Support selective highlighting of lines

Instead of highlighting all lines when not all of them are
needed, only highlight specific lines.

The `BlobPresenter#highlight` method has been updated to
support `since` and `to` params. These params will be used to
limit the content to be highlighted.

Modify `Gitlab::Highlight` to support `since` param which will
then be used to determine the starting line number.

1 files changed, 8 insertions, 0 deletions

diff --git a/spec/lib/gitlab/highlight_spec.rb b/spec/lib/gitlab/highlight_spec.rb
index 4676db6b8d8..a410e4eab45 100644
--- a/spec/lib/gitlab/highlight_spec.rb
+++ b/spec/lib/gitlab/highlight_spec.rb
@@ -62,6 +62,14 @@ describe Gitlab::Highlight do
       expect(lines[2].text).to eq('        """')
     end
 
+    context 'since param is present' do
+      it 'highlights with the LC starting from "since" param' do
+        lines = described_class.highlight(file_name, content, since: 2).lines
+
+        expect(lines[0]).to include('LC2')
+      end
+    end
+
     context 'diff highlighting' do
       let(:file_name) { 'test.diff' }
       let(:content) { "+aaa\n+bbb\n- ccc\n ddd\n"}