Merge pull request #518 from simPod/fix-internal-directives

Fix internal directives

.gitattributes

@@ -2,6 +2,7 @@
 * text eol=lf
 /benchmarks export-ignore
 /tests export-ignore
+/examples export-ignore
 /tools export-ignore
 .gitattributes export-ignore
 .gitignore export-ignore

.gitignore

@@ -4,3 +4,4 @@ composer.phar
 phpcs.xml
 phpstan.neon
 vendor/
+/.idea

CHANGELOG.md

@@ -1,4 +1,8 @@
 # Changelog
+
+## Unreleased
+- Add schema validation: Input Objects must not contain non-nullable circular references (#492)
+
 #### v0.13.5
 - Fix coroutine executor when using with promise (#486) 
 

CONTRIBUTING.md

@@ -10,8 +10,9 @@ For smaller contributions just use this workflow:
 * Fork the project.
 * Add your features and or bug fixes.
 * Add tests. Tests are important for us.
-* Check your changes using `composer check-all`
+* Check your changes using `composer check-all`.
-* Send a pull request
+* Add an entry to the [Changelog's Unreleases section](CHANGELOG.md#unreleased).
+* Send a pull request.
 
 ## Setup the Development Environment
 First, copy the URL of your fork and `git clone` it to your local machine.

README.md

@@ -49,4 +49,4 @@ Support this project by becoming a sponsor. Your logo will show up here with a l
 
 ## License
 
-See [LICENCE](LICENSE).
+See [LICENSE](LICENSE).

UPGRADE.md

@@ -1,3 +1,8 @@
+## Master
+
+### Breaking (major): dropped deprecations
+ - dropped deprecated `GraphQL\Schema`. Use `GraphQL\Type\Schema`.
+
 ## Upgrade v0.12.x > v0.13.x
 
 ### Breaking (major): minimum supported version of PHP

benchmarks/Utils/SchemaGenerator.php

@@ -152,7 +152,7 @@ class SchemaGenerator
         ];
     }
 
-    public function resolveField($value, $args, $context, $resolveInfo)
+    public function resolveField($objectValue, $args, $context, $resolveInfo)
     {
         return $resolveInfo->fieldName . '-value';
     }

composer.json

@@ -16,9 +16,9 @@
   "require-dev": {
     "doctrine/coding-standard": "^6.0",
     "phpbench/phpbench": "^0.14.0",
-    "phpstan/phpstan": "^0.11.4",
+    "phpstan/phpstan": "^0.11.12",
-    "phpstan/phpstan-phpunit": "^0.11.0",
+    "phpstan/phpstan-phpunit": "^0.11.2",
-    "phpstan/phpstan-strict-rules": "^0.11.0",
+    "phpstan/phpstan-strict-rules": "^0.11.1",
     "phpunit/phpcov": "^5.0",
     "phpunit/phpunit": "^7.2",
     "psr/http-message": "^1.0",

docs/complementary-tools.md

@@ -3,6 +3,7 @@
 * [Standard Server](executing-queries.md/#using-server) – Out of the box integration with any PSR-7 compatible framework (like [Slim](http://slimframework.com) or [Zend Expressive](http://zendframework.github.io/zend-expressive/)).
 * [Relay Library for graphql-php](https://github.com/ivome/graphql-relay-php) – Helps construct Relay related schema definitions.
 * [Lighthouse](https://github.com/nuwave/lighthouse) – Laravel based, uses Schema Definition Language
+* [Laravel GraphQL](https://github.com/rebing/graphql-laravel) - Laravel wrapper for Facebook's GraphQL
 * [OverblogGraphQLBundle](https://github.com/overblog/GraphQLBundle) – Bundle for Symfony
 * [WP-GraphQL](https://github.com/wp-graphql/wp-graphql) - GraphQL API for WordPress
 

docs/data-fetching.md

@@ -103,23 +103,25 @@ for a field you simply override this default resolver.
 **graphql-php** provides following default field resolver:
 ```php
 <?php
-function defaultFieldResolver($source, $args, $context, \GraphQL\Type\Definition\ResolveInfo $info)
+function defaultFieldResolver($objectValue, $args, $context, \GraphQL\Type\Definition\ResolveInfo $info)
-{
+    {
-    $fieldName = $info->fieldName;
+        $fieldName = $info->fieldName;
-    $property = null;
+        $property  = null;
 
-    if (is_array($source) || $source instanceof \ArrayAccess) {
+        if (is_array($objectValue) || $objectValue instanceof \ArrayAccess) {
-        if (isset($source[$fieldName])) {
+            if (isset($objectValue[$fieldName])) {
-            $property = $source[$fieldName];
+                $property = $objectValue[$fieldName];
-        }
+            }
-    } else if (is_object($source)) {
+        } elseif (is_object($objectValue)) {
-        if (isset($source->{$fieldName})) {
+            if (isset($objectValue->{$fieldName})) {
-            $property = $source->{$fieldName};
+                $property = $objectValue->{$fieldName};
+            }
         }
+
+        return $property instanceof Closure
+            ? $property($objectValue, $args, $context, $info)
+            : $property;
     }
-
-    return $property instanceof Closure ? $property($source, $args, $context, $info) : $property;
-}
 ```
 
 As you see it returns value by key (for arrays) or property (for objects). 
@@ -161,7 +163,6 @@ $userType = new ObjectType([
 Keep in mind that **field resolver** has precedence over **default field resolver per type** which in turn
  has precedence over **default field resolver**.
 
-
 # Solving N+1 Problem
 Since: 0.9.0
 

docs/getting-started.md

@@ -54,8 +54,8 @@ $queryType = new ObjectType([
             'args' => [
                 'message' => Type::nonNull(Type::string()),
             ],
-            'resolve' => function ($root, $args) {
+            'resolve' => function ($rootValue, $args) {
-                return $root['prefix'] . $args['message'];
+                return $rootValue['prefix'] . $args['message'];
             }
         ],
     ],

docs/reference.md

@@ -33,7 +33,7 @@ See [related documentation](executing-queries.md).
  * fieldResolver:
  *    A resolver function to use when one is not provided by the schema.
  *    If not provided, the default field resolver is used (which looks for a
- *    value on the source value with the field's name).
+ *    value on the object value with the field's name).
  * validationRules:
  *    A set of rules for query validation step. Default value is all available rules.
  *    Empty array would allow to skip query validation (may be convenient for persisted
@@ -299,7 +299,7 @@ static function getNullableType($type)
 ```
 # GraphQL\Type\Definition\ResolveInfo
 Structure containing information useful for field resolution process.
-Passed as 3rd argument to every field resolver. See [docs on field resolving (data fetching)](data-fetching.md).
+Passed as 4th argument to every field resolver. See [docs on field resolving (data fetching)](data-fetching.md).
 
 **Class Props:** 
 ```php

docs/type-system/enum-types.md

@@ -158,7 +158,7 @@ $heroType = new ObjectType([
             'args' => [
                 'episode' => Type::nonNull($enumType)
             ],
-            'resolve' => function($_value, $args) {
+            'resolve' => function($hero, $args) {
                 return $args['episode'] === 5 ? true : false; 
             }
         ]

docs/type-system/input-types.md

@@ -131,7 +131,7 @@ $queryType = new ObjectType([
             'type' => Type::listOf($storyType),
             'args' => [
                 'filters' => [
-                    'type' => Type::nonNull($filters),
+                    'type' => $filters,
                     'defaultValue' => [
                         'popular' => true
                     ]

docs/type-system/object-types.md

@@ -80,7 +80,7 @@ Option | Type | Notes
 name | `string` | **Required.** Name of the field. When not set - inferred from **fields** array key (read about [shorthand field definition](#shorthand-field-definitions) below)
 type | `Type` | **Required.** An instance of internal or custom type. Note: type must be represented by a single instance within one schema (see also [Type Registry](index.md#type-registry))
 args | `array` | An array of possible type arguments. Each entry is expected to be an array with keys: **name**, **type**, **description**, **defaultValue**. See [Field Arguments](#field-arguments) section below.
-resolve | `callable` | **function($value, $args, $context, [ResolveInfo](../reference.md#graphqltypedefinitionresolveinfo) $info)**<br> Given the **$value** of this type, it is expected to return actual value of the current field. See section on [Data Fetching](../data-fetching.md) for details
+resolve | `callable` | **function($objectValue, $args, $context, [ResolveInfo](../reference.md#graphqltypedefinitionresolveinfo) $info)**<br> Given the **$objectValue** of this type, it is expected to return actual value of the current field. See section on [Data Fetching](../data-fetching.md) for details
 complexity | `callable` | **function($childrenComplexity, $args)**<br> Used to restrict query complexity. The feature is disabled by default, read about [Security](../security.md#query-complexity-analysis) to use it.
 description | `string` | Plain-text description of this field for clients (e.g. used by [GraphiQL](https://github.com/graphql/graphiql) for auto-generated documentation)
 deprecationReason | `string` | Text describing why this field is deprecated. When not empty - field will not be returned by introspection queries (unless forced)

docs/type-system/schema.md

@@ -62,7 +62,7 @@ $mutationType = new ObjectType([
                 'episode' => $episodeEnum,
                 'review' => $reviewInputObject
             ],
-            'resolve' => function($val, $args) {
+            'resolve' => function($rootValue, $args) {
                 // TODOC
             }
         ]

examples/00-hello-world/graphql.php

@@ -19,8 +19,8 @@ try {
                 'args' => [
                     'message' => ['type' => Type::string()],
                 ],
-                'resolve' => function ($root, $args) {
+                'resolve' => function ($rootValue, $args) {
-                    return $root['prefix'] . $args['message'];
+                    return $rootValue['prefix'] . $args['message'];
                 }
             ],
         ],
@@ -35,7 +35,7 @@ try {
                     'x' => ['type' => Type::int()],
                     'y' => ['type' => Type::int()],
                 ],
-                'resolve' => function ($root, $args) {
+                'resolve' => function ($calc, $args) {
                     return $args['x'] + $args['y'];
                 },
             ],

examples/01-blog/Blog/Type/CommentType.php

@@ -35,12 +35,12 @@ class CommentType extends ObjectType
                     Types::htmlField('body')
                 ];
             },
-            'resolveField' => function($value, $args, $context, ResolveInfo $info) {
+            'resolveField' => function($comment, $args, $context, ResolveInfo $info) {
                 $method = 'resolve' . ucfirst($info->fieldName);
                 if (method_exists($this, $method)) {
-                    return $this->{$method}($value, $args, $context, $info);
+                    return $this->{$method}($comment, $args, $context, $info);
                 } else {
-                    return $value->{$info->fieldName};
+                    return $comment->{$info->fieldName};
                 }
             }
         ];

examples/01-blog/Blog/Type/QueryType.php

@@ -57,8 +57,8 @@ class QueryType extends ObjectType
                 ],
                 'hello' => Type::string()
             ],
-            'resolveField' => function($val, $args, $context, ResolveInfo $info) {
+            'resolveField' => function($rootValue, $args, $context, ResolveInfo $info) {
-                return $this->{$info->fieldName}($val, $args, $context, $info);
+                return $this->{$info->fieldName}($rootValue, $args, $context, $info);
             }
         ];
         parent::__construct($config);

examples/01-blog/Blog/Type/StoryType.php

@@ -75,12 +75,12 @@ class StoryType extends ObjectType
             'interfaces' => [
                 Types::node()
             ],
-            'resolveField' => function($value, $args, $context, ResolveInfo $info) {
+            'resolveField' => function($story, $args, $context, ResolveInfo $info) {
                 $method = 'resolve' . ucfirst($info->fieldName);
                 if (method_exists($this, $method)) {
-                    return $this->{$method}($value, $args, $context, $info);
+                    return $this->{$method}($story, $args, $context, $info);
                 } else {
-                    return $value->{$info->fieldName};
+                    return $story->{$info->fieldName};
                 }
             }
         ];

