Merge branch 'jej-note-search-uses-finder' into 'security'

Fix missing Note access checks in by moving Note#search to updated NoteFinder

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

### Note lookup without access check

- [x] :white_check_mark: app/finders/notes_finder.rb:13 :download_code check
- [x] :white_check_mark: app/finders/notes_finder.rb:19 `SnippetsFinder`
- [x] :white_check_mark: app/models/note.rb:121 [`Issue#visible_to_user`]
- [x] :white_check_mark: lib/gitlab/project_search_results.rb:113
  - This is the only use of `app/models/note.rb:121` above, but importantly has no access checks at all. This means it leaks MR comments and snippets when those features are `team-only` in addition to the issue comments which would be fixed by `app/models/note.rb:121`.
  - It is only called from SearchController where `can?(current_user, :download_code, @project)` is checked, so commit comments are not leaked.

### Previous discussions
- [x] https://dev.gitlab.org/gitlab/gitlabhq/merge_requests/2024/diffs#b915c5267a63628b0bafd23d37792ae73ceae272_13_13 `: download_code` check on commit
- [x] https://dev.gitlab.org/gitlab/gitlabhq/merge_requests/2024/diffs#b915c5267a63628b0bafd23d37792ae73ceae272_19_19 `SnippetsFinder` should be used
  - `SnippetsFinder` should check if the snippets feature is enabled -> https://gitlab.com/gitlab-org/gitlab-ce/issues/25223

###  Acceptance criteria met?
- [x] Tests added for new code
- [x] TODO comments removed
- [x] Squashed and removed skipped tests
- [x] Changelog entry
- [ ] State Gitlab versions affected and issue severity in description
- [ ] Create technical debt issue for NotesFinder.
  - Either split into `NotesFinder::ForTarget` and `NotesFinder::Search` or consider object per notable type such as `NotesFinder::OnIssue`. For the first option could create `NotesFinder::Base` which is either inherited from or which can be included in the other two.
  - Avoid case statement anti-pattern in this finder with use of `NotesFinder::OnCommit` etc. Consider something on the finder for this? `Model.finder(user, project)`
  - Move `inc_author` to the controller, and implement `related_notes` to replace `non_diff_notes`/`mr_and_commit_notes`

See merge request !2035

2 files changed, 2 insertions, 4 deletions

diff --git a/lib/gitlab/project_search_results.rb b/lib/gitlab/project_search_results.rb
index 66e6b29e798..6bdf3db9cb8 100644
--- a/lib/gitlab/project_search_results.rb
+++ b/lib/gitlab/project_search_results.rb
@@ -110,7 +110,7 @@ module Gitlab
     end
 
     def notes
-      @notes ||= project.notes.user.search(query, as_user: @current_user).order('updated_at DESC')
+      @notes ||= NotesFinder.new(project, @current_user, search: query).execute.user.order('updated_at DESC')
     end
 
     def commits
diff --git a/lib/gitlab/sql/union.rb b/lib/gitlab/sql/union.rb
index 1cd89b3a9c4..222021e8802 100644
--- a/lib/gitlab/sql/union.rb
+++ b/lib/gitlab/sql/union.rb
@@ -22,9 +22,7 @@ module Gitlab
         # By using "unprepared_statements" we remove the usage of placeholders
         # (thus fixing this problem), at a slight performance cost.
         fragments = ActiveRecord::Base.connection.unprepared_statement do
-          @relations.map do |rel|
-            rel.reorder(nil).to_sql
-          end
+          @relations.map { |rel| rel.reorder(nil).to_sql }.reject(&:blank?)
         end
 
         fragments.join("\nUNION\n")