Add diffs_metadata.json to startupjs on Changes tab

Basically we want to avoid adding the diffs_metadata.json
request to startup.js if the page is not rendering the
Changes tab right away.

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

@@ -151,10 +151,12 @@ export const fetchDiffFilesBatch = ({ commit, state, dispatch }) => {
             // eslint-disable-next-line promise/catch-or-return,promise/no-nesting
             import('~/code_navigation').then(m =>
               m.default({
-                blobs: state.diffFiles.map(f => ({
-                  path: f.new_path,
-                  codeNavigationPath: f.code_navigation_path,
-                })),
+                blobs: state.diffFiles
+                  .filter(f => f.code_navigation_path)
+                  .map(f => ({
+                    path: f.new_path,
+                    codeNavigationPath: f.code_navigation_path,
+                  })),
                 definitionPathPrefix: state.definitionPathPrefix,
               }),
             );

app/controllers/projects/merge_requests_controller.rb

@@ -86,6 +86,7 @@ class Projects::MergeRequestsController < Projects::MergeRequests::ApplicationCo
         @show_whitespace_default = current_user.nil? || current_user.show_whitespace_in_diffs
         @file_by_file_default = Feature.enabled?(:view_diffs_file_by_file) && current_user&.view_diffs_file_by_file
         @coverage_path = coverage_reports_project_merge_request_path(@project, @merge_request, format: :json) if @merge_request.has_coverage_reports?
+        @endpoint_metadata_url = endpoint_metadata_url(@project, @merge_request)
 
         set_pipeline_variables
 
@@ -435,6 +436,13 @@ class Projects::MergeRequestsController < Projects::MergeRequests::ApplicationCo
   def authorize_read_actual_head_pipeline!
     return render_404 unless can?(current_user, :read_build, merge_request.actual_head_pipeline)
   end
+
+  def endpoint_metadata_url(project, merge_request)
+    params = request.query_parameters
+    params[:view] = cookies[:diff_view] if params[:view].blank? && cookies[:diff_view].present?
+
+    diffs_metadata_project_json_merge_request_path(project, merge_request, 'json', params)
+  end
 end
 
 Projects::MergeRequestsController.prepend_if_ee('EE::Projects::MergeRequestsController')

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

@@ -7,8 +7,9 @@
 - page_card_attributes @merge_request.card_attributes
 - suggest_changes_help_path = help_page_path('user/discussions/index.md', anchor: 'suggest-changes')
 - number_of_pipelines = @pipelines.size
+- mr_action = j(params[:tab].presence || 'show')
 
-.merge-request{ data: { mr_action: j(params[:tab].presence || 'show'), url: merge_request_path(@merge_request, format: :json), project_path: project_path(@merge_request.project), lock_version: @merge_request.lock_version } }
+.merge-request{ data: { mr_action: mr_action, url: merge_request_path(@merge_request, format: :json), project_path: project_path(@merge_request.project), lock_version: @merge_request.lock_version } }
   = render "projects/merge_requests/mr_title"
 
   .merge-request-details.issuable-details{ data: { id: @merge_request.project.id } }
@@ -76,9 +77,11 @@
       = render "projects/merge_requests/tabs/pane", name: "pipelines", id: "pipelines", class: "pipelines" do
         - if number_of_pipelines.nonzero?
           = render 'projects/commit/pipelines_list', disable_initialization: true, endpoint: pipelines_project_merge_request_path(@project, @merge_request)
+      - if mr_action === "diffs"
+        - add_page_startup_api_call @endpoint_metadata_url
       = 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', request.query_parameters),
-        endpoint_metadata: diffs_metadata_project_json_merge_request_path(@project, @merge_request, 'json', request.query_parameters),
+        endpoint_metadata: @endpoint_metadata_url,
         endpoint_batch: diffs_batch_project_json_merge_request_path(@project, @merge_request, 'json', request.query_parameters),
         endpoint_coverage: @coverage_path,
         help_page_path: suggest_changes_help_path,