Convert OStatus tag to ActivityPub id on in_reply_to resolution (#4756)

app/lib/ostatus/activity/base.rb

@@ -56,6 +56,16 @@ class OStatus::Activity::Base
     Status.find_by(uri: uri)
   end
 
+  def find_activitypub_status(uri, href)
+    tag_matches = /tag:([^,:]+)[^:]*:objectId=([\d]+)/.match(uri)
+    href_matches = %r{/users/([^/]+)}.match(href)
+
+    unless tag_matches.nil? || href_matches.nil?
+      uri = "https://#{tag_matches[1]}/users/#{href_matches[1]}/statuses/#{tag_matches[2]}"
+      Status.find_by(uri: uri)
+    end
+  end
+
   def redis
     Redis.current
   end

app/lib/ostatus/activity/creation.rb

@@ -36,7 +36,7 @@ class OStatus::Activity::Creation < OStatus::Activity::Base
         language: content_language,
         visibility: visibility_scope,
         conversation: find_or_create_conversation,
-        thread: thread? ? find_status(thread.first) : nil
+        thread: thread? ? find_status(thread.first) || find_activitypub_status(thread.first, thread.second) : nil
       )
 
       save_mentions(status)