Add a feature flag for MarkerRanges

Issue: https://gitlab.com/gitlab-org/gitlab/-/issues/324068

config/feature_flags/development/introduce_marker_ranges.yml

+---
+name: introduce_marker_ranges
+introduced_by_url: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/55669
+rollout_issue_url: https://gitlab.com/gitlab-org/gitlab/-/issues/324068
+milestone: '13.10'
+type: development
+group: group::source code
+default_enabled: false

lib/gitlab/diff/highlight.rb

@@ -3,12 +3,13 @@
 module Gitlab
   module Diff
     class Highlight
-      attr_reader :diff_file, :diff_lines, :raw_lines, :repository
+      attr_reader :diff_file, :diff_lines, :raw_lines, :repository, :project
 
       delegate :old_path, :new_path, :old_sha, :new_sha, to: :diff_file, prefix: :diff
 
       def initialize(diff_lines, repository: nil)
         @repository = repository
+        @project = repository&.project
 
         if diff_lines.is_a?(Gitlab::Diff::File)
           @diff_file = diff_lines
@@ -30,6 +31,12 @@ module Gitlab
 
           if line_inline_diffs = inline_diffs[i]
             begin
+              # MarkerRange objects are converted to Ranges to keep the previous behavior
+              # Issue: https://gitlab.com/gitlab-org/gitlab/-/issues/324068
+              if Feature.disabled?(:introduce_marker_ranges, project, default_enabled: :yaml)
+                line_inline_diffs = line_inline_diffs.map { |marker_range| marker_range.to_range }
+              end
+
               rich_line = InlineDiffMarker.new(diff_line.text, rich_line).mark(line_inline_diffs)
             # This should only happen when the encoding of the diff doesn't
             # match the blob, which is a bug. But we shouldn't fail to render

lib/gitlab/marker_range.rb

@@ -20,6 +20,10 @@ module Gitlab
       @mode = mode
     end
 
+    def to_range
+      Range.new(self.begin, self.end, self.exclude_end?)
+    end
+
     attr_reader :mode
   end
 end

spec/lib/gitlab/diff/highlight_spec.rb

@@ -55,6 +55,18 @@ RSpec.describe Gitlab::Diff::Highlight do
         expect(subject[5].rich_text).to eq(code)
       end
 
+      context 'when introduce_marker_ranges is false' do
+        before do
+          stub_feature_flags(introduce_marker_ranges: false)
+        end
+
+        it 'keeps the old bevavior (without mode classes)' do
+          code = %Q{+<span id="LC9" class="line" lang="ruby">      <span class="k">raise</span> <span class="no"><span class="idiff left">RuntimeError</span></span><span class="p"><span class="idiff">,</span></span><span class="idiff right"> </span><span class="s2">"System commands must be given as an array of strings"</span></span>\n}
+
+          expect(subject[5].rich_text).to eq(code)
+        end
+      end
+
       context 'when no diff_refs' do
         before do
           allow(diff_file).to receive(:diff_refs).and_return(nil)

spec/lib/gitlab/marker_range_spec.rb

@@ -27,6 +27,20 @@ RSpec.describe Gitlab::MarkerRange do
     end
   end
 
+  describe '#to_range' do
+    subject { marker_range.to_range }
+
+    it { is_expected.to eq(first..last) }
+
+    context 'when mode is provided' do
+      let(:mode) { :deletion }
+
+      it 'is omitted during transformation' do
+        is_expected.not_to respond_to(:mode)
+      end
+    end
+  end
+
   describe '.from_range' do
     subject { described_class.from_range(range) }