Adding initial tracking for file size highlight limits

config/feature_flags/development/track_file_size_over_highlight_limit.yml

+---
+name: track_file_size_over_highlight_limit
+introduced_by_url: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/61273
+rollout_issue_url: https://gitlab.com/gitlab-org/gitlab/-/issues/330374
+milestone: '13.12'
+type: development
+group: group::code review
+default_enabled: false

lib/gitlab/highlight.rb

@@ -11,7 +11,11 @@ module Gitlab
     end
 
     def self.too_large?(size)
-      size.to_i > Gitlab.config.extra['maximum_text_highlight_size_kilobytes']
+      return false unless size.to_i > Gitlab.config.extra['maximum_text_highlight_size_kilobytes']
+
+      over_highlight_size_limit.increment(source: "text highlighter") if Feature.enabled?(:track_file_size_over_highlight_limit)
+
+      true
     end
 
     attr_reader :blob_name
@@ -96,5 +100,12 @@ module Gitlab
         'Counts the times highlights have timed out'
       )
     end
+
+    def self.over_highlight_size_limit
+      @over_highlight_size_limit ||= Gitlab::Metrics.counter(
+        :over_highlight_size_limit,
+        'Count the times files have been over the highlight size limit'
+      )
+    end
   end
 end

spec/lib/gitlab/highlight_spec.rb

@@ -46,13 +46,21 @@ RSpec.describe Gitlab::Highlight do
       expect(result).to eq(%[<span id="LC1" class="line" lang="plaintext">plain text contents</span>])
     end
 
-    it 'returns plain version for long content' do
+    context 'when content is too long to be highlighted' do
+      let(:result) { described_class.highlight(file_name, content) } # content is 44 bytes
+
+      before do
         stub_config(extra: { 'maximum_text_highlight_size_kilobytes' => 0.0001 } ) # 1.024 bytes
+      end
 
-      result = described_class.highlight(file_name, content) # content is 44 bytes
+      it 'increments the metric for oversized files' do
+        expect { result }.to change { over_highlight_size_limit('text highlighter') }.by(1)
+      end
 
+      it 'returns plain version for long content' do
         expect(result).to eq(%[<span id="LC1" class="line" lang="">(make-pathname :defaults name</span>\n<span id="LC2" class="line" lang="">:type "assem")</span>])
       end
+    end
 
     it 'highlights multi-line comments' do
       result = described_class.highlight(file_name, multiline_content)
@@ -168,4 +176,11 @@ RSpec.describe Gitlab::Highlight do
       .counter(:highlight_timeout, 'Counts the times highlights have timed out')
       .get(source: source)
   end
+
+  def over_highlight_size_limit(source)
+    Gitlab::Metrics
+      .counter(:over_highlight_size_limit,
+               'Count the times text has been over the highlight size limit')
+      .get(source: source)
+  end
 end