasible to format the generated code readably.
        /// </summary>
-        public GeneratedClrTypeInfo(Type clrType, MessageParser parser, string[] propertyNames, string[] oneofNames, Type[] nestedEnums, GeneratedClrTypeInfo[] nestedTypes)
+        public GeneratedClrTypeInfo(
+            // Preserve all public members on message types when trimming is enabled.
+            // This ensures that members used by reflection, e.g. JSON serialization, are preserved.
+            [DynamicallyAccessedMembers(MessageAccessibility)]
+            Type clrType, MessageParser parser, string[] propertyNames, string[] oneofNames, Type[] nestedEnums, GeneratedClrTypeInfo[] nestedTypes)
            : this(clrType, parser, propertyNames, oneofNames, nestedEnums, null, nestedTypes)
        {
        }
--- a/csharp/src/Google.Protobuf/Reflection/MessageDescriptor.cs
+++ b/csharp/src/Google.Protobuf/Reflection/MessageDescriptor.cs
@ -33,6 +33,7 @@
 using System;
 using System.Collections.Generic;
 using System.Collections.ObjectModel;
+using System.Diagnostics.CodeAnalysis;
 using System.Linq;
 using System.Reflection;
 #if NET35
@ -150,6 +151,14 @@ namespace Google.Protobuf.Reflection

        internal DescriptorProto Proto { get; }

+        /// <summary>
+        /// Returns a clone of the underlying <see cref="DescriptorProto"/> describing this message.
+        /// Note that a copy is taken every time this method is called, so clients using it frequently
+        /// (and not modifying it) may want to cache the returned value.
+        /// </summary>
+        /// <returns>A protobuf representation of this message descriptor.</returns>
+        public DescriptorProto ToProto() => Proto.Clone();
+
        internal bool IsExtensionsInitialized(IMessage message)
        {
            if (Proto.ExtensionRange.Count == 0)
@ -182,6 +191,7 @@ namespace Google.Protobuf.Reflection
        /// a wrapper type, and handle the result appropriately.
        /// </para>
        /// </remarks>
+        [DynamicallyAccessedMembers(GeneratedClrTypeInfo.MessageAccessibility)]
        public Type ClrType { get; }

        /// <summary>
--- a/csharp/src/Google.Protobuf/Reflection/MethodDescriptor.cs
+++ b/csharp/src/Google.Protobuf/Reflection/MethodDescriptor.cs
@ -114,6 +114,14 @@ namespace Google.Protobuf.Reflection

        internal MethodDescriptorProto Proto { get { return proto; } }

+        /// <summary>
+        /// Returns a clone of the underlying <see cref="MethodDescriptorProto"/> describing this method.
+        /// Note that a copy is taken every time this method is called, so clients using it frequently
+        /// (and not modifying it) may want to cache the returned value.
+        /// </summary>
+        /// <returns>A protobuf representation of this method descriptor.</returns>
+        public MethodDescriptorProto ToProto() => Proto.Clone();
+
        /// <summary>
        /// The brief name of the descriptor's target.
        /// </summary>
--- a/csharp/src/Google.Protobuf/Reflection/OneofDescriptor.cs
+++ b/csharp/src/Google.Protobuf/Reflection/OneofDescriptor.cs
@ -45,7 +45,6 @@ namespace Google.Protobuf.Reflection
    /// </summary>
    public sealed class OneofDescriptor : DescriptorBase
    {
-        private readonly OneofDescriptorProto proto;
        private MessageDescriptor containingType;
        private IList<FieldDescriptor> fields;
        private readonly OneofAccessor accessor;
@ -53,7 +52,7 @@ namespace Google.Protobuf.Reflection
        internal OneofDescriptor(OneofDescriptorProto proto, FileDescriptor file, MessageDescriptor parent, int index, string clrName)
            : base(file, file.ComputeFullName(parent, proto.Name), index)
        {
-            this.proto = proto;
+            this.Proto = proto;
            containingType = parent;
            file.DescriptorPool.AddSymbol(this);

@ -68,7 +67,18 @@ namespace Google.Protobuf.Reflection
        /// <summary>
        /// The brief name of the descriptor's target.
        /// </summary>
-        public override string Name { get { return proto.Name; } }
+        public override string Name => Proto.Name;
+
+        // Visible for testing
+        internal OneofDescriptorProto Proto { get; }
+
+        /// <summary>
+        /// Returns a clone of the underlying <see cref="OneofDescriptorProto"/> describing this oneof.
+        /// Note that a copy is taken every time this method is called, so clients using it frequently
+        /// (and not modifying it) may want to cache the returned value.
+        /// </summary>
+        /// <returns>A protobuf representation of this oneof descriptor.</returns>
+        public OneofDescriptorProto ToProto() => Proto.Clone();

        /// <summary>
        /// Gets the message type containing this oneof.
@ -118,7 +128,7 @@ namespace Google.Protobuf.Reflection
        /// The (possibly empty) set of custom options for this oneof.
        /// </summary>
        [Obsolete("CustomOptions are obsolete. Use the GetOptions method.")]
-        public CustomOptions CustomOptions => new CustomOptions(proto.Options?._extensions?.ValuesByNumber);
+        public CustomOptions CustomOptions => new CustomOptions(Proto.Options?._extensions?.ValuesByNumber);

        /// <summary>
        /// The <c>OneofOptions</c>, defined in <c>descriptor.proto</c>.
@ -126,7 +136,7 @@ namespace Google.Protobuf.Reflection
        /// Custom options can be retrieved as extensions of the returned message.
        /// NOTE: A defensive copy is created each time this property is retrieved.
        /// </summary>
-        public OneofOptions GetOptions() => proto.Options?.Clone();
+        public OneofOptions GetOptions() => Proto.Options?.Clone();

        /// <summary>
        /// Gets a single value oneof option for this descriptor
@ -134,7 +144,7 @@ namespace Google.Protobuf.Reflection
        [Obsolete("GetOption is obsolete. Use the GetOptions() method.")]
        public T GetOption<T>(Extension<OneofOptions, T> extension)
        {
-            var value = proto.Options.GetExtension(extension);
+            var value = Proto.Options.GetExtension(extension);
            return value is IDeepCloneable<T> ? (value as IDeepCloneable<T>).Clone() : value;
        }

@ -144,7 +154,7 @@ namespace Google.Protobuf.Reflection
        [Obsolete("GetOption is obsolete. Use the GetOptions() method.")]
        public RepeatedField<T> GetOption<T>(RepeatedExtension<OneofOptions, T> extension)
        {
-            return proto.Options.GetExtension(extension).Clone();
+            return Proto.Options.GetExtension(extension).Clone();
        }

        internal void CrossLink()
--- a/csharp/src/Google.Protobuf/Reflection/ReflectionUtil.cs
+++ b/csharp/src/Google.Protobuf/Reflection/ReflectionUtil.cs
@ -32,6 +32,7 @@

 using Google.Protobuf.Compatibility;
 using System;
+using System.Diagnostics.CodeAnalysis;
 using System.Reflection;

 namespace Google.Protobuf.Reflection
@ -115,13 +116,15 @@ namespace Google.Protobuf.Reflection
        internal static Func<IMessage, bool> CreateFuncIMessageBool(MethodInfo method) =>
            GetReflectionHelper(method.DeclaringType, method.ReturnType).CreateFuncIMessageBool(method);

-        internal static Func<IMessage, bool> CreateIsInitializedCaller(Type msg) =>
+        [UnconditionalSuppressMessage("Trimming", "IL2026", Justification = "Type parameter members are preserved with DynamicallyAccessedMembers on GeneratedClrTypeInfo.ctor clrType parameter.")]
+        internal static Func<IMessage, bool> CreateIsInitializedCaller([DynamicallyAccessedMembers(GeneratedClrTypeInfo.MessageAccessibility)]Type msg) =>
            ((IExtensionSetReflector)Activator.CreateInstance(typeof(ExtensionSetReflector<>).MakeGenericType(msg))).CreateIsInitializedCaller();

        /// <summary>
        /// Creates a delegate which will execute the given method after casting the first argument to
        /// the type that declares the method, and the second argument to the first parameter type of the method.
        /// </summary>
+        [UnconditionalSuppressMessage("Trimming", "IL2026", Justification = "Type parameter members are preserved with DynamicallyAccessedMembers on GeneratedClrTypeInfo.ctor clrType parameter.")]
        internal static IExtensionReflectionHelper CreateExtensionHelper(Extension extension) =>
            (IExtensionReflectionHelper)Activator.CreateInstance(typeof(ExtensionReflectionHelper<,>).MakeGenericType(extension.TargetType, extension.GetType().GenericTypeArguments[1]), extension);

@ -131,6 +134,7 @@ namespace Google.Protobuf.Reflection
        /// they can be garbage collected. We could cache them by type if that proves to be important, but creating
        /// an object is pretty cheap.
        /// </summary>
+        [UnconditionalSuppressMessage("Trimming", "IL2026", Justification = "Type parameter members are preserved with DynamicallyAccessedMembers on GeneratedClrTypeInfo.ctor clrType parameter.")]
        private static IReflectionHelper GetReflectionHelper(Type t1, Type t2) =>
            (IReflectionHelper) Activator.CreateInstance(typeof(ReflectionHelper<,>).MakeGenericType(t1, t2));

@ -308,16 +312,14 @@ namespace Google.Protobuf.Reflection
            }
        }

-        private class ExtensionSetReflector<T1> : IExtensionSetReflector where T1 : IExtendableMessage<T1>
+        private class ExtensionSetReflector<
+            [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicProperties | DynamicallyAccessedMemberTypes.NonPublicProperties)]
+            T1> : IExtensionSetReflector where T1 : IExtendableMessage<T1>
        {
            public Func<IMessage, bool> CreateIsInitializedCaller()
            {
                var prop = typeof(T1).GetTypeInfo().GetDeclaredProperty("_Extensions");
-#if NET35
-                var getFunc = (Func<T1, ExtensionSet<T1>>)prop.GetGetMethod(true).CreateDelegate(typeof(Func<T1, ExtensionSet<T1>>));
-#else
                var getFunc = (Func<T1, ExtensionSet<T1>>)prop.GetMethod.CreateDelegate(typeof(Func<T1, ExtensionSet<T1>>));
-#endif
                var initializedFunc = (Func<ExtensionSet<T1>, bool>)
                    typeof(ExtensionSet<T1>)
                        .GetTypeInfo()
--- a/csharp/src/Google.Protobuf/Reflection/ServiceDescriptor.cs
+++ b/csharp/src/Google.Protobuf/Reflection/ServiceDescriptor.cs
@ -73,6 +73,14 @@ namespace Google.Protobuf.Reflection

        internal ServiceDescriptorProto Proto { get { return proto; } }

+        /// <summary>
+        /// Returns a clone of the underlying <see cref="ServiceDescriptorProto"/> describing this service.
+        /// Note that a copy is taken every time this method is called, so clients using it frequently
+        /// (and not modifying it) may want to cache the returned value.
+        /// </summary>
+        /// <returns>A protobuf representation of this service descriptor.</returns>
+        public ServiceDescriptorProto ToProto() => Proto.Clone();
+
        /// <value>
        /// An unmodifiable list of methods in this service.
        /// </value>
--- a/csharp/src/Google.Protobuf/Reflection/SingleFieldAccessor.cs
+++ b/csharp/src/Google.Protobuf/Reflection/SingleFieldAccessor.cs
@ -31,6 +31,8 @@
 #endregion

 using System;
+using System.Diagnostics;
+using System.Diagnostics.CodeAnalysis;
 using System.Reflection;
 using Google.Protobuf.Compatibility;

@ -50,7 +52,9 @@ namespace Google.Protobuf.Reflection
        private readonly Action<IMessage> clearDelegate;
        private readonly Func<IMessage, bool> hasDelegate;

-        internal SingleFieldAccessor(PropertyInfo property, FieldDescriptor descriptor) : base(property, descriptor)
+        internal SingleFieldAccessor(
+            [DynamicallyAccessedMembers(GeneratedClrTypeInfo.MessageAccessibility)]
+            Type messageType, PropertyInfo property, FieldDescriptor descriptor) : base(property, descriptor)
        {
            if (!property.CanWrite)
            {
@ -87,13 +91,13 @@ namespace Google.Protobuf.Reflection
            // Primitive fields always support presence in proto2, and support presence in proto3 for optional fields.
            else if (descriptor.File.Syntax == Syntax.Proto2 || descriptor.Proto.Proto3Optional)
            {
-                MethodInfo hasMethod = property.DeclaringType.GetRuntimeProperty("Has" + property.Name).GetMethod;
+                MethodInfo hasMethod = messageType.GetRuntimeProperty("Has" + property.Name).GetMethod;
                if (hasMethod == null)
                {
                    throw new ArgumentException("Not all required properties/methods are available");
                }
                hasDelegate = ReflectionUtil.CreateFuncIMessageBool(hasMethod);
-                MethodInfo clearMethod = property.DeclaringType.GetRuntimeMethod("Clear" + property.Name, ReflectionUtil.EmptyTypes);
+                MethodInfo clearMethod = messageType.GetRuntimeMethod("Clear" + property.Name, ReflectionUtil.EmptyTypes);
                if (clearMethod == null)
                {
                    throw new ArgumentException("Not all required properties/methods are available");
@ -107,16 +111,48 @@ namespace Google.Protobuf.Reflection
                hasDelegate = message => { throw new InvalidOperationException("Presence is not implemented for this field"); };

