Add dispensable_render methods

When an error occurs in a template that is not essential,
instead of returning a 500 error, omit it and track the error.

Changelog: other

app/helpers/application_helper.rb

@@ -18,6 +18,28 @@ module ApplicationHelper
     end
   end
 
+  def dispensable_render(...)
+    render(...)
+  rescue StandardError => error
+    if Feature.enabled?(:dispensable_render, default_enabled: :yaml)
+      Gitlab::ErrorTracking.track_and_raise_for_dev_exception(error)
+      nil
+    else
+      raise error
+    end
+  end
+
+  def dispensable_render_if_exists(...)
+    render_if_exists(...)
+  rescue StandardError => error
+    if Feature.enabled?(:dispensable_render, default_enabled: :yaml)
+      Gitlab::ErrorTracking.track_and_raise_for_dev_exception(error)
+      nil
+    else
+      raise error
+    end
+  end
+
   def partial_exists?(partial)
     lookup_context.exists?(partial, [], true)
   end

app/views/layouts/_page.html.haml

@@ -3,23 +3,23 @@
     = render "layouts/nav/sidebar/#{nav}"
   .content-wrapper.content-wrapper-margin{ class: "#{@content_wrapper_class}" }
     .mobile-overlay
-    = render_if_exists 'layouts/header/verification_reminder'
+    = dispensable_render_if_exists 'layouts/header/verification_reminder'
     .alert-wrapper.gl-force-block-formatting-context
-      = render 'shared/outdated_browser'
-      = render_if_exists "layouts/header/licensed_user_count_threshold"
-      = render_if_exists "layouts/header/token_expiry_notification"
-      = render "layouts/broadcast"
-      = render "layouts/header/read_only_banner"
-      = render "layouts/header/registration_enabled_callout"
-      = render "layouts/nav/classification_level_banner"
+      = dispensable_render 'shared/outdated_browser'
+      = dispensable_render_if_exists "layouts/header/licensed_user_count_threshold"
+      = dispensable_render_if_exists "layouts/header/token_expiry_notification"
+      = dispensable_render "layouts/broadcast"
+      = dispensable_render "layouts/header/read_only_banner"
+      = dispensable_render "layouts/header/registration_enabled_callout"
+      = dispensable_render "layouts/nav/classification_level_banner"
       = yield :flash_message
-      = render "shared/service_ping_consent"
+      = dispensable_render "shared/service_ping_consent"
       = render_two_factor_auth_recovery_settings_check
-      = render_if_exists "layouts/header/ee_subscribable_banner"
-      = render_if_exists "layouts/header/seats_count_alert"
-      = render_if_exists "shared/namespace_storage_limit_alert"
-      = render_if_exists "shared/namespace_user_cap_reached_alert"
-      = render_if_exists "shared/new_user_signups_cap_reached_alert"
+      = dispensable_render_if_exists "layouts/header/ee_subscribable_banner"
+      = dispensable_render_if_exists "layouts/header/seats_count_alert"
+      = dispensable_render_if_exists "shared/namespace_storage_limit_alert"
+      = dispensable_render_if_exists "shared/namespace_user_cap_reached_alert"
+      = dispensable_render_if_exists "shared/new_user_signups_cap_reached_alert"
       = yield :page_level_alert
       = yield :group_invite_members_banner
       - unless @hide_breadcrumbs

config/feature_flags/development/dispensable_render.yml

+---
+name: dispensable_render
+introduced_by_url: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/81546
+rollout_issue_url: https://gitlab.com/gitlab-org/gitlab/-/issues/354337
+milestone: '14.9'
+type: development
+group: group::activation
+default_enabled: true

spec/helpers/application_helper_spec.rb

@@ -517,4 +517,112 @@ RSpec.describe ApplicationHelper do
       end
     end
   end
+
+  describe '#dispensable_render' do
+    context 'when an error occurs in the template to be rendered' do
+      before do
+        allow(helper).to receive(:render).and_raise
+      end
+
+      it 'calls `track_and_raise_for_dev_exception`' do
+        expect(Gitlab::ErrorTracking).to receive(:track_and_raise_for_dev_exception)
+        helper.dispensable_render
+      end
+
+      context 'for development environment' do
+        before do
+          stub_rails_env('development')
+        end
+
+        it 'raises an error' do
+          expect { helper.dispensable_render }.to raise_error(StandardError)
+        end
+      end
+
+      context 'for production environments' do
+        before do
+          stub_rails_env('production')
+        end
+
+        it 'returns nil' do
+          expect(helper.dispensable_render).to be_nil
+        end
+
+        context 'when the feature flag is disabled' do
+          before do
+            stub_feature_flags(dispensable_render: false)
+          end
+
+          it 'raises an error' do
+            expect { helper.dispensable_render }.to raise_error(StandardError)
+          end
+        end
+      end
+    end
+
+    context 'when no error occurs in the template to be rendered' do
+      before do
+        allow(helper).to receive(:render).and_return('foo')
+      end
+
+      it 'does not track or raise and returns the rendered content' do
+        expect(Gitlab::ErrorTracking).not_to receive(:track_and_raise_for_dev_exception)
+        expect(helper.dispensable_render).to eq('foo')
+      end
+    end
+  end
+
+  describe '#dispensable_render_if_exists' do
+    context 'when an error occurs in the template to be rendered' do
+      before do
+        allow(helper).to receive(:render_if_exists).and_raise
+      end
+
+      it 'calls `track_and_raise_for_dev_exception`' do
+        expect(Gitlab::ErrorTracking).to receive(:track_and_raise_for_dev_exception)
+        helper.dispensable_render_if_exists
+      end
+
+      context 'for development environment' do
+        before do
+          stub_rails_env('development')
+        end
+
+        it 'raises an error' do
+          expect { helper.dispensable_render_if_exists }.to raise_error(StandardError)
+        end
+      end
+
+      context 'for production environments' do
+        before do
+          stub_rails_env('production')
+        end
+
+        it 'returns nil' do
+          expect(helper.dispensable_render_if_exists).to be_nil
+        end
+
+        context 'when the feature flag is disabled' do
+          before do
+            stub_feature_flags(dispensable_render: false)
+          end
+
+          it 'raises an error' do
+            expect { helper.dispensable_render_if_exists }.to raise_error(StandardError)
+          end
+        end
+      end
+    end
+
+    context 'when no error occurs in the template to be rendered' do
+      before do
+        allow(helper).to receive(:render_if_exists).and_return('foo')
+      end
+
+      it 'does not track or raise' do
+        expect(Gitlab::ErrorTracking).not_to receive(:track_and_raise_for_dev_exception)
+        expect(helper.dispensable_render_if_exists).to eq('foo')
+      end
+    end
+  end
 end