go/vcs: accept plain file for .vcs (instead of directory)

Sometimes .git is a plain file; maybe others will follow.

Fixes golang/go#10322.

Change-Id: Id57424998c207080c3ed5826b1e5e091fa26aad5
Reviewed-on: https://go-review.googlesource.com/21430
Run-TryBot: Russ Cox <[email protected]>
Reviewed-by: Brad Fitzpatrick <[email protected]>
TryBot-Result: Gobot Gobot <[email protected]>

Author: rsc

go/vcs/vcs.go

@@ -347,7 +347,7 @@ func FromDir(dir, srcRoot string) (vcs *Cmd, root string, err error) {
 	origDir := dir
 	for len(dir) > len(srcRoot) {
 		for _, vcs := range vcsList {
-			if fi, err := os.Stat(filepath.Join(dir, "."+vcs.Cmd)); err == nil && fi.IsDir() {
+			if _, err := os.Stat(filepath.Join(dir, "."+vcs.Cmd)); err == nil {
 				return vcs, filepath.ToSlash(dir[len(srcRoot)+1:]), nil
 			}
 		}

go/vcs/vcs_test.go

@@ -56,11 +56,23 @@ func TestFromDir(t *testing.T) {
 	}
 	defer os.RemoveAll(tempDir)
 
-	for _, vcs := range vcsList {
+	for j, vcs := range vcsList {
 		dir := filepath.Join(tempDir, "example.com", vcs.Name, "."+vcs.Cmd)
-		err := os.MkdirAll(dir, 0755)
-		if err != nil {
-			t.Fatal(err)
+		if j&1 == 0 {
+			err := os.MkdirAll(dir, 0755)
+			if err != nil {
+				t.Fatal(err)
+			}
+		} else {
+			err := os.MkdirAll(filepath.Dir(dir), 0755)
+			if err != nil {
+				t.Fatal(err)
+			}
+			f, err := os.Create(dir)
+			if err != nil {
+				t.Fatal(err)
+			}
+			f.Close()
 		}
 
 		want := RepoRoot{