                // While presence isn't supported, clearing still is; it's just setting to a default value.
-                var clrType = property.PropertyType;
-
-                object defaultValue =
-                    clrType == typeof(string) ? ""
-                    : clrType == typeof(ByteString) ? ByteString.Empty
-                    : Activator.CreateInstance(clrType);
+                object defaultValue = GetDefaultValue(descriptor);
                clearDelegate = message => SetValue(message, defaultValue);
            }
        }

+        private static object GetDefaultValue(FieldDescriptor descriptor)
+        {
+            switch (descriptor.FieldType)
+            {
+                case FieldType.Bool:
+                    return false;
+                case FieldType.Bytes:
+                    return ByteString.Empty;
+                case FieldType.String:
+                    return "";
+                case FieldType.Double:
+                    return 0.0;
+                case FieldType.SInt32:
+                case FieldType.Int32:
+                case FieldType.SFixed32:
+                case FieldType.Enum:
+                    return 0;
+                case FieldType.Fixed32:
+                case FieldType.UInt32:
+                    return (uint)0;
+                case FieldType.Fixed64:
+                case FieldType.UInt64:
+                    return 0UL;
+                case FieldType.SFixed64:
+                case FieldType.Int64:
+                case FieldType.SInt64:
+                    return 0L;
+                case FieldType.Float:
+                    return 0f;
+                case FieldType.Message:
+                case FieldType.Group: // Never expect to get this, but...
+                    return null;
+                default:
+                    throw new ArgumentException("Invalid field type");
+            }
+        }
+
        public override void Clear(IMessage message) => clearDelegate(message);
        public override bool HasValue(IMessage message) => hasDelegate(message);
        public override void SetValue(IMessage message, object value) => setValueDelegate(message, value);
--- a/csharp/src/Google.Protobuf/WellKnownTypes/FieldMaskPartial.cs
+++ b/csharp/src/Google.Protobuf/WellKnownTypes/FieldMaskPartial.cs
@ -33,6 +33,7 @@
 using System;
 using System.Collections;
 using System.Collections.Generic;
+using System.Diagnostics.CodeAnalysis;
 using System.IO;
 using System.Linq;
 using Google.Protobuf.Reflection;
@ -115,7 +116,7 @@ namespace Google.Protobuf.WellKnownTypes
        /// Parses from a string to a FieldMask and validates all field paths.
        /// </summary>
        /// <typeparam name="T">The type to validate the field paths against.</typeparam>
-        public static FieldMask FromString<T>(string value) where T : IMessage
+        public static FieldMask FromString<[DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicParameterlessConstructor)]T>(string value) where T : IMessage
        {
            return FromStringEnumerable<T>(new List<string>(value.Split(FIELD_PATH_SEPARATOR)));
        }
@ -124,7 +125,7 @@ namespace Google.Protobuf.WellKnownTypes
        /// Constructs a FieldMask for a list of field paths in a certain type.
        /// </summary>
        /// <typeparam name="T">The type to validate the field paths against.</typeparam>
-        public static FieldMask FromStringEnumerable<T>(IEnumerable<string> paths) where T : IMessage
+        public static FieldMask FromStringEnumerable<[DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicParameterlessConstructor)]T>(IEnumerable<string> paths) where T : IMessage
        {
            var mask = new FieldMask();
            foreach (var path in paths)
@ -151,7 +152,7 @@ namespace Google.Protobuf.WellKnownTypes
        /// Constructs a FieldMask from the passed field numbers.
        /// </summary>
        /// <typeparam name="T">The type to validate the field paths against.</typeparam>
-        public static FieldMask FromFieldNumbers<T>(params int[] fieldNumbers) where T : IMessage
+        public static FieldMask FromFieldNumbers<[DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicParameterlessConstructor)]T>(params int[] fieldNumbers) where T : IMessage
        {
            return FromFieldNumbers<T>((IEnumerable<int>)fieldNumbers);
        }
@ -160,7 +161,7 @@ namespace Google.Protobuf.WellKnownTypes
        /// Constructs a FieldMask from the passed field numbers.
        /// </summary>
        /// <typeparam name="T">The type to validate the field paths against.</typeparam>
-        public static FieldMask FromFieldNumbers<T>(IEnumerable<int> fieldNumbers) where T : IMessage
+        public static FieldMask FromFieldNumbers<[DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicParameterlessConstructor)]T>(IEnumerable<int> fieldNumbers) where T : IMessage
        {
            var descriptor = Activator.CreateInstance<T>().Descriptor;

@ -208,7 +209,7 @@ namespace Google.Protobuf.WellKnownTypes
        /// Checks whether paths in a given fields mask are valid.
        /// </summary>
        /// <typeparam name="T">The type to validate the field paths against.</typeparam>
-        public static bool IsValid<T>(FieldMask fieldMask) where T : IMessage
+        public static bool IsValid<[DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicParameterlessConstructor)]T>(FieldMask fieldMask) where T : IMessage
        {
            var descriptor = Activator.CreateInstance<T>().Descriptor;

@ -235,7 +236,7 @@ namespace Google.Protobuf.WellKnownTypes
        /// Checks whether a given field path is valid.
        /// </summary>
        /// <typeparam name="T">The type to validate the field paths against.</typeparam>
-        public static bool IsValid<T>(string path) where T : IMessage
+        public static bool IsValid<[DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicParameterlessConstructor)]T>(string path) where T : IMessage
        {
            var descriptor = Activator.CreateInstance<T>().Descriptor;

--- a/docs/options.md
+++ b/docs/options.md
@ -292,3 +292,11 @@ with info about your project (name and website) so we can add an entry for you.
 1. Protoc-gen-jsonschema
   * Website: https://github.com/chrusty/protoc-gen-jsonschema
   * Extension: 1125-1129
+
+1. Protoc-gen-checker
+   * Website: https://github.com/Intrinsec/protoc-gen-checker
+   * Extension: 1130-1139
+
+1. Protoc-gen-go-svc
+   * Website: https://github.com/dane/protoc-gen-go-svc
+   * Extension: 1140
--- a/docs/third_party.md
+++ b/docs/third_party.md
@ -2,31 +2,32 @@

 This page lists code related to Protocol Buffers which is developed and maintained by third parties.  You may find this code useful, but note that **these projects are not affiliated with or endorsed by Google (unless explicitly marked)**; try them at your own risk.  Also note that many projects here are in the early stages of development and not production-ready.

-If you have a project that should be listed here, please [send us a pull request](https://github.com/google/protobuf/pulls) to update this page.
+If you have a project that should be listed here, please
+[send us a pull request](https://github.com/protocolbuffers/protobuf/pulls) to update this page.

 ## Programming Languages

 These are projects we know about implementing Protocol Buffers for other programming languages:
-* Action Script: http://code.google.com/p/protobuf-actionscript3/
+* Action Script: https://code.google.com/p/protobuf-actionscript3/
 * Action Script: https://code.google.com/p/protoc-gen-as3/
 * Action Script: https://github.com/matrix3d/JProtoc
 * Action Script: https://github.com/zhongfq/protobuf-as3/
 * Ada: https://github.com/reznikmm/protobuf
 * C: https://github.com/protobuf-c/protobuf-c
-* C: http://koti.kapsi.fi/jpa/nanopb/
+* C: https://koti.kapsi.fi/jpa/nanopb/
 * C: https://github.com/cloudwu/pbc/
 * C: https://github.com/haberman/upb/wiki
 * C: https://github.com/squidfunk/protobluff
 * C: https://github.com/eerimoq/pbtools
-* C++: https://github.com/google/protobuf (Google-official implementation)
+* C++: https://github.com/protocolbuffers/protobuf (Google-official implementation)
 * C++: https://EmbeddedProto.com
 * C/C++: http://spbc.sf.net/
-* C#: http://code.google.com/p/protobuf-csharp-port
+* C#: https://code.google.com/p/protobuf-csharp-port
 * C#: https://silentorbit.com/protobuf/
-* C#/.NET/WCF/VB: http://code.google.com/p/protobuf-net/
+* C#/.NET/WCF/VB: https://code.google.com/p/protobuf-net/
 * Clojure: http://github.com/ninjudd/clojure-protobuf
 * Clojure: https://github.com/clojusc/protobuf
-* Clojure: https://protojure.github.io
+* Clojure: https://protojure.readthedocs.io
 * Common Lisp: http://github.com/brown/protobuf
 * Common Lisp: http://github.com/qitab/cl-protobuf
 * D: https://github.com/dcarp/protobuf-d
@ -48,21 +49,20 @@ These are projects we know about implementing Protocol Buffers for other program
 * Go: https://github.com/akunspy/gopbuf
 * Go: https://github.com/gogo/protobuf
 * GopherJS: https://github.com/johanbrandhorst/protobuf
-* Haskell: http://hackage.haskell.org/package/hprotoc
+* Haskell: https://hackage.haskell.org/package/hprotoc
 * Haskell: https://github.com/google/proto-lens (Google-unofficial implementation)
 * Haskell: https://github.com/awakesecurity/proto3-suite (code generator) https://github.com/awakesecurity/proto3-wire (binary serializer/deserializer)
 * Haxe: https://github.com/Atry/protoc-gen-haxe
-* Java: https://github.com/google/protobuf (Google-official implementation)
+* Java: https://github.com/protocolbuffers/protobuf (Google-official implementation)
 * Java/Android: https://github.com/square/wire
 * Java: https://github.com/HebiRobotics/QuickBuffers/
-* Java ME: http://code.google.com/p/protobuf-javame/
+* Java ME: https://code.google.com/p/protobuf-javame/
 * Java ME: http://swingme.sourceforge.net/encode.shtml
-* Java ME: http://code.google.com/p/protobuf-j2me/
-* Javascript: http://code.google.com/p/protobuf-js/
+* Javascript: https://code.google.com/p/protobuf-js/
 * Javascript: http://github.com/sirikata/protojs
 * Javascript: https://github.com/dcodeIO/ProtoBuf.js
-* Javascript: http://code.google.com/p/protobuf-for-node/
-* Javascript: http://code.google.com/p/protostuff/
+* Javascript: https://code.google.com/p/protobuf-for-node/
+* Javascript: https://code.google.com/p/protostuff/
 * Javascript: https://github.com/seishun/node-protoc-plugin (Node.js port of plugin.h)
 * Javascript: https://github.com/seishun/node-protoc-gen-javascript (Node.js port of the Google-official implementation)
 * Javascript: https://github.com/ButterCam/sisyphus-js
@ -71,43 +71,45 @@ These are projects we know about implementing Protocol Buffers for other program
 * Kotlin: https://github.com/Kotlin/kotlinx.serialization
 * Kotlin: https://github.com/ButterCam/sisyphus
 * Kotlin: https://github.com/open-toast/protokt
-* Lua: http://code.google.com/p/protoc-gen-lua/
+* Lua: https://code.google.com/p/protoc-gen-lua/
 * Lua: http://github.com/indygreg/lua-protobuf
 * Lua: https://github.com/Neopallium/lua-pb
-* Matlab: http://code.google.com/p/protobuf-matlab/
-* Mercury: http://code.google.com/p/protobuf-mercury/
-* Objective C: http://code.google.com/p/protobuf-objc/
+* Matlab: https://code.google.com/p/protobuf-matlab/
+* Mercury: https://code.google.com/p/protobuf-mercury/
+* Objective C: https://code.google.com/p/protobuf-objc/
 * Objective C: https://github.com/alexeyxo/protobuf-objc
 * OCaml: http://piqi.org/
 * Perl: http://groups.google.com/group/protobuf-perl
-* Perl: http://search.cpan.org/perldoc?Google::ProtocolBuffers
+* Perl: https://metacpan.org/pod/Google::ProtocolBuffers
 * Perl: https://metacpan.org/pod/Google::ProtocolBuffers::Dynamic
-* Perl/XS: http://code.google.com/p/protobuf-perlxs/
-* PHP: http://code.google.com/p/pb4php/
+* Perl/XS: https://code.google.com/p/protobuf-perlxs/
+* PHP: https://code.google.com/p/pb4php/
 * PHP: https://github.com/allegro/php-protobuf/
 * PHP: https://github.com/chobie/php-protocolbuffers
-* PHP: http://drslump.github.com/Protobuf-PHP
 * Prolog: http://www.swi-prolog.org/pldoc/package/protobufs.html
 * Purescript: https://github.com/xc-jp/purescript-protobuf
-* Python: https://github.com/google/protobuf (Google-official implementation)
+* Python: https://github.com/protocolbuffers/protobuf (Google-official implementation)
 * Python: https://github.com/eigenein/protobuf
 * Python: https://github.com/danielgtaylor/python-betterproto
 * R: http://cran.r-project.org/package=RProtoBuf
-* Ruby: http://code.google.com/p/ruby-protobuf/
+* Ruby: https://code.google.com/p/ruby-protobuf/
 * Ruby: http://github.com/mozy/ruby-protocol-buffers
 * Ruby: https://github.com/bmizerany/beefcake/tree/master/lib/beefcake
 * Ruby: https://github.com/localshred/protobuf
+* Rust: https://github.com/tokio-rs/prost
 * Rust: https://github.com/stepancheg/rust-protobuf/
+* Rust: https://github.com/tafia/quick-protobuf
 * Scala: http://github.com/jeffplaisance/scala-protobuf
-* Scala: http://code.google.com/p/protobuf-scala
+* Scala: https://code.google.com/p/protobuf-scala
 * Scala: https://github.com/SandroGrzicic/ScalaBuff
 * Scala: https://scalapb.github.io
 * Solidity: https://github.com/celer-network/pb3-gen-sol
 * Swift: https://github.com/alexeyxo/protobuf-swift
 * Swift: https://github.com/apple/swift-protobuf/
 * Typescript: https://github.com/thesayyn/protoc-gen-ts
+* Typescript: https://github.com/pbkit/pbkit
 * Vala: https://launchpad.net/protobuf-vala
-* Visual Basic: http://code.google.com/p/protobuf-net/
+* Visual Basic: https://code.google.com/p/protobuf-net/

