Adds reviewers to merge conflicts sidebar

Closes https://gitlab.com/gitlab-org/gitlab/-/issues/342494

app/assets/javascripts/merge_conflicts/components/inline_conflict_lines.vue

@@ -35,7 +35,11 @@ export default {
         <td :class="lineCssClass(line)" class="diff-line-num header"></td>
         <td :class="lineCssClass(line)" class="line_content header">
           <strong>{{ line.richText }}</strong>
-          <button type="button" @click="handleSelected({ file, line })">
+          <button
+            type="button"
+            class="gl-border-1 gl-border-solid"
+            @click="handleSelected({ file, line })"
+          >
             {{ line.buttonTitle }}
           </button>
         </td>

app/assets/javascripts/merge_conflicts/components/parallel_conflict_lines.vue

@@ -35,7 +35,11 @@ export default {
           <td class="diff-line-num header" :class="lineCssClass(line)"></td>
           <td class="line_content header" :class="lineCssClass(line)">
             <strong>{{ line.richText }}</strong>
-            <button type="button" @click="handleSelected({ file, line })">
+            <button
+              type="button"
+              class="gl-border-1 gl-border-solid"
+              @click="handleSelected({ file, line })"
+            >
               {{ line.buttonTitle }}
             </button>
           </td>

app/views/projects/merge_requests/conflicts/show.html.haml

@@ -6,7 +6,7 @@
 .merge-request-details.issuable-details
   = render "projects/merge_requests/mr_box"
 
-= render 'shared/issuable/sidebar', issuable_sidebar: @issuable_sidebar, assignees: @merge_request.assignees, source_branch: @merge_request.source_branch
+= render 'shared/issuable/sidebar', issuable_sidebar: @issuable_sidebar, assignees: @merge_request.assignees, reviewers: @merge_request.reviewers, source_branch: @merge_request.source_branch
 
 #conflicts{ data: { conflicts_path: conflicts_project_merge_request_path(@merge_request.project, @merge_request, format: :json),
     resolve_conflicts_path: resolve_conflicts_project_merge_request_path(@merge_request.project, @merge_request),

spec/features/merge_request/user_resolves_conflicts_spec.rb

@@ -9,7 +9,7 @@ RSpec.describe 'Merge request > User resolves conflicts', :js do
   let(:user) { project.creator }
 
   def create_merge_request(source_branch)
-    create(:merge_request, source_branch: source_branch, target_branch: 'conflict-start', source_project: project, merge_status: :unchecked) do |mr|
+    create(:merge_request, source_branch: source_branch, target_branch: 'conflict-start', source_project: project, merge_status: :unchecked, reviewers: [user]) do |mr|
       mr.mark_as_unmergeable
     end
   end
@@ -178,6 +178,23 @@ RSpec.describe 'Merge request > User resolves conflicts', :js do
     end
   end
 
+  context 'sidebar' do
+    let(:merge_request) { create_merge_request('conflict-resolvable') }
+
+    before do
+      project.add_developer(user)
+      sign_in(user)
+
+      visit conflicts_project_merge_request_path(project, merge_request)
+    end
+
+    it 'displays reviewers' do
+      page.within '.issuable-sidebar' do
+        expect(page).to have_selector('[data-testid="reviewer"]', count: 1)
+      end
+    end
+  end
+
   unresolvable_conflicts = {
     'conflict-too-large' => 'when the conflicts contain a large file',
     'conflict-binary-file' => 'when the conflicts contain a binary file',