cmd/go: correct directory used in checkNestedVCS test

This error was not used when using git because nested git is permitted.
Add test using Mercurial, so that at least we have a test, even though
the test is not run by default.

Fixes #22157
Fixes #22201

Change-Id: If521f3c09b0754e00e56fa3cd0364764a57a43ad
Reviewed-on: https://go-review.googlesource.com/69670
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Russ Cox <rsc@golang.org>

src/cmd/go/go_test.go

@@ -1245,7 +1245,7 @@ func testMove(t *testing.T, vcs, url, base, config string) {
 	tg.runFail("get", "-d", "-u", url)
 	tg.grepStderr("is a custom import path for", "go get -d -u "+url+" failed for wrong reason")
 	tg.runFail("get", "-d", "-f", "-u", url)
-	tg.grepStderr("validating server certificate|not found", "go get -d -f -u "+url+" failed for wrong reason")
+	tg.grepStderr("validating server certificate|[nN]ot [fF]ound", "go get -d -f -u "+url+" failed for wrong reason")
 }
 
 func TestInternalPackageErrorsAreHandled(t *testing.T) {
@@ -1266,10 +1266,9 @@ func TestMoveGit(t *testing.T) {
 	testMove(t, "git", "rsc.io/pdf", "pdf", "rsc.io/pdf/.git/config")
 }
 
-// TODO(rsc): Set up a test case on bitbucket for hg.
-// func TestMoveHG(t *testing.T) {
-// 	testMove(t, "hg", "rsc.io/x86/x86asm", "x86", "rsc.io/x86/.hg/hgrc")
-// }
+func TestMoveHG(t *testing.T) {
+	testMove(t, "hg", "vcs-test.golang.org/go/custom-hg-hello", "custom-hg-hello", "vcs-test.golang.org/go/custom-hg-hello/.hg/hgrc")
+}
 
 // TODO(rsc): Set up a test case on SourceForge (?) for svn.
 // func testMoveSVN(t *testing.T) {

src/cmd/go/internal/get/vcs.go

@@ -599,7 +599,7 @@ func checkNestedVCS(vcs *vcsCmd, dir, srcRoot string) error {
 	otherDir := dir
 	for len(otherDir) > len(srcRoot) {
 		for _, otherVCS := range vcsList {
-			if _, err := os.Stat(filepath.Join(dir, "."+otherVCS.cmd)); err == nil {
+			if _, err := os.Stat(filepath.Join(otherDir, "."+otherVCS.cmd)); err == nil {
 				// Allow expected vcs in original dir.
 				if otherDir == dir && otherVCS == vcs {
 					continue