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, 6 insertions, 6 deletions

diff --git a/app/services/compare_service.rb b/app/services/compare_service.rb
index 53f16a236d2..1db91c3c90c 100644
--- a/app/services/compare_service.rb
+++ b/app/services/compare_service.rb
@@ -1,17 +1,17 @@
 require 'securerandom'
 
-# Compare 2 branches for one repo or between repositories
+# Compare 2 refs for one repo or between repositories
 # and return Gitlab::Git::Compare object that responds to commits and diffs
 class CompareService
-  attr_reader :start_project, :start_branch_name
+  attr_reader :start_project, :start_ref_name
 
-  def initialize(new_start_project, new_start_branch_name)
+  def initialize(new_start_project, new_start_ref_name)
     @start_project = new_start_project
-    @start_branch_name = new_start_branch_name
+    @start_ref_name = new_start_ref_name
   end
 
-  def execute(target_project, target_branch, straight: false)
-    raw_compare = target_project.repository.compare_source_branch(target_branch, start_project.repository, start_branch_name, straight: straight)
+  def execute(target_project, target_ref, straight: false)
+    raw_compare = target_project.repository.compare_source_branch(target_ref, start_project.repository, start_ref_name, straight: straight)
 
     Compare.new(raw_compare, target_project, straight: straight) if raw_compare
   end