Fix bug where notes weren’t shown in discussion when the code had changed after creation

app/models/concerns/note_on_diff.rb

@@ -17,6 +17,10 @@ module NoteOnDiff
     raise NotImplementedError
   end
+  def original_line_code
+    raise NotImplementedError
+  end
+
   def diff_attributes
     raise NotImplementedError
   end

app/models/diff_note.rb

@@ -57,6 +57,10 @@ class DiffNote < Note
     diff_file.position(line) == self.original_position
   end
+  def original_line_code
+    self.diff_file.line_code(self.diff_line)
+  end
+
   def active?(diff_refs = nil)
     return false unless supported?
     return true if for_commit?

app/models/discussion.rb

@@ -12,6 +12,7 @@ class Discussion
             :for_merge_request?,
             :line_code,
+            :original_line_code,
             :diff_file,
             :for_line?,
             :active?,

app/models/legacy_diff_note.rb

@@ -49,6 +49,10 @@ class LegacyDiffNote < Note
     !line.meta? && diff_file.line_code(line) == self.line_code
   end
+  def original_line_code
+    self.line_code
+  end
+
   # Check if this note is part of an "active" discussion
   #
   # This will always return true for anything except MergeRequest noteables,

app/views/discussions/_diff_with_notes.html.haml

@@ -7,7 +7,7 @@
   .diff-content.code.js-syntax-highlight
     %table
-      - discussions = { discussion.line_code => discussion }
+      - discussions = { discussion.original_line_code => discussion }
       = render partial: "projects/diffs/line",
         collection: discussion.truncated_diff_lines,
         as: :line,