fix(instances): record the instance when refreshing known users too

Hosts without a row (IPv6 literals skipped by the backfill, rows deleted
later) were never added again, because known users take the update path.

lib/pleroma/web/activity_pub/activity_pub.ex

@@ -2058,6 +2058,8 @@ defmodule Pleroma.Web.ActivityPub.ActivityPub do
   def make_user_from_ap_id(ap_id, additional \\ []) do
     with {:ok, data} <- fetch_and_prepare_user_from_ap_id(ap_id, additional) do
       enqueue_pin_fetches(data)
+      # Keeps the instances table complete, so it can list our peers.
+      Instance.ensure_exists(data.ap_id)
 
       # the fetched actor's id differs from ap_id when it was fetched from a display URL
       user = User.get_cached_by_ap_id(data.ap_id)
@@ -2069,11 +2071,10 @@ defmodule Pleroma.Web.ActivityPub.ActivityPub do
       else
         maybe_handle_clashing_nickname(data)
 
-        with {:ok, user} <- data |> User.remote_user_changeset() |> Repo.insert() do
-          # Keeps the instances table complete, so it can list our peers.
-          Instance.ensure_exists(user.ap_id)
-          User.set_cache({:ok, user})
-        end
+        data
+        |> User.remote_user_changeset()
+        |> Repo.insert()
+        |> User.set_cache()
       end
     end
   end

test/pleroma/web/activity_pub/activity_pub_test.exs

@@ -193,6 +193,15 @@ defmodule Pleroma.Web.ActivityPub.ActivityPubTest do
                Repo.get_by(Pleroma.Instances.Instance, host: "mastodon.example.org")
     end
 
+    test "it records the instance of a known user when refreshing it" do
+      insert(:user, local: false, ap_id: "http://mastodon.example.org/users/admin")
+      refute Repo.get_by(Pleroma.Instances.Instance, host: "mastodon.example.org")
+
+      {:ok, _user} = ActivityPub.make_user_from_ap_id("http://mastodon.example.org/users/admin")
+
+      assert Repo.get_by(Pleroma.Instances.Instance, host: "mastodon.example.org")
+    end
+
     test "it keeps an existing instance record" do
       unreachable_since = ~N[2020-01-01 00:00:00.000000]
       insert(:instance, host: "mastodon.example.org", unreachable_since: unreachable_since)