Merge branch 'bad-mrf' into 'develop'

Startup detection for configured MRF modules that are missing or incorrectly defined

See merge request pleroma/pleroma!4110

changelog.d/missing-mrfs.add

@@ -0,0 +1 @@
+Startup detection for configured MRF modules that are missing or incorrectly defined

lib/pleroma/application_requirements.ex

@@ -28,6 +28,7 @@ def verify! do
     |> check_welcome_message_config!()
     |> check_rum!()
     |> check_repo_pool_size!()
+    |> check_mrfs()
     |> handle_result()
   end
 
@@ -234,4 +235,25 @@ defp check_filter(filter, command_required) do
       true
     end
   end
+
+  defp check_mrfs(:ok) do
+    mrfs = Config.get!([:mrf, :policies])
+
+    missing_mrfs =
+      Enum.reduce(mrfs, [], fn x, acc ->
+        if Code.ensure_compiled(x) do
+          acc
+        else
+          acc ++ [x]
+        end
+      end)
+
+    if Enum.empty?(missing_mrfs) do
+      :ok
+    else
+      {:error, "The following MRF modules are configured but missing: #{inspect(missing_mrfs)}"}
+    end
+  end
+
+  defp check_mrfs(result), do: result
 end