Revert "os/exec: avoid calling LookPath in cmd.Start for resolved paths"

This reverts CL 512155.

Reason for revert: CL 512155 introduced a race in that it caused
cmd.Start to set cmd.Path. Previously it was fine if code looked
at cmd.Path in one goroutine while calling cmd.Start in a different
goroutine.

A test case for this race is in CL 527495.

Change-Id: Ic18fdadf6763727f8ea748280d5f0e601b9bf374
Reviewed-on: https://go-review.googlesource.com/c/go/+/527337
Auto-Submit: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Ian Lance Taylor <iant@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>

diff --git a/src/os/exec/exec.go b/src/os/exec/exec.go
index 2881345fb3868e4e853931e9f9b2b813e65fe7eb..dfede0e7e2029ff4cbd2f55bb4c6a558bd4f580c 100644 (file)
--- a/src/os/exec/exec.go
+++ b/src/os/exec/exec.go
@@ -590,6 +590,32 @@ func (c *Cmd) Run() error {
        return c.Wait()
 }
 
+// lookExtensions finds windows executable by its dir and path.
+// It uses LookPath to try appropriate extensions.
+// lookExtensions does not search PATH, instead it converts `prog` into `.\prog`.
+func lookExtensions(path, dir string) (string, error) {
+       if filepath.Base(path) == path {
+               path = "." + string(filepath.Separator) + path
+       }
+       if dir == "" {
+               return LookPath(path)
+       }
+       if filepath.VolumeName(path) != "" {
+               return LookPath(path)
+       }
+       if len(path) > 1 && os.IsPathSeparator(path[0]) {
+               return LookPath(path)
+       }
+       dirandpath := filepath.Join(dir, path)
+       // We assume that LookPath will only add file extension.
+       lp, err := LookPath(dirandpath)
+       if err != nil {
+               return "", err
+       }
+       ext := strings.TrimPrefix(lp, dirandpath)
+       return path + ext, nil
+}
+
 // Start starts the specified command but does not wait for it to complete.
 //
 // If Start returns successfully, the c.Process field will be set.
@@ -623,11 +649,13 @@ func (c *Cmd) Start() error {
                }
                return c.Err
        }
-       lp, err := lookExtensions(c.Path, c.Dir)
-       if err != nil {
-               return err
+       if runtime.GOOS == "windows" {
+               lp, err := lookExtensions(c.Path, c.Dir)
+               if err != nil {
+                       return err
+               }
+               c.Path = lp
        }
-       c.Path = lp
        if c.Cancel != nil && c.ctx == nil {
                return errors.New("exec: command with a non-nil Cancel was not created with CommandContext")
        }

diff --git a/src/os/exec/lp_plan9.go b/src/os/exec/lp_plan9.go
index dffdbac35f8e01e0ef2a3c0f4f3a5f1dca2ae019..9344b14e8cdfe6ffc24955018d7e9235c9c6f9b9 100644 (file)
--- a/src/os/exec/lp_plan9.go
+++ b/src/os/exec/lp_plan9.go
@@ -64,9 +64,3 @@ func LookPath(file string) (string, error) {
        }
        return "", &Error{file, ErrNotFound}
 }
-
-// lookExtensions is a no-op on non-Windows platforms, since
-// they do not restrict executables to specific extensions.
-func lookExtensions(path, dir string) (string, error) {
-       return path, nil
-}

diff --git a/src/os/exec/lp_unix.go b/src/os/exec/lp_unix.go
index 37871320786aef2f36203919273009a39dba8651..fd2c6efbef08cd8e18774c651159e9be61883bfe 100644 (file)
--- a/src/os/exec/lp_unix.go
+++ b/src/os/exec/lp_unix.go
@@ -80,9 +80,3 @@ func LookPath(file string) (string, error) {
        }
        return "", &Error{file, ErrNotFound}
 }
-
-// lookExtensions is a no-op on non-Windows platforms, since
-// they do not restrict executables to specific extensions.
-func lookExtensions(path, dir string) (string, error) {
-       return path, nil
-}

diff --git a/src/os/exec/lp_wasm.go b/src/os/exec/lp_wasm.go
index 3c819049bab3420e0a04e6b294e406bb557e855f..f2c8e9c5de47903835a4db859f18b70c539017d8 100644 (file)
--- a/src/os/exec/lp_wasm.go
+++ b/src/os/exec/lp_wasm.go
@@ -21,9 +21,3 @@ func LookPath(file string) (string, error) {
        // Wasm can not execute processes, so act as if there are no executables at all.
        return "", &Error{file, ErrNotFound}
 }
-
-// lookExtensions is a no-op on non-Windows platforms, since
-// they do not restrict executables to specific extensions.
-func lookExtensions(path, dir string) (string, error) {
-       return path, nil
-}

diff --git a/src/os/exec/lp_windows.go b/src/os/exec/lp_windows.go
index 7f13347c505b7c92b3a53ce48e992ea191c8a4cd..066d38dfdb981b7c0a4972a6100e2950b95cae9f 100644 (file)
--- a/src/os/exec/lp_windows.go
+++ b/src/os/exec/lp_windows.go
@@ -63,45 +63,6 @@ func findExecutable(file string, exts []string) (string, error) {
 // As of Go 1.19, LookPath will instead return that path along with an error satisfying
 // errors.Is(err, ErrDot). See the package documentation for more details.
 func LookPath(file string) (string, error) {
-       return lookPath(file, pathExt())
-}
-
-// lookExtensions finds windows executable by its dir and path.
-// It uses LookPath to try appropriate extensions.
-// lookExtensions does not search PATH, instead it converts `prog` into `.\prog`.
-func lookExtensions(path, dir string) (string, error) {
-       if filepath.Base(path) == path {
-               path = "." + string(filepath.Separator) + path
-       }
-       exts := pathExt()
-       if ext := filepath.Ext(path); ext != "" {
-               for _, e := range exts {
-                       if strings.EqualFold(ext, e) {
-                               // Assume that path has already been resolved.
-                               return path, nil
-                       }
-               }
-       }
-       if dir == "" {
-               return lookPath(path, exts)
-       }
-       if filepath.VolumeName(path) != "" {
-               return lookPath(path, exts)
-       }
-       if len(path) > 1 && os.IsPathSeparator(path[0]) {
-               return lookPath(path, exts)
-       }
-       dirandpath := filepath.Join(dir, path)
-       // We assume that LookPath will only add file extension.
-       lp, err := lookPath(dirandpath, exts)
-       if err != nil {
-               return "", err
-       }
-       ext := strings.TrimPrefix(lp, dirandpath)
-       return path + ext, nil
-}
-
-func pathExt() []string {
        var exts []string
        x := os.Getenv(`PATHEXT`)
        if x != "" {
@@ -117,11 +78,7 @@ func pathExt() []string {
        } else {
                exts = []string{".com", ".exe", ".bat", ".cmd"}
        }
-       return exts
-}
 
-// lookPath implements LookPath for the given PATHEXT list.
-func lookPath(file string, exts []string) (string, error) {
        if strings.ContainsAny(file, `:\/`) {
                f, err := findExecutable(file, exts)
                if err == nil {