Auto resolve new notes of resolved discussions

**Why?**

The previous behavior had resolved discussions being unresolved
when commented on. This was strange UX, especially since there
is a separate button for "Comment & unresolve discussion".

https://gitlab.com/gitlab-org/gitlab-ce/issues/24128

**Note:**

- Also adds changelog

app/services/notes/build_service.rb

@@ -3,6 +3,7 @@
 module Notes
   class BuildService < ::BaseService
     def execute
+      should_resolve = false
       in_reply_to_discussion_id = params.delete(:in_reply_to_discussion_id)
 
       if in_reply_to_discussion_id.present?
@@ -15,12 +16,17 @@ module Notes
         end
 
         params.merge!(discussion.reply_attributes)
+        should_resolve = discussion.resolved?
       end
 
       note = Note.new(params)
       note.project = project
       note.author = current_user
 
+      if should_resolve
+        note.resolve_without_save(current_user)
+      end
+
       note
     end
 

changelogs/unreleased/24128-fix-comment-unresolve-discussions.yml

+---
+title: Fix resolved discussions being unresolved when commented on
+merge_request: 21881
+author:
+type: fixed

spec/features/merge_request/user_resolves_diff_notes_and_discussions_resolve_spec.rb

@@ -149,6 +149,20 @@ describe 'Merge request > User resolves diff notes and discussions', :js do
             end
           end
 
+          it 'allows user to comment' do
+            page.within '.diff-content' do
+              find('.js-note-text').set 'testing'
+
+              click_button 'Comment'
+
+              wait_for_requests
+            end
+
+            page.within '.line-resolve-all-container' do
+              expect(page).to have_content('1/1 discussion resolved')
+            end
+          end
+
           it 'allows user to unresolve from reply form without a comment' do
             page.within '.diff-content' do
               click_button 'Unresolve discussion'

spec/services/notes/build_service_spec.rb

@@ -4,6 +4,8 @@ describe Notes::BuildService do
   let(:note) { create(:discussion_note_on_issue) }
   let(:project) { note.project }
   let(:author) { note.author }
+  let(:merge_request) { create(:merge_request, source_project: project) }
+  let(:mr_note) { create(:discussion_note_on_merge_request, noteable: merge_request, project: project, author: author) }
 
   describe '#execute' do
     context 'when in_reply_to_discussion_id is specified' do
@@ -12,6 +14,19 @@ describe Notes::BuildService do
           new_note = described_class.new(project, author, note: 'Test', in_reply_to_discussion_id: note.discussion_id).execute
           expect(new_note).to be_valid
           expect(new_note.in_reply_to?(note)).to be_truthy
+          expect(new_note.resolved?).to be_falsey
+        end
+
+        context 'when discussion is resolved' do
+          before do
+            mr_note.resolve!(author)
+          end
+
+          it 'resolves the note' do
+            new_note = described_class.new(project, author, note: 'Test', in_reply_to_discussion_id: mr_note.discussion_id).execute
+            expect(new_note).to be_valid
+            expect(new_note.resolved?).to be_truthy
+          end
         end
       end