cmd/go/internal/toolchain: use sync.OnceValue

Rename initPathExts to pathExts, make it return the slice of extensions,
and wrap into sync.OnceValue.

While at it, return early if PATHEXT is empty.

Change-Id: I33508762e87edd226e0a52df4063473c496c0210
Reviewed-on: https://go-review.googlesource.com/c/go/+/611017
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
Auto-Submit: Ian Lance Taylor <iant@google.com>

diff --git a/src/cmd/go/internal/toolchain/path_windows.go b/src/cmd/go/internal/toolchain/path_windows.go
index 086c591e0589dfef2f8a60d59fc7e03691302331..d88945ddc8ecea06ce7be12d04adb2a9e1f7ca9f 100644 (file)
--- a/src/cmd/go/internal/toolchain/path_windows.go
+++ b/src/cmd/go/internal/toolchain/path_windows.go
@@ -14,30 +14,24 @@ import (
        "cmd/go/internal/gover"
 )
 
-// pathExts is a cached PATHEXT list.
-var pathExts struct {
-       once sync.Once
-       list []string
-}
+var pathExts = sync.OnceValue(func() []string {
+       x := os.Getenv(`PATHEXT`)
+       if x == "" {
+               return []string{".com", ".exe", ".bat", ".cmd"}
+       }
 
-func initPathExts() {
        var exts []string
-       x := os.Getenv(`PATHEXT`)
-       if x != "" {
-               for _, e := range strings.Split(strings.ToLower(x), `;`) {
-                       if e == "" {
-                               continue
-                       }
-                       if e[0] != '.' {
-                               e = "." + e
-                       }
-                       exts = append(exts, e)
+       for _, e := range strings.Split(strings.ToLower(x), `;`) {
+               if e == "" {
+                       continue
+               }
+               if e[0] != '.' {
+                       e = "." + e
                }
-       } else {
-               exts = []string{".com", ".exe", ".bat", ".cmd"}
+               exts = append(exts, e)
        }
-       pathExts.list = exts
-}
+       return exts
+})
 
 // pathDirs returns the directories in the system search path.
 func pathDirs() []string {
@@ -48,8 +42,7 @@ func pathDirs() []string {
 // described by de and info in directory dir.
 // The analysis only uses the name itself; it does not run the program.
 func pathVersion(dir string, de fs.DirEntry, info fs.FileInfo) (string, bool) {
-       pathExts.once.Do(initPathExts)
-       name, _, ok := cutExt(de.Name(), pathExts.list)
+       name, _, ok := cutExt(de.Name(), pathExts())
        if !ok {
                return "", false
        }