Allow nullable return for deferred type loaders

When a field/query is configured with a deferred type loader for return,
while the field is nullable itself, it should not call the type loader.
Instead it should just return null.

Author: jerowork

phpstan-baseline.php

@@ -367,6 +367,12 @@
 	'count' => 1,
 	'path' => __DIR__ . '/tests/Doubles/FullFeatured/Query/DeprecatedQuery.php',
 ];
+$ignoreErrors[] = [
+	'message' => '#^Method Jerowork\\\\GraphqlAttributeSchema\\\\Test\\\\Doubles\\\\FullFeatured\\\\Query\\\\WithNullableReturnDeferredTypeLoader\\:\\:__invoke\\(\\) never returns string so it can be removed from the return type\\.$#',
+	'identifier' => 'return.unusedType',
+	'count' => 1,
+	'path' => __DIR__ . '/tests/Doubles/FullFeatured/Query/WithNullableReturnDeferredTypeLoader.php',
+];
 $ignoreErrors[] = [
 	'message' => '#^Method Jerowork\\\\GraphqlAttributeSchema\\\\Test\\\\Doubles\\\\FullFeatured\\\\Query\\\\WithUnionOutputQuery\\:\\:getUnionQuery\\(\\) never returns Jerowork\\\\GraphqlAttributeSchema\\\\Test\\\\Doubles\\\\FullFeatured\\\\Type\\\\AgentType so it can be removed from the return type\\.$#',
 	'identifier' => 'return.unusedType',

src/Resolver/Type/Field/FieldResolver.php

@@ -136,12 +136,12 @@ public function resolveField(FieldNode $node, TypeResolverSelector $typeResolver
     {
         if ($node->fieldType === FieldNodeType::Property) {
             return function (object $object) use ($node, $typeResolverSelector): mixed {
-                /** @var list<int|string|Stringable>|int|string|Stringable $result */
+                /** @var null|list<int|string|Stringable>|int|string|Stringable $result */
                 $result = $typeResolverSelector
                     ->getResolver($node->reference)
                     ->resolve($node->reference, fn() => $object->{$node->propertyName});
 
-                if ($node->deferredTypeLoader !== null) {
+                if ($node->deferredTypeLoader !== null && $result !== null) {
                     return $this->deferredTypeResolver->resolve($node->deferredTypeLoader, $result);
                 }
 
@@ -158,12 +158,12 @@ public function resolveField(FieldNode $node, TypeResolverSelector $typeResolver
                 $arguments[] = $this->argumentNodeResolver->resolve($argumentNode, $args, $typeResolverSelector);
             }
 
-            /** @var list<int|string|Stringable>|int|string|Stringable $result */
+            /** @var null|list<int|string|Stringable>|int|string|Stringable $result */
             $result = $typeResolverSelector
                 ->getResolver($node->reference)
                 ->resolve($node->reference, fn() => $object->{$node->methodName}(...$arguments));
 
-            if ($node->deferredTypeLoader !== null) {
+            if ($node->deferredTypeLoader !== null && $result !== null) {
                 return $this->deferredTypeResolver->resolve($node->deferredTypeLoader, $result);
             }
 

tests/Doubles/FullFeatured/Query/WithNullableReturnDeferredTypeLoader.php

@@ -0,0 +1,17 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Jerowork\GraphqlAttributeSchema\Test\Doubles\FullFeatured\Query;
+
+use Jerowork\GraphqlAttributeSchema\Attribute\Query;
+use Jerowork\GraphqlAttributeSchema\Test\Doubles\Type\Loader\TestTypeLoader;
+
+final readonly class WithNullableReturnDeferredTypeLoader
+{
+    #[Query(name: 'withNullableReturnDeferredTypeLoader', description: 'A description', deferredTypeLoader: TestTypeLoader::class)]
+    public function __invoke(): ?string
+    {
+        return null;
+    }
+}

