Fix: A diff comment on a change at last line of a file shows as two comments in discussion

app/helpers/diff_helper.rb

@@ -66,12 +66,12 @@ module DiffHelper
 
     discussions_left = discussions_right = nil
 
-    if left && (left.unchanged? || left.removed?)
+    if left && (left.unchanged? || left.discussable?)
       line_code = diff_file.line_code(left)
       discussions_left = @grouped_diff_discussions[line_code]
     end
 
-    if right && right.added?
+    if right&.discussable?
       line_code = diff_file.line_code(right)
       discussions_right = @grouped_diff_discussions[line_code]
     end

app/views/projects/diffs/_line.html.haml

@@ -3,7 +3,7 @@
 - discussions = local_assigns.fetch(:discussions, nil)
 - type = line.type
 - line_code = diff_file.line_code(line)
-- if discussions && !line.meta?
+- if discussions && line.discussable?
   - line_discussions = discussions[line_code]
 %tr.line_holder{ class: type, id: (line_code unless plain) }
   - case type

lib/gitlab/diff/line.rb

@@ -59,6 +59,10 @@ module Gitlab
         type == 'match'
       end
 
+      def discussable?
+        !['match', 'new-nonewline', 'old-nonewline'].include?(type)
+      end
+
       def as_json(opts = nil)
         {
           type: type,

spec/helpers/diff_helper_spec.rb

@@ -129,6 +129,32 @@ describe DiffHelper do
     end
   end
 
+  describe '#parallel_diff_discussions' do
+    it 'does not put comments on nonewline lines' do
+      discussion = {'abc_3_3' => 'comment'}
+      helper.instance_variable_set(:@grouped_diff_discussions, discussion)
+      diff_file = double(line_code: 'abc_3_3')
+      left = Gitlab::Diff::Line.new('\\nonewline', 'old-nonewline', 3, 3, 3)
+      right = Gitlab::Diff::Line.new('\\nonewline', 'new-nonewline', 3, 3, 3)
+
+      result = helper.parallel_diff_discussions(left, right, diff_file)
+
+      expect(result).to eq([nil, nil])
+    end
+
+    it 'puts comments on added lines' do
+      discussion = {'abc_3_3' => 'comment'}
+      helper.instance_variable_set(:@grouped_diff_discussions, discussion)
+      diff_file = double(line_code: 'abc_3_3')
+      left = Gitlab::Diff::Line.new('\\nonewline', 'old-nonewline', 3, 3, 3)
+      right = Gitlab::Diff::Line.new('new line', 'add', 3, 3, 3)
+
+      result = helper.parallel_diff_discussions(left, right, diff_file)
+
+      expect(result).to eq([nil, 'comment'])
+    end
+  end
+
   describe "#diff_match_line" do
     let(:old_pos) { 40 }
     let(:new_pos) { 50 }