Cache highlighted diff lines for merge requests

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

4 files changed, 15 insertions, 11 deletions

diff --git a/app/controllers/concerns/diff_for_path.rb b/app/controllers/concerns/diff_for_path.rb
index 026d8b2e1e0..aeec3009f15 100644
--- a/app/controllers/concerns/diff_for_path.rb
+++ b/app/controllers/concerns/diff_for_path.rb
@@ -1,8 +1,8 @@
 module DiffForPath
   extend ActiveSupport::Concern
 
-  def render_diff_for_path(diffs, diff_refs, project)
-    diff_file = safe_diff_files(diffs, diff_refs: diff_refs, repository: project.repository).find do |diff|
+  def render_diff_for_path(diffs)
+    diff_file = diffs.diff_files.find do |diff|
       diff.old_path == params[:old_path] && diff.new_path == params[:new_path]
     end
 
@@ -14,7 +14,7 @@ module DiffForPath
     locals = {
       diff_file: diff_file,
       diff_commit: diff_commit,
-      diff_refs: diff_refs,
+      diff_refs: diffs.diff_refs,
       blob: blob,
       project: project
     }
diff --git a/app/controllers/projects/commit_controller.rb b/app/controllers/projects/commit_controller.rb
index 7ae034f9398..6060b6e55bc 100644
--- a/app/controllers/projects/commit_controller.rb
+++ b/app/controllers/projects/commit_controller.rb
@@ -28,7 +28,7 @@ class Projects::CommitController < Projects::ApplicationController
   end
 
   def diff_for_path
-    render_diff_for_path(@diffs, @commit.diff_refs, @project)
+    render_diff_for_path(SafeDiffs::Commit.new(@commit, diff_options: diff_options))
   end
 
   def builds
@@ -110,7 +110,7 @@ class Projects::CommitController < Projects::ApplicationController
     opts = diff_options
     opts[:ignore_whitespace_change] = true if params[:format] == 'diff'
 
-    @diffs = commit.diffs(opts)
+    @diffs = SafeDiffs::Commit.new(commit, diff_options: opts)
     @notes_count = commit.notes.count
   end
 
diff --git a/app/controllers/projects/compare_controller.rb b/app/controllers/projects/compare_controller.rb
index 8c004724f02..2eda950a1bd 100644
--- a/app/controllers/projects/compare_controller.rb
+++ b/app/controllers/projects/compare_controller.rb
@@ -21,7 +21,7 @@ class Projects::CompareController < Projects::ApplicationController
   def diff_for_path
     return render_404 unless @compare
 
-    render_diff_for_path(@diffs, @diff_refs, @project)
+    render_diff_for_path(SafeDiffs::Compare.new(@compare, project: @project, diff_options: diff_options))
   end
 
   def create
@@ -46,12 +46,12 @@ class Projects::CompareController < Projects::ApplicationController
       @commit = @project.commit(@head_ref)
       @base_commit = @project.merge_base_commit(@start_ref, @head_ref)
 
-      @diffs = @compare.diffs(diff_options)
-      @diff_refs = Gitlab::Diff::DiffRefs.new(
+      diff_refs = Gitlab::Diff::DiffRefs.new(
         base_sha: @base_commit.try(:sha),
         start_sha: @start_commit.try(:sha),
         head_sha: @commit.try(:sha)
       )
+      @diffs = SafeDiffs::Compare.new(@compare, project: @project, diff_options: diff_options, diff_refs: diff_refs)
 
       @diff_notes_disabled = true
       @grouped_diff_discussions = {}
diff --git a/app/controllers/projects/merge_requests_controller.rb b/app/controllers/projects/merge_requests_controller.rb
index 116e7904a4e..78a6a3c5715 100644
--- a/app/controllers/projects/merge_requests_controller.rb
+++ b/app/controllers/projects/merge_requests_controller.rb
@@ -103,9 +103,8 @@ class Projects::MergeRequestsController < Projects::ApplicationController
     end
 
     define_commit_vars
-    diffs = @merge_request.diffs(diff_options)
 
-    render_diff_for_path(diffs, @merge_request.diff_refs, @merge_request.project)
+    render_diff_for_path(SafeDiffs::MergeRequest.new(merge_request, diff_options: diff_options))
   end
 
   def commits
@@ -153,7 +152,12 @@ class Projects::MergeRequestsController < Projects::ApplicationController
     @commits = @merge_request.compare_commits.reverse
     @commit = @merge_request.diff_head_commit
     @base_commit = @merge_request.diff_base_commit
-    @diffs = @merge_request.compare.diffs(diff_options) if @merge_request.compare
+    if @merge_request.compare
+      @diffs = SafeDiffs::Compare.new(@merge_request.compare,
+        project:      @merge_request.project,
+        diff_refs:    @merge_request.diff_refs,
+        diff_options: diff_options)
+    end
     @diff_notes_disabled = true
 
     @pipeline = @merge_request.pipeline