Create the source branch for a GitHub import

When the GitHub importer creates a merge request, it retrieves the SHA
but does not actually create the source branch. This makes it impossible
to merge an open merge request, particularly if the source branch were
from a forked project. In that case, the branch will never exist because
the original `project-name:source-branch` name is never created, nor
is it a valid branch name.

To prevent possible branch name conflicts, forked source branches
are now renamed `github/fork/project-name/source-branch` and created
when necessary.

Note that we only create the source branch if the merge request
is open. For projects that have many merge requests, the project
would end up with a lot of possibly dead branches.

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/57370

2 files changed, 37 insertions, 3 deletions

diff --git a/spec/lib/gitlab/github_import/importer/pull_request_importer_spec.rb b/spec/lib/gitlab/github_import/importer/pull_request_importer_spec.rb
index 0f21b8843b6..15e59718dce 100644
--- a/spec/lib/gitlab/github_import/importer/pull_request_importer_spec.rb
+++ b/spec/lib/gitlab/github_import/importer/pull_request_importer_spec.rb
@@ -89,7 +89,7 @@ describe Gitlab::GithubImport::Importer::PullRequestImporter, :clean_gitlab_redi
               description: 'This is my pull request',
               source_project_id: project.id,
               target_project_id: project.id,
-              source_branch: 'alice:feature',
+              source_branch: 'github/fork/alice/feature',
               target_branch: 'master',
               state: :merged,
               milestone_id: milestone.id,
@@ -134,7 +134,7 @@ describe Gitlab::GithubImport::Importer::PullRequestImporter, :clean_gitlab_redi
               description: "*Created by: alice*\n\nThis is my pull request",
               source_project_id: project.id,
               target_project_id: project.id,
-              source_branch: 'alice:feature',
+              source_branch: 'github/fork/alice/feature',
               target_branch: 'master',
               state: :merged,
               milestone_id: milestone.id,
@@ -259,6 +259,40 @@ describe Gitlab::GithubImport::Importer::PullRequestImporter, :clean_gitlab_redi
         .and_return(user.id)
     end
 
+    it 'does not create the source branch if merge request is merged' do
+      mr, exists = importer.create_merge_request
+
+      importer.insert_git_data(mr, exists)
+
+      expect(project.repository.branch_exists?(mr.source_branch)).to be_falsey
+      expect(project.repository.branch_exists?(mr.target_branch)).to be_truthy
+    end
+
+    it 'creates the source branch if merge request is open' do
+      mr, exists = importer.create_merge_request
+      mr.state = 'opened'
+      mr.save
+
+      importer.insert_git_data(mr, exists)
+
+      expect(project.repository.branch_exists?(mr.source_branch)).to be_truthy
+      expect(project.repository.branch_exists?(mr.target_branch)).to be_truthy
+    end
+
+    it 'ignores Git errors when creating a branch' do
+      mr, exists = importer.create_merge_request
+      mr.state = 'opened'
+      mr.save
+
+      expect(project.repository).to receive(:add_branch).and_raise(Gitlab::Git::CommandError)
+      expect(Gitlab::Sentry).to receive(:track_acceptable_exception).and_call_original
+
+      importer.insert_git_data(mr, exists)
+
+      expect(project.repository.branch_exists?(mr.source_branch)).to be_falsey
+      expect(project.repository.branch_exists?(mr.target_branch)).to be_truthy
+    end
+
     it 'creates the merge request diffs' do
       mr, exists = importer.create_merge_request
 
diff --git a/spec/lib/gitlab/github_import/representation/pull_request_spec.rb b/spec/lib/gitlab/github_import/representation/pull_request_spec.rb
index 33f6ff0ae6a..d478e5ae899 100644
--- a/spec/lib/gitlab/github_import/representation/pull_request_spec.rb
+++ b/spec/lib/gitlab/github_import/representation/pull_request_spec.rb
@@ -238,7 +238,7 @@ describe Gitlab::GithubImport::Representation::PullRequest do
           target_repository_id: 2
         )
 
-        expect(pr.formatted_source_branch).to eq('foo:branch')
+        expect(pr.formatted_source_branch).to eq('github/fork/foo/branch')
       end
     end