 ## RPC Implementations

@ -128,6 +130,7 @@ GRPC (http://www.grpc.io/) is Google's RPC implementation for Protocol Buffers.
 * https://github.com/awakesecurity/gRPC-haskell (Haskell)
 * https://github.com/Yeolar/raster (C++)
 * https://github.com/jnordberg/wsrpc (JavaScript Node.js/Browser)
+* https://github.com/pbkit/npm-packages/blob/main/frpc-test/src/index.spec.ts (TypeScript Node.js/Browser)
 * https://github.com/ppissias/xsrpcj (Java)
 * https://github.com/twitchtv/twirp (Multiple languages)

@ -157,24 +160,23 @@ There are miscellaneous other things you may find useful as a Protocol Buffers d
    * [rules_closure](https://github.com/bazelbuild/rules_closure) `js-closure`
    * [rules_go](https://github.com/bazelbuild/rules_go) `go`
    * [rules_protobuf](https://github.com/pubref/rules_protobuf) `java` `c++` `c#` `go` `js-closure` `js-node` `python` `ruby`
-* [NetBeans IDE plugin](http://code.google.com/p/protobuf-netbeans-plugin/)
-* [Wireshark/Ethereal packet sniffer plugin](http://code.google.com/p/protobuf-wireshark/)
-* [Alternate encodings (JSON, XML, HTML) for Java protobufs](http://code.google.com/p/protobuf-java-format/)
+* [NetBeans IDE plugin](https://code.google.com/p/protobuf-netbeans-plugin/)
+* [Wireshark/Ethereal packet sniffer plugin](https://code.google.com/p/protobuf-wireshark/)
+* [Alternate encodings (JSON, XML, HTML) for Java protobufs](https://code.google.com/p/protobuf-java-format/)
 * [Another JSON encoder/decoder for Java](https://github.com/sijuv/protobuf-codec)
-* [Editor for serialized protobufs](http://code.google.com/p/protobufeditor/)
+* [Editor for serialized protobufs](https://code.google.com/p/protobufeditor/)
 * [IntelliJ IDEA plugin](http://github.com/jvolkman/intellij-protobuf-editor)
 * [IntelliJ Protobuf Plugin](https://github.com/devkanro/intellij-protobuf-plugin)
 * [TextMate syntax highlighting](http://github.com/michaeledgar/protobuf-tmbundle)
-* [Oracle PL SQL plugin](http://code.google.com/p/protocol-buffer-plsql/)
-* [Eclipse editor for protobuf (from Google)](http://code.google.com/p/protobuf-dt/)
+* [Oracle PL SQL plugin](https://code.google.com/p/protocol-buffer-plsql/)
+* [Eclipse editor for protobuf (from Google)](https://code.google.com/p/protobuf-dt/)
 * [C++ Builder compatible protobuf](https://github.com/saadware/protobuf-cppbuilder)
 * Maven Protobuf Compiler Plugin
    * By xolstice.org ([Documentation](https://www.xolstice.org/protobuf-maven-plugin/)) ([Source](https://github.com/xolstice/protobuf-maven-plugin/)) [![Maven Central](https://img.shields.io/maven-central/v/org.xolstice.maven.plugins/protobuf-maven-plugin.svg)](https://repo1.maven.org/maven2/org/xolstice/maven/plugins/protobuf-maven-plugin/)
-    * http://igor-petruk.github.com/protobuf-maven-plugin/
-    * http://code.google.com/p/maven-protoc-plugin/
+    * https://code.google.com/p/maven-protoc-plugin/
    * https://github.com/os72/protoc-jar-maven-plugin
 * [Documentation generator plugin (Markdown/HTML/DocBook/...)](https://github.com/pseudomuto/protoc-gen-doc)
-* [DocBook generator for .proto files](http://code.google.com/p/protoc-gen-docbook/)
+* [DocBook generator for .proto files](https://code.google.com/p/protoc-gen-docbook/)
 * [Protobuf for nginx module](https://github.com/dbcode/protobuf-nginx/)
 * [RSpec matchers and Cucumber step defs for testing Protocol Buffers](https://github.com/connamara/protobuf_spec)
 * [Sbt plugin for Protocol Buffers](https://github.com/Atry/sbt-cppp)
--- a/editors/protobuf-mode.el
+++ b/editors/protobuf-mode.el
@ -193,7 +193,7 @@
 ;;;###autoload (add-to-list 'auto-mode-alist '("\\.proto\\'" . protobuf-mode))

 ;;;###autoload
-(defun protobuf-mode ()
+(define-derived-mode protobuf-mode prog-mode "Protobuf"
  "Major mode for editing Protocol Buffers description language.

 The hook `c-mode-common-hook' is run with no argument at mode
--- a/examples/Makefile
+++ b/examples/Makefile
@ -16,7 +16,7 @@ clean:
 	rm -f javac_middleman AddPerson*.class ListPeople*.class com/example/tutorial/*.class
 	rm -f protoc_middleman addressbook.pb.cc addressbook.pb.h addressbook_pb2.py com/example/tutorial/AddressBookProtos.java
 	rm -f *.pyc
-	rm -f protoc_middleman_go tutorial/*.pb.go add_person_go list_people_go go.mod go.sum
+	rm -f go/tutorialpb/*.pb.go add_person_go list_people_go
 	rm -f protoc_middleman_dart dart_tutorial/*.pb*.dart
 	rmdir dart_tutorial 2>/dev/null || true
 	rmdir tutorial 2>/dev/null || true
@ -28,10 +28,9 @@ protoc_middleman: addressbook.proto
 	protoc $$PROTO_PATH --cpp_out=. --java_out=. --python_out=. addressbook.proto
 	@touch protoc_middleman

-protoc_middleman_go: addressbook.proto
-	mkdir -p tutorial # make directory for go package
-	protoc $$PROTO_PATH --go_out=tutorial addressbook.proto
-	@touch protoc_middleman_go
+go/tutorialpb/addressbook.pb.go: addressbook.proto
+	mkdir -p go/tutorialpb # make directory for go package
+	protoc $$PROTO_PATH --go_opt=paths=source_relative --go_out=go/tutorialpb addressbook.proto

 protoc_middleman_dart: addressbook.proto
 	mkdir -p dart_tutorial # make directory for the dart package
@ -51,21 +50,17 @@ add_person_dart: add_person.dart protoc_middleman_dart

 list_people_dart: list_people.dart protoc_middleman_dart

-go_mod:
-	go mod init github.com/protocolbuffers/protobuf/examples
-	go mod tidy
+add_person_go: go/cmd/add_person/add_person.go go/tutorialpb/addressbook.pb.go
+	cd go && go build -o ../add_person_go ./cmd/add_person

-add_person_go: add_person.go protoc_middleman_go go_mod
-	go build -o add_person_go add_person.go
+add_person_gotest: go/tutorialpb/addressbook.pb.go
+	cd go && go test ./cmd/add_person

-add_person_gotest: add_person_test.go add_person_go go_mod
-	go test add_person.go add_person_test.go
+list_people_go: go/cmd/list_people/list_people.go go/tutorialpb/addressbook.pb.go
+	cd go && go build -o ../list_people_go ./cmd/list_people

-list_people_go: list_people.go protoc_middleman_go go_mod
-	go build -o list_people_go list_people.go
-
-list_people_gotest: list_people.go list_people_go go_mod
-	go test list_people.go list_people_test.go
+list_people_gotest: go/tutorialpb/addressbook.pb.go
+	cd go && go test ./cmd/list_people

 javac_middleman: AddPerson.java ListPeople.java protoc_middleman
 	javac -cp $$CLASSPATH AddPerson.java ListPeople.java com/example/tutorial/AddressBookProtos.java
--- a/examples/README.md
+++ b/examples/README.md
@ -91,22 +91,18 @@ scripts) and can be used to create/display an address book data file.

 ### Go

-The Go example requires a plugin to the protocol buffer compiler, so it is not
-build with all the other examples.  See:
+Follow instructions in [../README.md](../README.md) to install protoc. Then
+install the Go protoc plugin (protoc-gen-go):

-    https://github.com/golang/protobuf
+    $ go install google.golang.org/protobuf/cmd/protoc-gen-go@latest

-for more information about Go protocol buffer support.
+The "go install" command will install protoc-gen-go into the GOBIN
+directory.  You can set the $GOBIN environment variable before
+running "go install" to change the install location.  Make sure the
+install directory is in your shell $PATH.

-First, install the Protocol Buffers compiler (protoc).
-
-Then, install the Go Protocol Buffers plugin ($GOPATH/bin must be in your $PATH
-for protoc to find it):
-
-    go get github.com/golang/protobuf/protoc-gen-go
-
-Build the Go samples in this directory with "make go".  This creates the
-following executable files in the current directory:
+Build the Go samples with "make go".  This creates the following
+executable files in the current directory:

    add_person_go      list_people_go

--- a/examples/addressbook.proto
+++ b/examples/addressbook.proto
@ -24,7 +24,7 @@ option csharp_namespace = "Google.Protobuf.Examples.AddressBook";
 // [END csharp_declaration]

 // [START go_declaration]
-option go_package = "../tutorial";
+option go_package = "github.com/protocolbuffers/protobuf/examples/go/tutorialpb";
 // [END go_declaration]

 // [START messages]
--- a/examples/go/cmd/add_person/add_person.go
+++ b/examples/go/cmd/add_person/add_person.go
@ -9,8 +9,8 @@ import (
 	"os"
 	"strings"

-	"github.com/golang/protobuf/proto"
-	pb "github.com/protocolbuffers/protobuf/examples/tutorial"
+	pb "github.com/protocolbuffers/protobuf/examples/go/tutorialpb"
+	"google.golang.org/protobuf/proto"
 )

 func promptForAddress(r io.Reader) (*pb.Person, error) {
--- a/examples/go/cmd/add_person/add_person_test.go
+++ b/examples/go/cmd/add_person/add_person_test.go
@ -4,8 +4,8 @@ import (
 	"strings"
 	"testing"

-	"github.com/golang/protobuf/proto"
-	pb "github.com/protocolbuffers/protobuf/examples/tutorial"
+	pb "github.com/protocolbuffers/protobuf/examples/go/tutorialpb"
+	"google.golang.org/protobuf/proto"
 )

 func TestPromptForAddressReturnsAddress(t *testing.T) {
@ -51,7 +51,7 @@ unknown
 	}
 	for i := 0; i < phones; i++ {
 		if !proto.Equal(got.Phones[i], want[i]) {
-			t.Errorf("want phone %q, got %q", *want[i], *got.Phones[i])
+			t.Errorf("want phone %q, got %q", want[i], got.Phones[i])
 		}

 	}
--- a/examples/go/cmd/list_people/list_people.go
+++ b/examples/go/cmd/list_people/list_people.go
@ -7,8 +7,8 @@ import (
 	"log"
 	"os"

