Check mergeability in merge to ref service

and add spec

Add changelog

ok

ok

app/models/merge_request.rb

@@ -807,8 +807,7 @@ def mergeable_state?(skip_ci_check: false, skip_discussions_check: false)
   end
 
   def mergeable_to_ref?
-    return false if merged?
-    return false if broken?
+    return false unless mergeable_state?(skip_ci_check: true, skip_discussions_check: true)
 
     # Given the `merge_ref_path` will have the same
     # state the `target_branch` would have. Ideally

app/services/merge_requests/merge_to_ref_service.rb

@@ -41,9 +41,7 @@ def error_check!
       super
 
       error =
-        if Feature.disabled?(:merge_to_tmp_merge_ref_path, project)
-          'Feature is not enabled'
-        elsif !hooks_validation_pass?(merge_request)
+        if !hooks_validation_pass?(merge_request)
           hooks_validation_error(merge_request)
         elsif !@merge_request.mergeable_to_ref?
           "Merge request is not mergeable to #{target_ref}"

changelogs/unreleased/check-mergeability-in-merge-to-ref-service.yml

+---
+title: Check mergeability in MergeToRefService
+merge_request: 26757
+author:
+type: changed

spec/models/merge_request_spec.rb

@@ -3081,6 +3081,38 @@ def create_pipeline(status)
     end
   end
 
+  describe '#mergeable_to_ref?' do
+    it 'returns true when merge request is mergeable' do
+      subject = create(:merge_request)
+
+      expect(subject.mergeable_to_ref?).to be(true)
+    end
+
+    it 'returns false when merge request is already merged' do
+      subject = create(:merge_request, :merged)
+
+      expect(subject.mergeable_to_ref?).to be(false)
+    end
+
+    it 'returns false when merge request is closed' do
+      subject = create(:merge_request, :closed)
+
+      expect(subject.mergeable_to_ref?).to be(false)
+    end
+
+    it 'returns false when merge request is work in progress' do
+      subject = create(:merge_request, title: 'WIP: The feature')
+
+      expect(subject.mergeable_to_ref?).to be(false)
+    end
+
+    it 'returns false when merge request has no commits' do
+      subject = create(:merge_request, source_branch: 'empty-branch', target_branch: 'master')
+
+      expect(subject.mergeable_to_ref?).to be(false)
+    end
+  end
+
   describe '#merge_participants' do
     it 'contains author' do
       expect(subject.merge_participants).to eq([subject.author])

spec/services/merge_requests/merge_to_ref_service_spec.rb

@@ -40,15 +40,6 @@
   end
 
   shared_examples_for 'successfully evaluates pre-condition checks' do
-    it 'returns error when feature is disabled' do
-      stub_feature_flags(merge_to_tmp_merge_ref_path: false)
-
-      result = service.execute(merge_request)
-
-      expect(result[:status]).to eq(:error)
-      expect(result[:message]).to eq('Feature is not enabled')
-    end
-
     it 'returns an error when the failing to process the merge' do
       allow(project.repository).to receive(:merge_to_ref).and_return(nil)
 
@@ -180,6 +171,17 @@ def process_merge_to_ref
       it { expect(todo).not_to be_done }
     end
 
+    context 'when merge request is WIP state' do
+      it 'fails to merge' do
+        merge_request = create(:merge_request, title: 'WIP: The feature')
+
+        result = service.execute(merge_request)
+
+        expect(result[:status]).to eq(:error)
+        expect(result[:message]).to eq("Merge request is not mergeable to #{merge_request.merge_ref_path}")
+      end
+    end
+
     it 'returns error when user has no authorization to admin the merge request' do
       unauthorized_user = create(:user)
       project.add_reporter(unauthorized_user)