fix: Fix/1537 improve domain error message (#2545)

* fix: improve error reporting for duplicate use of Ash.Domain

Author: TravelCurry02

lib/ash/domain/domain.ex

@@ -51,6 +51,23 @@ defmodule Ash.Domain do
   @impl Spark.Dsl
   def handle_opts(opts) do
     quote do
+      if Module.get_attribute(__MODULE__, :__ash_domain_used__) do
+        first_line = Module.get_attribute(__MODULE__, :__ash_domain_used__)
+
+        raise CompileError,
+          file: __ENV__.file,
+          line: __ENV__.line,
+          description: """
+          `use Ash.Domain` can only be called once per module.
+
+          It was already called on line #{first_line}.
+          Remove the duplicate `use Ash.Domain` invocation.
+          """
+      end
+
+      # Mark that `use Ash.Domain` has been called and store the line number
+      @__ash_domain_used__ __ENV__.line
+
       @behaviour Ash.Domain
 
       @impl Ash.Domain

lib/ash/domain/interface.ex

@@ -6,21 +6,6 @@ defmodule Ash.Domain.Interface do
   @moduledoc false
 
   defmacro __using__(_) do
-    env = __CALLER__
-
-    ash_domain_already_using =
-      Module.get_attribute(env.module, :__ash_domain_used__) || false
-
-    if ash_domain_already_using do
-      raise CompileError,
-        file: env.file,
-        line: env.line,
-        description: "use Ash.Domain can be called only one time in module "
-    end
-
-    Module.register_attribute(env.module, :__ash_domain_used__, [])
-    Module.put_attribute(env.module, :__ash_domain_used__, env.line)
-
     quote bind_quoted: [], generated: true do
       @spec can?(
               query_or_changeset_or_action ::

test/domain/domain_test.exs

@@ -40,9 +40,11 @@ defmodule Ash.Test.Resource.DomainTest do
       flunk("expected CompileError on the second `use Ash.Domain`")
     rescue
       e in CompileError ->
-        assert e.line == 1
+        # Error should point to line 3 (the second `use Ash.Domain` invocation)
+        assert e.line == 3
         assert String.contains?(e.description, "use Ash.Domain")
-        assert String.contains?(e.description, "only one")
+        assert String.contains?(e.description, "can only be called once")
+        assert String.contains?(e.description, "Remove the duplicate")
     end
   end