examples/01-blog/Blog/Type/UserType.php

@@ -44,12 +44,12 @@ class UserType extends ObjectType
             'interfaces' => [
                 Types::node()
             ],
-            'resolveField' => function($value, $args, $context, ResolveInfo $info) {
+            'resolveField' => function($user, $args, $context, ResolveInfo $info) {
                 $method = 'resolve' . ucfirst($info->fieldName);
                 if (method_exists($this, $method)) {
-                    return $this->{$method}($value, $args, $context, $info);
+                    return $this->{$method}($user, $args, $context, $info);
                 } else {
-                    return $value->{$info->fieldName};
+                    return $user->{$info->fieldName};
                 }
             }
         ];

examples/02-shorthand/rootvalue.php

@@ -1,12 +1,12 @@
 <?php
 
 interface Resolver {
-    public function resolve($root, $args, $context);
+    public function resolve($rootValue, $args, $context);
 }
 
 class Addition implements Resolver
 {
-    public function resolve($root, $args, $context)
+    public function resolve($rootValue, $args, $context)
     {
         return $args['x'] + $args['y'];
     }
@@ -14,22 +14,22 @@ class Addition implements Resolver
 
 class Echoer implements Resolver
 {
-    public function resolve($root, $args, $context)
+    public function resolve($rootValue, $args, $context)
     {
-        return $root['prefix'].$args['message'];
+        return $rootValue['prefix'].$args['message'];
     }
 }
 
 return [
-    'sum' => function($root, $args, $context) {
+    'sum' => function($rootValue, $args, $context) {
         $sum = new Addition();
 
-        return $sum->resolve($root, $args, $context);
+        return $sum->resolve($rootValue, $args, $context);
     },
-    'echo' => function($root, $args, $context) {
+    'echo' => function($rootValue, $args, $context) {
         $echo = new Echoer();
 
-        return $echo->resolve($root, $args, $context);
+        return $echo->resolve($rootValue, $args, $context);
     },
     'prefix' => 'You said: ',
 ];

examples/03-server/graphql.php

@@ -19,8 +19,8 @@ try {
                 'args' => [
                     'message' => ['type' => Type::string()],
                 ],
-                'resolve' => function ($root, $args) {
+                'resolve' => function ($rootValue, $args) {
-                    return $root['prefix'] . $args['message'];
+                    return $rootValue['prefix'] . $args['message'];
                 }
             ],
         ],
@@ -35,7 +35,7 @@ try {
                     'x' => ['type' => Type::int()],
                     'y' => ['type' => Type::int()],
                 ],
-                'resolve' => function ($root, $args) {
+                'resolve' => function ($calc, $args) {
                     return $args['x'] + $args['y'];
                 },
             ],

src/Error/Warning.php

@@ -4,6 +4,8 @@ declare(strict_types=1);
 
 namespace GraphQL\Error;
 
+use GraphQL\Exception\InvalidArgument;
+use function is_int;
 use function trigger_error;
 use const E_USER_WARNING;
 
@@ -15,12 +17,12 @@ use const E_USER_WARNING;
  */
 final class Warning
 {
-    const WARNING_ASSIGN             = 2;
+    public const WARNING_ASSIGN             = 2;
-    const WARNING_CONFIG             = 4;
+    public const WARNING_CONFIG             = 4;
-    const WARNING_FULL_SCHEMA_SCAN   = 8;
+    public const WARNING_FULL_SCHEMA_SCAN   = 8;
-    const WARNING_CONFIG_DEPRECATION = 16;
+    public const WARNING_CONFIG_DEPRECATION = 16;
-    const WARNING_NOT_A_TYPE         = 32;
+    public const WARNING_NOT_A_TYPE         = 32;
-    const ALL                        = 63;
+    public const ALL                        = 63;
 
     /** @var int */
     private static $enableWarnings = self::ALL;
@@ -37,7 +39,7 @@ final class Warning
      *
      * @api
      */
-    public static function setWarningHandler(?callable $warningHandler = null)
+    public static function setWarningHandler(?callable $warningHandler = null) : void
     {
         self::$warningHandler = $warningHandler;
     }
@@ -54,14 +56,16 @@ final class Warning
      *
      * @api
      */
-    public static function suppress($suppress = true)
+    public static function suppress($suppress = true) : void
     {
         if ($suppress === true) {
             self::$enableWarnings = 0;
         } elseif ($suppress === false) {
             self::$enableWarnings = self::ALL;
-        } else {
+        } elseif (is_int($suppress)) {
             self::$enableWarnings &= ~$suppress;
+        } else {
+            throw InvalidArgument::fromExpectedTypeAndArgument('bool|int', $suppress);
         }
     }
 
@@ -77,20 +81,22 @@ final class Warning
      *
      * @api
      */
-    public static function enable($enable = true)
+    public static function enable($enable = true) : void
     {
         if ($enable === true) {
             self::$enableWarnings = self::ALL;
         } elseif ($enable === false) {
             self::$enableWarnings = 0;
-        } else {
+        } elseif (is_int($enable)) {
             self::$enableWarnings |= $enable;
+        } else {
+            throw InvalidArgument::fromExpectedTypeAndArgument('bool|int', $enable);
         }
     }
 
-    public static function warnOnce($errorMessage, $warningId, $messageLevel = null)
+    public static function warnOnce(string $errorMessage, int $warningId, ?int $messageLevel = null) : void
     {
-        if (self::$warningHandler) {
+        if (self::$warningHandler !== null) {
             $fn = self::$warningHandler;
             $fn($errorMessage, $warningId);
         } elseif ((self::$enableWarnings & $warningId) > 0 && ! isset(self::$warned[$warningId])) {
@@ -99,9 +105,9 @@ final class Warning
         }
     }
 
-    public static function warn($errorMessage, $warningId, $messageLevel = null)
+    public static function warn(string $errorMessage, int $warningId, ?int $messageLevel = null) : void
     {
-        if (self::$warningHandler) {
+        if (self::$warningHandler !== null) {
             $fn = self::$warningHandler;
             $fn($errorMessage, $warningId);
         } elseif ((self::$enableWarnings & $warningId) > 0) {

src/Exception/InvalidArgument.php

@@ -0,0 +1,20 @@
+<?php
+
+declare(strict_types=1);
+
+namespace GraphQL\Exception;
+
+use InvalidArgumentException;
+use function gettype;
+use function sprintf;
+
+final class InvalidArgument extends InvalidArgumentException
+{
+    /**
+     * @param mixed $argument
+     */
+    public static function fromExpectedTypeAndArgument(string $expectedType, $argument) : self
+    {
+        return new self(sprintf('Expected type "%s", got "%s"', $expectedType, gettype($argument)));
+    }
+}

src/Executor/ExecutionContext.php

@@ -14,7 +14,7 @@ use GraphQL\Type\Schema;
  * Data that must be available at all points during query execution.
  *
  * Namely, schema of the type system that is currently executing,
- * and the fragments defined in the query document
+ * and the fragments defined in the query document.
  *
  * @internal
  */
@@ -45,28 +45,28 @@ class ExecutionContext
     public $errors;
 
     /** @var PromiseAdapter */
-    public $promises;
+    public $promiseAdapter;
 
     public function __construct(
         $schema,
         $fragments,
-        $root,
+        $rootValue,
         $contextValue,
         $operation,
-        $variables,
+        $variableValues,
         $errors,
         $fieldResolver,
         $promiseAdapter
     ) {
         $this->schema         = $schema;
         $this->fragments      = $fragments;
-        $this->rootValue      = $root;
+        $this->rootValue      = $rootValue;
         $this->contextValue   = $contextValue;
         $this->operation      = $operation;
-        $this->variableValues = $variables;
+        $this->variableValues = $variableValues;
         $this->errors         = $errors ?: [];
         $this->fieldResolver  = $fieldResolver;
-        $this->promises       = $promiseAdapter;
+        $this->promiseAdapter = $promiseAdapter;
     }
 
     public function addError(Error $error)

src/Executor/Executor.php

@@ -157,31 +157,33 @@ class Executor
 
     /**
      * If a resolve function is not given, then a default resolve behavior is used
-     * which takes the property of the source object of the same name as the field
+     * which takes the property of the root value of the same name as the field
      * and returns it as the result, or if it's a function, returns the result
      * of calling that function while passing along args and context.
      *
-     * @param mixed      $source
+     * @param mixed      $objectValue
      * @param mixed[]    $args
      * @param mixed|null $context
      *
      * @return mixed|null
      */
-    public static function defaultFieldResolver($source, $args, $context, ResolveInfo $info)
+    public static function defaultFieldResolver($objectValue, $args, $context, ResolveInfo $info)
     {
         $fieldName = $info->fieldName;
         $property  = null;
 
-        if (is_array($source) || $source instanceof ArrayAccess) {
+        if (is_array($objectValue) || $objectValue instanceof ArrayAccess) {
-            if (isset($source[$fieldName])) {
+            if (isset($objectValue[$fieldName])) {
-                $property = $source[$fieldName];
+                $property = $objectValue[$fieldName];
             }
-        } elseif (is_object($source)) {
+        } elseif (is_object($objectValue)) {
-            if (isset($source->{$fieldName})) {
+            if (isset($objectValue->{$fieldName})) {
-                $property = $source->{$fieldName};
+                $property = $objectValue->{$fieldName};
             }
         }
 
-        return $property instanceof Closure ? $property($source, $args, $context, $info) : $property;
+        return $property instanceof Closure
+            ? $property($objectValue, $args, $context, $info)
+            : $property;
     }
 }

src/Executor/Promise/Adapter/SyncPromise.php

@@ -38,16 +38,16 @@ class SyncPromise
      */
     private $waiting = [];
 
-    public static function runQueue()
+    public static function runQueue() : void
     {
         $q = self::$queue;
-        while ($q && ! $q->isEmpty()) {
+        while ($q !== null && ! $q->isEmpty()) {
             $task = $q->dequeue();
             $task();
         }
     }
 
-    public function resolve($value)
+    public function resolve($value) : self
     {
         switch ($this->state) {
             case self::PENDING:
@@ -83,7 +83,7 @@ class SyncPromise
         return $this;
     }
 
-    public function reject($reason)
+    public function reject($reason) : self
     {
         if (! $reason instanceof Exception && ! $reason instanceof Throwable) {
             throw new Exception('SyncPromise::reject() has to be called with an instance of \Throwable');
@@ -107,7 +107,7 @@ class SyncPromise
         return $this;
     }
 
-    private function enqueueWaitingPromises()
+    private function enqueueWaitingPromises() : void
     {
         Utils::invariant(
             $this->state !== self::PENDING,
@@ -116,7 +116,7 @@ class SyncPromise
 
         foreach ($this->waiting as $descriptor) {
             self::getQueue()->enqueue(function () use ($descriptor) {
-                /** @var $promise self */
+                /** @var self $promise */
                 [$promise, $onFulfilled, $onRejected] = $descriptor;
 
                 if ($this->state === self::FULFILLED) {
@@ -145,17 +145,17 @@ class SyncPromise
         $this->waiting = [];
     }
 
