Allow multiple comments on the same diff line

This issue occurs when the unified diff components
feature flag is enabled.

Closes https://gitlab.com/gitlab-org/gitlab/-/issues/255626

app/assets/javascripts/diffs/components/diff_view.vue

@@ -61,10 +61,10 @@ export default {
     ...mapActions(['setSelectedCommentPosition']),
     ...mapActions('diffs', ['showCommentForm']),
     showCommentLeft(line) {
-      return !this.inline || line.left;
+      return line.left && !line.right;
     },
     showCommentRight(line) {
-      return !this.inline || (line.right && !line.left);
+      return line.right && !line.left;
     },
     onStartDragging(line) {
       this.dragStart = line;
@@ -138,24 +138,20 @@ export default {
         :class="line.commentRowClasses"
         class="diff-grid-comments diff-tr notes_holder"
       >
-        <div v-if="showCommentLeft(line)" class="diff-td notes-content parallel old">
+        <div v-if="line.left" :class="{ parallel: !inline }" class="diff-td notes-content old">
           <diff-comment-cell
-            v-if="line.left"
             :line="line.left"
             :diff-file-hash="diffFile.file_hash"
             :help-page-path="helpPagePath"
-            :has-draft="line.left.hasDraft"
             line-position="left"
           />
         </div>
-        <div v-if="showCommentRight(line)" class="diff-td notes-content parallel new">
+        <div v-if="line.right" :class="{ parallel: !inline }" class="diff-td notes-content new">
           <diff-comment-cell
-            v-if="line.right"
             :line="line.right"
             :diff-file-hash="diffFile.file_hash"
             :line-index="index"
             :help-page-path="helpPagePath"
-            :has-draft="line.right.hasDraft"
             line-position="right"
           />
         </div>

changelogs/unreleased/ph-255626-allowMultipleCommentsInInlineView.yml

+---
+title: Allow multiple comments on diff lines in inline view
+merge_request:
+author:
+type: fixed

spec/frontend/diffs/components/diff_view_spec.js

@@ -59,8 +59,8 @@ describe('DiffView', () => {
     ${'parallel'} | ${'left'}  | ${'.old'} | ${{ left: { lineDraft: {} }, right: { lineDraft: {} } }} | ${2}
     ${'parallel'} | ${'right'} | ${'.new'} | ${{ left: { lineDraft: {} }, right: { lineDraft: {} } }} | ${2}
     ${'inline'}   | ${'left'}  | ${'.old'} | ${{ left: { lineDraft: {} } }}                           | ${1}
-    ${'inline'}   | ${'right'} | ${'.new'} | ${{ right: { lineDraft: {} } }}                          | ${1}
-    ${'inline'}   | ${'left'}  | ${'.old'} | ${{ left: { lineDraft: {} }, right: { lineDraft: {} } }} | ${1}
+    ${'inline'}   | ${'left'}  | ${'.old'} | ${{ left: { lineDraft: {} } }}                           | ${1}
+    ${'inline'}   | ${'left'}  | ${'.old'} | ${{ left: { lineDraft: {} } }}                           | ${1}
   `(
     'renders a $type comment row with comment cell on $side',
     ({ type, container, sides, total }) => {