fix: make results nullable again if root level errors are enabled

Building upon #110, this restores the old behaviour of the result being nullable
when root level errors are present.

While the result is guaranteed to not be nullable in standard conditions (since
either result or errors are always present), when errors are moved to the root
level it could become null, so declaring it non-nullable propagates the null up
to the data field.

This actually causes compatibility problems with some client libraries (e.g.
Relay) that expect the inner result to be null, _not_ data, if there's an error.

This also adds dedicated RootLevelErrors versions of the Api and the Schema
since the configuration is accessed at compile time now, so put_env was not
enough to test them correctly.

lib/resource/resource.ex

@@ -610,9 +610,7 @@ defmodule AshGraphql.Resource do
             module: schema,
             name: to_string(mutation.name),
             description: Ash.Resource.Info.action(resource, mutation.action).description,
-            type: %Absinthe.Blueprint.TypeReference.NonNull{
-              of_type: String.to_atom("#{mutation.name}_result")
-            },
+            type: mutation_result_type(mutation.name, api),
             __reference__: ref(__ENV__)
           }
         end
@@ -656,9 +654,7 @@ defmodule AshGraphql.Resource do
           module: schema,
           name: to_string(mutation.name),
           description: Ash.Resource.Info.action(resource, mutation.action).description,
-          type: %Absinthe.Blueprint.TypeReference.NonNull{
-            of_type: String.to_atom("#{mutation.name}_result")
-          },
+          type: mutation_result_type(mutation.name, api),
           __reference__: ref(__ENV__)
         }
 
@@ -710,13 +706,18 @@ defmodule AshGraphql.Resource do
       module: schema,
       name: to_string(mutation.name),
       description: Ash.Resource.Info.action(resource, mutation.action).description,
-      type: %Absinthe.Blueprint.TypeReference.NonNull{
-        of_type: String.to_atom("#{mutation.name}_result")
-      },
+      type: mutation_result_type(mutation.name, api),
       __reference__: ref(__ENV__)
     }
   end
 
+  defp mutation_result_type(mutation_name, api) do
+    type = String.to_atom("#{mutation_name}_result")
+    root_level_errors? = AshGraphql.Api.Info.root_level_errors?(api)
+
+    maybe_wrap_non_null(type, not root_level_errors?)
+  end
+
   defp mutation_args(%{identity: false} = mutation, resource, schema) do
     mutation_read_args(mutation, resource, schema)
   end

test/errors_test.exs

@@ -12,8 +12,6 @@ defmodule AshGraphql.ErrorsTest do
   end
 
   test "errors can be configured to be shown in the root" do
-    Application.put_env(:ash_graphql, AshGraphql.Test.Api, graphql: [root_level_errors?: true])
-
     resp =
       """
       mutation CreatePost($input: CreatePostInput) {
@@ -27,7 +25,7 @@ defmodule AshGraphql.ErrorsTest do
         }
       }
       """
-      |> Absinthe.run(AshGraphql.Test.Schema,
+      |> Absinthe.run(AshGraphql.Test.RootLevelErrorsSchema,
         variables: %{
           "input" => %{
             "text" => "foobar",
@@ -38,7 +36,7 @@ defmodule AshGraphql.ErrorsTest do
 
     assert {:ok, result} = resp
 
-    assert %{data: nil, errors: [%{message: message}]} = result
+    assert %{data: %{"createPost" => nil}, errors: [%{message: message}]} = result
 
     assert message =~ "confirmation did not match value"
   end
@@ -111,8 +109,8 @@ defmodule AshGraphql.ErrorsTest do
   end
 
   test "showing raised errors alongside root errors shows raised errors in the root" do
-    Application.put_env(:ash_graphql, AshGraphql.Test.Api,
-      graphql: [show_raised_errors?: true, root_level_errors?: true]
+    Application.put_env(:ash_graphql, AshGraphql.Test.RootLevelErrorsApi,
+      graphql: [show_raised_errors?: true]
     )
 
     resp =
@@ -128,7 +126,7 @@ defmodule AshGraphql.ErrorsTest do
         }
       }
       """
-      |> Absinthe.run(AshGraphql.Test.Schema,
+      |> Absinthe.run(AshGraphql.Test.RootLevelErrorsSchema,
         variables: %{
           "input" => %{
             "text" => "foobar"
@@ -139,7 +137,7 @@ defmodule AshGraphql.ErrorsTest do
     assert {:ok, result} = resp
 
     assert %{
-             data: nil,
+             data: %{"createPostWithError" => nil},
              errors: [
                %{message: message}
              ]
@@ -415,4 +413,60 @@ defmodule AshGraphql.ErrorsTest do
     assert fields["type"]["ofType"]["kind"] == "NON_NULL"
     assert fields["type"]["ofType"]["ofType"]["name"] == "String"
   end
+
+  test "mutation result is non nullable without root level errors" do
+    {:ok, %{data: data}} =
+      """
+      query {
+        __schema {
+          mutationType {
+            name
+            fields {
+              name
+              type {
+                kind
+                ofType {
+                  name
+                }
+              }
+            }
+          }
+        }
+      }
+      """
+      |> Absinthe.run(AshGraphql.Test.Schema)
+
+    create_post_mutation =
+      data["__schema"]["mutationType"]["fields"]
+      |> Enum.find(fn field -> field["name"] == "createPost" end)
+
+    assert create_post_mutation["type"]["kind"] == "NON_NULL"
+    assert create_post_mutation["type"]["ofType"]["name"] == "CreatePostResult"
+  end
+
+  test "mutation result is nullable with root level errors" do
+    {:ok, %{data: data}} =
+      """
+      query {
+        __schema {
+          mutationType {
+            name
+            fields {
+              name
+              type {
+                name
+              }
+            }
+          }
+        }
+      }
+      """
+      |> Absinthe.run(AshGraphql.Test.RootLevelErrorsSchema)
+
+    create_post_mutation =
+      data["__schema"]["mutationType"]["fields"]
+      |> Enum.find(fn field -> field["name"] == "createPost" end)
+
+    assert create_post_mutation["type"]["name"] == "CreatePostResult"
+  end
 end

test/support/root_level_errors_api.ex

@@ -0,0 +1,17 @@
+defmodule AshGraphql.Test.RootLevelErrorsApi do
+  @moduledoc false
+
+  use Ash.Api,
+    extensions: [
+      AshGraphql.Api
+    ],
+    otp_app: :ash_graphql
+
+  graphql do
+    root_level_errors? true
+  end
+
+  resources do
+    registry(AshGraphql.Test.Registry)
+  end
+end

test/support/root_level_errors_schema.ex

@@ -0,0 +1,30 @@
+defmodule AshGraphql.Test.RootLevelErrorsSchema do
+  @moduledoc false
+
+  use Absinthe.Schema
+
+  @apis [AshGraphql.Test.RootLevelErrorsApi]
+
+  use AshGraphql, apis: @apis
+
+  query do
+  end
+
+  mutation do
+  end
+
+  object :foo do
+    field(:foo, :string)
+    field(:bar, :string)
+  end
+
+  input_object :foo_input do
+    field(:foo, non_null(:string))
+    field(:bar, non_null(:string))
+  end
+
+  enum :status do
+    value(:open, description: "The post is open")
+    value(:closed, description: "The post is closed")
+  end
+end