-    public static function getQueue()
+    public static function getQueue() : SplQueue
     {
         return self::$queue ?: self::$queue = new SplQueue();
     }
 
     public function then(?callable $onFulfilled = null, ?callable $onRejected = null)
     {
-        if ($this->state === self::REJECTED && ! $onRejected) {
+        if ($this->state === self::REJECTED && $onRejected === null) {
             return $this;
         }
-        if ($this->state === self::FULFILLED && ! $onFulfilled) {
+        if ($this->state === self::FULFILLED && $onFulfilled === null) {
             return $this;
         }
         $tmp             = new self();

src/Executor/ReferenceExecutor.php

@@ -134,30 +134,30 @@ class ReferenceExecutor implements ExecutorImplementation
     ) {
         $errors    = [];
         $fragments = [];
-        /** @var OperationDefinitionNode $operation */
+        /** @var OperationDefinitionNode|null $operation */
         $operation                    = null;
         $hasMultipleAssumedOperations = false;
         foreach ($documentNode->definitions as $definition) {
-            switch ($definition->kind) {
+            switch (true) {
-                case NodeKind::OPERATION_DEFINITION:
+                case $definition instanceof OperationDefinitionNode:
-                    if (! $operationName && $operation) {
+                    if ($operationName === null && $operation !== null) {
                         $hasMultipleAssumedOperations = true;
                     }
-                    if (! $operationName ||
+                    if ($operationName === null ||
                         (isset($definition->name) && $definition->name->value === $operationName)) {
                         $operation = $definition;
                     }
                     break;
-                case NodeKind::FRAGMENT_DEFINITION:
+                case $definition instanceof FragmentDefinitionNode:
                     $fragments[$definition->name->value] = $definition;
                     break;
             }
         }
         if ($operation === null) {
-            if ($operationName) {
+            if ($operationName === null) {
-                $errors[] = new Error(sprintf('Unknown operation named "%s".', $operationName));
-            } else {
                 $errors[] = new Error('Must provide an operation.');
+            } else {
+                $errors[] = new Error(sprintf('Unknown operation named "%s".', $operationName));
             }
         } elseif ($hasMultipleAssumedOperations) {
             $errors[] = new Error(
@@ -199,7 +199,7 @@ class ReferenceExecutor implements ExecutorImplementation
     public function doExecute() : Promise
     {
         // Return a Promise that will eventually resolve to the data described by
-        // The "Response" section of the GraphQL specification.
+        // the "Response" section of the GraphQL specification.
         //
         // If errors are encountered while executing a GraphQL field, only that
         // field and its descendants will be omitted, and sibling fields will still
@@ -212,7 +212,7 @@ class ReferenceExecutor implements ExecutorImplementation
         // But for the "sync" case it is always fulfilled
         return $this->isPromise($result)
             ? $result
-            : $this->exeContext->promises->createFulfilled($result);
+            : $this->exeContext->promiseAdapter->createFulfilled($result);
     }
 
     /**
@@ -237,7 +237,7 @@ class ReferenceExecutor implements ExecutorImplementation
     /**
      * Implements the "Evaluating operations" section of the spec.
      *
-     * @param  mixed[] $rootValue
+     * @param  mixed $rootValue
      *
      * @return Promise|stdClass|mixed[]
      */
@@ -252,16 +252,18 @@ class ReferenceExecutor implements ExecutorImplementation
         //
         // Similar to completeValueCatchingError.
         try {
-            $result = $operation->operation === 'mutation' ?
+            $result = $operation->operation === 'mutation'
-                $this->executeFieldsSerially($type, $rootValue, $path, $fields) :
+                ? $this->executeFieldsSerially($type, $rootValue, $path, $fields)
-                $this->executeFields($type, $rootValue, $path, $fields);
+                : $this->executeFields($type, $rootValue, $path, $fields);
             if ($this->isPromise($result)) {
                 return $result->then(
                     null,
                     function ($error) {
-                        $this->exeContext->addError($error);
+                        if ($error instanceof Error) {
+                            $this->exeContext->addError($error);
 
-                        return $this->exeContext->promises->createFulfilled(null);
+                            return $this->exeContext->promiseAdapter->createFulfilled(null);
+                        }
                     }
                 );
             }
@@ -286,7 +288,7 @@ class ReferenceExecutor implements ExecutorImplementation
         switch ($operation->operation) {
             case 'query':
                 $queryType = $schema->getQueryType();
-                if (! $queryType) {
+                if ($queryType === null) {
                     throw new Error(
                         'Schema does not define the required query root type.',
                         [$operation]
@@ -296,7 +298,7 @@ class ReferenceExecutor implements ExecutorImplementation
                 return $queryType;
             case 'mutation':
                 $mutationType = $schema->getMutationType();
-                if (! $mutationType) {
+                if ($mutationType === null) {
                     throw new Error(
                         'Schema is not configured for mutations.',
                         [$operation]
@@ -306,7 +308,7 @@ class ReferenceExecutor implements ExecutorImplementation
                 return $mutationType;
             case 'subscription':
                 $subscriptionType = $schema->getSubscriptionType();
-                if (! $subscriptionType) {
+                if ($subscriptionType === null) {
                     throw new Error(
                         'Schema is not configured for subscriptions.',
                         [$operation]
@@ -343,8 +345,8 @@ class ReferenceExecutor implements ExecutorImplementation
     ) {
         $exeContext = $this->exeContext;
         foreach ($selectionSet->selections as $selection) {
-            switch ($selection->kind) {
+            switch (true) {
-                case NodeKind::FIELD:
+                case $selection instanceof FieldNode:
                     if (! $this->shouldIncludeNode($selection)) {
                         break;
                     }
@@ -354,7 +356,7 @@ class ReferenceExecutor implements ExecutorImplementation
                     }
                     $fields[$name][] = $selection;
                     break;
-                case NodeKind::INLINE_FRAGMENT:
+                case $selection instanceof InlineFragmentNode:
                     if (! $this->shouldIncludeNode($selection) ||
                         ! $this->doesFragmentConditionMatch($selection, $runtimeType)
                     ) {
@@ -367,7 +369,7 @@ class ReferenceExecutor implements ExecutorImplementation
                         $visitedFragmentNames
                     );
                     break;
-                case NodeKind::FRAGMENT_SPREAD:
+                case $selection instanceof FragmentSpreadNode:
                     $fragName = $selection->name->value;
                     if (! empty($visitedFragmentNames[$fragName]) || ! $this->shouldIncludeNode($selection)) {
                         break;
@@ -375,7 +377,7 @@ class ReferenceExecutor implements ExecutorImplementation
                     $visitedFragmentNames[$fragName] = true;
                     /** @var FragmentDefinitionNode|null $fragment */
                     $fragment = $exeContext->fragments[$fragName] ?? null;
-                    if (! $fragment || ! $this->doesFragmentConditionMatch($fragment, $runtimeType)) {
+                    if ($fragment === null || ! $this->doesFragmentConditionMatch($fragment, $runtimeType)) {
                         break;
                     }
                     $this->collectFields(
@@ -396,10 +398,8 @@ class ReferenceExecutor implements ExecutorImplementation
      * directives, where @skip has higher precedence than @include.
      *
      * @param FragmentSpreadNode|FieldNode|InlineFragmentNode $node
-     *
-     * @return bool
      */
-    private function shouldIncludeNode($node)
+    private function shouldIncludeNode($node) : bool
     {
         $variableValues = $this->exeContext->variableValues;
         $skipDirective  = Directive::skipDirective();
@@ -423,12 +423,10 @@ class ReferenceExecutor implements ExecutorImplementation
 
     /**
      * Implements the logic to compute the key of a given fields entry
-     *
-     * @return string
      */
-    private static function getFieldEntryKey(FieldNode $node)
+    private static function getFieldEntryKey(FieldNode $node) : string
     {
-        return $node->alias ? $node->alias->value : $node->name->value;
+        return $node->alias === null ? $node->name->value : $node->alias->value;
     }
 
     /**
@@ -461,26 +459,26 @@ class ReferenceExecutor implements ExecutorImplementation
      * Implements the "Evaluating selection sets" section of the spec
      * for "write" mode.
      *
-     * @param mixed[]     $sourceValue
+     * @param mixed       $rootValue
      * @param mixed[]     $path
      * @param ArrayObject $fields
      *
      * @return Promise|stdClass|mixed[]
      */
-    private function executeFieldsSerially(ObjectType $parentType, $sourceValue, $path, $fields)
+    private function executeFieldsSerially(ObjectType $parentType, $rootValue, $path, $fields)
     {
         $result = $this->promiseReduce(
             array_keys($fields->getArrayCopy()),
-            function ($results, $responseName) use ($path, $parentType, $sourceValue, $fields) {
+            function ($results, $responseName) use ($path, $parentType, $rootValue, $fields) {
                 $fieldNodes  = $fields[$responseName];
                 $fieldPath   = $path;
                 $fieldPath[] = $responseName;
-                $result      = $this->resolveField($parentType, $sourceValue, $fieldNodes, $fieldPath);
+                $result      = $this->resolveField($parentType, $rootValue, $fieldNodes, $fieldPath);
                 if ($result === self::$UNDEFINED) {
                     return $results;
                 }
                 $promise = $this->getPromise($result);
-                if ($promise) {
+                if ($promise !== null) {
                     return $promise->then(static function ($resolvedResult) use ($responseName, $results) {
                         $results[$responseName] = $resolvedResult;
 
@@ -503,28 +501,33 @@ class ReferenceExecutor implements ExecutorImplementation
     }
 
     /**
-     * Resolves the field on the given source object. In particular, this
+     * Resolves the field on the given root value.
-     * figures out the value that the field returns by calling its resolve function,
-     * then calls completeValue to complete promises, serialize scalars, or execute
-     * the sub-selection-set for objects.
      *
-     * @param object|null $source
+     * In particular, this figures out the value that the field returns
+     * by calling its resolve function, then calls completeValue to complete promises,
+     * serialize scalars, or execute the sub-selection-set for objects.
+     *
+     * @param mixed       $rootValue
      * @param FieldNode[] $fieldNodes
      * @param mixed[]     $path
      *
      * @return mixed[]|Exception|mixed|null
      */
-    private function resolveField(ObjectType $parentType, $source, $fieldNodes, $path)
+    private function resolveField(ObjectType $parentType, $rootValue, $fieldNodes, $path)
     {
         $exeContext = $this->exeContext;
         $fieldNode  = $fieldNodes[0];
         $fieldName  = $fieldNode->name->value;
         $fieldDef   = $this->getFieldDef($exeContext->schema, $parentType, $fieldName);
-        if (! $fieldDef) {
+        if ($fieldDef === null) {
             return self::$UNDEFINED;
         }
         $returnType = $fieldDef->getType();
-        // The resolve function's optional third argument is a collection of
+        // The resolve function's optional 3rd argument is a context value that
+        // is provided to every resolve function within an execution. It is commonly
+        // used to represent an authenticated user, or request-specific caches.
+        $context = $exeContext->contextValue;
+        // The resolve function's optional 4th argument is a collection of
         // information about the current execution state.
         $info = new ResolveInfo(
             $fieldName,
@@ -545,17 +548,13 @@ class ReferenceExecutor implements ExecutorImplementation
         } else {
             $resolveFn = $this->exeContext->fieldResolver;
         }
-        // The resolve function's optional third argument is a context value that
-        // is provided to every resolve function within an execution. It is commonly
-        // used to represent an authenticated user, or request-specific caches.
-        $context = $exeContext->contextValue;
         // Get the resolve function, regardless of if its result is normal
         // or abrupt (error).
         $result = $this->resolveOrError(
             $fieldDef,
             $fieldNode,
             $resolveFn,
-            $source,
+            $rootValue,
             $context,
             $info
         );
@@ -572,18 +571,15 @@ class ReferenceExecutor implements ExecutorImplementation
 
