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, 31 insertions, 1 deletions

diff --git a/spec/services/merge_requests/build_service_spec.rb b/spec/services/merge_requests/build_service_spec.rb
index b46c419de14..fee293760f5 100644
--- a/spec/services/merge_requests/build_service_spec.rb
+++ b/spec/services/merge_requests/build_service_spec.rb
@@ -29,13 +29,27 @@ describe MergeRequests::BuildService do
 
   before do
     project.team << [user, :guest]
+  end
 
+  def stub_compare
     allow(CompareService).to receive_message_chain(:new, :execute).and_return(compare)
     allow(project).to receive(:commit).and_return(commit_1)
     allow(project).to receive(:commit).and_return(commit_2)
   end
 
-  describe 'execute' do
+  describe '#execute' do
+    it 'calls the compare service with the correct arguments' do
+      expect(CompareService).to receive(:new)
+                                  .with(project, Gitlab::Git::BRANCH_REF_PREFIX + source_branch)
+                                  .and_call_original
+
+      expect_any_instance_of(CompareService).to receive(:execute)
+                                                  .with(project, Gitlab::Git::BRANCH_REF_PREFIX + target_branch)
+                                                  .and_call_original
+
+      merge_request
+    end
+
     context 'missing source branch' do
       let(:source_branch) { '' }
 
@@ -52,6 +66,10 @@ describe MergeRequests::BuildService do
       let(:target_branch) { nil }
       let(:commits) { Commit.decorate([commit_1], project) }
 
+      before do
+        stub_compare
+      end
+
       it 'creates compare object with target branch as default branch' do
         expect(merge_request.compare).to be_present
         expect(merge_request.target_branch).to eq(project.default_branch)
@@ -77,6 +95,10 @@ describe MergeRequests::BuildService do
     context 'no commits in the diff' do
       let(:commits) { [] }
 
+      before do
+        stub_compare
+      end
+
       it 'allows the merge request to be created' do
         expect(merge_request.can_be_created).to eq(true)
       end
@@ -89,6 +111,10 @@ describe MergeRequests::BuildService do
     context 'one commit in the diff' do
       let(:commits) { Commit.decorate([commit_1], project) }
 
+      before do
+        stub_compare
+      end
+
       it 'allows the merge request to be created' do
         expect(merge_request.can_be_created).to eq(true)
       end
@@ -149,6 +175,10 @@ describe MergeRequests::BuildService do
     context 'more than one commit in the diff' do
       let(:commits) { Commit.decorate([commit_1, commit_2], project) }
 
+      before do
+        stub_compare
+      end
+
       it 'allows the merge request to be created' do
         expect(merge_request.can_be_created).to eq(true)
       end