Merge branch 'jej-23867-use-mr-finder-instead-of-access-check' into 'security'

Replace MR access checks with use of MergeRequestsFinder

Split from !2024 to partially solve https://gitlab.com/gitlab-org/gitlab-ce/issues/23867

## Which fixes are in this MR?

:warning: - Potentially untested  
:bomb: - No test coverage  
:traffic_light: - Test coverage of some sort exists (a test failed when error raised)  
:vertical_traffic_light: - Test coverage of return value (a test failed when nil used)  
:white_check_mark: - Permissions check tested

### MR lookup from project

- [x] :bomb:  app/finders/notes_finder.rb:17
- [x] :warning:  app/views/layouts/nav/_project.html.haml:80 [`.count`]
- [x] :bomb:  app/controllers/concerns/creates_commit.rb:84
- [x] :traffic_light:  app/controllers/projects/commits_controller.rb:24
- [x] :traffic_light:  app/controllers/projects/compare_controller.rb:56
- [x] :vertical_traffic_light:  app/controllers/projects/discussions_controller.rb:29
- [x] :white_check_mark:  app/controllers/projects/todos_controller.rb:27
- [x] :vertical_traffic_light:  app/models/commit.rb:268
- [x] :white_check_mark: lib/gitlab/search_results.rb:71

### Previous discussions
- [x] https://dev.gitlab.org/gitlab/gitlabhq/merge_requests/2024/diffs#d1c10892daedb4d4dd3d4b12b6d071091eea83df_267_266 Memoize ` merged_merge_request(current_user)`
- [x] https://dev.gitlab.org/gitlab/gitlabhq/merge_requests/2024/diffs#d1c10892daedb4d4dd3d4b12b6d071091eea83df_248_247 Expected side effect for `merged_merge_request!`, consider `skip_authorization: true`.
- [x] https://dev.gitlab.org/gitlab/gitlabhq/merge_requests/2024/diffs#d1c10892daedb4d4dd3d4b12b6d071091eea83df_269_269 Scary use  of unchecked `merged_merge_request?`

See merge request !2033

1 files changed, 1 insertions, 1 deletions

diff --git a/app/controllers/projects/compare_controller.rb b/app/controllers/projects/compare_controller.rb
index bee3d56076c..ec02fc15d35 100644
--- a/app/controllers/projects/compare_controller.rb
+++ b/app/controllers/projects/compare_controller.rb
@@ -53,7 +53,7 @@ class Projects::CompareController < Projects::ApplicationController
   end
 
   def merge_request
-    @merge_request ||= @project.merge_requests.opened.
+    @merge_request ||= MergeRequestsFinder.new(current_user, project_id: @project.id).execute.opened.
       find_by(source_project: @project, source_branch: @head_ref, target_branch: @start_ref)
   end
 end