     /**
      * This method looks up the field on the given type definition.
+     *
      * It has special casing for the two introspection fields, __schema
      * and __typename. __typename is special because it can always be
      * queried as a field, even in situations where no other fields
      * are allowed, like on a Union. __schema could get automatically
      * added to the query type, but that would require mutating type
      * definitions, which would cause issues.
-     *
-     * @param string $fieldName
-     *
-     * @return FieldDefinition
      */
-    private function getFieldDef(Schema $schema, ObjectType $parentType, $fieldName)
+    private function getFieldDef(Schema $schema, ObjectType $parentType, string $fieldName) : ?FieldDefinition
     {
         static $schemaMetaFieldDef, $typeMetaFieldDef, $typeNameMetaFieldDef;
         $schemaMetaFieldDef   = $schemaMetaFieldDef ?: Introspection::schemaMetaFieldDef();
@@ -606,22 +602,22 @@ class ReferenceExecutor implements ExecutorImplementation
     }
 
     /**
-     * Isolates the "ReturnOrAbrupt" behavior to not de-opt the `resolveField`
+     * Isolates the "ReturnOrAbrupt" behavior to not de-opt the `resolveField` function.
-     * function. Returns the result of resolveFn or the abrupt-return Error object.
+     * Returns the result of resolveFn or the abrupt-return Error object.
      *
      * @param FieldDefinition $fieldDef
      * @param FieldNode       $fieldNode
      * @param callable        $resolveFn
-     * @param mixed           $source
+     * @param mixed           $rootValue
      * @param mixed           $context
      * @param ResolveInfo     $info
      *
      * @return Throwable|Promise|mixed
      */
-    private function resolveOrError($fieldDef, $fieldNode, $resolveFn, $source, $context, $info)
+    private function resolveOrError($fieldDef, $fieldNode, $resolveFn, $rootValue, $context, $info)
     {
         try {
-            // Build hash of arguments from the field.arguments AST, using the
+            // Build a map of arguments from the field.arguments AST, using the
             // variables scope to fulfill any variable references.
             $args = Values::getArgumentValues(
                 $fieldDef,
@@ -629,7 +625,7 @@ class ReferenceExecutor implements ExecutorImplementation
                 $this->exeContext->variableValues
             );
 
-            return $resolveFn($source, $args, $context, $info);
+            return $resolveFn($rootValue, $args, $context, $info);
         } catch (Exception $error) {
             return $error;
         } catch (Throwable $error) {
@@ -677,13 +673,13 @@ class ReferenceExecutor implements ExecutorImplementation
                 $result
             );
             $promise   = $this->getPromise($completed);
-            if ($promise) {
+            if ($promise !== null) {
                 return $promise->then(
                     null,
                     function ($error) use ($exeContext) {
                         $exeContext->addError($error);
 
-                        return $this->exeContext->promises->createFulfilled(null);
+                        return $this->exeContext->promiseAdapter->createFulfilled(null);
                     }
                 );
             }
@@ -726,11 +722,11 @@ class ReferenceExecutor implements ExecutorImplementation
                 $result
             );
             $promise   = $this->getPromise($completed);
-            if ($promise) {
+            if ($promise !== null) {
                 return $promise->then(
                     null,
                     function ($error) use ($fieldNodes, $path) {
-                        return $this->exeContext->promises->createRejected(Error::createLocatedError(
+                        return $this->exeContext->promiseAdapter->createRejected(Error::createLocatedError(
                             $error,
                             $fieldNodes,
                             $path
@@ -786,7 +782,7 @@ class ReferenceExecutor implements ExecutorImplementation
     ) {
         $promise = $this->getPromise($result);
         // If result is a Promise, apply-lift over completeValue.
-        if ($promise) {
+        if ($promise !== null) {
             return $promise->then(function (&$resolved) use ($returnType, $fieldNodes, $info, $path) {
                 return $this->completeValue($returnType, $fieldNodes, $info, $path, $resolved);
             });
@@ -824,7 +820,7 @@ class ReferenceExecutor implements ExecutorImplementation
         // instance than `resolveType` or $field->getType() or $arg->getType()
         if ($returnType !== $this->exeContext->schema->getType($returnType->name)) {
             $hint = '';
-            if ($this->exeContext->schema->getConfig()->typeLoader) {
+            if ($this->exeContext->schema->getConfig()->typeLoader !== null) {
                 $hint = sprintf(
                     'Make sure that type loader returns the same instance as defined in %s.%s',
                     $info->parentType,
@@ -862,7 +858,7 @@ class ReferenceExecutor implements ExecutorImplementation
      */
     private function isPromise($value)
     {
-        return $value instanceof Promise || $this->exeContext->promises->isThenable($value);
+        return $value instanceof Promise || $this->exeContext->promiseAdapter->isThenable($value);
     }
 
     /**
@@ -878,12 +874,12 @@ class ReferenceExecutor implements ExecutorImplementation
         if ($value === null || $value instanceof Promise) {
             return $value;
         }
-        if ($this->exeContext->promises->isThenable($value)) {
+        if ($this->exeContext->promiseAdapter->isThenable($value)) {
-            $promise = $this->exeContext->promises->convertThenable($value);
+            $promise = $this->exeContext->promiseAdapter->convertThenable($value);
             if (! $promise instanceof Promise) {
                 throw new InvariantViolation(sprintf(
                     '%s::convertThenable is expected to return instance of GraphQL\Executor\Promise\Promise, got: %s',
-                    get_class($this->exeContext->promises),
+                    get_class($this->exeContext->promiseAdapter),
                     Utils::printSafe($promise)
                 ));
             }
@@ -904,7 +900,7 @@ class ReferenceExecutor implements ExecutorImplementation
      * @param mixed[]            $values
      * @param Promise|mixed|null $initialValue
      *
-     * @return mixed[]
+     * @return mixed
      */
     private function promiseReduce(array $values, callable $callback, $initialValue)
     {
@@ -912,7 +908,7 @@ class ReferenceExecutor implements ExecutorImplementation
             $values,
             function ($previous, $value) use ($callback) {
                 $promise = $this->getPromise($previous);
-                if ($promise) {
+                if ($promise !== null) {
                     return $promise->then(static function ($resolved) use ($callback, $value) {
                         return $callback($resolved, $value);
                     });
@@ -925,38 +921,40 @@ class ReferenceExecutor implements ExecutorImplementation
     }
 
     /**
-     * Complete a list value by completing each item in the list with the
+     * Complete a list value by completing each item in the list with the inner type.
-     * inner type
      *
-     * @param FieldNode[] $fieldNodes
+     * @param FieldNode[]         $fieldNodes
-     * @param mixed[]     $path
+     * @param mixed[]             $path
-     * @param mixed       $result
+     * @param mixed[]|Traversable $results
      *
      * @return mixed[]|Promise
      *
      * @throws Exception
      */
-    private function completeListValue(ListOfType $returnType, $fieldNodes, ResolveInfo $info, $path, &$result)
+    private function completeListValue(ListOfType $returnType, $fieldNodes, ResolveInfo $info, $path, &$results)
     {
         $itemType = $returnType->getWrappedType();
         Utils::invariant(
-            is_array($result) || $result instanceof Traversable,
+            is_array($results) || $results instanceof Traversable,
             'User Error: expected iterable, but did not find one for field ' . $info->parentType . '.' . $info->fieldName . '.'
         );
         $containsPromise = false;
         $i               = 0;
         $completedItems  = [];
-        foreach ($result as $item) {
+        foreach ($results as $item) {
             $fieldPath     = $path;
             $fieldPath[]   = $i++;
+            $info->path    = $fieldPath;
             $completedItem = $this->completeValueCatchingError($itemType, $fieldNodes, $info, $fieldPath, $item);
-            if (! $containsPromise && $this->getPromise($completedItem)) {
+            if (! $containsPromise && $this->getPromise($completedItem) !== null) {
                 $containsPromise = true;
             }
             $completedItems[] = $completedItem;
         }
 
-        return $containsPromise ? $this->exeContext->promises->all($completedItems) : $completedItems;
+        return $containsPromise
+            ? $this->exeContext->promiseAdapter->all($completedItems)
+            : $completedItems;
     }
 
     /**
@@ -1007,7 +1005,7 @@ class ReferenceExecutor implements ExecutorImplementation
             $runtimeType = self::defaultTypeResolver($result, $exeContext->contextValue, $info, $returnType);
         }
         $promise = $this->getPromise($runtimeType);
-        if ($promise) {
+        if ($promise !== null) {
             return $promise->then(function ($resolvedRuntimeType) use (
                 $returnType,
                 $fieldNodes,
@@ -1069,7 +1067,8 @@ class ReferenceExecutor implements ExecutorImplementation
         ) {
             return $value['__typename'];
         }
-        if ($abstractType instanceof InterfaceType && $info->schema->getConfig()->typeLoader) {
+
+        if ($abstractType instanceof InterfaceType && $info->schema->getConfig()->typeLoader !== null) {
             Warning::warnOnce(
                 sprintf(
                     'GraphQL Interface Type `%s` returned `null` from its `resolveType` function ' .
@@ -1091,14 +1090,14 @@ class ReferenceExecutor implements ExecutorImplementation
                 continue;
             }
             $promise = $this->getPromise($isTypeOfResult);
-            if ($promise) {
+            if ($promise !== null) {
                 $promisedIsTypeOfResults[$index] = $promise;
             } elseif ($isTypeOfResult) {
                 return $type;
             }
         }
         if (! empty($promisedIsTypeOfResults)) {
-            return $this->exeContext->promises->all($promisedIsTypeOfResults)
+            return $this->exeContext->promiseAdapter->all($promisedIsTypeOfResults)
                 ->then(static function ($isTypeOfResults) use ($possibleTypes) {
                     foreach ($isTypeOfResults as $index => $result) {
                         if ($result) {
@@ -1132,7 +1131,7 @@ class ReferenceExecutor implements ExecutorImplementation
         $isTypeOf = $returnType->isTypeOf($result, $this->exeContext->contextValue, $info);
         if ($isTypeOf !== null) {
             $promise = $this->getPromise($isTypeOf);
-            if ($promise) {
+            if ($promise !== null) {
                 return $promise->then(function ($isTypeOfResult) use (
                     $returnType,
                     $fieldNodes,
@@ -1184,7 +1183,7 @@ class ReferenceExecutor implements ExecutorImplementation
     /**
      * @param FieldNode[] $fieldNodes
      * @param mixed[]     $path
-     * @param mixed[]     $result
+     * @param mixed       $result
      *
      * @return mixed[]|Promise|stdClass
      *
@@ -1231,24 +1230,24 @@ class ReferenceExecutor implements ExecutorImplementation
      * Implements the "Evaluating selection sets" section of the spec
      * for "read" mode.
      *
-     * @param mixed|null  $source
+     * @param mixed       $rootValue
      * @param mixed[]     $path
      * @param ArrayObject $fields
      *
      * @return Promise|stdClass|mixed[]
      */
-    private function executeFields(ObjectType $parentType, $source, $path, $fields)
+    private function executeFields(ObjectType $parentType, $rootValue, $path, $fields)
     {
         $containsPromise = false;
         $finalResults    = [];
         foreach ($fields as $responseName => $fieldNodes) {
             $fieldPath   = $path;
             $fieldPath[] = $responseName;
-            $result      = $this->resolveField($parentType, $source, $fieldNodes, $fieldPath);
+            $result      = $this->resolveField($parentType, $rootValue, $fieldNodes, $fieldPath);
             if ($result === self::$UNDEFINED) {
                 continue;
             }
-            if (! $containsPromise && $this->getPromise($result)) {
+            if (! $containsPromise && $this->getPromise($result) !== null) {
                 $containsPromise = true;
             }
             $finalResults[$responseName] = $result;
@@ -1296,7 +1295,7 @@ class ReferenceExecutor implements ExecutorImplementation
     {
         $keys              = array_keys($assoc);
         $valuesAndPromises = array_values($assoc);
-        $promise           = $this->exeContext->promises->all($valuesAndPromises);
+        $promise           = $this->exeContext->promiseAdapter->all($valuesAndPromises);
 
         return $promise->then(static function ($values) use ($keys) {
             $resolvedResults = [];
@@ -1310,7 +1309,6 @@ class ReferenceExecutor implements ExecutorImplementation
 
