cmd/go: accept go get domain.root

Fixes #9357.

Change-Id: I11f0652758c4ea80debec29c3b99a72baca6d745
Reviewed-on: https://go-review.googlesource.com/12193Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

src/cmd/go/go_test.go

@@ -2133,6 +2133,7 @@ func TestGoGetUpdate(t *testing.T) {
 	// golang.org/issue/9224.
 	// The recursive updating was trying to walk to
 	// former dependencies, not current ones.
+
 	testenv.MustHaveExternalNetwork(t)
 
 	tg := testgo(t)
@@ -2157,3 +2158,29 @@ func TestGoGetUpdate(t *testing.T) {
 	rewind()
 	tg.run("get", "-d", "-u", "github.com/rsc/go-get-issue-9224-cmd")
 }
+
+func TestGoGetDomainRoot(t *testing.T) {
+	// golang.org/issue/9357.
+	// go get foo.io (not foo.io/subdir) was not working consistently.
+
+	testenv.MustHaveExternalNetwork(t)
+
+	tg := testgo(t)
+	defer tg.cleanup()
+	tg.makeTempdir()
+	tg.setenv("GOPATH", tg.path("."))
+
+	// go-get-issue-9357.appspot.com is running
+	// the code at github.com/rsc/go-get-issue-9357,
+	// a trivial Go on App Engine app that serves a
+	// <meta> tag for the domain root.
+	tg.run("get", "-d", "go-get-issue-9357.appspot.com")
+	tg.run("get", "go-get-issue-9357.appspot.com")
+	tg.run("get", "-u", "go-get-issue-9357.appspot.com")
+
+	tg.must(os.RemoveAll(tg.path("src/go-get-issue-9357.appspot.com")))
+	tg.run("get", "go-get-issue-9357.appspot.com")
+
+	tg.must(os.RemoveAll(tg.path("src/go-get-issue-9357.appspot.com")))
+	tg.run("get", "-u", "go-get-issue-9357.appspot.com")
+}

src/cmd/go/vcs.go

@@ -650,11 +650,11 @@ func repoRootForImportPathStatic(importPath, scheme string, security securityMod
 // repoRootForImportDynamic finds a *repoRoot for a custom domain that's not
 // statically known by repoRootForImportPathStatic.
 //
-// This handles custom import paths like "name.tld/pkg/foo".
+// This handles custom import paths like "name.tld/pkg/foo" or just "name.tld".
 func repoRootForImportDynamic(importPath string, security securityMode) (*repoRoot, error) {
 	slash := strings.Index(importPath, "/")
 	if slash < 0 {
-		return nil, errors.New("import path does not contain a slash")
+		slash = len(importPath)
 	}
 	host := importPath[:slash]
 	if !strings.Contains(host, ".") {