cmd/fix: support go versions with patch release

Support go version with patch release(e.g. 1.21.0)
and release candidates(e.g. 1.21rc1)
when parsing the go version in the fix command
by using new "go/version" package.

Fixes #62584

Change-Id: I0ec16137c7a396c68039d374c770c4021fb54b4e
GitHub-Last-Rev: 76bced5
GitHub-Pull-Request: #62586
Reviewed-on: https://go-review.googlesource.com/c/go/+/527342
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Russ Cox <rsc@golang.org>
Auto-Submit: Bryan Mills <bcmills@google.com>
Reviewed-by: Alex Bozhenko <alexbozhenko@gmail.com>
Reviewed-by: Bryan Mills <bcmills@google.com>

src/cmd/fix/buildtag.go

@@ -6,14 +6,15 @@ package main
 
 import (
 	"go/ast"
+	"go/version"
 	"strings"
 )
 
 func init() {
 	register(buildtagFix)
 }
 
-const buildtagGoVersionCutoff = 1_18
+const buildtagGoVersionCutoff = "go1.18"
 
 var buildtagFix = fix{
 	name: "buildtag",
@@ -23,7 +24,7 @@ var buildtagFix = fix{
 }
 
 func buildtag(f *ast.File) bool {
-	if goVersion < buildtagGoVersionCutoff {
+	if version.Compare(*goVersion, buildtagGoVersionCutoff) < 0 {
 		return false
 	}
 

src/cmd/fix/buildtag_test.go

@@ -11,7 +11,7 @@ func init() {
 var buildtagTests = []testCase{
 	{
 		Name:    "buildtag.oldGo",
-		Version: 1_10,
+		Version: "go1.10",
 		In: `//go:build yes
 // +build yes
 
@@ -20,7 +20,7 @@ package main
 	},
 	{
 		Name:    "buildtag.new",
-		Version: 1_99,
+		Version: "go1.99",
 		In: `//go:build yes
 // +build yes
 

src/cmd/fix/main.go

@@ -13,13 +13,13 @@ import (
 	"go/parser"
 	"go/scanner"
 	"go/token"
+	"go/version"
 	"internal/diff"
 	"io"
 	"io/fs"
 	"os"
 	"path/filepath"
 	"sort"
-	"strconv"
 	"strings"
 )
 
@@ -37,10 +37,8 @@ var forceRewrites = flag.String("force", "",
 var allowed, force map[string]bool
 
 var (
-	doDiff       = flag.Bool("diff", false, "display diffs instead of rewriting files")
-	goVersionStr = flag.String("go", "", "go language version for files")
-
-	goVersion int // 115 for go1.15
+	doDiff    = flag.Bool("diff", false, "display diffs instead of rewriting files")
+	goVersion = flag.String("go", "", "go language version for files")
 )
 
 // enable for debugging fix failures
@@ -68,24 +66,9 @@ func main() {
 	flag.Usage = usage
 	flag.Parse()
 
-	if *goVersionStr != "" {
-		if !strings.HasPrefix(*goVersionStr, "go") {
-			report(fmt.Errorf("invalid -go=%s", *goVersionStr))
-			os.Exit(exitCode)
-		}
-		majorStr := (*goVersionStr)[len("go"):]
-		minorStr := "0"
-		if before, after, found := strings.Cut(majorStr, "."); found {
-			majorStr, minorStr = before, after
-		}
-		major, err1 := strconv.Atoi(majorStr)
-		minor, err2 := strconv.Atoi(minorStr)
-		if err1 != nil || err2 != nil || major < 0 || major >= 100 || minor < 0 || minor >= 100 {
-			report(fmt.Errorf("invalid -go=%s", *goVersionStr))
-			os.Exit(exitCode)
-		}
-
-		goVersion = major*100 + minor
+	if !version.IsValid(*goVersion) {
+		report(fmt.Errorf("invalid -go=%s", *goVersion))
+		os.Exit(exitCode)
 	}
 
 	sort.Sort(byDate(fixes))

src/cmd/fix/main_test.go

@@ -17,7 +17,7 @@ import (
 type testCase struct {
 	Name    string
 	Fn      func(*ast.File) bool
-	Version int
+	Version string
 	In      string
 	Out     string
 }
@@ -96,7 +96,7 @@ func TestRewrite(t *testing.T) {
 	for _, tt := range testCases {
 		tt := tt
 		t.Run(tt.Name, func(t *testing.T) {
-			if tt.Version == 0 {
+			if tt.Version == "" {
 				if testing.Verbose() {
 					// Don't run in parallel: cmd/fix sometimes writes directly to stderr,
 					// and since -v prints which test is currently running we want that
@@ -105,10 +105,10 @@ func TestRewrite(t *testing.T) {
 					t.Parallel()
 				}
 			} else {
-				old := goVersion
-				goVersion = tt.Version
+				old := *goVersion
+				*goVersion = tt.Version
 				defer func() {
-					goVersion = old
+					*goVersion = old
 				}()
 			}