     /**
      * @param string|ObjectType|null $runtimeTypeOrName
-     * @param FieldNode[]            $fieldNodes
      * @param mixed                  $result
      *
      * @return ObjectType
@@ -1321,9 +1319,9 @@ class ReferenceExecutor implements ExecutorImplementation
         ResolveInfo $info,
         &$result
     ) {
-        $runtimeType = is_string($runtimeTypeOrName) ?
+        $runtimeType = is_string($runtimeTypeOrName)
-            $this->exeContext->schema->getType($runtimeTypeOrName) :
+            ? $this->exeContext->schema->getType($runtimeTypeOrName)
-            $runtimeTypeOrName;
+            : $runtimeTypeOrName;
         if (! $runtimeType instanceof ObjectType) {
             throw new InvariantViolation(
                 sprintf(

src/Executor/Values.php

@@ -92,7 +92,7 @@ class Values
                             ),
                             [$varDefNode]
                         );
-                    } elseif ($varDefNode->defaultValue) {
+                    } elseif ($varDefNode->defaultValue !== null) {
                         $coercedValues[$varName] = AST::valueFromAST($varDefNode->defaultValue, $varType);
                     }
                 }
@@ -196,7 +196,7 @@ class Values
             $argType           = $argumentDefinition->getType();
             $argumentValueNode = $argumentValueMap[$name] ?? null;
 
-            if (! $argumentValueNode) {
+            if ($argumentValueNode === null) {
                 if ($argumentDefinition->defaultValueExists()) {
                     $coercedValues[$name] = $argumentDefinition->defaultValue;
                 } elseif ($argType instanceof NonNull) {
@@ -209,7 +209,7 @@ class Values
             } elseif ($argumentValueNode instanceof VariableNode) {
                 $variableName = $argumentValueNode->name->value;
 
-                if ($variableValues && array_key_exists($variableName, $variableValues)) {
+                if ($variableValues !== null && array_key_exists($variableName, $variableValues)) {
                     // Note: this does not check that this variable value is correct.
                     // This assumes that this query has been validated and the variable
                     // usage here is of the correct type.
@@ -273,6 +273,7 @@ class Values
                     return $error->getMessage();
                 },
                 $errors
-            ) : [];
+            )
+            : [];
     }
 }

src/Experimental/Executor/Collector.php

@@ -64,7 +64,7 @@ class Collector
         foreach ($documentNode->definitions as $definitionNode) {
             /** @var DefinitionNode|Node $definitionNode */
 
-            if ($definitionNode->kind === NodeKind::OPERATION_DEFINITION) {
+            if ($definitionNode instanceof OperationDefinitionNode) {
                 /** @var OperationDefinitionNode $definitionNode */
                 if ($operationName === null && $this->operation !== null) {
                     $hasMultipleAssumedOperations = true;
@@ -74,7 +74,7 @@ class Collector
                 ) {
                     $this->operation = $definitionNode;
                 }
-            } elseif ($definitionNode->kind === NodeKind::FRAGMENT_DEFINITION) {
+            } elseif ($definitionNode instanceof FragmentDefinitionNode) {
                 /** @var FragmentDefinitionNode $definitionNode */
                 $this->fragments[$definitionNode->name->value] = $definitionNode;
             }
@@ -196,17 +196,17 @@ class Collector
                 }
             }
 
-            if ($selection->kind === NodeKind::FIELD) {
+            if ($selection instanceof FieldNode) {
                 /** @var FieldNode $selection */
 
-                $resultName = $selection->alias ? $selection->alias->value : $selection->name->value;
+                $resultName = $selection->alias === null ? $selection->name->value : $selection->alias->value;
 
                 if (! isset($this->fields[$resultName])) {
                     $this->fields[$resultName] = [];
                 }
 
                 $this->fields[$resultName][] = $selection;
-            } elseif ($selection->kind === NodeKind::FRAGMENT_SPREAD) {
+            } elseif ($selection instanceof FragmentSpreadNode) {
                 /** @var FragmentSpreadNode $selection */
 
                 $fragmentName = $selection->name->value;
@@ -249,7 +249,7 @@ class Collector
                 }
 
                 $this->doCollectFields($runtimeType, $fragmentDefinition->selectionSet);
-            } elseif ($selection->kind === NodeKind::INLINE_FRAGMENT) {
+            } elseif ($selection instanceof InlineFragmentNode) {
                 /** @var InlineFragmentNode $selection */
 
                 if ($selection->typeCondition !== null) {

src/Experimental/Executor/CoroutineExecutor.php

@@ -498,7 +498,7 @@ class CoroutineExecutor implements Runtime, ExecutorImplementation
 
         if ($type !== $this->schema->getType($type->name)) {
             $hint = '';
-            if ($this->schema->getConfig()->typeLoader) {
+            if ($this->schema->getConfig()->typeLoader !== null) {
                 $hint = sprintf(
                     'Make sure that type loader returns the same instance as defined in %s.%s',
                     $ctx->type,
@@ -620,8 +620,9 @@ class CoroutineExecutor implements Runtime, ExecutorImplementation
             foreach ($value as $itemValue) {
                 ++$index;
 
-                $itemPath   = $path;
+                $itemPath               = $path;
-                $itemPath[] = $index; // !!! use arrays COW semantics
+                $itemPath[]             = $index; // !!! use arrays COW semantics
+                $ctx->resolveInfo->path = $itemPath;
 
                 try {
                     if (! $this->completeValueFast($ctx, $itemType, $itemValue, $itemPath, $itemReturnValue)) {
@@ -646,7 +647,7 @@ class CoroutineExecutor implements Runtime, ExecutorImplementation
         } else {
             if ($type !== $this->schema->getType($type->name)) {
                 $hint = '';
-                if ($this->schema->getConfig()->typeLoader) {
+                if ($this->schema->getConfig()->typeLoader !== null) {
                     $hint = sprintf(
                         'Make sure that type loader returns the same instance as defined in %s.%s',
                         $ctx->type,
@@ -820,7 +821,10 @@ class CoroutineExecutor implements Runtime, ExecutorImplementation
                 } else {
                     $childContexts = [];
 
-                    foreach ($this->collector->collectFields($objectType, $ctx->shared->mergedSelectionSet ?? $this->mergeSelectionSets($ctx)) as $childShared) {
+                    foreach ($this->collector->collectFields(
+                        $objectType,
+                        $ctx->shared->mergedSelectionSet ?? $this->mergeSelectionSets($ctx)
+                    ) as $childShared) {
                         /** @var CoroutineContextShared $childShared */
 
                         $childPath   = $path;
@@ -904,7 +908,7 @@ class CoroutineExecutor implements Runtime, ExecutorImplementation
             return $this->schema->getType($value['__typename']);
         }
 
-        if ($abstractType instanceof InterfaceType && $this->schema->getConfig()->typeLoader) {
+        if ($abstractType instanceof InterfaceType && $this->schema->getConfig()->typeLoader !== null) {
             Warning::warnOnce(
                 sprintf(
                     'GraphQL Interface Type `%s` returned `null` from its `resolveType` function ' .

src/Language/AST/ListTypeNode.php

@@ -9,6 +9,6 @@ class ListTypeNode extends Node implements TypeNode
     /** @var string */
     public $kind = NodeKind::LIST_TYPE;
 
-    /** @var Node */
+    /** @var TypeNode */
     public $type;
 }

src/Language/AST/Location.php

@@ -69,7 +69,7 @@ class Location
         $this->endToken   = $endToken;
         $this->source     = $source;
 
-        if (! $startToken || ! $endToken) {
+        if ($startToken === null || $endToken === null) {
             return;
         }
 

src/Language/AST/Node.php

@@ -106,7 +106,7 @@ abstract class Node
 
         $tmp = (array) $this;
 
-        if ($this->loc) {
+        if ($this->loc !== null) {
             $tmp['loc'] = [
                 'start' => $this->loc->start,
                 'end'   => $this->loc->end,
@@ -125,7 +125,7 @@ abstract class Node
             'kind' => $node->kind,
         ];
 
-        if ($node->loc) {
+        if ($node->loc !== null) {
             $result['loc'] = [
                 'start' => $node->loc->start,
                 'end'   => $node->loc->end,

src/Language/AST/NonNullTypeNode.php

@@ -9,6 +9,6 @@ class NonNullTypeNode extends Node implements TypeNode
     /** @var string */
     public $kind = NodeKind::NON_NULL_TYPE;
 
-    /** @var NameNode | ListTypeNode */
+    /** @var NamedTypeNode | ListTypeNode */
     public $type;
 }

src/Language/Lexer.php

@@ -314,11 +314,11 @@ class Lexer
         $start         = $this->position;
         [$char, $code] = $this->readChar();
 
-        while ($code && (
+        while ($code !== null && (
                 $code === 95 || // _
-                $code >= 48 && $code <= 57 || // 0-9
+                ($code >= 48 && $code <= 57) || // 0-9
-                $code >= 65 && $code <= 90 || // A-Z
+                ($code >= 65 && $code <= 90) || // A-Z
-                $code >= 97 && $code <= 122 // a-z
+                ($code >= 97 && $code <= 122) // a-z
             )) {
             $value        .= $char;
             [$char, $code] = $this->moveStringCursor(1, 1)->readChar();
@@ -695,7 +695,7 @@ class Lexer
         do {
             [$char, $code, $bytes] = $this->moveStringCursor(1, $bytes)->readChar();
             $value                .= $char;
-        } while ($code &&
+        } while ($code !== null &&
         // SourceCharacter but not LineTerminator
         ($code > 0x001F || $code === 0x0009)
         );

src/Language/Parser.php

@@ -512,15 +512,15 @@ class Parser
      */
     private function parseVariableDefinitions()
     {
-        return $this->peek(Token::PAREN_L) ?
+        return $this->peek(Token::PAREN_L)
-            $this->many(
+            ? $this->many(
                 Token::PAREN_L,
                 function () {
                     return $this->parseVariableDefinition();
                 },
                 Token::PAREN_R
-            ) :
+            )
-            new NodeList([]);
+            : new NodeList([]);
     }
 
     /**
@@ -592,9 +592,9 @@ class Parser
      */
     private function parseSelection()
     {
-        return $this->peek(Token::SPREAD) ?
+        return $this->peek(Token::SPREAD)
-            $this->parseFragment() :
+            ? $this->parseFragment()
-            $this->parseField();
+            : $this->parseField();
     }
 
     /**
@@ -634,17 +634,17 @@ class Parser
      */
     private function parseArguments($isConst)
     {
-        $parseFn = $isConst ?
+        $parseFn = $isConst
-            function () {
+            ? function () {
                 return $this->parseConstArgument();
-            } :
+            }
-            function () {
+            : function () {
                 return $this->parseArgument();
             };
 
-        return $this->peek(Token::PAREN_L) ?
+        return $this->peek(Token::PAREN_L)
-            $this->many(Token::PAREN_L, $parseFn, Token::PAREN_R) :
+            ? $this->many(Token::PAREN_L, $parseFn, Token::PAREN_R)
-            new NodeList([]);
+            : new NodeList([]);
     }
 
