improvement: move subject_name uniqueness validation to compile time.

lib/ash_authentication/plug.ex

@@ -69,9 +69,10 @@ defmodule AshAuthentication.Plug do
   do useful things like session and query param fetching.
   """
 
-  alias Ash.{Changeset, Resource}
+  alias Ash.{Api, Changeset, Resource}
   alias AshAuthentication.Plug.Helpers
   alias Plug.Conn
+  alias Spark.Dsl.Extension
 
   @type authenticator_config :: %{
           api: module,
@@ -110,9 +111,44 @@ defmodule AshAuthentication.Plug do
       |> Keyword.fetch!(:otp_app)
       |> Macro.expand_once(__CALLER__)
 
-    AshAuthentication.Validations.validate_unique_subject_names(otp_app)
-
     quote do
+      require Ash.Api.Info
+
+      unquote(otp_app)
+      |> Application.compile_env(:ash_apis, [])
+      |> Stream.flat_map(&Api.Info.depend_on_resources(&1))
+      |> Stream.map(&{&1, Extension.get_persisted(&1, :authentication)})
+      |> Stream.reject(&(elem(&1, 1) == nil))
+      |> Stream.map(&{elem(&1, 0), elem(&1, 1).subject_name})
+      |> Enum.group_by(&elem(&1, 1), &elem(&1, 0))
+      |> Enum.reject(&(length(elem(&1, 1)) < 2))
+      |> case do
+        [] ->
+          nil
+
+        duplicates ->
+          import AshAuthentication.Utils, only: [to_sentence: 2]
+
+          duplicates =
+            duplicates
+            |> Enum.map(fn {subject_name, resources} ->
+              resources =
+                resources
+                |> Enum.map(&"`#{inspect(&1)}`")
+                |> to_sentence(final: "and")
+
+              "  `#{subject_name}`: #{resources}\n"
+            end)
+
+          raise """
+          Error: There are multiple resources configured with the same subject name.
+
+          This is bad because we will be unable to correctly convert between subjects and resources.
+
+          #{duplicates}
+          """
+      end
+
       @behaviour AshAuthentication.Plug
       import Plug.Conn
 

lib/ash_authentication/validations.ex

@@ -49,28 +49,6 @@ defmodule AshAuthentication.Validations do
     {:error, "Expected `#{inspect(field)}` to be present and contain one of #{values}"}
   end
 
-  @doc """
-  Validates the uniqueness of all subject names per otp app.
-  """
-  @spec validate_unique_subject_names(module) :: :ok | no_return
-  def validate_unique_subject_names(otp_app) do
-    otp_app
-    |> AshAuthentication.authenticated_resources()
-    |> Enum.group_by(& &1.subject_name)
-    |> Enum.each(fn
-      {subject_name, configs} when length(configs) > 1 ->
-        resources =
-          configs
-          |> Enum.map(&"`#{inspect(&1.resource)}`")
-          |> AshAuthentication.Utils.to_sentence()
-
-        raise "Error: multiple resources use the `#{subject_name}` subject name: #{resources}"
-
-      _ ->
-        :ok
-    end)
-  end
-
   @doc """
   Find and return a named attribute in the DSL state.
   """