Remove duplication around highlighting.

app/helpers/blob_helper.rb

 module BlobHelper
-  def rouge_formatter(options = {})
-    default_options = {
-      nowrap: false,
-      cssclass: 'code highlight',
-      lineanchors: true,
-      lineanchorsid: 'LC'
-    }
-
-    Rouge::Formatters::HTMLGitlab.new(default_options.merge!(options))
-  end
-
   def highlight(blob_name, blob_content, nowrap: false, continue: false)
-    formatter = rouge_formatter(nowrap: nowrap)
-
-    @lexer ||= Rouge::Lexer.guess(filename: blob_name, source: blob_content).new rescue Rouge::Lexers::PlainText
-    formatter.format(@lexer.lex(blob_content, continue: continue)).html_safe
+    Gitlab::Highlight.highlight(blob_name, blob_content, nowrap: nowrap, continue: continue)
   end
 
   def no_highlight_files

lib/gitlab/diff/highlight.rb

@@ -20,18 +20,7 @@ module Gitlab
         blob = repository.blob_at(ref, file_name)
         return [] unless blob
 
-        content = blob.data
-        lexer = Rouge::Lexer.guess(filename: file_name, source: content).new rescue Rouge::Lexers::PlainText.new
-        formatter.format(lexer.lex(content)).lines.map!(&:html_safe)
-      end
-
-      def self.formatter
-        @formatter ||= Rouge::Formatters::HTMLGitlab.new(
-          nowrap: true,
-          cssclass: 'code highlight',
-          lineanchors: true,
-          lineanchorsid: 'LC'
-        )
+        Gitlab::Highlight.highlight(file_name, blob.data).lines.map!(&:html_safe)
       end
 
       def initialize(diff_file)

lib/gitlab/highlight.rb

+module Gitlab
+  class Highlight
+    def self.highlight(blob_name, blob_content, nowrap: true, continue: false)
+      formatter = rouge_formatter(nowrap: nowrap)
+
+      lexer = Rouge::Lexer.guess(filename: blob_name, source: blob_content).new rescue Rouge::Lexers::PlainText
+      formatter.format(lexer.lex(blob_content, continue: continue)).html_safe
+    end
+
+    private
+
+    def self.rouge_formatter(options = {})
+      options = options.reverse_merge(
+        nowrap: true,
+        cssclass: 'code highlight',
+        lineanchors: true,
+        lineanchorsid: 'LC'
+      )
+
+      Rouge::Formatters::HTMLGitlab.new(options)
+    end
+  end
+end