     /**
@@ -1208,8 +1208,8 @@ class Parser
             do {
                 $types[] = $this->parseNamedType();
             } while ($this->skip(Token::AMP) ||
-            // Legacy support for the SDL?
+                // Legacy support for the SDL?
-            (! empty($this->lexer->options['allowLegacySDLImplementsInterfaces']) && $this->peek(Token::NAME))
+                (! empty($this->lexer->options['allowLegacySDLImplementsInterfaces']) && $this->peek(Token::NAME))
             );
         }
 
@@ -1545,7 +1545,8 @@ class Parser
                 Token::BRACE_L,
                 [$this, 'parseOperationTypeDefinition'],
                 Token::BRACE_R
-            ) : [];
+            )
+            : [];
         if (count($directives) === 0 && count($operationTypes) === 0) {
             $this->unexpected();
         }
@@ -1655,9 +1656,7 @@ class Parser
         $name       = $this->parseName();
         $directives = $this->parseDirectives(true);
         $types      = $this->parseUnionMemberTypes();
-        if (count($directives) === 0 &&
+        if (count($directives) === 0 && count($types) === 0) {
-            ! $types
-        ) {
             throw $this->unexpected();
         }
 

src/Language/Printer.php

@@ -28,6 +28,7 @@ use GraphQL\Language\AST\IntValueNode;
 use GraphQL\Language\AST\ListTypeNode;
 use GraphQL\Language\AST\ListValueNode;
 use GraphQL\Language\AST\NamedTypeNode;
+use GraphQL\Language\AST\NameNode;
 use GraphQL\Language\AST\Node;
 use GraphQL\Language\AST\NodeKind;
 use GraphQL\Language\AST\NonNullTypeNode;
@@ -47,6 +48,7 @@ use GraphQL\Language\AST\StringValueNode;
 use GraphQL\Language\AST\UnionTypeDefinitionNode;
 use GraphQL\Language\AST\UnionTypeExtensionNode;
 use GraphQL\Language\AST\VariableDefinitionNode;
+use GraphQL\Language\AST\VariableNode;
 use GraphQL\Utils\Utils;
 use function count;
 use function implode;
@@ -97,11 +99,11 @@ class Printer
             $ast,
             [
                 'leave' => [
-                    NodeKind::NAME => static function (Node $node) {
+                    NodeKind::NAME => static function (NameNode $node) {
                         return '' . $node->value;
                     },
 
-                    NodeKind::VARIABLE => static function ($node) {
+                    NodeKind::VARIABLE => static function (VariableNode $node) {
                         return '$' . $node->name;
                     },
 

src/Language/Token.php

@@ -11,28 +11,28 @@ namespace GraphQL\Language;
 class Token
 {
     // Each kind of token.
-    const SOF          = '<SOF>';
+    public const SOF          = '<SOF>';
-    const EOF          = '<EOF>';
+    public const EOF          = '<EOF>';
-    const BANG         = '!';
+    public const BANG         = '!';
-    const DOLLAR       = '$';
+    public const DOLLAR       = '$';
-    const AMP          = '&';
+    public const AMP          = '&';
-    const PAREN_L      = '(';
+    public const PAREN_L      = '(';
-    const PAREN_R      = ')';
+    public const PAREN_R      = ')';
-    const SPREAD       = '...';
+    public const SPREAD       = '...';
-    const COLON        = ':';
+    public const COLON        = ':';
-    const EQUALS       = '=';
+    public const EQUALS       = '=';
-    const AT           = '@';
+    public const AT           = '@';
-    const BRACKET_L    = '[';
+    public const BRACKET_L    = '[';
-    const BRACKET_R    = ']';
+    public const BRACKET_R    = ']';
-    const BRACE_L      = '{';
+    public const BRACE_L      = '{';
-    const PIPE         = '|';
+    public const PIPE         = '|';
-    const BRACE_R      = '}';
+    public const BRACE_R      = '}';
-    const NAME         = 'Name';
+    public const NAME         = 'Name';
-    const INT          = 'Int';
+    public const INT          = 'Int';
-    const FLOAT        = 'Float';
+    public const FLOAT        = 'Float';
-    const STRING       = 'String';
+    public const STRING       = 'String';
-    const BLOCK_STRING = 'BlockString';
+    public const BLOCK_STRING = 'BlockString';
-    const COMMENT      = 'Comment';
+    public const COMMENT      = 'Comment';
 
     /**
      * The kind of Token (see one of constants above).
@@ -104,18 +104,15 @@ class Token
         $this->value  = $value;
     }
 
-    /**
+    public function getDescription() : string
-     * @return string
-     */
-    public function getDescription()
     {
-        return $this->kind . ($this->value ? ' "' . $this->value . '"' : '');
+        return $this->kind . ($this->value === null ? '' : ' "' . $this->value . '"');
     }
 
     /**
      * @return (string|int|null)[]
      */
-    public function toArray()
+    public function toArray() : array
     {
         return [
             'kind'   => $this->kind,

src/Language/Visitor.php

@@ -251,8 +251,18 @@ class Visitor
                 $inArray = $stack['inArray'];
                 $stack   = $stack['prev'];
             } else {
-                $key  = $parent !== null ? ($inArray ? $index : $keys[$index]) : $UNDEFINED;
+                $key  = $parent !== null
-                $node = $parent !== null ? ($parent instanceof NodeList || is_array($parent) ? $parent[$key] : $parent->{$key}) : $newRoot;
+                    ? ($inArray
+                        ? $index
+                        : $keys[$index]
+                    )
+                    : $UNDEFINED;
+                $node = $parent !== null
+                    ? ($parent instanceof NodeList || is_array($parent)
+                        ? $parent[$key]
+                        : $parent->{$key}
+                    )
+                    : $newRoot;
                 if ($node === null || $node === $UNDEFINED) {
                     continue;
                 }

src/Schema.php

@@ -1,22 +0,0 @@
-<?php
-
-declare(strict_types=1);
-
-namespace GraphQL;
-
-use function trigger_error;
-use const E_USER_DEPRECATED;
-
-trigger_error(
-    'GraphQL\Schema is moved to GraphQL\Type\Schema',
-    E_USER_DEPRECATED
-);
-
-/**
- * Schema Definition
- *
- * @deprecated moved to GraphQL\Type\Schema
- */
-class Schema extends \GraphQL\Type\Schema
-{
-}

src/Server/Helper.php

@@ -73,10 +73,14 @@ class Helper
             }
 
             if (stripos($contentType, 'application/graphql') !== false) {
-                $rawBody    = $readRawBodyFn ? $readRawBodyFn() : $this->readRawBody();
+                $rawBody    = $readRawBodyFn
+                    ? $readRawBodyFn()
+                    : $this->readRawBody();
                 $bodyParams = ['query' => $rawBody ?: ''];
             } elseif (stripos($contentType, 'application/json') !== false) {
-                $rawBody    = $readRawBodyFn ? $readRawBodyFn() : $this->readRawBody();
+                $rawBody    = $readRawBodyFn ?
+                    $readRawBodyFn()
+                    : $this->readRawBody();
                 $bodyParams = json_decode($rawBody ?: '', true);
 
                 if (json_last_error()) {
@@ -272,7 +276,9 @@ class Helper
                 );
             }
 
-            $doc = $op->queryId ? $this->loadPersistedQuery($config, $op) : $op->query;
+            $doc = $op->queryId
+                ? $this->loadPersistedQuery($config, $op)
+                : $op->query;
 
             if (! $doc instanceof DocumentNode) {
                 $doc = Parser::parse($doc);
@@ -385,13 +391,13 @@ class Helper
      */
     private function resolveRootValue(ServerConfig $config, OperationParams $params, DocumentNode $doc, $operationType)
     {
-        $root = $config->getRootValue();
+        $rootValue = $config->getRootValue();
 
-        if (is_callable($root)) {
+        if (is_callable($rootValue)) {
-            $root = $root($params, $doc, $operationType);
+            $rootValue = $rootValue($params, $doc, $operationType);
         }
 
-        return $root;
+        return $rootValue;
     }
 
     /**

src/Server/OperationParams.php

@@ -9,6 +9,7 @@ use function is_string;
 use function json_decode;
 use function json_last_error;
 use const CASE_LOWER;
+use const JSON_ERROR_NONE;
 
 /**
  * Structure representing parsed HTTP parameters for GraphQL operation
@@ -93,7 +94,7 @@ class OperationParams
             }
 
             $tmp = json_decode($params[$param], true);
-            if (json_last_error()) {
+            if (json_last_error() !== JSON_ERROR_NONE) {
                 continue;
             }
 

src/Type/Definition/BooleanType.php

@@ -20,11 +20,14 @@ class BooleanType extends ScalarType
     public $description = 'The `Boolean` scalar type represents `true` or `false`.';
 
     /**
-     * @param mixed $value
+     * Coerce the given value to a boolean.
      *
-     * @return bool
+     * The GraphQL spec leaves this up to the implementations, so we just do what
+     * PHP does natively to make this intuitive for developers.
+     *
+     * @param mixed $value
      */
-    public function serialize($value)
+    public function serialize($value) : bool
     {
         return (bool) $value;
     }

src/Type/Definition/Directive.php

@@ -8,21 +8,19 @@ use GraphQL\Language\AST\DirectiveDefinitionNode;
 use GraphQL\Language\DirectiveLocation;
 use GraphQL\Utils\Utils;
 use function array_key_exists;
-use function array_keys;
-use function in_array;
 use function is_array;
 
 class Directive
 {
     public const DEFAULT_DEPRECATION_REASON = 'No longer supported';
 
-    const INCLUDE_NAME         = 'include';
+    public const INCLUDE_NAME         = 'include';
-    const IF_ARGUMENT_NAME     = 'if';
+    public const IF_ARGUMENT_NAME     = 'if';
-    const SKIP_NAME            = 'skip';
+    public const SKIP_NAME            = 'skip';
-    const DEPRECATED_NAME      = 'deprecated';
+    public const DEPRECATED_NAME      = 'deprecated';
-    const REASON_ARGUMENT_NAME = 'reason';
+    public const REASON_ARGUMENT_NAME = 'reason';
 
-    /** @var Directive[] */
+    /** @var Directive[]|null */
     public static $internalDirectives;
 
     // Schema Definitions
@@ -84,9 +82,9 @@ class Directive
     /**
      * @return Directive[]
      */
-    public static function getInternalDirectives()
+    public static function getInternalDirectives() : array
     {
-        if (! self::$internalDirectives) {
+        if (self::$internalDirectives === null) {
             self::$internalDirectives = [
                 'include'    => new self([
                     'name'        => self::INCLUDE_NAME,

src/Type/Definition/InputObjectType.php

@@ -69,7 +69,9 @@ class InputObjectType extends Type implements InputType, NullableType, NamedType
         if ($this->fields === null) {
             $this->fields = [];
             $fields       = $this->config['fields'] ?? [];
-            $fields       = is_callable($fields) ? call_user_func($fields) : $fields;
+            $fields       = is_callable($fields)
+                ? call_user_func($fields)
+                : $fields;
 
             if (! is_array($fields)) {
                 throw new InvariantViolation(

src/Type/Definition/ListOfType.php

@@ -31,6 +31,8 @@ class ListOfType extends Type implements WrappingType, OutputType, NullableType,
     {
         $type = $this->ofType;
 
-        return $recurse && $type instanceof WrappingType ? $type->getWrappedType($recurse) : $type;
+        return $recurse && $type instanceof WrappingType
+            ? $type->getWrappedType($recurse)
+            : $type;
     }
 }

src/Type/Definition/NonNull.php

@@ -66,6 +66,8 @@ class NonNull extends Type implements WrappingType, OutputType, InputType
     {
         $type = $this->ofType;
 
