Add initial highlight timeout metrics behind a feature flag [RUN ALL RSPEC] [RUN AS-IF-FOSS]

config/feature_flags/development/track_highlight_timeouts.yml

+---
+name: track_highlight_timeouts
+introduced_by_url: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/60956
+rollout_issue_url: https://gitlab.com/gitlab-org/gitlab/-/issues/329909
+milestone: '13.12'
+type: development
+group: group::code review
+default_enabled: false

lib/gitlab/highlight.rb

@@ -64,6 +64,8 @@ module Gitlab
       tokens = lexer.lex(text, continue: continue)
       Timeout.timeout(timeout_time) { @formatter.format(tokens, context.merge(tag: tag)).html_safe }
     rescue Timeout::Error => e
+      add_highlight_timeout_metric
+
       Gitlab::ErrorTracking.track_and_raise_for_dev_exception(e)
       highlight_plain(text)
     rescue StandardError
@@ -81,5 +83,18 @@ module Gitlab
     def maximum_text_highlight_size
       Gitlab.config.extra['maximum_text_highlight_size_kilobytes']
     end
+
+    def add_highlight_timeout_metric
+      return unless Feature.enabled?(:track_highlight_timeouts)
+
+      highlight_timeout.increment(source: Gitlab::Runtime.sidekiq? ? "background" : "foreground")
+    end
+
+    def highlight_timeout
+      @highlight_timeout ||= Gitlab::Metrics.counter(
+        :highlight_timeout,
+        'Counts the times highlights have timed out'
+      )
+    end
   end
 end

spec/lib/gitlab/highlight_spec.rb

@@ -133,5 +133,39 @@ RSpec.describe Gitlab::Highlight do
         subject.highlight("Content")
       end
     end
+
+    describe 'highlight timeouts' do
+      context 'when there is a timeout error while highlighting' do
+        let(:result) { described_class.highlight(file_name, content) }
+
+        before do
+          allow(Timeout).to receive(:timeout).twice.and_raise(Timeout::Error)
+          # This is done twice because it's rescued first and then
+          # calls the original exception
+        end
+
+        it "increments the foreground counter if it's in the foreground" do
+          expect { result }
+            .to raise_error(Timeout::Error)
+            .and change { highlight_timeout_total('foreground') }.by(1)
+            .and not_change { highlight_timeout_total('background') }
+        end
+
+        it "increments the background counter if it's in the background" do
+          allow(Gitlab::Runtime).to receive(:sidekiq?).and_return(true)
+
+          expect { result }
+            .to raise_error(Timeout::Error)
+            .and change { highlight_timeout_total('background') }.by(1)
+            .and not_change { highlight_timeout_total('foreground') }
+        end
+      end
+    end
+  end
+
+  def highlight_timeout_total(source)
+    Gitlab::Metrics
+      .counter(:highlight_timeout, 'Counts the times highlights have timed out')
+      .get(source: source)
   end
 end