[cli] check main after master (#8463)

* Allow specifying a branch with url#branch

* Probe for master and main

* Update CHANGELOG

* Fix linter errors

* Remove unnecessary feature

* Fix lint

* Update changelog to reflect new limited scope.

We only talk about the master -> main probing, because that is all the
PR does. It used to duplicate another feature.

CHANGELOG_PENDING.md

@@ -1,5 +1,9 @@
 ### Improvements
 
+- [cli] - When running `pulumi new https://github.com/name/repo`, check 
+  for branch `main` if branch `master` doesn't exist.
+  [#8463](https://github.com/pulumi/pulumi/pull/8463)
+
 - [codegen/python] - Program generator now uses `fn_output` forms where
   appropriate, simplifying auto-generated examples.
   [#8433](https://github.com/pulumi/pulumi/pull/8433)

sdk/go/common/util/gitutil/git.go

@@ -296,6 +296,35 @@ func GitCloneOrPull(url string, referenceName plumbing.ReferenceName, path strin
 	return nil
 }
 
+// We currently accept Gist URLs in the form: https://gist.github.com/owner/id.
+// We may want to consider supporting https://gist.github.com/id at some point,
+// as well as arbitrary revisions, e.g. https://gist.github.com/owner/id/commit.
+func parseGistURL(u *url.URL) (string, error) {
+	path := strings.Trim(u.Path, "/")
+	paths := strings.Split(path, "/")
+	if len(paths) != 2 {
+		return "", errors.New("invalid Gist URL")
+	}
+
+	owner := paths[0]
+	if owner == "" {
+		return "", errors.New("invalid Gist URL; no owner")
+	}
+
+	id := paths[1]
+	if id == "" {
+		return "", errors.New("invalid Gist URL; no id")
+	}
+
+	if !strings.HasSuffix(id, ".git") {
+		id = id + ".git"
+	}
+
+	resultURL := u.Scheme + "://" + u.Host + "/" + id
+	return resultURL, nil
+
+}
+
 // ParseGitRepoURL returns the URL to the Git repository and path from a raw URL.
 // For example, an input of "https://github.com/pulumi/templates/templates/javascript" returns
 // "https://github.com/pulumi/templates.git" and "templates/javascript".
@@ -309,37 +338,16 @@ func ParseGitRepoURL(rawurl string) (string, string, error) {
 		return "", "", errors.New("invalid URL scheme")
 	}
 
-	path := strings.TrimPrefix(u.Path, "/")
-
 	// Special case Gists.
 	if u.Hostname() == "gist.github.com" {
-		// We currently accept Gist URLs in the form: https://gist.github.com/owner/id.
-		// We may want to consider supporting https://gist.github.com/id at some point,
-		// as well as arbitrary revisions, e.g. https://gist.github.com/owner/id/commit.
-		path = strings.TrimSuffix(path, "/")
-		paths := strings.Split(path, "/")
-		if len(paths) != 2 {
-			return "", "", errors.New("invalid Gist URL")
+		repo, err := parseGistURL(u)
+		if err != nil {
+			return "", "", err
 		}
-
-		owner := paths[0]
-		if owner == "" {
-			return "", "", errors.New("invalid Gist URL; no owner")
-		}
-
-		id := paths[1]
-		if id == "" {
-			return "", "", errors.New("invalid Gist URL; no id")
-		}
-
-		if !strings.HasSuffix(id, ".git") {
-			id = id + ".git"
-		}
-
-		resultURL := u.Scheme + "://" + u.Host + "/" + id
-		return resultURL, "", nil
+		return repo, "", nil
 	}
 
+	path := strings.TrimPrefix(u.Path, "/")
 	paths := strings.Split(path, "/")
 	if len(paths) < 2 {
 		return "", "", errors.New("invalid Git URL")
@@ -361,6 +369,7 @@ func ParseGitRepoURL(rawurl string) (string, string, error) {
 
 	resultURL := u.Scheme + "://" + u.Host + "/" + owner + "/" + repo
 	resultPath := strings.TrimSuffix(strings.Join(paths[2:], "/"), "/")
+
 	return resultURL, resultPath, nil
 }
 

sdk/go/common/util/gitutil/git_test.go

@@ -25,7 +25,7 @@ import (
 )
 
 func TestParseGitRepoURL(t *testing.T) {
-	test := func(expectedURL string, expectedURLPath string, rawurl string) {
+	test := func(expectedURL, expectedURLPath string, rawurl string) {
 		actualURL, actualURLPath, err := ParseGitRepoURL(rawurl)
 		assert.NoError(t, err)
 		assert.Equal(t, expectedURL, actualURL)

sdk/go/common/workspace/templates.go

@@ -287,7 +287,7 @@ func retrieveURLTemplates(rawurl string, offline bool, templateKind TemplateKind
 
 	var fullPath string
 	if fullPath, err = RetrieveGitFolder(rawurl, temp); err != nil {
-		return TemplateRepository{}, err
+		return TemplateRepository{}, fmt.Errorf("Failed to retrieve git folder: %w", err)
 	}
 
 	return TemplateRepository{
@@ -372,16 +372,35 @@ func RetrieveGitFolder(rawurl string, path string) (string, error) {
 
 	ref, commit, subDirectory, err := gitutil.GetGitReferenceNameOrHashAndSubDirectory(url, urlPath)
 	if err != nil {
-		return "", err
+		return "", fmt.Errorf("failed to get git ref: %w", err)
 	}
-
 	if ref != "" {
-		if cloneErr := gitutil.GitCloneOrPull(url, ref, path, true /*shallow*/); cloneErr != nil {
-			return "", cloneErr
+
+		// Different reference attempts to cycle through
+		// We default to master then main in that order. We need to order them to avoid breaking
+		// already existing processes for repos that already have a master and main branch.
+		refAttempts := []plumbing.ReferenceName{plumbing.Master, plumbing.NewBranchReferenceName("main")}
+
+		if ref != plumbing.HEAD {
+			// If we have a non-default reference, we just use it
+			refAttempts = []plumbing.ReferenceName{ref}
 		}
+
+		var cloneErr error
+		for _, ref := range refAttempts {
+			// Attempt the clone. If it succeeds, break
+			cloneErr := gitutil.GitCloneOrPull(url, ref, path, true /*shallow*/)
+			if cloneErr == nil {
+				break
+			}
+		}
+		if cloneErr != nil {
+			return "", fmt.Errorf("failed to clone ref '%s': %w", refAttempts[len(refAttempts)-1], cloneErr)
+		}
+
 	} else {
 		if cloneErr := gitutil.GitCloneAndCheckoutCommit(url, commit, path); cloneErr != nil {
-			return "", cloneErr
+			return "", fmt.Errorf("failed to clone and checkout %s(%s): %w", url, commit, cloneErr)
 		}
 	}