chore: a few small error case improvements

lib/ash/code_interface.ex

@@ -31,7 +31,17 @@ defmodule Ash.CodeInterface do
           {:argument, argument}
       end
 
-    if !field.allow_nil? do
+    cond do
+      field.allow_nil? && !(field.name in Map.get(action, :require_attributes, [])) ->
+        :ok
+
+      field.name in Map.get(action, :allow_nil_input, []) ->
+        :ok
+
+      !(field.name in Map.get(action, :accept, [])) ->
+        :ok
+
+      true ->
         raise "Code interface for #{action.name} has optional argument #{key} but it is not optional"
     end
 

lib/ash/engine/engine.ex

@@ -255,6 +255,7 @@ defmodule Ash.Engine do
   def must_be_local?(request) do
     [request.resource | request.touches_resources || []]
     |> Enum.filter(& &1)
+    |> Enum.filter(&is_atom/1)
     |> Enum.any?(fn resource ->
       (Ash.DataLayer.data_layer_can?(resource, :transact) &&
          Ash.DataLayer.in_transaction?(resource)) ||

lib/ash/resource.ex

@@ -113,6 +113,10 @@ defmodule Ash.Resource do
       end
 
       if api = Ash.Resource.Info.define_interface_for(__MODULE__) do
+        if api == __MODULE__ do
+          raise "code_interface.define_for should be set to the API module you want it to call, not the resource."
+        end
+
         require Ash.CodeInterface
         Ash.CodeInterface.define_interface(api, __MODULE__)
       end

lib/ash/resource/interface.ex

@@ -8,11 +8,11 @@ defmodule Ash.Resource.Interface do
 
   defmacro __using__(_) do
     quote bind_quoted: [], generated: true do
-      if Ash.Resource.Info.define_interface_for(__MODULE__) do
+      if define_for = Ash.Resource.Info.define_interface_for(__MODULE__) do
         require Ash.CodeInterface
 
         Ash.CodeInterface.define_interface(
-          Ash.Resource.Info.define_interface_for(__MODULE__),
+          define_for,
           __MODULE__
         )
       end