-	"github.com/golang/protobuf/proto"
-	pb "github.com/protocolbuffers/protobuf/examples/tutorial"
+	pb "github.com/protocolbuffers/protobuf/examples/go/tutorialpb"
+	"google.golang.org/protobuf/proto"
 )

 func writePerson(w io.Writer, p *pb.Person) {
--- a/examples/go/cmd/list_people/list_people_test.go
+++ b/examples/go/cmd/list_people/list_people_test.go
@ -5,7 +5,7 @@ import (
 	"strings"
 	"testing"

-	pb "github.com/protocolbuffers/protobuf/examples/tutorial"
+	pb "github.com/protocolbuffers/protobuf/examples/go/tutorialpb"
 )

 func TestWritePersonWritesPerson(t *testing.T) {
--- a/examples/go/go.mod
+++ b/examples/go/go.mod
@ -0,0 +1,5 @@
+module github.com/protocolbuffers/protobuf/examples/go
+
+go 1.14
+
+require google.golang.org/protobuf v1.27.1
--- a/examples/go/go.sum
+++ b/examples/go/go.sum
@ -0,0 +1,6 @@
+github.com/golang/protobuf v1.5.0/go.mod h1:FsONVRAS9T7sI+LIUmWTfcYkHO4aIWwzhcaSAoJOfIk=
+github.com/google/go-cmp v0.5.5/go.mod h1:v8dTdLbMG2kIc/vJvl+f65V22dbkXbowE6jgT/gNBxE=
+golang.org/x/xerrors v0.0.0-20191204190536-9bdfabe68543/go.mod h1:I/5z698sn9Ka8TeJc9MKroUUfqBBauWjQqLJ2OPfmY0=
+google.golang.org/protobuf v1.26.0-rc.1/go.mod h1:jlhhOSvTdKEhbULTjvd4ARK9grFBp09yW+WbY/TyQbw=
+google.golang.org/protobuf v1.27.1 h1:SnqbnDw1V7RiZcXPx5MEeqPv2s79L9i7BJUlG/+RurQ=
+google.golang.org/protobuf v1.27.1/go.mod h1:9q0QmTI4eRPtz6boOQmLYwt+qCgq0jsYwAQnmE0givc=
--- a/global.json
+++ b/global.json
@ -1,6 +1,6 @@
 {
  "sdk": {
-    "version": "5.0.102",
+    "version": "6.0.100",
    "rollForward": "latestMinor"
  }
 }
--- a/java/BUILD
+++ b/java/BUILD
@ -2,6 +2,8 @@ test_suite(
    name = "tests",
    tests = [
        "//java/core:tests",
+        "//java/kotlin:tests",
+        "//java/kotlin-lite:tests",
        "//java/lite:tests",
        "//java/util:tests",
    ],
@ -13,4 +15,4 @@ filegroup(
        "//java/core:release", # contains lite.
        "//java/util:release",
    ]
-)
+)
--- a/java/README.md
+++ b/java/README.md
@ -23,7 +23,7 @@ If you are using Maven, use the following:
 <dependency>
  <groupId>com.google.protobuf</groupId>
  <artifactId>protobuf-java</artifactId>
-  <version>3.18.0</version>
+  <version>3.19.4</version>
 </dependency>
 ```

@ -37,7 +37,7 @@ protobuf-java-util package:
 <dependency>
  <groupId>com.google.protobuf</groupId>
  <artifactId>protobuf-java-util</artifactId>
-  <version>3.18.0</version>
+  <version>3.19.4</version>
 </dependency>
 ```

@ -45,7 +45,7 @@ protobuf-java-util package:

 If you are using Gradle, add the following to your `build.gradle` file's dependencies:
 ```
-    implementation 'com.google.protobuf:protobuf-java:3.18.0'
+    implementation 'com.google.protobuf:protobuf-java:3.19.4'
 ```
 Again, be sure to check that the version number matches (or is newer than) the version number of protoc that you are using.

--- a/java/bom/pom.xml
+++ b/java/bom/pom.xml
@ -4,7 +4,7 @@

  <groupId>com.google.protobuf</groupId>
  <artifactId>protobuf-bom</artifactId>
-  <version>3.18.1</version>
+  <version>3.19.4</version>
  <packaging>pom</packaging>

  <name>Protocol Buffers [BOM]</name>
@ -29,7 +29,7 @@

  <licenses>
    <license>
-      <name>3-Clause BSD License</name>
+      <name>BSD-3-Clause</name>
      <url>https://opensource.org/licenses/BSD-3-Clause</url>
    </license>
  </licenses>
--- a/java/core/BUILD
+++ b/java/core/BUILD
@ -1,5 +1,5 @@
 load("@bazel_skylib//rules:build_test.bzl", "build_test")
-load("@rules_java//java:defs.bzl", "java_library", "java_proto_library", "java_lite_proto_library")
+load("@rules_java//java:defs.bzl", "java_library", "java_lite_proto_library", "java_proto_library")
 load("@rules_jvm_external//:defs.bzl", "java_export")
 load("@rules_proto//proto:defs.bzl", "proto_lang_toolchain", "proto_library")
 load("//:internal.bzl", "conformance_test")
@ -103,7 +103,7 @@ LITE_SRCS = [
 java_library(
    name = "lite",
    srcs = LITE_SRCS + [
-        "//:gen_well_known_protos_javalite"
+        "//:gen_well_known_protos_javalite",
    ],
    visibility = [
        "//java/lite:__pkg__",
@ -115,10 +115,10 @@ java_export(
    name = "lite_mvn",
    maven_coordinates = "com.google.protobuf:protobuf-javalite:%s" % PROTOBUF_VERSION,
    pom_template = "//java/lite:pom_template.xml",
-    runtime_deps = [":lite"],
    resources = [
        "//:lite_well_known_protos",
    ],
+    runtime_deps = [":lite"],
 )

 java_library(
@ -150,25 +150,25 @@ java_export(
    name = "core_mvn",
    maven_coordinates = "com.google.protobuf:protobuf-java:%s" % PROTOBUF_VERSION,
    pom_template = "pom_template.xml",
-    runtime_deps = [":core"],
    resources = [
        "//:well_known_protos",
    ],
+    runtime_deps = [":core"],
 )

 filegroup(
    name = "release",
-    visibility = ["//java:__pkg__"],
    srcs = [
-        ":core_mvn-pom",
-        ":core_mvn-maven-source",
        ":core_mvn-docs",
+        ":core_mvn-maven-source",
+        ":core_mvn-pom",
        ":core_mvn-project",
-        ":lite_mvn-pom",
-        ":lite_mvn-maven-source",
        ":lite_mvn-docs",
+        ":lite_mvn-maven-source",
+        ":lite_mvn-pom",
        ":lite_mvn-project",
-    ]
+    ],
+    visibility = ["//java:__pkg__"],
 )

 proto_lang_toolchain(
@ -176,6 +176,21 @@ proto_lang_toolchain(
    command_line = "--java_out=$(OUT)",
    runtime = ":core",
    visibility = ["//visibility:public"],
+    # keep this in sync w/ WELL_KNOWN_PROTO_MAP in //:BUILD
+    blacklisted_protos = [
+        "//:any_proto",
+        "//:api_proto",
+        "//:compiler_plugin_proto",
+        "//:descriptor_proto",
+        "//:duration_proto",
+        "//:empty_proto",
+        "//:field_mask_proto",
+        "//:source_context_proto",
+        "//:struct_proto",
+        "//:timestamp_proto",
+        "//:type_proto",
+        "//:wrappers_proto",
+    ],
 )

 proto_library(
@ -207,23 +222,25 @@ java_library(
    name = "test_util",
    srcs = [
        "src/test/java/com/google/protobuf/TestUtil.java",
-        "src/test/java/com/google/protobuf/TestUtilLite.java"
+        "src/test/java/com/google/protobuf/TestUtilLite.java",
    ],
    deps = [
        ":core",
        ":generic_test_protos_java_proto",
        ":java_test_protos_java_proto",
-        "//external:guava",
-        "//external:junit",
+        "@maven//:com_google_guava_guava",
+        "@maven//:junit_junit",
    ],
+    visibility = ["//java:__subpackages__"],
 )

 test_suite(
    name = "tests",
    tests = [
-        "core_build_test",
        "conformance_test",
+        "core_build_test",
        "core_tests",
+        "utf8_tests",
    ],
 )

@ -236,30 +253,52 @@ build_test(

 conformance_test(
    name = "conformance_test",
-    testee = "//:conformance_java",
    failure_list = "//:conformance/failure_list_java.txt",
+    testee = "//:conformance_java",
    text_format_failure_list = "//:conformance/text_format_failure_list_java.txt",
 )

 junit_tests(
    name = "core_tests",
-    srcs = glob(["src/test/java/**/*.java"], exclude = [
-        "src/test/java/com/google/protobuf/TestUtil.java",
-        "src/test/java/com/google/protobuf/TestUtilLite.java",
-    ]),
+    size = "small",
+    srcs = glob(
+        ["src/test/java/**/*.java"],
+        exclude = [
+            "src/test/java/com/google/protobuf/DecodeUtf8Test.java",
+            "src/test/java/com/google/protobuf/IsValidUtf8Test.java",
+            "src/test/java/com/google/protobuf/TestUtil.java",
+            "src/test/java/com/google/protobuf/TestUtilLite.java",
+        ],
+    ),
    data = ["//:testdata"],
-    size = "large",
    deps = [
        ":core",
        ":generic_test_protos_java_proto",
        ":java_test_protos_java_proto",
        ":test_util",
-        "//external:easymock",
-        "//external:easymock_classextension",
-        "//external:guava",
-        "//external:junit",
-        "//external:truth",
-    ]
+        "@maven//:com_google_guava_guava",
+        "@maven//:com_google_truth_truth",
+        "@maven//:junit_junit",
+        "@maven//:org_easymock_easymock",
+    ],
+)
+
+# The UTF-8 validation tests are much slower than the other tests, so they get
+# their own test target with a longer timeout.
+junit_tests(
+    name = "utf8_tests",
+    size = "large",
+    srcs = [
+        "src/test/java/com/google/protobuf/DecodeUtf8Test.java",
+        "src/test/java/com/google/protobuf/IsValidUtf8Test.java",
+        "src/test/java/com/google/protobuf/IsValidUtf8TestUtil.java",
+    ],
+    deps = [
+        ":core",
+        "@maven//:com_google_guava_guava",
+        "@maven//:com_google_truth_truth",
+        "@maven//:junit_junit",
+    ],
 )

 java_lite_proto_library(
@ -282,27 +321,28 @@ genrule(
    name = "rewrite_javalite_test_util",
    srcs = [
        "//java/lite:lite.awk",
-        "src/test/java/com/google/protobuf/TestUtil.java"
+        "src/test/java/com/google/protobuf/TestUtil.java",
    ],
    outs = ["TestUtil.java"],
-    cmd = "awk -f $(location //java/lite:lite.awk) $(location src/test/java/com/google/protobuf/TestUtil.java) > $@"
+    cmd = "awk -f $(location //java/lite:lite.awk) $(location src/test/java/com/google/protobuf/TestUtil.java) > $@",
 )

 java_library(
    name = "test_util_lite",
    srcs = [
+        "src/test/java/com/google/protobuf/TestUtilLite.java",
        ":rewrite_javalite_test_util",
-        "src/test/java/com/google/protobuf/TestUtilLite.java"
    ],
    visibility = [
        "//java/lite:__pkg__",
+        "//java/kotlin-lite:__pkg__",
    ],
    deps = [
        ":generic_test_protos_java_proto_lite",
        ":java_test_protos_java_proto_lite",
        ":lite_runtime_only",
-        "//external:guava",
-        "//external:junit",
+        "@maven//:com_google_guava_guava",
+        "@maven//:junit_junit",
    ],
 )

