Create DiffFilter and change SystemNoteService#change_title to use Gitlab::Diff::InlineDiff

3 files changed, 43 insertions, 8 deletions

diff --git a/lib/banzai/filter/inline_diff_filter.rb b/lib/banzai/filter/inline_diff_filter.rb
new file mode 100644
index 00000000000..9e75edd4d4c
--- /dev/null
+++ b/lib/banzai/filter/inline_diff_filter.rb
@@ -0,0 +1,22 @@
+module Banzai
+  module Filter
+    class InlineDiffFilter < HTML::Pipeline::Filter
+      IGNORED_ANCESTOR_TAGS = %w(pre code tt).to_set
+
+      def call
+        search_text_nodes(doc).each do |node|
+          next if has_ancestor?(node, IGNORED_ANCESTOR_TAGS)
+
+          content = node.to_html
+          content = content.gsub(/(?:\[\-(.*?)\-\]|\{\-(.*?)\-\})/, '<span class="idiff left right deletion">\1\2</span>')
+          content = content.gsub(/(?:\[\+(.*?)\+\]|\{\+(.*?)\+\})/, '<span class="idiff left right addition">\1\2</span>')
+
+          next if html == content
+
+          node.replace(content)
+        end
+        doc
+      end
+    end
+  end
+end
diff --git a/lib/banzai/pipeline/gfm_pipeline.rb b/lib/banzai/pipeline/gfm_pipeline.rb
index ed3cfd6b023..b27ecf3c923 100644
--- a/lib/banzai/pipeline/gfm_pipeline.rb
+++ b/lib/banzai/pipeline/gfm_pipeline.rb
@@ -23,7 +23,8 @@ module Banzai
           Filter::LabelReferenceFilter,
           Filter::MilestoneReferenceFilter,
 
-          Filter::TaskListFilter
+          Filter::TaskListFilter,
+          Filter::InlineDiffFilter
         ]
       end
 
diff --git a/lib/gitlab/diff/inline_diff_marker.rb b/lib/gitlab/diff/inline_diff_marker.rb
index dccb717e95d..c9601d42d50 100644
--- a/lib/gitlab/diff/inline_diff_marker.rb
+++ b/lib/gitlab/diff/inline_diff_marker.rb
@@ -1,6 +1,11 @@
 module Gitlab
   module Diff
     class InlineDiffMarker
+      MARKDOWN_SYMBOLS = {
+        addition: "+",
+        deletion: "-"
+      }
+
       attr_accessor :raw_line, :rich_line
 
       def initialize(raw_line, rich_line = raw_line)
@@ -8,7 +13,7 @@ module Gitlab
         @rich_line = ERB::Util.html_escape(rich_line)
       end
 
-      def mark(line_inline_diffs)
+      def mark(line_inline_diffs, mode: nil, markdown: false)
         return rich_line unless line_inline_diffs
 
         marker_ranges = []
@@ -20,13 +25,12 @@ module Gitlab
         end
 
         offset = 0
-        # Mark each range
-        marker_ranges.each_with_index do |range, i|
-          class_names = ["idiff"]
-          class_names << "left"   if i == 0
-          class_names << "right"  if i == marker_ranges.length - 1
 
-          offset = insert_around_range(rich_line, range, "<span class='#{class_names.join(" ")}'>", "</span>", offset)
+        # Mark each range
+        marker_ranges.each_with_index do |range, index|
+          before_content = markdown ? "{#{MARKDOWN_SYMBOLS[mode]}" : "<span class='#{html_class_names(marker_ranges, mode, index)}'>"
+          after_content = markdown ? "#{MARKDOWN_SYMBOLS[mode]}}" : "</span>"
+          offset = insert_around_range(rich_line, range, before_content, after_content, offset)
         end
 
         rich_line.html_safe
@@ -34,6 +38,14 @@ module Gitlab
 
       private
 
+      def html_class_names(marker_ranges, mode, index)
+        class_names = ["idiff"]
+        class_names << "left"  if index == 0
+        class_names << "right" if index == marker_ranges.length - 1
+        class_names << mode if mode
+        class_names.join(" ")
+      end
+
       # Mapping of character positions in the raw line, to the rich (highlighted) line
       def position_mapping
         @position_mapping ||= begin