terraform-ls: Prefill required fields and ability to validate on save (#3976)

* Implement additional features supporting latest terraform-ls

* docs: Prefill required fields

* Update changelog

CHANGELOG.org

@@ -1,5 +1,6 @@
 * Changelog
 ** Unreleased 8.0.1
+  * terraform-ls now supports prefill requied fields and the ability to validate on save.
   * ~lsp-bash~ now supports ~bash-ts-mode~
   * ~lsp-ruby-syntax-tree~, ~lsp-solargraph~, ~lsp-sorbet~, ~lsp-steep~, and ~lsp-typeprof~ now support ~ruby-ts-mode~
   * Drop support for emacs 26.1 and 26.2

clients/lsp-terraform.el

@@ -32,7 +32,7 @@
 ;; terraform-lsp
 
 (defgroup lsp-terraform nil
-  "LSP support for Terraform, using terraform-lsp"
+  "LSP support for Terraform, using terraform-lsp."
   :group 'lsp-mode
   :link '(url-link "https://github.com/juliosueiras/terraform-lsp")
   :package-version `(lsp-mode . "6.2"))
@@ -96,6 +96,24 @@ language server."
   :type 'boolean
   :package-version '(lsp-mode . "8.0.1"))
 
+(defcustom lsp-terraform-ls-validate-on-save nil
+  "Enable validating the current open file on save.
+
+This is an experimental feature provided by the language server."
+  :group 'lsp-terraform-ls
+  :type 'boolean
+  :package-version '(lsp-mode . "8.0.1"))
+
+(defcustom lsp-terraform-ls-prefill-required-fields nil
+  "Enable completion of required fields.
+
+Enable autocompletion for required fields when completing
+Terraform blocks.  This is an experimental feature provided by the
+language server."
+  :group 'lsp-terraform-ls
+  :type 'boolean
+  :package-version '(lsp-mode . "8.0.1"))
+
 (defcustom lsp-terraform-ls-providers-position-params nil
   "The optional providers tree position params.
 Defaults to side following treemacs default."
@@ -128,6 +146,11 @@ Defaults to side following treemacs default."
   (when lsp-terraform-ls-enable-show-reference
     '((experimental . ((showReferencesCommandId . "client.showReferences"))))))
 
+(defun lsp-terraform-ls--init-options ()
+  "Construct initialization options for the lanague server."
+  `((experimentalFeatures . ((validateOnSave . ,(lsp-json-bool lsp-terraform-ls-validate-on-save))
+                             (prefillRequiredFields . ,(lsp-json-bool lsp-terraform-ls-prefill-required-fields))))))
+
 (defcustom lsp-terraform-semantic-token-faces
   '(("namespace" . lsp-face-semhl-namespace)
     ("type" . lsp-face-semhl-type)
@@ -209,6 +232,7 @@ Defaults to side following treemacs default."
                                                      :discard-default-types t
                                                      :modifiers ,lsp-terraform-semantic-token-modifier-faces
                                                      :types ,lsp-terraform-semantic-token-faces)
+                  :initialization-options (lsp-terraform-ls--init-options)
                   :custom-capabilities (lsp-terraform-ls--custom-capabilities)))
 
 (defun lsp-terraform-ls-validate ()

docs/manual-language-docs/lsp-terraform-ls.md

@@ -106,6 +106,19 @@ There are two ways to open the link:
 - Key binding: Alt + Enter
 - Clicking the middle button of your mouse
 
+### Prefill required fields
+
+This is an experimental feature which can be enabled via the option
+`lsp-terraform-ls-prefill-required-fields`:
+
+``` emacs-lisp
+(setq lsp-terraform-ls-prefill-required-fields t)
+```
+
+This gif demonstrates how this feature is used:
+
+![](../examples/terraform-ls-prefill.gif)
+
 ### Treeview controls
 
 For this feature to work, make sure that you have [lsp-treemacs](https://github.com/emacs-lsp/lsp-treemacs)