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

Follow up on CL 511458, see https://go-review.googlesource.com/c/go/+/511458/2..4/src/cmd/go/main.go#b270 .

For #36768.

Change-Id: Icc2a4dbb1219b1d69dd10a900478957b0e975847

Change-Id: Icc2a4dbb1219b1d69dd10a900478957b0e975847
GitHub-Last-Rev: bac7e66496806d505270c5b90d53672d80a1ca29
GitHub-Pull-Request: golang/go#61517
Reviewed-on: https://go-review.googlesource.com/c/go/+/512155
Auto-Submit: Bryan Mills <bcmills@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
Reviewed-by: Bryan Mills <bcmills@google.com>
Run-TryBot: Bryan Mills <bcmills@google.com>

1 files changed, 4 insertions, 32 deletions

diff --git a/src/os/exec/exec.go b/src/os/exec/exec.go
index 138be29ecf..a23d1c4a2d 100644
--- a/src/os/exec/exec.go
+++ b/src/os/exec/exec.go
@@ -590,32 +590,6 @@ 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.
@@ -649,13 +623,11 @@ func (c *Cmd) Start() error {
 		}
 		return c.Err
 	}
-	if runtime.GOOS == "windows" {
-		lp, err := lookExtensions(c.Path, c.Dir)
-		if err != nil {
-			return err
-		}
-		c.Path = lp
+	lp, err := lookExtensions(c.Path, c.Dir)
+	if err != nil {
+		return err
 	}
+	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")
 	}