@ -344,6 +384,7 @@ LITE_TEST_EXCLUSIONS = [
    "src/test/java/com/google/protobuf/TypeRegistryTest.java",
    "src/test/java/com/google/protobuf/UnknownEnumValueTest.java",
    "src/test/java/com/google/protobuf/UnknownFieldSetLiteTest.java",
+    "src/test/java/com/google/protobuf/UnknownFieldSetPerformanceTest.java",
    "src/test/java/com/google/protobuf/UnknownFieldSetTest.java",
    "src/test/java/com/google/protobuf/WellKnownTypesTest.java",
    "src/test/java/com/google/protobuf/WireFormatTest.java",
@ -351,18 +392,20 @@ LITE_TEST_EXCLUSIONS = [

 junit_tests(
    name = "lite_tests",
-    srcs = glob(["src/test/java/**/*.java"], exclude = LITE_TEST_EXCLUSIONS),
+    size = "large",
+    srcs = glob(
+        ["src/test/java/**/*.java"],
+        exclude = LITE_TEST_EXCLUSIONS,
+    ),
    data = ["//:testdata"],
    test_prefix = "Lite",
-    size = "large",
    deps = [
-        ":lite",
        ":generic_test_protos_java_proto_lite",
        ":java_test_protos_java_proto_lite",
+        ":lite",
        ":test_util_lite",
-        "//external:easymock",
-        "//external:junit",
-        "//external:truth",
-    ]
+        "@maven//:com_google_truth_truth",
+        "@maven//:junit_junit",
+        "@maven//:org_easymock_easymock",
+    ],
 )
-
--- a/java/core/generate-test-sources-build.xml
+++ b/java/core/generate-test-sources-build.xml
@ -30,7 +30,6 @@
        <arg value="${test.proto.dir}/com/google/protobuf/map_initialization_order_test.proto"/>
        <arg value="${test.proto.dir}/com/google/protobuf/map_lite_test.proto"/>
        <arg value="${test.proto.dir}/com/google/protobuf/map_test.proto"/>
-        <arg value="${test.proto.dir}/com/google/protobuf/message_lite_extension_util_test.proto"/>
        <arg value="${test.proto.dir}/com/google/protobuf/multiple_files_test.proto"/>
        <arg value="${test.proto.dir}/com/google/protobuf/nested_builders_test.proto"/>
        <arg value="${test.proto.dir}/com/google/protobuf/nested_extension.proto"/>
--- a/java/core/pom.xml
+++ b/java/core/pom.xml
@ -4,7 +4,7 @@
  <parent>
    <groupId>com.google.protobuf</groupId>
    <artifactId>protobuf-parent</artifactId>
-    <version>3.18.1</version>
+    <version>3.19.4</version>
  </parent>

  <artifactId>protobuf-java</artifactId>
--- a/java/core/src/main/java/com/google/protobuf/AbstractMessage.java
+++ b/java/core/src/main/java/com/google/protobuf/AbstractMessage.java
@ -224,7 +224,7 @@ public abstract class AbstractMessage
  }

  /**
-   * Compares two set of fields. This method is used to implement {@link
+   * Compares two sets of fields. This method is used to implement {@link
   * AbstractMessage#equals(Object)} and {@link AbstractMutableMessage#equals(Object)}. It takes
   * special care of bytes fields because immutable messages and mutable messages use different Java
   * type to represent a bytes field and this method should be able to compare immutable messages,
@ -242,8 +242,8 @@ public abstract class AbstractMessage
      Object value2 = b.get(descriptor);
      if (descriptor.getType() == FieldDescriptor.Type.BYTES) {
        if (descriptor.isRepeated()) {
-          List list1 = (List) value1;
-          List list2 = (List) value2;
+          List<?> list1 = (List) value1;
+          List<?> list2 = (List) value2;
          if (list1.size() != list2.size()) {
            return false;
          }
@ -383,8 +383,6 @@ public abstract class AbstractMessage
      //   them to insure that they don't change after verification (since
      //   the Message interface itself cannot enforce immutability of
      //   implementations).
-      // TODO(kenton):  Provide a function somewhere called makeDeepCopy()
-      //   which allows people to make secure deep copies of messages.

      for (final Map.Entry<FieldDescriptor, Object> entry : allFields.entrySet()) {
        final FieldDescriptor field = entry.getKey();
@ -568,17 +566,6 @@ public abstract class AbstractMessage
        final InputStream input, final ExtensionRegistryLite extensionRegistry) throws IOException {
      return (BuilderType) super.mergeFrom(input, extensionRegistry);
    }
-
-    @Override
-    public boolean mergeDelimitedFrom(final InputStream input) throws IOException {
-      return super.mergeDelimitedFrom(input);
-    }
-
-    @Override
-    public boolean mergeDelimitedFrom(
-        final InputStream input, final ExtensionRegistryLite extensionRegistry) throws IOException {
-      return super.mergeDelimitedFrom(input, extensionRegistry);
-    }
  }

  /**
--- a/java/core/src/main/java/com/google/protobuf/AbstractMessageLite.java
+++ b/java/core/src/main/java/com/google/protobuf/AbstractMessageLite.java
@ -89,9 +89,9 @@ public abstract class AbstractMessageLite<
    final int serialized = getSerializedSize();
    final int bufferSize =
        CodedOutputStream.computePreferredBufferSize(
-            CodedOutputStream.computeRawVarint32Size(serialized) + serialized);
+            CodedOutputStream.computeUInt32SizeNoTag(serialized) + serialized);
    final CodedOutputStream codedOutput = CodedOutputStream.newInstance(output, bufferSize);
-    codedOutput.writeRawVarint32(serialized);
+    codedOutput.writeUInt32NoTag(serialized);
    writeTo(codedOutput);
    codedOutput.flush();
  }
@ -316,8 +316,11 @@ public abstract class AbstractMessageLite<

      @Override
      public long skip(final long n) throws IOException {
-        final long result = super.skip(Math.min(n, limit));
+        // because we take the minimum of an int and a long, result is guaranteed to be
+        // less than or equal to Integer.MAX_INT so this cast is safe
+        int result = (int) super.skip(Math.min(n, limit));
        if (result >= 0) {
+          // if the superclass adheres to the contract for skip, this condition is always true
          limit -= result;
        }
        return result;
--- a/java/core/src/main/java/com/google/protobuf/AllocatedBuffer.java
+++ b/java/core/src/main/java/com/google/protobuf/AllocatedBuffer.java
@ -38,6 +38,7 @@ import java.nio.ByteBuffer;
 * A buffer that was allocated by a {@link BufferAllocator}. For every buffer, it is guaranteed that
 * at least one of {@link #hasArray()} or {@link #hasNioBuffer()} will be {@code true}.
 */
+@CheckReturnValue
@ExperimentalApi
 abstract class AllocatedBuffer {
  /**
@ -106,6 +107,7 @@ abstract class AllocatedBuffer {
   * @return This buffer
   * @throws IllegalArgumentException If the preconditions on {@code position} do not hold
   */
+  @CanIgnoreReturnValue
  public abstract AllocatedBuffer position(int position);

  /**
--- a/java/core/src/main/java/com/google/protobuf/ArrayDecoders.java
+++ b/java/core/src/main/java/com/google/protobuf/ArrayDecoders.java
@ -43,6 +43,7 @@ import java.io.IOException;
 * IndexOutOfBoundsException and convert it to protobuf's InvalidProtocolBufferException when
 * crossing protobuf public API boundaries.
 */
+@CheckReturnValue
 final class ArrayDecoders {
  /**
   * A helper used to return multiple values in a Java function. Java doesn't natively support
@ -548,7 +549,6 @@ final class ArrayDecoders {
  }

  /** Decodes a packed sint64 field. Returns the position after all read values. */
-  @SuppressWarnings("unchecked")
  static int decodePackedSInt64List(
      byte[] data, int position, ProtobufList<?> list, Registers registers) throws IOException {
    final LongArrayList output = (LongArrayList) list;
--- a/java/core/src/main/java/com/google/protobuf/BinaryReader.java
+++ b/java/core/src/main/java/com/google/protobuf/BinaryReader.java
@ -48,6 +48,7 @@ import java.util.Map;
 * A {@link Reader} that reads from a buffer containing a message serialized with the binary
 * protocol.
 */
+@CheckReturnValue
@ExperimentalApi
 abstract class BinaryReader implements Reader {
  private static final int FIXED32_MULTIPLE_MASK = FIXED32_SIZE - 1;
@ -271,6 +272,7 @@ abstract class BinaryReader implements Reader {
      }
    }

+    @Deprecated
    @Override
    public <T> T readGroup(Class<T> clazz, ExtensionRegistryLite extensionRegistry)
        throws IOException {
@ -278,6 +280,7 @@ abstract class BinaryReader implements Reader {
      return readGroup(Protobuf.getInstance().schemaFor(clazz), extensionRegistry);
    }

+    @Deprecated
    @Override
    public <T> T readGroupBySchemaWithCheck(
        Schema<T> schema, ExtensionRegistryLite extensionRegistry) throws IOException {
@ -956,6 +959,7 @@ abstract class BinaryReader implements Reader {
      }
    }

+    @Deprecated
    @Override
    public <T> void readGroupList(
        List<T> target, Class<T> targetType, ExtensionRegistryLite extensionRegistry)
@ -964,6 +968,7 @@ abstract class BinaryReader implements Reader {
      readGroupList(target, schema, extensionRegistry);
    }

+    @Deprecated
    @Override
    public <T> void readGroupList(
        List<T> target, Schema<T> schema, ExtensionRegistryLite extensionRegistry)
--- a/java/core/src/main/java/com/google/protobuf/BinaryWriter.java
+++ b/java/core/src/main/java/com/google/protobuf/BinaryWriter.java
@ -65,6 +65,7 @@ import java.util.Queue;
 * The {@link #getTotalBytesWritten()} will continue to reflect the total of the write and will not
 * be reset.
 */
+@CheckReturnValue
@ExperimentalApi
 abstract class BinaryWriter extends ByteOutput implements Writer {
  public static final int DEFAULT_CHUNK_SIZE = 4096;
@ -162,6 +163,7 @@ abstract class BinaryWriter extends ByteOutput implements Writer {
   * <p>After calling this method, the writer can not be reused. Create a new writer for future
   * writes.
   */
+  @CanIgnoreReturnValue
  public final Queue<AllocatedBuffer> complete() {
    finishCurrentBuffer();
    return buffers;
@ -808,6 +810,7 @@ abstract class BinaryWriter extends ByteOutput implements Writer {
    }
  }

+  @Deprecated
  @Override
  public final void writeGroupList(int fieldNumber, List<?> list) throws IOException {
    for (int i = list.size() - 1; i >= 0; i--) {
@ -815,6 +818,7 @@ abstract class BinaryWriter extends ByteOutput implements Writer {
    }
  }

+  @Deprecated
  @Override
  public final void writeGroupList(int fieldNumber, List<?> list, Schema schema)
      throws IOException {
@ -1080,6 +1084,7 @@ abstract class BinaryWriter extends ByteOutput implements Writer {
      writeTag(fieldNumber, WIRETYPE_LENGTH_DELIMITED);
    }

+    @Deprecated
    @Override
    public void writeGroup(int fieldNumber, Object value) throws IOException {
      writeTag(fieldNumber, WIRETYPE_END_GROUP);
@ -1497,8 +1502,8 @@ abstract class BinaryWriter extends ByteOutput implements Writer {
      this.allocatedBuffer = allocatedBuffer;
      this.buffer = allocatedBuffer.array();
      int arrayOffset = allocatedBuffer.arrayOffset();
-      this.limit = arrayOffset + allocatedBuffer.limit();
-      this.offset = arrayOffset + allocatedBuffer.position();
+      this.limit = (long) arrayOffset + allocatedBuffer.limit();
+      this.offset = (long) arrayOffset + allocatedBuffer.position();
      this.offsetMinusOne = offset - 1;
      this.limitMinusOne = limit - 1;
      this.pos = limitMinusOne;
@ -2148,6 +2153,7 @@ abstract class BinaryWriter extends ByteOutput implements Writer {
      writeTag(fieldNumber, WIRETYPE_LENGTH_DELIMITED);
    }

+    @Deprecated
    @Override
    public void writeGroup(int fieldNumber, Object value) throws IOException {
      writeTag(fieldNumber, WIRETYPE_END_GROUP);
@ -2162,11 +2168,13 @@ abstract class BinaryWriter extends ByteOutput implements Writer {
      writeTag(fieldNumber, WIRETYPE_START_GROUP);
    }

+    @Deprecated
    @Override
    public void writeStartGroup(int fieldNumber) {
      writeTag(fieldNumber, WIRETYPE_START_GROUP);
    }

+    @Deprecated
    @Override
    public void writeEndGroup(int fieldNumber) {
      writeTag(fieldNumber, WIRETYPE_END_GROUP);
@ -2719,11 +2727,13 @@ abstract class BinaryWriter extends ByteOutput implements Writer {
      writeTag(fieldNumber, WIRETYPE_START_GROUP);
    }

+    @Deprecated
    @Override
    public void writeStartGroup(int fieldNumber) {
      writeTag(fieldNumber, WIRETYPE_START_GROUP);
    }

