Cache highlighted diff lines for merge requests

Introducing the concept of SafeDiffs which relates 
diffs with UI highlighting.

3 files changed, 22 insertions, 4 deletions

diff --git a/lib/gitlab/diff/file.rb b/lib/gitlab/diff/file.rb
index b09ca1fb8b0..77b3798d78f 100644
--- a/lib/gitlab/diff/file.rb
+++ b/lib/gitlab/diff/file.rb
@@ -63,15 +63,18 @@ module Gitlab
         diff_refs.try(:head_sha)
       end
 
+      attr_writer :diff_lines, :highlighted_diff_lines
+
       # Array of Gitlab::Diff::Line objects
       def diff_lines
-        @lines ||= Gitlab::Diff::Parser.new.parse(raw_diff.each_line).to_a
+        @diff_lines ||= Gitlab::Diff::Parser.new.parse(raw_diff.each_line).to_a
       end
 
       def highlighted_diff_lines
         @highlighted_diff_lines ||= Gitlab::Diff::Highlight.new(self, repository: self.repository).highlight
       end
 
+      # Array[<Hash>] with right/left keys that contains Gitlab::Diff::Line objects which text is hightlighted
       def parallel_diff_lines
         @parallel_diff_lines ||= Gitlab::Diff::ParallelDiff.new(self).parallelize
       end
diff --git a/lib/gitlab/diff/highlight.rb b/lib/gitlab/diff/highlight.rb
index 649a265a02c..9ea976e18fa 100644
--- a/lib/gitlab/diff/highlight.rb
+++ b/lib/gitlab/diff/highlight.rb
@@ -40,8 +40,6 @@ module Gitlab
       def highlight_line(diff_line)
         return unless diff_file && diff_file.diff_refs
 
-        line_prefix = diff_line.text.match(/\A(.)/) ? $1 : ' '
-
         rich_line =
           if diff_line.unchanged? || diff_line.added?
             new_lines[diff_line.new_pos - 1]
@@ -51,7 +49,10 @@ module Gitlab
 
         # Only update text if line is found. This will prevent
         # issues with submodules given the line only exists in diff content.
-        "#{line_prefix}#{rich_line}".html_safe if rich_line
+        if rich_line
+          line_prefix = diff_line.text.match(/\A(.)/) ? $1 : ' '
+          "#{line_prefix}#{rich_line}".html_safe
+        end
       end
 
       def inline_diffs
diff --git a/lib/gitlab/diff/line.rb b/lib/gitlab/diff/line.rb
index c6189d660c2..cf097e0d0de 100644
--- a/lib/gitlab/diff/line.rb
+++ b/lib/gitlab/diff/line.rb
@@ -9,6 +9,20 @@ module Gitlab
         @old_pos, @new_pos = old_pos, new_pos
       end
 
+      def self.init_from_hash(hash)
+        new(hash[:text], hash[:type], hash[:index], hash[:old_pos], hash[:new_pos])
+      end
+
+      def serialize_keys
+        @serialize_keys ||= %i(text type index old_pos new_pos)
+      end
+
+      def to_hash
+        hash = {}
+        serialize_keys.each { |key| hash[key] = send(key) }
+        hash
+      end
+
       def old_line
         old_pos unless added? || meta?
       end