Detect MarkerRanges for word-diff mode

Contributes to https://gitlab.com/gitlab-org/gitlab/-/issues/16950

Follow-up for
https://gitlab.com/gitlab-org/gitlab/-/merge_requests/55105

Extend to Gitlab::WordDiff::ChunkCollection class to generate
`marker_ranges` based on chunks received from `git diff
--word-diff=porcelain` output.

Each chunk can be an unchanged string (starts with ` `), new
string (starts with `+`) or removed string (starts with `-`).

While parsing we collect chunks until we receive a newline
delimiter. Then we are combining them together to generate
Gitlab::Diff::Line object and assign MarkerRanges for changed parts of
the diff line.

lib/gitlab/marker_range.rb

@@ -24,6 +24,12 @@ def to_range
       Range.new(self.begin, self.end, self.exclude_end?)
     end
+    def ==(other)
+      return false unless other.is_a?(self.class)
+
+      self.mode == other.mode && super
+    end
+
     attr_reader :mode
   end
 end

lib/gitlab/word_diff/chunk_collection.rb

@@ -18,6 +18,27 @@ def content
       def reset
         @chunks = []
       end
+
+      def marker_ranges
+        start = 0
+
+        @chunks.each_with_object([]) do |element, ranges|
+          mode = mode_for_element(element)
+
+          ranges << Gitlab::MarkerRange.new(start, start + element.length - 1, mode: mode) if mode
+
+          start += element.length
+        end
+      end
+
+      private
+
+      def mode_for_element(element)
+        return Gitlab::MarkerRange::DELETION if element.removed?
+        return Gitlab::MarkerRange::ADDITION if element.added?
+
+        nil
+      end
     end
   end
 end

lib/gitlab/word_diff/parser.rb

@@ -31,7 +31,7 @@ def parse(lines, diff_file: nil)
               @chunks.add(segment)
             when Segments::Newline
-              yielder << build_line(@chunks.content, nil, parent_file: diff_file)
+              yielder << build_line(@chunks.content, nil, parent_file: diff_file).tap { |line| line.set_marker_ranges(@chunks.marker_ranges) }
               @chunks.reset
               counter.increase_pos_num

spec/lib/gitlab/diff/char_diff_spec.rb

@@ -49,15 +49,15 @@
         old_diffs, new_diffs = subject
         expect(old_diffs).to eq([])
-        expect(new_diffs).to eq([0..12])
+        expect(new_diffs).to eq([Gitlab::MarkerRange.new(0, 12, mode: :addition)])
       end
     end
     it 'returns ranges of changes' do
       old_diffs, new_diffs = subject
-      expect(old_diffs).to eq([11..11])
-      expect(new_diffs).to eq([3..3])
+      expect(old_diffs).to eq([Gitlab::MarkerRange.new(11, 11, mode: :deletion)])
+      expect(new_diffs).to eq([Gitlab::MarkerRange.new(3, 3, mode: :addition)])
     end
   end

spec/lib/gitlab/marker_range_spec.rb

@@ -9,7 +9,7 @@
   let(:last) { 10 }
   let(:mode) { nil }
-  it { is_expected.to eq(first..last) }
+  it { expect(marker_range.to_range).to eq(first..last) }
   it 'behaves like a Range' do
     is_expected.to be_kind_of(Range)
@@ -51,14 +51,14 @@
     end
     it 'keeps correct range' do
-      is_expected.to eq(range)
+      is_expected.to eq(described_class.new(1, 3))
     end
     context 'when range excludes end' do
       let(:range) { 1...3 }
       it 'keeps correct range' do
-        is_expected.to eq(range)
+        is_expected.to eq(described_class.new(1, 3, exclude_end: true))
       end
     end
@@ -68,4 +68,31 @@
       it { is_expected.to be(marker_range) }
     end
   end
+
+  describe '#==' do
+    subject { default_marker_range == another_marker_range }
+
+    let(:default_marker_range) { described_class.new(0, 1, mode: :addition) }
+    let(:another_marker_range) { default_marker_range }
+
+    it { is_expected.to be_truthy }
+
+    context 'when marker ranges have different modes' do
+      let(:another_marker_range) { described_class.new(0, 1, mode: :deletion) }
+
+      it { is_expected.to be_falsey }
+    end
+
+    context 'when marker ranges have different ranges' do
+      let(:another_marker_range) { described_class.new(0, 2, mode: :addition) }
+
+      it { is_expected.to be_falsey }
+    end
+
+    context 'when marker ranges is a simple range' do
+      let(:another_marker_range) { (0..1) }
+
+      it { is_expected.to be_falsey }
+    end
+  end
 end

