Allow config/2 to send errors in spec compliant format

lib/absinthe/phase/document/result.ex

@@ -109,6 +109,15 @@ defmodule Absinthe.Phase.Document.Result do
   defp field_name(%{alias: name}), do: name
   defp field_name(%{name: name}), do: name
 
+  defp format_error(%Phase.Error{message: %{message: _message} = error_object} = error, _opts) do
+    if Enum.empty?(error.locations) do
+      error_object
+    else
+      locations = Enum.flat_map(error.locations, &format_location/1)
+      Map.put_new(error_object, :locations, locations)
+    end
+  end
+
   defp format_error(%Phase.Error{locations: []} = error, opts) do
     error_object = %{message: error.message}
 

test/absinthe/execution/subscription_test.exs

@@ -214,6 +214,18 @@ defmodule Absinthe.Execution.SubscriptionTest do
           {:ok, topic: "*", context_id: "*", document_id: op_name}
         end
       end
+
+      field :config_error, :string do
+        config fn _, _ ->
+          {:error, "failed"}
+        end
+      end
+
+      field :config_error_with_map, :string do
+        config fn _, _ ->
+          {:error, %{message: "failed", extensions: %{code: "FAILED"}}}
+        end
+      end
     end
 
     mutation do
@@ -617,6 +629,36 @@ defmodule Absinthe.Execution.SubscriptionTest do
     assert_receive(:batch_get_group)
   end
 
+  @query """
+  subscription Example {
+    configError
+  }
+  """
+  test "config errors" do
+    assert {:ok, %{errors: [%{message: "failed"}]}} =
+             run_subscription(
+               @query,
+               Schema,
+               variables: %{},
+               context: %{pubsub: PubSub}
+             )
+  end
+
+  @query """
+  subscription Example {
+    configErrorWithMap
+  }
+  """
+  test "config errors with a map" do
+    assert {:ok, %{errors: [%{message: "failed", extensions: %{code: "FAILED"}}]}} =
+             run_subscription(
+               @query,
+               Schema,
+               variables: %{},
+               context: %{pubsub: PubSub}
+             )
+  end
+
   describe "subscription_ids" do
     @query """
     subscription {