+    @Deprecated
    @Override
    public void writeEndGroup(int fieldNumber) {
      writeTag(fieldNumber, WIRETYPE_END_GROUP);
--- a/java/core/src/main/java/com/google/protobuf/BufferAllocator.java
+++ b/java/core/src/main/java/com/google/protobuf/BufferAllocator.java
@ -36,6 +36,7 @@ import java.nio.ByteBuffer;
 * An object responsible for allocation of buffers. This is an extension point to enable buffer
 * pooling within an application.
 */
+@CheckReturnValue
@ExperimentalApi
 abstract class BufferAllocator {
  private static final BufferAllocator UNPOOLED =
--- a/java/core/src/main/java/com/google/protobuf/ByteString.java
+++ b/java/core/src/main/java/com/google/protobuf/ByteString.java
@ -236,6 +236,11 @@ public abstract class ByteString implements Iterable<Byte>, Serializable {
    return size() == 0;
  }

+  /** Returns an empty {@code ByteString} of size {@code 0}. */
+  public static final ByteString empty() {
+    return EMPTY;
+  }
+
  // =================================================================
  // Comparison

@ -253,6 +258,38 @@ public abstract class ByteString implements Iterable<Byte>, Serializable {
    return value & UNSIGNED_BYTE_MASK;
  }

+  /** Returns the numeric value of the given character in hex, or -1 if invalid. */
+  private static int hexDigit(char c) {
+    if (c >= '0' && c <= '9') {
+      return c - '0';
+    } else if (c >= 'A' && c <= 'F') {
+      return c - 'A' + 10;
+    } else if (c >= 'a' && c <= 'f') {
+      return c - 'a' + 10;
+    } else {
+      return -1;
+    }
+  }
+
+  /**
+   * Returns the numeric value of the given character at index in hexString.
+   *
+   * @throws NumberFormatException if the hexString character is invalid.
+   */
+  private static int extractHexDigit(String hexString, int index) {
+    int digit = hexDigit(hexString.charAt(index));
+    if (digit == -1) {
+      throw new NumberFormatException(
+          "Invalid hexString "
+              + hexString
+              + " must only contain [0-9a-fA-F] but contained "
+              + hexString.charAt(index)
+              + " at index "
+              + index);
+    }
+    return digit;
+  }
+
  /**
   * Compares two {@link ByteString}s lexicographically, treating their contents as unsigned byte
   * values between 0 and 255 (inclusive).
@ -282,8 +319,8 @@ public abstract class ByteString implements Iterable<Byte>, Serializable {
      };

  /**
-   * Returns a {@link Comparator} which compares {@link ByteString}-s lexicographically
-   * as sequences of unsigned bytes (i.e. values between 0 and 255, inclusive).
+   * Returns a {@link Comparator} which compares {@link ByteString}-s lexicographically as sequences
+   * of unsigned bytes (i.e. values between 0 and 255, inclusive).
   *
   * <p>For example, {@code (byte) -1} is considered to be greater than {@code (byte) 1} because it
   * is interpreted as an unsigned value, {@code 255}:
@ -346,6 +383,30 @@ public abstract class ByteString implements Iterable<Byte>, Serializable {
    return size() >= suffix.size() && substring(size() - suffix.size()).equals(suffix);
  }

+  // =================================================================
+  // String -> ByteString
+
+  /**
+   * Returns a {@code ByteString} from a hexadecimal String. Alternative CharSequences should use
+   * {@link ByteStrings#decode(CharSequence, BaseEncoding)}
+   *
+   * @param hexString String of hexadecimal digits to create {@code ByteString} from.
+   * @throws NumberFormatException if the hexString does not contain a parsable hex String.
+   */
+  public static ByteString fromHex(@CompileTimeConstant String hexString) {
+    if (hexString.length() % 2 != 0) {
+      throw new NumberFormatException(
+          "Invalid hexString " + hexString + " of length " + hexString.length() + " must be even.");
+    }
+    byte[] bytes = new byte[hexString.length() / 2];
+    for (int i = 0; i < bytes.length; i++) {
+      int d1 = extractHexDigit(hexString, 2 * i);
+      int d2 = extractHexDigit(hexString, 2 * i + 1);
+      bytes[i] = (byte) (d1 << 4 | d2);
+    }
+    return new LiteralByteString(bytes);
+  }
+
  // =================================================================
  // byte[] -> ByteString

--- a/java/core/src/main/java/com/google/protobuf/CodedInputStream.java
+++ b/java/core/src/main/java/com/google/protobuf/CodedInputStream.java
@ -680,33 +680,33 @@ public abstract class CodedInputStream {
        case WireFormat.WIRETYPE_VARINT:
          {
            long value = readInt64();
-            output.writeRawVarint32(tag);
+            output.writeUInt32NoTag(tag);
            output.writeUInt64NoTag(value);
            return true;
          }
        case WireFormat.WIRETYPE_FIXED64:
          {
            long value = readRawLittleEndian64();
-            output.writeRawVarint32(tag);
+            output.writeUInt32NoTag(tag);
            output.writeFixed64NoTag(value);
            return true;
          }
        case WireFormat.WIRETYPE_LENGTH_DELIMITED:
          {
            ByteString value = readBytes();
-            output.writeRawVarint32(tag);
+            output.writeUInt32NoTag(tag);
            output.writeBytesNoTag(value);
            return true;
          }
        case WireFormat.WIRETYPE_START_GROUP:
          {
-            output.writeRawVarint32(tag);
+            output.writeUInt32NoTag(tag);
            skipMessage(output);
            int endtag =
                WireFormat.makeTag(
                    WireFormat.getTagFieldNumber(tag), WireFormat.WIRETYPE_END_GROUP);
            checkLastTagWas(endtag);
-            output.writeRawVarint32(endtag);
+            output.writeUInt32NoTag(endtag);
            return true;
          }
        case WireFormat.WIRETYPE_END_GROUP:
@ -716,7 +716,7 @@ public abstract class CodedInputStream {
        case WireFormat.WIRETYPE_FIXED32:
          {
            int value = readRawLittleEndian32();
-            output.writeRawVarint32(tag);
+            output.writeUInt32NoTag(tag);
            output.writeFixed32NoTag(value);
            return true;
          }
@ -1395,33 +1395,33 @@ public abstract class CodedInputStream {
        case WireFormat.WIRETYPE_VARINT:
          {
            long value = readInt64();
-            output.writeRawVarint32(tag);
+            output.writeUInt32NoTag(tag);
            output.writeUInt64NoTag(value);
            return true;
          }
        case WireFormat.WIRETYPE_FIXED64:
          {
            long value = readRawLittleEndian64();
-            output.writeRawVarint32(tag);
+            output.writeUInt32NoTag(tag);
            output.writeFixed64NoTag(value);
            return true;
          }
        case WireFormat.WIRETYPE_LENGTH_DELIMITED:
          {
            ByteString value = readBytes();
-            output.writeRawVarint32(tag);
+            output.writeUInt32NoTag(tag);
            output.writeBytesNoTag(value);
            return true;
          }
        case WireFormat.WIRETYPE_START_GROUP:
          {
-            output.writeRawVarint32(tag);
+            output.writeUInt32NoTag(tag);
            skipMessage(output);
            int endtag =
                WireFormat.makeTag(
                    WireFormat.getTagFieldNumber(tag), WireFormat.WIRETYPE_END_GROUP);
            checkLastTagWas(endtag);
-            output.writeRawVarint32(endtag);
+            output.writeUInt32NoTag(endtag);
            return true;
          }
        case WireFormat.WIRETYPE_END_GROUP:
@ -1431,7 +1431,7 @@ public abstract class CodedInputStream {
        case WireFormat.WIRETYPE_FIXED32:
          {
            int value = readRawLittleEndian32();
-            output.writeRawVarint32(tag);
+            output.writeUInt32NoTag(tag);
            output.writeFixed32NoTag(value);
            return true;
          }
@ -2163,33 +2163,33 @@ public abstract class CodedInputStream {
        case WireFormat.WIRETYPE_VARINT:
          {
            long value = readInt64();
-            output.writeRawVarint32(tag);
+            output.writeUInt32NoTag(tag);
            output.writeUInt64NoTag(value);
            return true;
          }
        case WireFormat.WIRETYPE_FIXED64:
          {
            long value = readRawLittleEndian64();
-            output.writeRawVarint32(tag);
+            output.writeUInt32NoTag(tag);
            output.writeFixed64NoTag(value);
            return true;
          }
        case WireFormat.WIRETYPE_LENGTH_DELIMITED:
          {
            ByteString value = readBytes();
-            output.writeRawVarint32(tag);
+            output.writeUInt32NoTag(tag);
            output.writeBytesNoTag(value);
            return true;
          }
        case WireFormat.WIRETYPE_START_GROUP:
          {
-            output.writeRawVarint32(tag);
+            output.writeUInt32NoTag(tag);
            skipMessage(output);
            int endtag =
                WireFormat.makeTag(
                    WireFormat.getTagFieldNumber(tag), WireFormat.WIRETYPE_END_GROUP);
            checkLastTagWas(endtag);
-            output.writeRawVarint32(endtag);
+            output.writeUInt32NoTag(endtag);
            return true;
          }
        case WireFormat.WIRETYPE_END_GROUP:
@ -2199,7 +2199,7 @@ public abstract class CodedInputStream {
        case WireFormat.WIRETYPE_FIXED32:
          {
            int value = readRawLittleEndian32();
-            output.writeRawVarint32(tag);
+            output.writeUInt32NoTag(tag);
            output.writeFixed32NoTag(value);
            return true;
          }
@ -3284,33 +3284,33 @@ public abstract class CodedInputStream {
        case WireFormat.WIRETYPE_VARINT:
          {
            long value = readInt64();
-            output.writeRawVarint32(tag);
+            output.writeUInt32NoTag(tag);
            output.writeUInt64NoTag(value);
            return true;
          }
        case WireFormat.WIRETYPE_FIXED64:
          {
            long value = readRawLittleEndian64();
-            output.writeRawVarint32(tag);
+            output.writeUInt32NoTag(tag);
            output.writeFixed64NoTag(value);
            return true;
          }
        case WireFormat.WIRETYPE_LENGTH_DELIMITED:
          {
            ByteString value = readBytes();
-            output.writeRawVarint32(tag);
+            output.writeUInt32NoTag(tag);
            output.writeBytesNoTag(value);
            return true;
          }
        case WireFormat.WIRETYPE_START_GROUP:
          {
-            output.writeRawVarint32(tag);
+            output.writeUInt32NoTag(tag);
            skipMessage(output);
            int endtag =
                WireFormat.makeTag(
                    WireFormat.getTagFieldNumber(tag), WireFormat.WIRETYPE_END_GROUP);
            checkLastTagWas(endtag);
-            output.writeRawVarint32(endtag);
+            output.writeUInt32NoTag(endtag);
            return true;
          }
        case WireFormat.WIRETYPE_END_GROUP:
@ -3320,7 +3320,7 @@ public abstract class CodedInputStream {
        case WireFormat.WIRETYPE_FIXED32:
          {
            int value = readRawLittleEndian32();
-            output.writeRawVarint32(tag);
+            output.writeUInt32NoTag(tag);
            output.writeFixed32NoTag(value);
            return true;
          }
--- a/java/core/src/main/java/com/google/protobuf/CodedInputStreamReader.java
+++ b/java/core/src/main/java/com/google/protobuf/CodedInputStreamReader.java
@ -44,6 +44,7 @@ import java.util.List;
 import java.util.Map;

 /** An adapter between the {@link Reader} interface and {@link CodedInputStream}. */
+@CheckReturnValue
@ExperimentalApi
 final class CodedInputStreamReader implements Reader {
  private static final int FIXED32_MULTIPLE_MASK = FIXED32_SIZE - 1;
@ -165,7 +166,6 @@ final class CodedInputStreamReader implements Reader {
    return input.readStringRequireUtf8();
  }

-  @SuppressWarnings("unchecked")
  @Override
  public <T> T readMessage(Class<T> clazz, ExtensionRegistryLite extensionRegistry)
      throws IOException {
@ -181,7 +181,7 @@ final class CodedInputStreamReader implements Reader {
    return readMessage(schema, extensionRegistry);
  }

-  @SuppressWarnings("unchecked")
+  @Deprecated
  @Override
  public <T> T readGroup(Class<T> clazz, ExtensionRegistryLite extensionRegistry)
      throws IOException {
@ -189,7 +189,7 @@ final class CodedInputStreamReader implements Reader {
    return readGroup(Protobuf.getInstance().schemaFor(clazz), extensionRegistry);
  }

-  @SuppressWarnings("unchecked")
+  @Deprecated
  @Override
  public <T> T readGroupBySchemaWithCheck(Schema<T> schema, ExtensionRegistryLite extensionRegistry)
      throws IOException {
@ -821,6 +821,7 @@ final class CodedInputStreamReader implements Reader {
    }
  }

+  @Deprecated
  @Override
  public <T> void readGroupList(
      List<T> target, Class<T> targetType, ExtensionRegistryLite extensionRegistry)
@ -829,6 +830,7 @@ final class CodedInputStreamReader implements Reader {
    readGroupList(target, schema, extensionRegistry);
  }