spec/lib/gitlab/word_diff/chunk_collection_spec.rb

@@ -41,4 +41,27 @@
       expect(collection.content).to eq('')
     end
   end
+
+  describe '#marker_ranges' do
+    let(:chunks) do
+      [
+        Gitlab::WordDiff::Segments::Chunk.new(' Hello '),
+        Gitlab::WordDiff::Segments::Chunk.new('-World'),
+        Gitlab::WordDiff::Segments::Chunk.new('+GitLab'),
+        Gitlab::WordDiff::Segments::Chunk.new('+!!!')
+      ]
+    end
+
+    it 'returns marker ranges for every chunk with changes' do
+      chunks.each { |chunk| collection.add(chunk) }
+
+      expect(collection.marker_ranges).to eq(
+        [
+          Gitlab::MarkerRange.new(6, 10, mode: :deletion),
+          Gitlab::MarkerRange.new(11, 16, mode: :addition),
+          Gitlab::MarkerRange.new(17, 19, mode: :addition)
+        ]
+      )
+    end
+  end
 end

spec/lib/gitlab/word_diff/parser_spec.rb

@@ -36,15 +36,26 @@
       aggregate_failures do
         expect(diff_lines.count).to eq(7)
-        expect(diff_lines.map(&:to_hash)).to match_array(
+        expect(diff_lines.map { |line| diff_line_attributes(line) }).to eq(
           [
-            a_hash_including(index: 0, old_pos: 1, new_pos: 1, text: '', type: nil),
-            a_hash_including(index: 1, old_pos: 2, new_pos: 2, text: 'Unchanged line', type: nil),
-            a_hash_including(index: 2, old_pos: 3, new_pos: 3, text: '', type: nil),
-            a_hash_including(index: 3, old_pos: 4, new_pos: 4, text: 'Old changeNew addition unchanged content', type: nil),
-            a_hash_including(index: 4, old_pos: 50, new_pos: 50, text: '@@ -50,14 +50,13 @@', type: 'match'),
-            a_hash_including(index: 5, old_pos: 50, new_pos: 50, text: 'First change same same same_removed_added_end of the line', type: nil),
-            a_hash_including(index: 6, old_pos: 51, new_pos: 51, text: '', type: nil)
+            { index: 0, old_pos: 1, new_pos: 1, text: '', type: nil, marker_ranges: [] },
+            { index: 1, old_pos: 2, new_pos: 2, text: 'Unchanged line', type: nil, marker_ranges: [] },
+            { index: 2, old_pos: 3, new_pos: 3, text: '', type: nil, marker_ranges: [] },
+            { index: 3, old_pos: 4, new_pos: 4, text: 'Old changeNew addition unchanged content', type: nil,
+                             marker_ranges: [
+                               Gitlab::MarkerRange.new(0, 9, mode: :deletion),
+                               Gitlab::MarkerRange.new(10, 21, mode: :addition)
+                             ] },
+
+            { index: 4, old_pos: 50, new_pos: 50, text: '@@ -50,14 +50,13 @@', type: 'match', marker_ranges: [] },
+            { index: 5, old_pos: 50, new_pos: 50, text: 'First change same same same_removed_added_end of the line', type: nil,
+                             marker_ranges: [
+                               Gitlab::MarkerRange.new(0, 11, mode: :addition),
+                               Gitlab::MarkerRange.new(28, 35, mode: :deletion),
+                               Gitlab::MarkerRange.new(36, 41, mode: :addition)
+                             ] },
+
+            { index: 6, old_pos: 51, new_pos: 51, text: '', type: nil, marker_ranges: [] }
           ]
         )
       end
@@ -64,4 +75,17 @@
       it { is_expected.to eq([]) }
     end
   end
+
+  private
+
+  def diff_line_attributes(diff_line)
+    {
+      index: diff_line.index,
+      old_pos: diff_line.old_pos,
+      new_pos: diff_line.new_pos,
+      text: diff_line.text,
+      type: diff_line.type,
+      marker_ranges: diff_line.marker_ranges
+    }
+  end
 end