Only search for MR revert commits on notes after MR was merged

app/models/commit.rb

@@ -342,10 +342,11 @@ class Commit
     @merged_merge_request_hash[current_user]
   end
 
-  def has_been_reverted?(current_user, noteable = self)
+  def has_been_reverted?(current_user, notes_association = nil)
     ext = all_references(current_user)
+    notes_association ||= notes_with_associations
 
-    noteable.notes_with_associations.system.each do |note|
+    notes_association.system.each do |note|
       note.all_references(current_user, extractor: ext)
     end
 

app/models/merge_request.rb

@@ -982,7 +982,16 @@ class MergeRequest < ActiveRecord::Base
   end
 
   def can_be_reverted?(current_user)
-    merge_commit && !merge_commit.has_been_reverted?(current_user, self)
+    return false unless merge_commit
+
+    merged_at = metrics&.merged_at
+    notes_association = notes_with_associations
+
+    if merged_at
+      notes_association = notes_association.where('created_at > ?', merged_at)
+    end
+
+    !merge_commit.has_been_reverted?(current_user, notes_association)
   end
 
   def can_be_cherry_picked?

changelogs/unreleased/41807-15665-consistently-502s-because-it-fetches-every-commit.yml

+---
+title: Speed up loading merged merge requests when they contained a lot of commits
+  before merging
+merge_request: 16320
+author:
+type: performance

spec/models/commit_range_spec.rb

@@ -151,11 +151,11 @@ describe CommitRange do
         .with(commit1, user)
         .and_return(true)
 
-      expect(commit1.has_been_reverted?(user, issue)).to eq(true)
+      expect(commit1.has_been_reverted?(user, issue.notes_with_associations)).to eq(true)
     end
 
-    it 'returns false a commit has not been reverted' do
-      expect(commit1.has_been_reverted?(user, issue)).to eq(false)
+    it 'returns false if the commit has not been reverted' do
+      expect(commit1.has_been_reverted?(user, issue.notes_with_associations)).to eq(false)
     end
   end
 end

spec/models/merge_request_spec.rb

@@ -1035,6 +1035,83 @@ describe MergeRequest do
     end
   end
 
+  describe '#can_be_reverted?' do
+    context 'when there is no merged_at for the MR' do
+      before do
+        subject.metrics.update!(merged_at: nil)
+      end
+
+      it 'returns false' do
+        expect(subject.can_be_reverted?(nil)).to be_falsey
+      end
+    end
+
+    context 'when there is no merge_commit for the MR' do
+      before do
+        subject.metrics.update!(merged_at: Time.now.utc)
+      end
+
+      it 'returns false' do
+        expect(subject.can_be_reverted?(nil)).to be_falsey
+      end
+    end
+
+    context 'when the MR has been merged' do
+      before do
+        MergeRequests::MergeService
+          .new(subject.target_project, subject.author)
+          .execute(subject)
+      end
+
+      context 'when there is no revert commit' do
+        it 'returns true' do
+          expect(subject.can_be_reverted?(nil)).to be_truthy
+        end
+      end
+
+      context 'when there is a revert commit' do
+        let(:current_user) { subject.author }
+        let(:branch) { subject.target_branch }
+        let(:project) { subject.target_project }
+
+        let(:revert_commit_id) do
+          params = {
+            commit: subject.merge_commit,
+            branch_name: branch,
+            start_branch: branch
+          }
+
+          Commits::RevertService.new(project, current_user, params).execute[:result]
+        end
+
+        before do
+          project.add_master(current_user)
+
+          ProcessCommitWorker.new.perform(project.id,
+                                          current_user.id,
+                                          project.commit(revert_commit_id).to_hash,
+                                          project.default_branch == branch)
+        end
+
+        context 'when the revert commit is mentioned in a note after the MR was merged' do
+          it 'returns false' do
+            expect(subject.can_be_reverted?(current_user)).to be_falsey
+          end
+        end
+
+        context 'when the revert commit is mentioned in a note before the MR was merged' do
+          before do
+            subject.notes.last.update!(created_at: subject.metrics.merged_at - 1.second)
+          end
+
+          it 'returns true' do
+            expect(subject.can_be_reverted?(current_user)).to be_truthy
+          end
+        end
+      end
+    end
+  end
+
   describe '#participants' do
     let(:project) { create(:project, :public) }