Include source branch in MR sidebar

app/assets/stylesheets/pages/issuable.scss

@@ -252,7 +252,8 @@
     }
   }
 
-  .cross-project-reference {
+  .cross-project-reference,
+  .sidebar-mr-source-branch {
     color: inherit;
 
     span {
@@ -389,7 +390,8 @@
       border-bottom: 0;
       overflow: hidden;
 
-      &:hover {
+      &.with-sub-blocks .sub-block:hover,
+      &:not(.with-sub-blocks):hover {
         background-color: $gray-100;
       }
 

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
+= render 'shared/issuable/sidebar', issuable_sidebar: @issuable_sidebar, assignees: @merge_request.assignees, source_branch: @merge_request.source_branch
 
 #conflicts{ "v-cloak" => "true", 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) } }

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

@@ -89,7 +89,7 @@
       .loading.hide
         .spinner.spinner-md
 
-= render 'shared/issuable/sidebar', issuable_sidebar: @issuable_sidebar, assignees: @merge_request.assignees
+= render 'shared/issuable/sidebar', issuable_sidebar: @issuable_sidebar, assignees: @merge_request.assignees, source_branch: @merge_request.source_branch
 
 - if @merge_request.can_be_reverted?(current_user)
   = render "projects/commit/change", type: 'revert', commit: @merge_request.merge_commit, title: @merge_request.title

app/views/shared/issuable/_sidebar.html.haml

@@ -151,15 +151,24 @@
           .js-sidebar-subscriptions-entry-point
 
         - project_ref = issuable_sidebar[:reference]
-        .block.project-reference
-          .sidebar-collapsed-icon.dont-change-state
-            = clipboard_button(text: project_ref, title: _('Copy reference'), placement: "left", boundary: 'viewport')
-          .cross-project-reference.hide-collapsed
-            %span
-              = _('Reference:')
-              %cite{ title: project_ref }
-                = project_ref
-            = clipboard_button(text: project_ref, title: _('Copy reference'), placement: "left", boundary: 'viewport')
+        .block.with-sub-blocks
+          .project-reference.sub-block
+            .sidebar-collapsed-icon.dont-change-state
+              = clipboard_button(text: project_ref, title: _('Copy reference'), placement: "left", boundary: 'viewport')
+            .cross-project-reference.hide-collapsed
+              %span
+                = _('Reference:')
+                %cite{ title: project_ref }
+                  = project_ref
+              = clipboard_button(text: project_ref, title: _('Copy reference'), placement: "left", boundary: 'viewport')
+          - if issuable_type == 'merge_request'
+            .sidebar-source-branch.sub-block
+              .sidebar-collapsed-icon.dont-change-state
+                = clipboard_button(text: source_branch, title: _('Copy branch name'), placement: "left", boundary: 'viewport')
+              .sidebar-mr-source-branch.hide-collapsed
+                %span
+                  = _('Source branch: %{source_branch_open}${source_branch}%{source_branch_close}').html_safe % { source_branch_open: "<cite class='ref-name' title='#{source_branch}'>".html_safe, source_branch_close: "</cite>".html_safe, source_branch: source_branch }
+                = clipboard_button(text: source_branch, title: _('Copy branch name'), placement: "left", boundary: 'viewport')
 
         - if issuable_sidebar.dig(:current_user, :can_move)
           .block.js-sidebar-move-issue-block

changelogs/unreleased/23767-add-branch-to-mr-sidebar.yml

+---
+title: Display Merge Request's source branch name in sidebar
+merge_request: 34901
+author: Ethan Reesor (@firelizzard)
+type: added

locale/gitlab.pot

@@ -23323,6 +23323,9 @@ msgstr ""
 msgid "Source (branch or tag)"
 msgstr ""
 
+msgid "Source branch: %{source_branch_open}${source_branch}%{source_branch_close}"
+msgstr ""
+
 msgid "Source code"
 msgstr ""