Ensure MRs always use branch refs for comparison

If a merge request was created with a branch name that also matched a tag name,
we'd generate a comparison to or from the tag respectively, rather than the
branch. Merging would still use the branch, of course.

To avoid this, ensure that when we get the branch heads, we prepend the
reference prefix for branches, which will ensure that we generate the correct
comparison.

1 files changed, 18 insertions, 3 deletions

diff --git a/spec/models/merge_request_spec.rb b/spec/models/merge_request_spec.rb
index 3cf8fc816ff..728028746d8 100644
--- a/spec/models/merge_request_spec.rb
+++ b/spec/models/merge_request_spec.rb
@@ -259,7 +259,7 @@ describe MergeRequest do
   end
 
   describe '#source_branch_sha' do
-    let(:last_branch_commit) { subject.source_project.repository.commit(subject.source_branch) }
+    let(:last_branch_commit) { subject.source_project.repository.commit(Gitlab::Git::BRANCH_REF_PREFIX + subject.source_branch) }
 
     context 'with diffs' do
       subject { create(:merge_request, :with_diffs) }
@@ -273,6 +273,21 @@ describe MergeRequest do
       it 'returns the sha of the source branch last commit' do
         expect(subject.source_branch_sha).to eq(last_branch_commit.sha)
       end
+
+      context 'when there is a tag name matching the branch name' do
+        let(:tag_name) { subject.source_branch }
+
+        it 'returns the sha of the source branch last commit' do
+          subject.source_project.repository.add_tag(subject.author,
+                                                    tag_name,
+                                                    subject.target_branch_sha,
+                                                    'Add a tag')
+
+          expect(subject.source_branch_sha).to eq(last_branch_commit.sha)
+
+          subject.source_project.repository.rm_tag(subject.author, tag_name)
+        end
+      end
     end
 
     context 'when the merge request is being created' do
@@ -933,7 +948,7 @@ describe MergeRequest do
 
       context 'with a completely different branch' do
         before do
-          subject.update(target_branch: 'v1.0.0')
+          subject.update(target_branch: 'csv')
         end
 
         it_behaves_like 'returning all SHA'
@@ -941,7 +956,7 @@ describe MergeRequest do
 
       context 'with a branch having no difference' do
         before do
-          subject.update(target_branch: 'v1.1.0')
+          subject.update(target_branch: 'branch-merged')
           subject.reload # make sure commits were not cached
         end