Hide the base version if the HEAD is available

app/assets/javascripts/diffs/store/getters_versions_dropdowns.js

@@ -22,7 +22,8 @@ export const diffCompareDropdownTargetVersions = (state, getters) => {
     version_index: DIFF_COMPARE_BASE_VERSION_INDEX,
     href: state.mergeRequestDiff.base_version_path,
     isBase: true,
-    selected: isBaseSelected,
+    selected:
+      isBaseSelected || (defaultMergeRefForDiffs && !state.mergeRequestDiff.head_version_path),
   };
 
   const headVersion = {
@@ -44,8 +45,10 @@ export const diffCompareDropdownTargetVersions = (state, getters) => {
 
   return [
     ...state.mergeRequestDiffs.slice(1).map(formatVersion),
-    defaultMergeRefForDiffs && baseVersion,
-    headVersion,
+    (!defaultMergeRefForDiffs ||
+      (defaultMergeRefForDiffs && !state.mergeRequestDiff.head_version_path)) &&
+      baseVersion,
+    state.mergeRequestDiff.head_version_path && headVersion,
   ].filter(a => a);
 };
 

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

@@ -74,9 +74,9 @@
       - if Feature.enabled?(:default_merge_ref_for_diffs, @project)
         - params = params.merge(diff_head: true)
       = render "projects/merge_requests/tabs/pane", name: "diffs", id: "js-diffs-app", class: "diffs", data: { "is-locked": @merge_request.discussion_locked?,
-        endpoint: diffs_project_merge_request_path(@project, @merge_request, 'json', params,
+        endpoint: diffs_project_merge_request_path(@project, @merge_request, 'json', params),
         endpoint_metadata: @endpoint_metadata_url,
-        endpoint_batch: diffs_batch_project_json_merge_request_path(@project, @merge_request, 'json', params,
+        endpoint_batch: diffs_batch_project_json_merge_request_path(@project, @merge_request, 'json', params),
         endpoint_coverage: @coverage_path,
         help_page_path: suggest_changes_help_path,
         current_user_data: @current_user_data,