cmd/go: detect which VCS to use with Bitbucket when the API call fails.

      The API call will fail when Bitbucket repositories are private. In
that case, probe for the repository using vcsCmd.ping.

      Fixes #5375

Change-Id: Ia604ecf9014805579dfda4b5c8e627a52783d56e
Reviewed-on: https://go-review.googlesource.com/1910Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/cmd/go/bootstrap.go

@@ -17,6 +17,14 @@ import (
 
 var errHTTP = errors.New("no http in bootstrap go command")
 
+type httpError struct {
+	statusCode int
+}
+
+func (e *httpError) Error() string {
+	panic("unreachable")
+}
+
 func httpGET(url string) ([]byte, error) {
 	return nil, errHTTP
 }

src/cmd/go/http.go

@@ -24,6 +24,16 @@ import (
 // changed by tests, without modifying http.DefaultClient.
 var httpClient = http.DefaultClient
 
+type httpError struct {
+	status     string
+	statusCode int
+	url        string
+}
+
+func (e *httpError) Error() string {
+	return fmt.Sprintf("%s: %s", e.url, e.status)
+}
+
 // httpGET returns the data from an HTTP GET request for the given URL.
 func httpGET(url string) ([]byte, error) {
 	resp, err := httpClient.Get(url)
@@ -32,7 +42,9 @@ func httpGET(url string) ([]byte, error) {
 	}
 	defer resp.Body.Close()
 	if resp.StatusCode != 200 {
-		return nil, fmt.Errorf("%s: %s", url, resp.Status)
+		err := &httpError{status: resp.Status, statusCode: resp.StatusCode, url: url}
+
+		return nil, err
 	}
 	b, err := ioutil.ReadAll(resp.Body)
 	if err != nil {

src/cmd/go/vcs.go

@@ -808,10 +808,25 @@ func bitbucketVCS(match map[string]string) error {
 	url := expand(match, "https://api.bitbucket.org/1.0/repositories/{bitname}")
 	data, err := httpGET(url)
 	if err != nil {
-		return err
-	}
-	if err := json.Unmarshal(data, &resp); err != nil {
-		return fmt.Errorf("decoding %s: %v", url, err)
+		if httpErr, ok := err.(*httpError); ok && httpErr.statusCode == 403 {
+			// this may be a private repository. If so, attempt to determine which
+			// VCS it uses. See issue 5375.
+			root := match["root"]
+			for _, vcs := range []string{"git", "hg"} {
+				if vcsByCmd(vcs).ping("https", root) == nil {
+					resp.SCM = vcs
+					break
+				}
+			}
+		}
+
+		if resp.SCM == "" {
+			return err
+		}
+	} else {
+		if err := json.Unmarshal(data, &resp); err != nil {
+			return fmt.Errorf("decoding %s: %v", url, err)
+		}
 	}
 
 	if vcsByCmd(resp.SCM) != nil {