+  @Deprecated
  @Override
  public <T> void readGroupList(
      List<T> target, Schema<T> schema, ExtensionRegistryLite extensionRegistry)
@ -1314,7 +1316,7 @@ final class CodedInputStreamReader implements Reader {
      case UINT64:
        return readUInt64();
      default:
-        throw new RuntimeException("unsupported field type.");
+        throw new IllegalArgumentException("unsupported field type.");
    }
  }

--- a/java/core/src/main/java/com/google/protobuf/CodedOutputStream.java
+++ b/java/core/src/main/java/com/google/protobuf/CodedOutputStream.java
@ -1056,7 +1056,7 @@ public abstract class CodedOutputStream extends ByteOutput {
   */
  @Deprecated
  public static int computeGroupSize(final int fieldNumber, final MessageLite value) {
-    return computeTagSize(fieldNumber) * 2 + computeGroupSizeNoTag(value);
+    return computeTagSize(fieldNumber) * 2 + value.getSerializedSize();
  }

  /**
@ -1072,6 +1072,7 @@ public abstract class CodedOutputStream extends ByteOutput {

  /** Compute the number of bytes that would be needed to encode a {@code group} field. */
  @Deprecated
+  @InlineMe(replacement = "value.getSerializedSize()")
  public static int computeGroupSizeNoTag(final MessageLite value) {
    return value.getSerializedSize();
  }
@ -1089,6 +1090,7 @@ public abstract class CodedOutputStream extends ByteOutput {
   * @deprecated use {@link #writeUInt32NoTag} instead.
   */
  @Deprecated
+  @InlineMe(replacement = "this.writeUInt32NoTag(value)")
  public final void writeRawVarint32(int value) throws IOException {
    writeUInt32NoTag(value);
  }
@ -1099,6 +1101,7 @@ public abstract class CodedOutputStream extends ByteOutput {
   * @deprecated use {@link #writeUInt64NoTag} instead.
   */
  @Deprecated
+  @InlineMe(replacement = "this.writeUInt64NoTag(value)")
  public final void writeRawVarint64(long value) throws IOException {
    writeUInt64NoTag(value);
  }
@ -1110,6 +1113,9 @@ public abstract class CodedOutputStream extends ByteOutput {
   * @deprecated use {@link #computeUInt32SizeNoTag(int)} instead.
   */
  @Deprecated
+  @InlineMe(
+      replacement = "CodedOutputStream.computeUInt32SizeNoTag(value)",
+      imports = "com.google.protobuf.CodedOutputStream")
  public static int computeRawVarint32Size(final int value) {
    return computeUInt32SizeNoTag(value);
  }
@ -1120,6 +1126,9 @@ public abstract class CodedOutputStream extends ByteOutput {
   * @deprecated use {@link #computeUInt64SizeNoTag(long)} instead.
   */
  @Deprecated
+  @InlineMe(
+      replacement = "CodedOutputStream.computeUInt64SizeNoTag(value)",
+      imports = "com.google.protobuf.CodedOutputStream")
  public static int computeRawVarint64Size(long value) {
    return computeUInt64SizeNoTag(value);
  }
@ -1130,6 +1139,7 @@ public abstract class CodedOutputStream extends ByteOutput {
   * @deprecated Use {@link #writeFixed32NoTag} instead.
   */
  @Deprecated
+  @InlineMe(replacement = "this.writeFixed32NoTag(value)")
  public final void writeRawLittleEndian32(final int value) throws IOException {
    writeFixed32NoTag(value);
  }
@ -1140,6 +1150,7 @@ public abstract class CodedOutputStream extends ByteOutput {
   * @deprecated Use {@link #writeFixed64NoTag} instead.
   */
  @Deprecated
+  @InlineMe(replacement = "this.writeFixed64NoTag(value)")
  public final void writeRawLittleEndian64(final long value) throws IOException {
    writeFixed64NoTag(value);
  }
--- a/java/core/src/main/java/com/google/protobuf/CodedOutputStreamWriter.java
+++ b/java/core/src/main/java/com/google/protobuf/CodedOutputStreamWriter.java
@ -39,6 +39,7 @@ import java.util.List;
 import java.util.Map;

 /** An adapter between the {@link Writer} interface and {@link CodedOutputStream}. */
+@CheckReturnValue
@ExperimentalApi
 final class CodedOutputStreamWriter implements Writer {
  private final CodedOutputStream output;
@ -154,6 +155,7 @@ final class CodedOutputStreamWriter implements Writer {
    output.writeMessage(fieldNumber, (MessageLite) value, schema);
  }

+  @Deprecated
  @Override
  public void writeGroup(int fieldNumber, Object value) throws IOException {
    output.writeGroup(fieldNumber, (MessageLite) value);
@ -164,11 +166,13 @@ final class CodedOutputStreamWriter implements Writer {
    output.writeGroup(fieldNumber, (MessageLite) value, schema);
  }

+  @Deprecated
  @Override
  public void writeStartGroup(int fieldNumber) throws IOException {
    output.writeTag(fieldNumber, WireFormat.WIRETYPE_START_GROUP);
  }

+  @Deprecated
  @Override
  public void writeEndGroup(int fieldNumber) throws IOException {
    output.writeTag(fieldNumber, WireFormat.WIRETYPE_END_GROUP);
@ -561,6 +565,7 @@ final class CodedOutputStreamWriter implements Writer {
    }
  }

+  @Deprecated
  @Override
  public void writeGroupList(int fieldNumber, List<?> value) throws IOException {
    for (int i = 0; i < value.size(); ++i) {
--- a/java/core/src/test/java/com/google/protobuf/ForceFieldBuildersPreRun.java
+++ b/java/core/src/test/java/com/google/protobuf/ForceFieldBuildersPreRun.java
@ -30,18 +30,18 @@

 package com.google.protobuf;

-/**
- * A prerun for a test suite that allows running the full protocol buffer tests in a mode that
- * disables the optimization for not using {@link RepeatedFieldBuilder} and {@link
- * SingleFieldBuilder} until they are requested. This allows us to run all the tests through both
- * code paths and ensures that both code paths produce identical results.
- *
- * @author jonp@google.com (Jon Perlow)
- */
-public class ForceFieldBuildersPreRun implements Runnable {
+import static java.lang.annotation.RetentionPolicy.CLASS;

-  @Override
-  public void run() {
-    GeneratedMessage.enableAlwaysUseFieldBuildersForTesting();
-  }
-}
+import java.lang.annotation.Documented;
+import java.lang.annotation.ElementType;
+import java.lang.annotation.Retention;
+import java.lang.annotation.Target;
+
+/**
+ * Annotation for method parameter and class field declarations, which denotes that corresponding
+ * actual values must be compile-time constant expressions.
+ */
+@Documented
+@Retention(CLASS)
+@Target({ElementType.PARAMETER, ElementType.FIELD})
+@interface CompileTimeConstant {}
--- a/java/core/src/main/java/com/google/protobuf/Descriptors.java
+++ b/java/core/src/main/java/com/google/protobuf/Descriptors.java
@ -278,14 +278,13 @@ public final class Descriptors {
    /**
     * Construct a {@code FileDescriptor}.
     *
-     * @param proto The protocol message form of the FileDescriptor.
-     * @param dependencies {@code FileDescriptor}s corresponding to all of the file's dependencies.
+     * @param proto the protocol message form of the FileDescriptort
+     * @param dependencies {@code FileDescriptor}s corresponding to all of the file's dependencies
     * @throws DescriptorValidationException {@code proto} is not a valid descriptor. This can occur
-     *     for a number of reasons, e.g. because a field has an undefined type or because two
-     *     messages were defined with the same name.
+     *     for a number of reasons; for instance, because a field has an undefined type or because
+     *     two messages were defined with the same name.
     */
-    public static FileDescriptor buildFrom(
-        final FileDescriptorProto proto, final FileDescriptor[] dependencies)
+    public static FileDescriptor buildFrom(FileDescriptorProto proto, FileDescriptor[] dependencies)
        throws DescriptorValidationException {
      return buildFrom(proto, dependencies, false);
    }
@ -293,18 +292,19 @@ public final class Descriptors {
    /**
     * Construct a {@code FileDescriptor}.
     *
-     * @param proto The protocol message form of the FileDescriptor.
-     * @param dependencies {@code FileDescriptor}s corresponding to all of the file's dependencies.
-     * @param allowUnknownDependencies If true, non-exist dependenncies will be ignored and
-     *     undefined message types will be replaced with a placeholder type.
+     * @param proto the protocol message form of the FileDescriptor
+     * @param dependencies {@code FileDescriptor}s corresponding to all of the file's dependencies
+     * @param allowUnknownDependencies if true, non-existing dependencies will be ignored and
+     *     undefined message types will be replaced with a placeholder type. Undefined enum types
+     *     still cause a DescriptorValidationException.
     * @throws DescriptorValidationException {@code proto} is not a valid descriptor. This can occur
-     *     for a number of reasons, e.g. because a field has an undefined type or because two
-     *     messages were defined with the same name.
+     *     for a number of reasons; for instance, because a field has an undefined type or because
+     *     two messages were defined with the same name.
     */
    public static FileDescriptor buildFrom(
-        final FileDescriptorProto proto,
-        final FileDescriptor[] dependencies,
-        final boolean allowUnknownDependencies)
+        FileDescriptorProto proto,
+        FileDescriptor[] dependencies,
+        boolean allowUnknownDependencies)
        throws DescriptorValidationException {
      // Building descriptors involves two steps:  translating and linking.
      // In the translation step (implemented by FileDescriptor's
@ -315,8 +315,8 @@ public final class Descriptors {
      // FieldDescriptor for an embedded message contains a pointer directly
      // to the Descriptor for that message's type.  We also detect undefined
      // types in the linking step.
-      final DescriptorPool pool = new DescriptorPool(dependencies, allowUnknownDependencies);
-      final FileDescriptor result =
+      DescriptorPool pool = new DescriptorPool(dependencies, allowUnknownDependencies);
+      FileDescriptor result =
          new FileDescriptor(proto, dependencies, pool, allowUnknownDependencies);
      result.crossLink();
      return result;
@ -1837,8 +1837,8 @@ public final class Descriptors {
      // The number represents an unknown enum value.
      synchronized (this) {
        if (cleanupQueue == null) {
-          cleanupQueue = new ReferenceQueue<EnumValueDescriptor>();
-          unknownValues = new HashMap<Integer, WeakReference<EnumValueDescriptor>>();
+          cleanupQueue = new ReferenceQueue<>();
+          unknownValues = new HashMap<>();
        } else {
          while (true) {
            UnknownEnumValueReference toClean = (UnknownEnumValueReference) cleanupQueue.poll();
@ -2415,7 +2415,7 @@ public final class Descriptors {
    }

    private final Set<FileDescriptor> dependencies;
-    private boolean allowUnknownDependencies;
+    private final boolean allowUnknownDependencies;

    private final Map<String, GenericDescriptor> descriptorsByName = new HashMap<>();

@ -2475,7 +2475,6 @@ public final class Descriptors {
        final GenericDescriptor relativeTo,
        final DescriptorPool.SearchFilter filter)
        throws DescriptorValidationException {
-      // TODO(kenton):  This could be optimized in a number of ways.

