Merge branch '23234-deleting-a-milestone-removes-source-branch-deletion-options-of-associated-merge-requests' into 'master'

Maintain "force_remove_source_branch" options on Merge Request unless specified

## What does this MR do?

Fixes a problem where Merge Requests were losing the state associated with the flag to remove the source branch upon merge

* Closes #23234 
* Closes #23191
* Closes #19351

See merge request !6817

3 files changed, 17 insertions, 1 deletions

diff --git a/CHANGELOG b/CHANGELOG
index 4b1ac9d2c3c..4de2069b9f8 100644
--- a/CHANGELOG
+++ b/CHANGELOG
@@ -33,6 +33,7 @@ v 8.13.0 (unreleased)
   - Update Gitlab Shell to fix some problems with moving projects between storages
   - Cache rendered markdown in the database, rather than Redis
   - Avoid database queries on Banzai::ReferenceParser::BaseParser for nodes without references
+  - Do not alter 'force_remove_source_branch' options on MergeRequest unless specified
   - Simplify Mentionable concern instance methods
   - API: Ability to retrieve version information (Robert Schilling)
   - Fix permission for setting an issue's due date
diff --git a/app/services/merge_requests/update_service.rb b/app/services/merge_requests/update_service.rb
index 9dbec49d163..a37cc3fdf21 100644
--- a/app/services/merge_requests/update_service.rb
+++ b/app/services/merge_requests/update_service.rb
@@ -15,7 +15,10 @@ module MergeRequests
         params.except!(:target_branch, :force_remove_source_branch)
       end
 
-      merge_request.merge_params['force_remove_source_branch'] = params.delete(:force_remove_source_branch)
+      if params[:force_remove_source_branch].present?
+        merge_request.merge_params['force_remove_source_branch'] = params.delete(:force_remove_source_branch)
+      end
+
       handle_wip_event(merge_request)
       update(merge_request)
     end
diff --git a/spec/services/merge_requests/update_service_spec.rb b/spec/services/merge_requests/update_service_spec.rb
index fd5f94047c2..2433a7dad06 100644
--- a/spec/services/merge_requests/update_service_spec.rb
+++ b/spec/services/merge_requests/update_service_spec.rb
@@ -105,6 +105,18 @@ describe MergeRequests::UpdateService, services: true do
         expect(note).not_to be_nil
         expect(note.note).to eq 'Target branch changed from `master` to `target`'
       end
+
+      context 'when not including source branch removal options' do
+        before do
+          opts.delete(:force_remove_source_branch)
+        end
+
+        it 'maintains the original options' do
+          update_merge_request(opts)
+
+          expect(@merge_request.merge_params["force_remove_source_branch"]).to eq("1")
+        end
+      end
     end
 
     context 'todos' do