-        return $recurse && $type instanceof WrappingType ? $type->getWrappedType($recurse) : $type;
+        return $recurse && $type instanceof WrappingType
+            ? $type->getWrappedType($recurse)
+            : $type;
     }
 }

src/Type/Definition/ObjectType.php

@@ -168,7 +168,7 @@ class ObjectType extends Type implements OutputType, CompositeType, NullableType
 
     private function getInterfaceMap()
     {
-        if (! $this->interfaceMap) {
+        if ($this->interfaceMap === null) {
             $this->interfaceMap = [];
             foreach ($this->getInterfaces() as $interface) {
                 $this->interfaceMap[$interface->name] = $interface;
@@ -185,7 +185,9 @@ class ObjectType extends Type implements OutputType, CompositeType, NullableType
     {
         if ($this->interfaces === null) {
             $interfaces = $this->config['interfaces'] ?? [];
-            $interfaces = is_callable($interfaces) ? call_user_func($interfaces) : $interfaces;
+            $interfaces = is_callable($interfaces)
+                ? call_user_func($interfaces)
+                : $interfaces;
 
             if ($interfaces !== null && ! is_array($interfaces)) {
                 throw new InvariantViolation(
@@ -200,19 +202,21 @@ class ObjectType extends Type implements OutputType, CompositeType, NullableType
     }
 
     /**
-     * @param mixed[]      $value
+     * @param mixed        $value
      * @param mixed[]|null $context
      *
      * @return bool|null
      */
     public function isTypeOf($value, $context, ResolveInfo $info)
     {
-        return isset($this->config['isTypeOf']) ? call_user_func(
+        return isset($this->config['isTypeOf'])
-            $this->config['isTypeOf'],
+            ? call_user_func(
-            $value,
+                $this->config['isTypeOf'],
-            $context,
+                $value,
-            $info
+                $context,
-        ) : null;
+                $info
+            )
+            : null;
     }
 
     /**

src/Type/Definition/QueryPlan.php

@@ -140,9 +140,11 @@ class QueryPlan
     /**
      * @return mixed[]
      *
+     * $parentType InterfaceType|ObjectType.
+     *
      * @throws Error
      */
-    private function analyzeSelectionSet(SelectionSetNode $selectionSet, ObjectType $parentType) : array
+    private function analyzeSelectionSet(SelectionSetNode $selectionSet, Type $parentType) : array
     {
         $fields = [];
         foreach ($selectionSet->selections as $selectionNode) {

src/Type/Definition/ResolveInfo.php

@@ -15,12 +15,13 @@ use function array_merge_recursive;
 
 /**
  * Structure containing information useful for field resolution process.
- * Passed as 3rd argument to every field resolver. See [docs on field resolving (data fetching)](data-fetching.md).
+ *
+ * Passed as 4th argument to every field resolver. See [docs on field resolving (data fetching)](data-fetching.md).
  */
 class ResolveInfo
 {
     /**
-     * The name of the field being resolved
+     * The name of the field being resolved.
      *
      * @api
      * @var string
@@ -36,7 +37,7 @@ class ResolveInfo
     public $fieldNodes = [];
 
     /**
-     * Expected return type of the field being resolved
+     * Expected return type of the field being resolved.
      *
      * @api
      * @var ScalarType|ObjectType|InterfaceType|UnionType|EnumType|ListOfType|NonNull
@@ -44,7 +45,7 @@ class ResolveInfo
     public $returnType;
 
     /**
-     * Parent type of the field being resolved
+     * Parent type of the field being resolved.
      *
      * @api
      * @var ObjectType
@@ -52,7 +53,7 @@ class ResolveInfo
     public $parentType;
 
     /**
-     * Path to this field from the very root value
+     * Path to this field from the very root value.
      *
      * @api
      * @var string[][]
@@ -60,7 +61,7 @@ class ResolveInfo
     public $path;
 
     /**
-     * Instance of a schema used for execution
+     * Instance of a schema used for execution.
      *
      * @api
      * @var Schema
@@ -68,7 +69,7 @@ class ResolveInfo
     public $schema;
 
     /**
-     * AST of all fragments defined in query
+     * AST of all fragments defined in query.
      *
      * @api
      * @var FragmentDefinitionNode[]
@@ -76,15 +77,15 @@ class ResolveInfo
     public $fragments = [];
 
     /**
-     * Root value passed to query execution
+     * Root value passed to query execution.
      *
      * @api
-     * @var mixed|null
+     * @var mixed
      */
     public $rootValue;
 
     /**
-     * AST of operation definition node (query, mutation)
+     * AST of operation definition node (query, mutation).
      *
      * @api
      * @var OperationDefinitionNode|null
@@ -92,7 +93,7 @@ class ResolveInfo
     public $operation;
 
     /**
-     * Array of variables passed to query execution
+     * Array of variables passed to query execution.
      *
      * @api
      * @var mixed[]
@@ -136,7 +137,7 @@ class ResolveInfo
 
     /**
      * Helper method that returns names of all fields selected in query for
-     * $this->fieldName up to $depth levels
+     * $this->fieldName up to $depth levels.
      *
      * Example:
      * query MyQuery{
@@ -177,7 +178,10 @@ class ResolveInfo
 
         /** @var FieldNode $fieldNode */
         foreach ($this->fieldNodes as $fieldNode) {
-            $fields = array_merge_recursive($fields, $this->foldSelectionSet($fieldNode->selectionSet, $depth));
+            $fields = array_merge_recursive(
+                $fields,
+                $this->foldSelectionSet($fieldNode->selectionSet, $depth)
+            );
         }
 
         return $fields;

src/Type/Definition/Type.php

@@ -345,7 +345,9 @@ abstract class Type implements JsonSerializable
      */
     public static function getNullableType($type)
     {
-        return $type instanceof NonNull ? $type->getWrappedType() : $type;
+        return $type instanceof NonNull
+            ? $type->getWrappedType()
+            : $type;
     }
 
     /**

src/Type/Introspection.php

@@ -488,7 +488,9 @@ EOD;
                         'type'         => [
                             'type'    => Type::nonNull(self::_type()),
                             'resolve' => static function ($value) {
-                                return method_exists($value, 'getType') ? $value->getType() : $value->type;
+                                return method_exists($value, 'getType')
+                                    ? $value->getType()
+                                    : $value->type;
                             },
                         ],
                         'defaultValue' => [
@@ -693,7 +695,7 @@ EOD;
         return self::$map['__DirectiveLocation'];
     }
 
-    public static function schemaMetaFieldDef()
+    public static function schemaMetaFieldDef() : FieldDefinition
     {
         if (! isset(self::$map[self::SCHEMA_FIELD_NAME])) {
             self::$map[self::SCHEMA_FIELD_NAME] = FieldDefinition::create([
@@ -715,7 +717,7 @@ EOD;
         return self::$map[self::SCHEMA_FIELD_NAME];
     }
 
-    public static function typeMetaFieldDef()
+    public static function typeMetaFieldDef() : FieldDefinition
     {
         if (! isset(self::$map[self::TYPE_FIELD_NAME])) {
             self::$map[self::TYPE_FIELD_NAME] = FieldDefinition::create([
@@ -734,7 +736,7 @@ EOD;
         return self::$map[self::TYPE_FIELD_NAME];
     }
 
-    public static function typeNameMetaFieldDef()
+    public static function typeNameMetaFieldDef() : FieldDefinition
     {
         if (! isset(self::$map[self::TYPE_NAME_FIELD_NAME])) {
             self::$map[self::TYPE_NAME_FIELD_NAME] = FieldDefinition::create([

src/Type/SchemaConfig.php

@@ -42,7 +42,7 @@ class SchemaConfig
     /** @var Directive[] */
     public $directives;
 
-    /** @var callable */
+    /** @var callable|null */
     public $typeLoader;
 
     /** @var SchemaDefinitionNode */

src/Type/SchemaValidationContext.php

@@ -29,6 +29,7 @@ use GraphQL\Type\Definition\NonNull;
 use GraphQL\Type\Definition\ObjectType;
 use GraphQL\Type\Definition\Type;
 use GraphQL\Type\Definition\UnionType;
+use GraphQL\Type\Validation\InputObjectCircularRefs;
 use GraphQL\Utils\TypeComparators;
 use GraphQL\Utils\Utils;
 use function array_filter;
@@ -48,9 +49,13 @@ class SchemaValidationContext
     /** @var Schema */
     private $schema;
 
+    /** @var InputObjectCircularRefs */
+    private $inputObjectCircularRefs;
+
     public function __construct(Schema $schema)
     {
-        $this->schema = $schema;
+        $this->schema                  = $schema;
+        $this->inputObjectCircularRefs = new InputObjectCircularRefs($this);
     }
 
     /**
@@ -99,7 +104,7 @@ class SchemaValidationContext
      * @param string                                       $message
      * @param Node[]|Node|TypeNode|TypeDefinitionNode|null $nodes
      */
-    private function reportError($message, $nodes = null)
+    public function reportError($message, $nodes = null)
     {
         $nodes = array_filter($nodes && is_array($nodes) ? $nodes : [$nodes]);
         $this->addError(new Error($message, $nodes));
@@ -247,7 +252,7 @@ class SchemaValidationContext
             if (! $type instanceof NamedType) {
                 $this->reportError(
                     'Expected GraphQL named type but got: ' . Utils::printSafe($type) . '.',
-                    is_object($type) ? $type->astNode : null
+                    $type instanceof Type ? $type->astNode : null
                 );
                 continue;
             }
@@ -275,6 +280,9 @@ class SchemaValidationContext
             } elseif ($type instanceof InputObjectType) {
                 // Ensure Input Object fields are valid.
                 $this->validateInputFields($type);
+
+                // Ensure Input Objects do not contain non-nullable circular references
+                $this->inputObjectCircularRefs->validate($type);
             }
         }
     }
@@ -760,8 +768,9 @@ class SchemaValidationContext
             );
         }
 
-        return $union->astNode ?
+        return $union->astNode
-            $union->astNode->types : null;
+            ? $union->astNode->types
+            : null;
     }
 
     private function validateEnumValues(EnumType $enumType)
@@ -816,8 +825,9 @@ class SchemaValidationContext
             );
         }
 
