improvement: Add error message when page is added but pagination is not enabled (#511)

lib/ash/api/api.ex

@@ -46,7 +46,8 @@ defmodule Ash.Api do
   alias Ash.Error.Invalid.{
     NoPrimaryAction,
     NoSuchAction,
-    NoSuchResource
+    NoSuchResource,
+    PageRequiresPagination
   }
 
   alias Ash.Error.Query.NotFound
@@ -1003,7 +1004,8 @@ defmodule Ash.Api do
     query = Ash.Query.set_api(query, api)
 
     with {:ok, opts} <- Spark.OptionsHelpers.validate(opts, @read_opts_schema),
-         {:ok, action} <- get_action(query.resource, opts, :read, query.action) do
+         {:ok, action} <- get_action(query.resource, opts, :read, query.action),
+         {:ok, action} <- pagination_check(action, query.resource, opts) do
       Read.run(query, action, opts)
     else
       {:error, error} ->
@@ -1194,6 +1196,19 @@ defmodule Ash.Api do
     end
   end
 
+  defp pagination_check(action, resource, opts) do
+    case Keyword.has_key?(opts, :page) && Map.get(action, :pagination) do
+      true ->
+        {:ok, action}
+
+      false ->
+        {:error,
+         Ash.Error.to_error_class(
+           PageRequiresPagination.exception(resource: resource, action: action)
+         )}
+    end
+  end
+
   defp unwrap_or_raise!(first, second, destroy? \\ false)
   defp unwrap_or_raise!(:ok, _, _), do: :ok
   defp unwrap_or_raise!({:ok, result}, _, false), do: result

lib/ash/error/invalid/page_requires_pagination.ex

@@ -0,0 +1,24 @@
+defmodule Ash.Error.Invalid.PageRequiresPagination do
+  @moduledoc "Used when page option is passed but pagination is not enabled."
+  use Ash.Error.Exception
+
+  def_ash_error([:resource, :action], class: :invalid)
+
+  defimpl Ash.ErrorKind do
+    def id(_), do: Ash.UUID.generate()
+
+    def code(_), do: "page_requires_pagination"
+
+    def message(%{resource: resource, action: action}) do
+      """
+      Pagination is not enabled on resource #{inspect(resource)} for the action #{inspect(action)}. Check that you've
+      enabled pagination in your action. For example:
+
+
+      read #{action.name} do
+        pagination offset?: true, keyset?: true, required?: false
+      end
+      """
+    end
+  end
+end

test/actions/read_test.exs

@@ -255,6 +255,15 @@ defmodule Ash.Test.Actions.ReadTest do
       assert res.message =~ ~r/Ash.Test.AnyApi.read!\/2/
       assert res.message =~ ~r/expected a keyword list, but instead got \[1\]/
     end
+
+    test "raises an error when page is sent but pagination is not enabled on a resource" do
+      res =
+        assert_raise Ash.Error.Invalid, fn ->
+          Api.read!(Post)
+        end
+
+      assert %Ash.Error.Invalid.PageRequiresPagination{resource: Post, action: _} = hd(res.errors)
+    end
   end
 
   describe "Api.read/2" do