tests/ParserTest.php

@@ -33,6 +33,7 @@
 use Jerowork\GraphqlAttributeSchema\Test\Doubles\FullFeatured\Query\WithInputObjectQuery;
 use Jerowork\GraphqlAttributeSchema\Test\Doubles\FullFeatured\Query\WithInterfaceOutputQuery;
 use Jerowork\GraphqlAttributeSchema\Test\Doubles\FullFeatured\Query\WithListOutputQuery;
+use Jerowork\GraphqlAttributeSchema\Test\Doubles\FullFeatured\Query\WithNullableReturnDeferredTypeLoader;
 use Jerowork\GraphqlAttributeSchema\Test\Doubles\FullFeatured\Query\WithOverwrittenTypeQuery;
 use Jerowork\GraphqlAttributeSchema\Test\Doubles\FullFeatured\Query\WithUnionOutputQuery;
 use Jerowork\GraphqlAttributeSchema\Test\Doubles\FullFeatured\Type\AbstractAdminType;
@@ -233,6 +234,16 @@ public function itShouldParseDirectory(): void
                 null,
                 null,
             ),
+            new QueryNode(
+                WithNullableReturnDeferredTypeLoader::class,
+                'withNullableReturnDeferredTypeLoader',
+                'A description',
+                [],
+                ScalarTypeReference::create('string')->setNullableValue(),
+                '__invoke',
+                null,
+                TestTypeLoader::class,
+            ),
             new QueryNode(
                 WithOverwrittenTypeQuery::class,
                 'withOverwrittenType',

tests/SchemaBuilderTest.php

@@ -22,6 +22,7 @@
 use Jerowork\GraphqlAttributeSchema\Test\Doubles\FullFeatured\Query\WithInputObjectQuery;
 use Jerowork\GraphqlAttributeSchema\Test\Doubles\FullFeatured\Query\WithInterfaceOutputQuery;
 use Jerowork\GraphqlAttributeSchema\Test\Doubles\FullFeatured\Query\WithListOutputQuery;
+use Jerowork\GraphqlAttributeSchema\Test\Doubles\FullFeatured\Query\WithNullableReturnDeferredTypeLoader;
 use Jerowork\GraphqlAttributeSchema\Test\Doubles\FullFeatured\Query\WithOverwrittenTypeQuery;
 use Jerowork\GraphqlAttributeSchema\Test\Doubles\FullFeatured\Query\WithUnionOutputQuery;
 use Jerowork\GraphqlAttributeSchema\Test\Doubles\Query\TestQuery;
@@ -91,6 +92,7 @@ public function itShouldBuildSchema(): void
         $this->container->set(WithOverwrittenTypeQuery::class, new WithOverwrittenTypeQuery());
         $this->container->set(WithUnionOutputQuery::class, new WithUnionOutputQuery());
         $this->container->set(WithDeferredTypeLoader::class, new WithDeferredTypeLoader());
+        $this->container->set(WithNullableReturnDeferredTypeLoader::class, new WithNullableReturnDeferredTypeLoader());
 
         $ast = $this->parser->parse(__DIR__ . '/Doubles/FullFeatured');
         $schema = $this->schemaBuilder->build($ast);
@@ -223,6 +225,13 @@ public function itShouldBuildSchema(): void
                     'deprecationReason' => null,
                     'args' => [],
                 ],
+                [
+                    'name' => 'withNullableReturnDeferredTypeLoader',
+                    'type' => 'String',
+                    'description' => 'A description',
+                    'deprecationReason' => null,
+                    'args' => [],
+                ],
                 [
                     'name' => 'withOverwrittenType',
                     'type' => 'Boolean',

tests/Util/Finder/Native/NativeFinderTest.php

@@ -45,6 +45,7 @@ public function itShouldRetrieveFilesFromFolder(): void
             'Doubles/FullFeatured/Query/WithInputObjectQuery.php',
             'Doubles/FullFeatured/Query/WithInterfaceOutputQuery.php',
             'Doubles/FullFeatured/Query/WithListOutputQuery.php',
+            'Doubles/FullFeatured/Query/WithNullableReturnDeferredTypeLoader.php',
             'Doubles/FullFeatured/Query/WithOverwrittenTypeQuery.php',
             'Doubles/FullFeatured/Query/WithUnionOutputQuery.php',
             'Doubles/FullFeatured/Type/AbstractAdminType.php',