Ensure replied-to is a status not a boost (mastodon#9129)

* Ensure replied-to is a status not a boost

* Consider case of not a reply

* Add test case for replying to boost

* Move reblog-reply resolution to model

* Remove unnecessary comment

app/models/status.rb

@@ -448,6 +448,8 @@ def set_visibility
   end
 
   def set_conversation
+    self.thread = thread.reblog if thread&.reblog?
+
     self.reply = !(in_reply_to_id.nil? && thread.nil?) unless reply
 
     if reply? && !thread.nil?

spec/services/post_status_service_spec.rb

@@ -25,6 +25,19 @@
     expect(status.thread).to eq in_reply_to_status
   end
 
+  it 'creates response to the original status of boost' do
+    boosted_status = Fabricate(:status)
+    in_reply_to_status = Fabricate(:status, reblog: boosted_status)
+    account = Fabricate(:account)
+    text = "test status update"
+
+    status = subject.call(account, text, in_reply_to_status)
+
+    expect(status).to be_persisted
+    expect(status.text).to eq text
+    expect(status.thread).to eq boosted_status
+  end
+
   it 'creates a sensitive status' do
     status = create_status_with_options(sensitive: true)