MRF.InlineQuotePolicy: Add link to post URL, not ID

"id" is used for the canonical link to the AS2 representation of an object.
"url" is typically used for the canonical link to the HTTP representation.
It is what we use, for example, when following the "external source" link
in the frontend. However, it's not the link we include in the post contents
for quote posts.

Using URL instead means we include a more user-friendly URL for Mastodon,
and a working (in the browser) URL for Threads

lib/pleroma/web/activity_pub/mrf/inline_quote_policy.ex

@@ -13,7 +13,10 @@ defmodule Pleroma.Web.ActivityPub.MRF.InlineQuotePolicy do
   end
 
   defp resolve_urls(quote_url) do
-    with %Object{} = obj <- Object.normalize(quote_url, fetch: true) do
+    # Fetching here can cause infinite recursion as we run this logic on inbound objects too
+    # This is probably not a problem - its an exceptional corner case for a local user to quote
+    # a post which doesn't exist
+    with %Object{} = obj <- Object.normalize(quote_url, fetch: false) do
       id = obj.data["id"]
       url = Map.get(obj.data, "url", id)
       {id, url, [id, url, quote_url]}

test/pleroma/web/activity_pub/mrf/inline_quote_policy_test.exs

@@ -4,6 +4,7 @@
 
 defmodule Pleroma.Web.ActivityPub.MRF.InlineQuotePolicyTest do
   alias Pleroma.Web.ActivityPub.MRF.InlineQuotePolicy
+  alias Pleroma.Object
   use Pleroma.DataCase
 
   setup_all do
@@ -24,6 +25,9 @@ defmodule Pleroma.Web.ActivityPub.MRF.InlineQuotePolicyTest do
       }
     }
 
+    # Prefetch the quoted post
+    %Object{} = Object.normalize(quote_url, fetch: true)
+
     {:ok, %{"object" => %{"content" => filtered}}} = InlineQuotePolicy.filter(activity)
 
     assert filtered ==