2 files changed, 92 insertions, 0 deletions
diff --git a/lib/gitlab/diff/suggestion_diff.rb b/lib/gitlab/diff/suggestion_diff.rb
new file mode 100644
index 00000000000..ee153c226b7
--- /dev/null
+++ b/lib/gitlab/diff/suggestion_diff.rb
@@ -0,0 +1,37 @@
+# frozen_string_literal: true
+
+module Gitlab
+  module Diff
+    class SuggestionDiff
+      include Gitlab::Utils::StrongMemoize
+
+      delegate :from_content, :to_content, :from_line, to: :@suggestible
+
+      def initialize(suggestible)
+        @suggestible = suggestible
+      end
+
+      def diff_lines
+        Gitlab::Diff::Parser.new.parse(raw_diff.each_line).to_a
+      end
+
+      private
+
+      def raw_diff
+        "#{diff_header}\n#{from_content_as_diff}#{to_content_as_diff}"
+      end
+
+      def diff_header
+        "@@ -#{from_line} +#{from_line}"
+      end
+
+      def from_content_as_diff
+        from_content.lines.map { |line| line.prepend('-') }.join
+      end
+
+      def to_content_as_diff
+        to_content.lines.map { |line| line.prepend('+') }.join
+      end
+    end
+  end
+end
diff --git a/spec/lib/gitlab/diff/suggestion_diff_spec.rb b/spec/lib/gitlab/diff/suggestion_diff_spec.rb
new file mode 100644
index 00000000000..5a32c2bea37
--- /dev/null
+++ b/spec/lib/gitlab/diff/suggestion_diff_spec.rb
@@ -0,0 +1,55 @@
+# frozen_string_literal: true
+
+require 'spec_helper'
+
+describe Gitlab::Diff::SuggestionDiff do
+  describe '#diff_lines' do
+    let(:from_content) do
+      <<-BLOB.strip_heredoc
+         "tags": ["devel", "development", "nightly"],
+         "desktop-file-name-prefix": "(Development) ",
+         "finish-args": "foo",
+      BLOB
+    end
+
+    let(:to_content) do
+      <<-BLOB.strip_heredoc
+         "buildsystem": "meson",
+         "builddir": true,
+         "name": "nautilus",
+         "bar": "bar",
+      BLOB
+    end
+
+    let(:suggestion) do
+      instance_double(Suggestion, from_line: 12,
+                                  from_content: from_content,
+                                  to_content: to_content)
+    end
+
+    subject { described_class.new(suggestion).diff_lines }
+
+    let(:expected_diff_lines) do
+      [
+        { old_pos: 12, new_pos: 12, type: "match", text: "@@ -12 +12" },
+        { old_pos: 12, new_pos: 12, type: "old", text: "-\"tags\": [\"devel\", \"development\", \"nightly\"]," },
+        { old_pos: 13, new_pos: 12, type: "old", text: "-\"desktop-file-name-prefix\": \"(Development) \"," },
+        { old_pos: 14, new_pos: 12, type: "old", text: "-\"finish-args\": \"foo\"," },
+        { old_pos: 15, new_pos: 12, type: "new", text: "+\"buildsystem\": \"meson\"," },
+        { old_pos: 15, new_pos: 13, type: "new", text: "+\"builddir\": true," },
+        { old_pos: 15, new_pos: 14, type: "new", text: "+\"name\": \"nautilus\"," },
+        { old_pos: 15, new_pos: 15, type: "new", text: "+\"bar\": \"bar\"," }
+      ]
+    end
+
+    it 'returns diff lines with correct line numbers' do
+      diff_lines = subject
+
+      expect(diff_lines).to all(be_a(Gitlab::Diff::Line))
+
+      expected_diff_lines.each_with_index do |expected_line, index|
+        expect(diff_lines[index].to_hash).to include(expected_line)
+      end
+    end
+  end
+end