      GenericDescriptor result;
      String fullname;
@ -2547,11 +2546,11 @@ public final class Descriptors {
          logger.warning(
              "The descriptor for message type \""
                  + name
-                  + "\" can not be found and a placeholder is created for it");
+                  + "\" cannot be found and a placeholder is created for it");
          // We create a dummy message descriptor here regardless of the
          // expected type. If the type should be message, this dummy
          // descriptor will work well and if the type should be enum, a
-          // DescriptorValidationException will be thrown latter. In either
+          // DescriptorValidationException will be thrown later. In either
          // case, the code works as expected: we allow unknown message types
          // but not unknown enum types.
          result = new Descriptor(fullname);
@ -2766,8 +2765,7 @@ public final class Descriptors {
        final OneofDescriptorProto proto,
        final FileDescriptor file,
        final Descriptor parent,
-        final int index)
-        throws DescriptorValidationException {
+        final int index) {
      this.proto = proto;
      fullName = computeFullName(file, parent, proto.getName());
      this.file = file;
--- a/java/core/src/main/java/com/google/protobuf/DynamicMessage.java
+++ b/java/core/src/main/java/com/google/protobuf/DynamicMessage.java
@ -38,6 +38,7 @@ import com.google.protobuf.Descriptors.FieldDescriptor;
 import com.google.protobuf.Descriptors.OneofDescriptor;
 import java.io.IOException;
 import java.io.InputStream;
+import java.util.Arrays;
 import java.util.Collections;
 import java.util.List;
 import java.util.Map;
@ -318,14 +319,14 @@ public final class DynamicMessage extends AbstractMessage {
  /** Builder for {@link DynamicMessage}s. */
  public static final class Builder extends AbstractMessage.Builder<Builder> {
    private final Descriptor type;
-    private FieldSet<FieldDescriptor> fields;
+    private FieldSet.Builder<FieldDescriptor> fields;
    private final FieldDescriptor[] oneofCases;
    private UnknownFieldSet unknownFields;

    /** Construct a {@code Builder} for the given type. */
    private Builder(Descriptor type) {
      this.type = type;
-      this.fields = FieldSet.newFieldSet();
+      this.fields = FieldSet.newBuilder();
      this.unknownFields = UnknownFieldSet.getDefaultInstance();
      this.oneofCases = new FieldDescriptor[type.toProto().getOneofDeclCount()];
    }
@ -335,11 +336,7 @@ public final class DynamicMessage extends AbstractMessage {

    @Override
    public Builder clear() {
-      if (fields.isImmutable()) {
-        fields = FieldSet.newFieldSet();
-      } else {
-        fields.clear();
-      }
+      fields = FieldSet.newBuilder();
      unknownFields = UnknownFieldSet.getDefaultInstance();
      return this;
    }
@ -353,7 +350,6 @@ public final class DynamicMessage extends AbstractMessage {
          throw new IllegalArgumentException(
              "mergeFrom(Message) can only merge messages of the same type.");
        }
-        ensureIsMutable();
        fields.mergeFrom(otherDynamicMessage.fields);
        mergeUnknownFields(otherDynamicMessage.unknownFields);
        for (int i = 0; i < oneofCases.length; i++) {
@ -378,10 +374,7 @@ public final class DynamicMessage extends AbstractMessage {
      if (!isInitialized()) {
        throw newUninitializedMessageException(
            new DynamicMessage(
-                type,
-                fields,
-                java.util.Arrays.copyOf(oneofCases, oneofCases.length),
-                unknownFields));
+                type, fields.build(), Arrays.copyOf(oneofCases, oneofCases.length), unknownFields));
      }
      return buildPartial();
    }
@ -395,8 +388,8 @@ public final class DynamicMessage extends AbstractMessage {
        throw newUninitializedMessageException(
                new DynamicMessage(
                    type,
-                    fields,
-                    java.util.Arrays.copyOf(oneofCases, oneofCases.length),
+                    fields.build(),
+                    Arrays.copyOf(oneofCases, oneofCases.length),
                    unknownFields))
            .asInvalidProtocolBufferException();
      }
@ -418,17 +411,16 @@ public final class DynamicMessage extends AbstractMessage {
        }
      }

-      fields.makeImmutable();
      DynamicMessage result =
          new DynamicMessage(
-              type, fields, java.util.Arrays.copyOf(oneofCases, oneofCases.length), unknownFields);
+              type, fields.build(), Arrays.copyOf(oneofCases, oneofCases.length), unknownFields);
      return result;
    }

    @Override
    public Builder clone() {
      Builder result = new Builder(type);
-      result.fields.mergeFrom(fields);
+      result.fields.mergeFrom(fields.build());
      result.mergeUnknownFields(unknownFields);
      System.arraycopy(oneofCases, 0, result.oneofCases, 0, oneofCases.length);
      return result;
@ -436,7 +428,17 @@ public final class DynamicMessage extends AbstractMessage {

    @Override
    public boolean isInitialized() {
-      return DynamicMessage.isInitialized(type, fields);
+      // Check that all required fields are present.
+      for (FieldDescriptor field : type.getFields()) {
+        if (field.isRequired()) {
+          if (!fields.hasField(field)) {
+            return false;
+          }
+        }
+      }
+
+      // Check that embedded messages are initialized.
+      return fields.isInitialized();
    }

    @Override
@ -517,15 +519,12 @@ public final class DynamicMessage extends AbstractMessage {
    @Override
    public Builder setField(FieldDescriptor field, Object value) {
      verifyContainingType(field);
-      ensureIsMutable();
      // TODO(xiaofeng): This check should really be put in FieldSet.setField()
      // where all other such checks are done. However, currently
      // FieldSet.setField() permits Integer value for enum fields probably
      // because of some internal features we support. Should figure it out
      // and move this check to a more appropriate place.
-      if (field.getType() == FieldDescriptor.Type.ENUM) {
-        ensureEnumValueDescriptor(field, value);
-      }
+      verifyType(field, value);
      OneofDescriptor oneofDescriptor = field.getContainingOneof();
      if (oneofDescriptor != null) {
        int index = oneofDescriptor.getIndex();
@ -550,7 +549,6 @@ public final class DynamicMessage extends AbstractMessage {
    @Override
    public Builder clearField(FieldDescriptor field) {
      verifyContainingType(field);
-      ensureIsMutable();
      OneofDescriptor oneofDescriptor = field.getContainingOneof();
      if (oneofDescriptor != null) {
        int index = oneofDescriptor.getIndex();
@ -577,7 +575,7 @@ public final class DynamicMessage extends AbstractMessage {
    @Override
    public Builder setRepeatedField(FieldDescriptor field, int index, Object value) {
      verifyContainingType(field);
-      ensureIsMutable();
+      verifySingularValueType(field, value);
      fields.setRepeatedField(field, index, value);
      return this;
    }
@ -585,7 +583,7 @@ public final class DynamicMessage extends AbstractMessage {
    @Override
    public Builder addRepeatedField(FieldDescriptor field, Object value) {
      verifyContainingType(field);
-      ensureIsMutable();
+      verifySingularValueType(field, value);
      fields.addRepeatedField(field, value);
      return this;
    }
@ -622,53 +620,116 @@ public final class DynamicMessage extends AbstractMessage {
      }
    }

-    /** Verifies that the value is EnumValueDescriptor and matches Enum Type. */
-    private void ensureSingularEnumValueDescriptor(FieldDescriptor field, Object value) {
-      checkNotNull(value);
-      if (!(value instanceof EnumValueDescriptor)) {
-        throw new IllegalArgumentException(
-            "DynamicMessage should use EnumValueDescriptor to set Enum Value.");
+    /**
+     * Verifies that {@code value} is of the appropriate type, in addition to the checks already
+     * performed by {@link FieldSet.Builder}.
+     */
+    private void verifySingularValueType(FieldDescriptor field, Object value) {
+      // Most type checks are performed by FieldSet.Builder, but FieldSet.Builder is more permissive
+      // than generated Message.Builder subclasses, so we perform extra checks in this class so that
+      // DynamicMessage.Builder's semantics more closely match the semantics of generated builders.
+      switch (field.getType()) {
+        case ENUM:
+          checkNotNull(value);
+          // FieldSet.Builder accepts Integer values for enum fields.
+          if (!(value instanceof EnumValueDescriptor)) {
+            throw new IllegalArgumentException(
+                "DynamicMessage should use EnumValueDescriptor to set Enum Value.");
+          }
+          // TODO(xiaofeng): Re-enable this check after Orgstore is fixed to not
+          // set incorrect EnumValueDescriptors.
+          // EnumDescriptor fieldType = field.getEnumType();
+          // EnumDescriptor fieldValueType = ((EnumValueDescriptor) value).getType();
+          // if (fieldType != fieldValueType) {
+          //  throw new IllegalArgumentException(String.format(
+          //      "EnumDescriptor %s of field doesn't match EnumDescriptor %s of field value",
+          //      fieldType.getFullName(), fieldValueType.getFullName()));
+          // }
+          break;
+        case MESSAGE:
+          // FieldSet.Builder accepts Message.Builder values for message fields.
+          if (value instanceof Message.Builder) {
+            throw new IllegalArgumentException(
+                String.format(
+                    "Wrong object type used with protocol message reflection.\n"
+                        + "Field number: %d, field java type: %s, value type: %s\n",
+                    field.getNumber(),
+                    field.getLiteType().getJavaType(),
+                    value.getClass().getName()));
+          }
+          break;
+        default:
+          break;
      }
-      // TODO(xiaofeng): Re-enable this check after Orgstore is fixed to not
-      // set incorrect EnumValueDescriptors.
-      // EnumDescriptor fieldType = field.getEnumType();
-      // EnumDescriptor fieldValueType = ((EnumValueDescriptor) value).getType();
-      // if (fieldType != fieldValueType) {
-      //  throw new IllegalArgumentException(String.format(
-      //      "EnumDescriptor %s of field doesn't match EnumDescriptor %s of field value",
-      //      fieldType.getFullName(), fieldValueType.getFullName()));
-      // }
    }

-    /** Verifies the value for an enum field. */
-    private void ensureEnumValueDescriptor(FieldDescriptor field, Object value) {
+    /**
+     * Verifies that {@code value} is of the appropriate type, in addition to the checks already
+     * performed by {@link FieldSet.Builder}.
+     */
+    private void verifyType(FieldDescriptor field, Object value) {
      if (field.isRepeated()) {
-        for (Object item : (List) value) {
-          ensureSingularEnumValueDescriptor(field, item);
+        for (Object item : (List<?>) value) {
+          verifySingularValueType(field, item);
        }
      } else {
-        ensureSingularEnumValueDescriptor(field, value);
-      }
-    }
-
-    private void ensureIsMutable() {
-      if (fields.isImmutable()) {
-        fields = fields.clone();
+        verifySingularValueType(field, value);
      }
    }

    @Override
    public com.google.protobuf.Message.Builder getFieldBuilder(FieldDescriptor field) {
-      // TODO(xiangl): need implementation for dynamic message
-      throw new UnsupportedOperationException(
-          "getFieldBuilder() called on a dynamic message type.");
+      verifyContainingType(field);
+      // Error messages chosen for parity with GeneratedMessage.getFieldBuilder.
+      if (field.isMapField()) {
+        throw new UnsupportedOperationException("Nested builder not supported for map fields.");
+      }
+      if (field.getJavaType() != FieldDescriptor.JavaType.MESSAGE) {
+        throw new UnsupportedOperationException("getFieldBuilder() called on a non-Message type.");
+      }
+
+      Object existingValue = fields.getFieldAllowBuilders(field);
+      Message.Builder builder =
+          existingValue == null
+              ? new Builder(field.getMessageType())
+              : toMessageBuilder(existingValue);
+      fields.setField(field, builder);
+      return builder;
    }

    @Override
    public com.google.protobuf.Message.Builder getRepeatedFieldBuilder(
        FieldDescriptor field, int index) {
-      throw new UnsupportedOperationException(
-          "getRepeatedFieldBuilder() called on a dynamic message type.");
+      verifyContainingType(field);
+      // Error messages chosen for parity with GeneratedMessage.getRepeatedFieldBuilder.
+      if (field.isMapField()) {
+        throw new UnsupportedOperationException("Map fields cannot be repeated");
+      }
+      if (field.getJavaType() != FieldDescriptor.JavaType.MESSAGE) {
+        throw new UnsupportedOperationException(
+            "getRepeatedFieldBuilder() called on a non-Message type.");
+      }
+
+      Message.Builder builder =
+          toMessageBuilder(fields.getRepeatedFieldAllowBuilders(field, index));
+      fields.setRepeatedField(field, index, builder);
+      return builder;
+    }
+
+    private static Message.Builder toMessageBuilder(Object o) {
+      if (o instanceof Message.Builder) {
+        return (Message.Builder) o;
+      }
+
+      if (o instanceof LazyField) {
+        o = ((LazyField) o).getValue();
+      }
+      if (o instanceof Message) {
+        return ((Message) o).toBuilder();
+      }
+
+      throw new IllegalArgumentException(
+          String.format("Cannot convert %s to Message.Builder", o.getClass()));
    }
  }
 }
--- a/java/core/src/main/java/com/google/protobuf/ExtensionRegistry.java
+++ b/java/core/src/main/java/com/google/protobuf/ExtensionRegistry.java
@ -154,7 +154,7 @@ public class ExtensionRegistry extends ExtensionRegistryLite {
    return mutableExtensionsByName.get(fullName);
  }

-  /** Deprecated. Use {@link #findImmutableExtensionByNumber( Descriptors.Descriptor, int)} */
+  /** Deprecated. Use {@link #findImmutableExtensionByNumber(Descriptors.Descriptor, int)} */
  @Deprecated
  public ExtensionInfo findExtensionByNumber(
      final Descriptor containingType, final int fieldNumber) {
--- a/java/core/src/main/java/com/google/protobuf/ExtensionSchema.java
+++ b/java/core/src/main/java/com/google/protobuf/ExtensionSchema.java
@ -33,6 +33,7 @@ package com.google.protobuf;
 import java.io.IOException;
 import java.util.Map;

+@CheckReturnValue
 abstract class ExtensionSchema<T extends FieldSet.FieldDescriptorLite<T>> {

  /** Returns true for messages that support extensions. */
--- a/Show More
+++ b/Show More