cmd/api: make check pickier about api/*.txt

We don't have a formatter for these files, so check here that
they are in the right form to allow 'cat next/*.txt >go1.X.txt'
at the end of each cycle.

Fix the api files that the check finds.

Change-Id: I0c5e4ab11751c7d0afce32503131d487313f41c0
Reviewed-on: https://go-review.googlesource.com/c/go/+/431335
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
Auto-Submit: Russ Cox <rsc@golang.org>
Reviewed-by: Dmitri Shuralyov <dmitshur@golang.org>
Run-TryBot: Russ Cox <rsc@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org>

api/next/42537.txt

@@ -1,4 +1,4 @@
 pkg bytes, func CutPrefix([]uint8, []uint8) ([]uint8, bool) #42537
 pkg bytes, func CutSuffix([]uint8, []uint8) ([]uint8, bool) #42537
 pkg strings, func CutPrefix(string, string) (string, bool) #42537
-pkg strings, func CutSuffix(string, string) (string, bool) #42537
+pkg strings, func CutSuffix(string, string) (string, bool) #42537

api/next/43620.txt

@@ -1 +1 @@
-pkg testing, method (*B) Elapsed() time.Duration #43620
+pkg testing, method (*B) Elapsed() time.Duration #43620

api/next/45899.txt

@@ -2,4 +2,4 @@ pkg io, type OffsetWriter struct #45899
 pkg io, func NewOffsetWriter(WriterAt, int64) *OffsetWriter #45899
 pkg io, method (*OffsetWriter) Write([]uint8) (int, error) #45899
 pkg io, method (*OffsetWriter) WriteAt([]uint8, int64) (int, error) #45899
-pkg io, method (*OffsetWriter) Seek(int64, int) (int64, error) #45899
+pkg io, method (*OffsetWriter) Seek(int64, int) (int64, error) #45899

api/next/46746.txt

@@ -1,2 +1,2 @@
 pkg reflect, method (Value) Comparable() bool #46746
-pkg reflect, method (Value) Equal(Value) bool #46746
+pkg reflect, method (Value) Equal(Value) bool #46746

api/next/50429.txt

@@ -1 +1 @@
-pkg go/ast, type RangeStmt struct, Range token.Pos #50429
+pkg go/ast, type RangeStmt struct, Range token.Pos #50429

api/next/51896.txt

@@ -1 +1 @@
-pkg unicode/utf16, func AppendRune([]uint16, int32) []uint16 #51896
+pkg unicode/utf16, func AppendRune([]uint16, int32) []uint16 #51896

api/next/53482.txt

@@ -1,2 +1,2 @@
-pkg net, const FlagRunning = 32 #53482
-pkg net, const FlagRunning Flags #53482
+pkg net, const FlagRunning = 32 #53482
+pkg net, const FlagRunning Flags #53482

src/cmd/api/goapi.go

@@ -126,7 +126,11 @@ func setContexts() {
 
 var internalPkg = regexp.MustCompile(`(^|/)internal($|/)`)
 
+var exitCode = 0
+
 func main() {
+	log.SetPrefix("api: ")
+	log.SetFlags(0)
 	flag.Parse()
 
 	if build.Default.GOROOT == "" {
@@ -199,16 +203,14 @@ func main() {
 		}
 	}
 
-	fail := false
+	bw := bufio.NewWriter(os.Stdout)
 	defer func() {
-		if fail {
-			os.Exit(1)
+		bw.Flush()
+		if exitCode != 0 {
+			os.Exit(exitCode)
 		}
 	}()
 
-	bw := bufio.NewWriter(os.Stdout)
-	defer bw.Flush()
-
 	if *checkFiles == "" {
 		sort.Strings(features)
 		for _, f := range features {
@@ -228,7 +230,9 @@ func main() {
 		}
 	}
 	exception := fileFeatures(*exceptFile)
-	fail = !compareAPI(bw, features, required, optional, exception, *allowNew)
+	if !compareAPI(bw, features, required, optional, exception, *allowNew) {
+		exitCode = 1
+	}
 }
 
 // export emits the exported package features.
@@ -362,9 +366,26 @@ func fileFeatures(filename string) []string {
 	}
 	bs, err := os.ReadFile(filename)
 	if err != nil {
-		log.Fatalf("Error reading file %s: %v", filename, err)
+		log.Fatal(err)
 	}
 	s := string(bs)
+
+	// Diagnose common mistakes people make,
+	// since there is no apifmt to format these files.
+	// The missing final newline is important for the
+	// final release step of cat next/*.txt >go1.X.txt.
+	// If the files don't end in full lines, the concatenation goes awry.
+	if strings.Contains(s, "\r") {
+		log.Printf("%s: contains CRLFs", filename)
+		exitCode = 1
+	}
+	if s == "" {
+		log.Printf("%s: empty file", filename)
+		exitCode = 1
+	} else if s[len(s)-1] != '\n' {
+		log.Printf("%s: missing final newline", filename)
+		exitCode = 1
+	}
 	s = aliasReplacer.Replace(s)
 	lines := strings.Split(s, "\n")
 	var nonblank []string
@@ -376,11 +397,13 @@ func fileFeatures(filename string) []string {
 		if needApproval {
 			feature, approval, ok := strings.Cut(line, "#")
 			if !ok {
-				log.Fatalf("%s:%d: missing proposal approval\n", filename, i+1)
+				log.Printf("%s:%d: missing proposal approval\n", filename, i+1)
+				exitCode = 1
 			}
 			_, err := strconv.Atoi(approval)
 			if err != nil {
-				log.Fatalf("%s:%d: malformed proposal approval #%s\n", filename, i+1, approval)
+				log.Printf("%s:%d: malformed proposal approval #%s\n", filename, i+1, approval)
+				exitCode = 1
 			}
 			line = strings.TrimSpace(feature)
 		}