Ensure replying to an individual note by email creates a note with its own discussion ID

app/models/individual_note_discussion.rb

@@ -10,4 +10,8 @@ class IndividualNoteDiscussion < Discussion
   def individual_note?
     true
   end
+
+  def reply_attributes
+    super.tap { |attrs| attrs.delete(:discussion_id) }
+  end
 end

app/models/out_of_context_discussion.rb

@@ -19,4 +19,8 @@ class OutOfContextDiscussion < Discussion
   def self.note_class
     Note
   end
+
+  def reply_attributes
+    super.tap { |attrs| attrs.delete(:discussion_id) }
+  end
 end

changelogs/unreleased/dm-fix-individual-notes-reply-attributes.yml

+---
+title: Ensure replying to an individual note by email creates a note with its own
+  discussion ID
+merge_request:
+author:

spec/models/sent_notification_spec.rb

@@ -69,6 +69,7 @@ describe SentNotification, model: true do
       it 'creates a comment on the issue' do
         new_note = subject.create_reply('Test')
         expect(new_note.in_reply_to?(note)).to be_truthy
+        expect(new_note.discussion_id).not_to eq(note.discussion_id)
       end
     end
 
@@ -79,6 +80,7 @@ describe SentNotification, model: true do
       it 'creates a reply on the discussion' do
         new_note = subject.create_reply('Test')
         expect(new_note.in_reply_to?(note)).to be_truthy
+        expect(new_note.discussion_id).to eq(note.discussion_id)
       end
     end
 
@@ -99,6 +101,7 @@ describe SentNotification, model: true do
       it 'creates a comment on the merge request' do
         new_note = subject.create_reply('Test')
         expect(new_note.in_reply_to?(note)).to be_truthy
+        expect(new_note.discussion_id).not_to eq(note.discussion_id)
       end
     end
 
@@ -109,6 +112,7 @@ describe SentNotification, model: true do
       it 'creates a reply on the discussion' do
         new_note = subject.create_reply('Test')
         expect(new_note.in_reply_to?(note)).to be_truthy
+        expect(new_note.discussion_id).to eq(note.discussion_id)
       end
     end
 
@@ -119,6 +123,7 @@ describe SentNotification, model: true do
       it 'creates a reply on the discussion' do
         new_note = subject.create_reply('Test')
         expect(new_note.in_reply_to?(note)).to be_truthy
+        expect(new_note.discussion_id).to eq(note.discussion_id)
       end
     end
 
@@ -140,6 +145,7 @@ describe SentNotification, model: true do
       it 'creates a comment on the commit' do
         new_note = subject.create_reply('Test')
         expect(new_note.in_reply_to?(note)).to be_truthy
+        expect(new_note.discussion_id).not_to eq(note.discussion_id)
       end
     end
 
@@ -150,6 +156,7 @@ describe SentNotification, model: true do
       it 'creates a reply on the discussion' do
         new_note = subject.create_reply('Test')
         expect(new_note.in_reply_to?(note)).to be_truthy
+        expect(new_note.discussion_id).to eq(note.discussion_id)
       end
     end
 
@@ -160,6 +167,7 @@ describe SentNotification, model: true do
       it 'creates a reply on the discussion' do
         new_note = subject.create_reply('Test')
         expect(new_note.in_reply_to?(note)).to be_truthy
+        expect(new_note.discussion_id).to eq(note.discussion_id)
       end
     end
   end