Support selective highlighting of lines65152-selective-highlight

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.

2 files changed, 8 insertions, 7 deletions

diff --git a/lib/gitlab/highlight.rb b/lib/gitlab/highlight.rb
index 381f1dd4e55..1f49a26f0a2 100644
--- a/lib/gitlab/highlight.rb
+++ b/lib/gitlab/highlight.rb
@@ -6,15 +6,16 @@ module Gitlab
     TIMEOUT_FOREGROUND = 3.seconds
     MAXIMUM_TEXT_HIGHLIGHT_SIZE = 1.megabyte
 
-    def self.highlight(blob_name, blob_content, language: nil, plain: false)
-      new(blob_name, blob_content, language: language)
+    def self.highlight(blob_name, blob_content, since: nil, language: nil, plain: false)
+      new(blob_name, blob_content, since: since, language: language)
         .highlight(blob_content, continue: false, plain: plain)
     end
 
     attr_reader :blob_name
 
-    def initialize(blob_name, blob_content, language: nil)
+    def initialize(blob_name, blob_content, since: nil, language: nil)
       @formatter = Rouge::Formatters::HTMLGitlab
+      @since = since
       @language = language
       @blob_name = blob_name
       @blob_content = blob_content
@@ -53,13 +54,13 @@ module Gitlab
     end
 
     def highlight_plain(text)
-      @formatter.format(Rouge::Lexers::PlainText.lex(text)).html_safe
+      @formatter.format(Rouge::Lexers::PlainText.lex(text), since: @since).html_safe
     end
 
     def highlight_rich(text, continue: true)
       tag = lexer.tag
       tokens = lexer.lex(text, continue: continue)
-      Timeout.timeout(timeout_time) { @formatter.format(tokens, tag: tag).html_safe }
+      Timeout.timeout(timeout_time) { @formatter.format(tokens, tag: tag, since: @since).html_safe }
     rescue Timeout::Error => e
       Gitlab::Sentry.track_exception(e)
       highlight_plain(text)
diff --git a/lib/rouge/formatters/html_gitlab.rb b/lib/rouge/formatters/html_gitlab.rb
index e2a7d3ef5ba..0d4ac504428 100644
--- a/lib/rouge/formatters/html_gitlab.rb
+++ b/lib/rouge/formatters/html_gitlab.rb
@@ -8,8 +8,8 @@ module Rouge
       # Creates a new <tt>Rouge::Formatter::HTMLGitlab</tt> instance.
       #
       # [+tag+]     The tag (language) of the lexer used to generate the formatted tokens
-      def initialize(tag: nil)
-        @line_number = 1
+      def initialize(tag: nil, since: nil)
+        @line_number = since || 1
         @tag = tag
       end