Merge branch 'disable-commenting-on-unrelatable-diff-line' into 'master'

Disable commenting on unrelatable diff line

## What does this MR do?

Fixes a bug where users can comment on diff lines that can't be commented on and attached to.

This is the case for unfolded lines and lines that appear as snippets in the discussion tab.

**!5864 should be merged before this MR.**

## Are there points in the code the reviewer needs to double check?

😕 

## Why was this MR needed?

Comments were getting lost on the discussion feed, unable to find their related diff.

## What are the relevant issue numbers?

Closes #20633.

## Screenshots (if relevant)

![diffs-comment-fix](/uploads/f902b687fda75492e38397f9705283e0/diffs-comment-fix.mp4)

## Does this MR meet the acceptance criteria?

- [ ] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added
- [ ] [Documentation created/updated](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/doc/development/doc_styleguide.md)
- [ ] API support added
- Tests
  - [ ] Added for this feature/bug
  - [ ] All builds are passing
- [ ] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [ ] Branch has no merge conflicts with `master` (if you do - rebase it please)
- [ ] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

See merge request !5681

CHANGELOG

@@ -3,6 +3,7 @@ Please view this file on the master branch, on stable branches it's out of date.
 v 8.12.0 (unreleased)
   - Change merge_error column from string to text type
   - Optimistic locking for Issues and Merge Requests (title and description overriding prevention)
+  - Added tests for diff notes
 
 v 8.11.1 (unreleased)
   - Fix file links on project page when default view is Files !5933

app/assets/javascripts/files_comment_button.js

@@ -39,12 +39,13 @@
     FilesCommentButton.prototype.render = function(e) {
       var $currentTarget, buttonParentElement, lineContentElement, textFileElement;
       $currentTarget = $(e.currentTarget);
+
       buttonParentElement = this.getButtonParent($currentTarget);
-      if (!this.shouldRender(e, buttonParentElement)) {
-        return;
-      }
-      textFileElement = this.getTextFileElement($currentTarget);
+      if (!this.validateButtonParent(buttonParentElement)) return;
       lineContentElement = this.getLineContent($currentTarget);
+      if (!this.validateLineContent(lineContentElement)) return;
+
+      textFileElement = this.getTextFileElement($currentTarget);
       buttonParentElement.append(this.buildButton({
         noteableType: textFileElement.attr('data-noteable-type'),
         noteableID: textFileElement.attr('data-noteable-id'),
@@ -119,10 +120,14 @@
       return newButtonParent.is(this.getButtonParent($(e.currentTarget)));
     };
 
-    FilesCommentButton.prototype.shouldRender = function(e, buttonParentElement) {
+    FilesCommentButton.prototype.validateButtonParent = function(buttonParentElement) {
       return !buttonParentElement.hasClass(EMPTY_CELL_CLASS) && !buttonParentElement.hasClass(UNFOLDABLE_LINE_CLASS) && $(COMMENT_BUTTON_CLASS, buttonParentElement).length === 0;
     };
 
+    FilesCommentButton.prototype.validateLineContent = function(lineContentElement) {
+      return lineContentElement.attr('data-discussion-id') && lineContentElement.attr('data-discussion-id') !== '';
+    };
+
     return FilesCommentButton;
 
   })();

spec/features/merge_requests/diff_notes_spec.rb

@@ -15,7 +15,7 @@ feature 'Diff notes', js: true, feature: true do
     let(:notes_holder_input_xpath) { './following-sibling::*[contains(concat(" ", @class, " "), " notes_holder ")]' }
     let(:test_note_comment) { 'this is a test note!' }
 
-    context 'when hovering over the parallel view diff file' do
+    context 'when hovering over a parallel view diff file' do
       before(:each) do
         visit diffs_namespace_project_merge_request_path(@project.namespace, @project, @merge_request, view: 'parallel')
       end
@@ -69,9 +69,28 @@ feature 'Diff notes', js: true, feature: true do
           should_not_allow_commenting(find('.match', match: :first).find(:xpath, '..'), 'right')
         end
       end
+
+      context 'with an unfolded line' do
+        before(:each) do
+          find('.js-unfold', match: :first).click
+          wait_for_ajax
+        end
+
+        # The first `.js-unfold` unfolds upwards, therefore the first
+        # `.line_holder` will be an unfolded line.
+        let(:line_holder) { first('.line_holder[id="1"]') }
+
+        it 'should not allow commenting on the left side' do
+          should_not_allow_commenting(line_holder, 'left')
         end
 
-    context 'when hovering over the inline view diff file' do
+        it 'should not allow commenting on the right side' do
+          should_not_allow_commenting(line_holder, 'right')
+        end
+      end
+    end
+
+    context 'when hovering over an inline view diff file' do
       before do
         visit diffs_namespace_project_merge_request_path(@project.namespace, @project, @merge_request, view: 'inline')
       end
@@ -99,6 +118,33 @@ feature 'Diff notes', js: true, feature: true do
           should_not_allow_commenting(find('.match', match: :first))
         end
       end
+
+      context 'with an unfolded line' do
+        before(:each) do
+          find('.js-unfold', match: :first).click
+          wait_for_ajax
+        end
+
+        # The first `.js-unfold` unfolds upwards, therefore the first
+        # `.line_holder` will be an unfolded line.
+        let(:line_holder) { first('.line_holder[id="1"]') }
+
+        it 'should not allow commenting' do
+          should_not_allow_commenting line_holder
+        end
+      end
+
+      context 'when hovering over a diff discussion' do
+        before do
+          visit diffs_namespace_project_merge_request_path(@project.namespace, @project, @merge_request, view: 'inline')
+          should_allow_commenting(find('[id="2f6fcd96b88b36ce98c38da085c795a27d92a3dd_7_7"]'))
+          visit namespace_project_merge_request_path(@project.namespace, @project, @merge_request)
+        end
+
+        it 'should not allow commenting' do
+          should_not_allow_commenting(find('.line_holder', match: :first))
+        end
+      end
     end
 
     def should_allow_commenting(line_holder, diff_side = nil)