-        return $enum->astNode ?
+        return $enum->astNode
-            $enum->astNode->values : null;
+            ? $enum->astNode->values
+            : null;
     }
 
     private function validateInputFields(InputObjectType $inputObj)

src/Type/Validation/InputObjectCircularRefs.php

@@ -0,0 +1,105 @@
+<?php
+
+declare(strict_types=1);
+
+namespace GraphQL\Type\Validation;
+
+use GraphQL\Language\AST\InputValueDefinitionNode;
+use GraphQL\Type\Definition\InputObjectField;
+use GraphQL\Type\Definition\InputObjectType;
+use GraphQL\Type\Definition\NonNull;
+use GraphQL\Type\SchemaValidationContext;
+use function array_map;
+use function array_pop;
+use function array_slice;
+use function count;
+use function implode;
+
+class InputObjectCircularRefs
+{
+    /** @var SchemaValidationContext */
+    private $schemaValidationContext;
+
+    /**
+     * Tracks already visited types to maintain O(N) and to ensure that cycles
+     * are not redundantly reported.
+     *
+     * @var InputObjectType[]
+     */
+    private $visitedTypes = [];
+
+    /** @var InputObjectField[] */
+    private $fieldPath = [];
+
+    /**
+     * Position in the type path.
+     *
+     * [string $typeName => int $index]
+     *
+     * @var int[]
+     */
+    private $fieldPathIndexByTypeName = [];
+
+    public function __construct(SchemaValidationContext $schemaValidationContext)
+    {
+        $this->schemaValidationContext = $schemaValidationContext;
+    }
+
+    /**
+     * This does a straight-forward DFS to find cycles.
+     * It does not terminate when a cycle was found but continues to explore
+     * the graph to find all possible cycles.
+     */
+    public function validate(InputObjectType $inputObj) : void
+    {
+        if (isset($this->visitedTypes[$inputObj->name])) {
+            return;
+        }
+
+        $this->visitedTypes[$inputObj->name]             = true;
+        $this->fieldPathIndexByTypeName[$inputObj->name] = count($this->fieldPath);
+
+        $fieldMap = $inputObj->getFields();
+        foreach ($fieldMap as $fieldName => $field) {
+            $type = $field->getType();
+
+            if ($type instanceof NonNull) {
+                $fieldType = $type->getWrappedType();
+
+                // If the type of the field is anything else then a non-nullable input object,
+                // there is no chance of an unbreakable cycle
+                if ($fieldType instanceof InputObjectType) {
+                    $this->fieldPath[] = $field;
+
+                    if (! isset($this->fieldPathIndexByTypeName[$fieldType->name])) {
+                        $this->validate($fieldType);
+                    } else {
+                        $cycleIndex = $this->fieldPathIndexByTypeName[$fieldType->name];
+                        $cyclePath  = array_slice($this->fieldPath, $cycleIndex);
+                        $fieldNames = array_map(
+                            static function (InputObjectField $field) : string {
+                                return $field->name;
+                            },
+                            $cyclePath
+                        );
+
+                        $this->schemaValidationContext->reportError(
+                            'Cannot reference Input Object "' . $fieldType->name . '" within itself '
+                            . 'through a series of non-null fields: "' . implode('.', $fieldNames) . '".',
+                            array_map(
+                                static function (InputObjectField $field) : ?InputValueDefinitionNode {
+                                    return $field->astNode;
+                                },
+                                $cyclePath
+                            )
+                        );
+                    }
+                }
+            }
+
+            array_pop($this->fieldPath);
+        }
+
+        unset($this->fieldPathIndexByTypeName[$inputObj->name]);
+    }
+}

src/Utils/AST.php

@@ -183,7 +183,7 @@ class AST
                     $valuesNodes[] = $itemNode;
                 }
 
-                return new ListValueNode(['values' => $valuesNodes]);
+                return new ListValueNode(['values' => new NodeList($valuesNodes)]);
             }
 
             return self::astFromValue($value, $itemType);
@@ -235,7 +235,7 @@ class AST
                 ]);
             }
 
-            return new ObjectValueNode(['fields' => $fieldNodes]);
+            return new ObjectValueNode(['fields' => new NodeList($fieldNodes)]);
         }
 
         if ($type instanceof ScalarType || $type instanceof EnumType) {
@@ -322,7 +322,7 @@ class AST
      *
      * @api
      */
-    public static function valueFromAST($valueNode, InputType $type, ?array $variables = null)
+    public static function valueFromAST($valueNode, Type $type, ?array $variables = null)
     {
         $undefined = Utils::undefined();
 

src/Utils/ASTDefinitionBuilder.php

@@ -17,7 +17,6 @@ use GraphQL\Language\AST\InterfaceTypeDefinitionNode;
 use GraphQL\Language\AST\ListTypeNode;
 use GraphQL\Language\AST\NamedTypeNode;
 use GraphQL\Language\AST\Node;
-use GraphQL\Language\AST\NodeKind;
 use GraphQL\Language\AST\NonNullTypeNode;
 use GraphQL\Language\AST\ObjectTypeDefinitionNode;
 use GraphQL\Language\AST\ScalarTypeDefinitionNode;
@@ -245,23 +244,20 @@ class ASTDefinitionBuilder
      *
      * @throws Error
      */
-    private function makeSchemaDef($def)
+    private function makeSchemaDef(Node $def)
     {
-        if (! $def) {
+        switch (true) {
-            throw new Error('def must be defined.');
+            case $def instanceof ObjectTypeDefinitionNode:
-        }
-        switch ($def->kind) {
-            case NodeKind::OBJECT_TYPE_DEFINITION:
                 return $this->makeTypeDef($def);
-            case NodeKind::INTERFACE_TYPE_DEFINITION:
+            case $def instanceof InterfaceTypeDefinitionNode:
                 return $this->makeInterfaceDef($def);
-            case NodeKind::ENUM_TYPE_DEFINITION:
+            case $def instanceof EnumTypeDefinitionNode:
                 return $this->makeEnumDef($def);
-            case NodeKind::UNION_TYPE_DEFINITION:
+            case $def instanceof UnionTypeDefinitionNode:
                 return $this->makeUnionDef($def);
-            case NodeKind::SCALAR_TYPE_DEFINITION:
+            case $def instanceof ScalarTypeDefinitionNode:
                 return $this->makeScalarDef($def);
-            case NodeKind::INPUT_OBJECT_TYPE_DEFINITION:
+            case $def instanceof InputObjectTypeDefinitionNode:
                 return $this->makeInputObjectDef($def);
             default:
                 throw new Error(sprintf('Type kind of %s not supported.', $def->kind));
@@ -398,8 +394,8 @@ class ASTDefinitionBuilder
                     function ($typeNode) {
                         return $this->buildType($typeNode);
                     }
-                ) :
+                )
-                [],
+                : [],
             'astNode'     => $def,
         ]);
     }
@@ -431,62 +427,48 @@ class ASTDefinitionBuilder
     }
 
     /**
-     * @param ObjectTypeDefinitionNode|InterfaceTypeDefinitionNode|EnumTypeExtensionNode|ScalarTypeDefinitionNode|InputObjectTypeDefinitionNode $def
+     * @param mixed[] $config
-     * @param mixed[]                                                                                                                           $config
      *
      * @return CustomScalarType|EnumType|InputObjectType|InterfaceType|ObjectType|UnionType
      *
      * @throws Error
      */
-    private function makeSchemaDefFromConfig($def, array $config)
+    private function makeSchemaDefFromConfig(Node $def, array $config)
     {
-        if (! $def) {
+        switch (true) {
-            throw new Error('def must be defined.');
+            case $def instanceof ObjectTypeDefinitionNode:
-        }
-        switch ($def->kind) {
-            case NodeKind::OBJECT_TYPE_DEFINITION:
                 return new ObjectType($config);
-            case NodeKind::INTERFACE_TYPE_DEFINITION:
+            case $def instanceof InterfaceTypeDefinitionNode:
                 return new InterfaceType($config);
-            case NodeKind::ENUM_TYPE_DEFINITION:
+            case $def instanceof EnumTypeDefinitionNode:
                 return new EnumType($config);
-            case NodeKind::UNION_TYPE_DEFINITION:
+            case $def instanceof UnionTypeDefinitionNode:
                 return new UnionType($config);
-            case NodeKind::SCALAR_TYPE_DEFINITION:
+            case $def instanceof ScalarTypeDefinitionNode:
                 return new CustomScalarType($config);
-            case NodeKind::INPUT_OBJECT_TYPE_DEFINITION:
+            case $def instanceof InputObjectTypeDefinitionNode:
                 return new InputObjectType($config);
             default:
                 throw new Error(sprintf('Type kind of %s not supported.', $def->kind));
         }
     }
 
-    /**
+    private function getNamedTypeNode(TypeNode $typeNode) : TypeNode
-     * @param TypeNode|ListTypeNode|NonNullTypeNode $typeNode
-     *
-     * @return TypeNode
-     */
-    private function getNamedTypeNode(TypeNode $typeNode)
     {
         $namedType = $typeNode;
-        while ($namedType->kind === NodeKind::LIST_TYPE || $namedType->kind === NodeKind::NON_NULL_TYPE) {
+        while ($namedType instanceof ListTypeNode || $namedType instanceof NonNullTypeNode) {
             $namedType = $namedType->type;
         }
 
         return $namedType;
     }
 
-    /**
+    private function buildWrappedType(Type $innerType, TypeNode $inputTypeNode) : Type
-     * @param TypeNode|ListTypeNode|NonNullTypeNode $inputTypeNode
-     *
-     * @return Type
-     */
-    private function buildWrappedType(Type $innerType, TypeNode $inputTypeNode)
     {
-        if ($inputTypeNode->kind === NodeKind::LIST_TYPE) {
+        if ($inputTypeNode instanceof ListTypeNode) {
             return Type::listOf($this->buildWrappedType($innerType, $inputTypeNode->type));
         }
-        if ($inputTypeNode->kind === NodeKind::NON_NULL_TYPE) {
+        if ($inputTypeNode instanceof NonNullTypeNode) {
             $wrappedType = $this->buildWrappedType($innerType, $inputTypeNode->type);
 
             return Type::nonNull(NonNull::assertNullableType($wrappedType));

src/Utils/BuildSchema.php

@@ -5,10 +5,16 @@ declare(strict_types=1);
 namespace GraphQL\Utils;
 
 use GraphQL\Error\Error;
+use GraphQL\Language\AST\DirectiveDefinitionNode;
 use GraphQL\Language\AST\DocumentNode;
+use GraphQL\Language\AST\EnumTypeDefinitionNode;
+use GraphQL\Language\AST\InputObjectTypeDefinitionNode;
+use GraphQL\Language\AST\InterfaceTypeDefinitionNode;
 use GraphQL\Language\AST\Node;
-use GraphQL\Language\AST\NodeKind;
+use GraphQL\Language\AST\ObjectTypeDefinitionNode;
+use GraphQL\Language\AST\ScalarTypeDefinitionNode;
 use GraphQL\Language\AST\SchemaDefinitionNode;
+use GraphQL\Language\AST\UnionTypeDefinitionNode;
 use GraphQL\Language\Parser;
 use GraphQL\Language\Source;
 use GraphQL\Type\Definition\Directive;
@@ -95,39 +101,38 @@ class BuildSchema
 
     public function buildSchema()
     {
-        /** @var SchemaDefinitionNode $schemaDef */
         $schemaDef     = null;
         $typeDefs      = [];
         $this->nodeMap = [];
         $directiveDefs = [];
-        foreach ($this->ast->definitions as $d) {
+        foreach ($this->ast->definitions as $definition) {
-            switch ($d->kind) {
+            switch (true) {
-                case NodeKind::SCHEMA_DEFINITION:
+                case $definition instanceof SchemaDefinitionNode:
-                    if ($schemaDef) {
+                    if ($schemaDef !== null) {
                         throw new Error('Must provide only one schema definition.');
                     }
-                    $schemaDef = $d;
+                    $schemaDef = $definition;
                     break;
-                case NodeKind::SCALAR_TYPE_DEFINITION:
+                case $definition instanceof ScalarTypeDefinitionNode:
-                case NodeKind::OBJECT_TYPE_DEFINITION:
+                case $definition instanceof ObjectTypeDefinitionNode:
-                case NodeKind::INTERFACE_TYPE_DEFINITION:
+                case $definition instanceof InterfaceTypeDefinitionNode:
-                case NodeKind::ENUM_TYPE_DEFINITION:
+                case $definition instanceof EnumTypeDefinitionNode:
-                case NodeKind::UNION_TYPE_DEFINITION:
+                case $definition instanceof UnionTypeDefinitionNode:
-                case NodeKind::INPUT_OBJECT_TYPE_DEFINITION:
+                case $definition instanceof InputObjectTypeDefinitionNode:
-                    $typeName = $d->name->value;
+                    $typeName = $definition->name->value;
                     if (! empty($this->nodeMap[$typeName])) {
                         throw new Error(sprintf('Type "%s" was defined more than once.', $typeName));
                     }
-                    $typeDefs[]               = $d;
+                    $typeDefs[]               = $definition;
-                    $this->nodeMap[$typeName] = $d;
+                    $this->nodeMap[$typeName] = $definition;
                     break;
-                case NodeKind::DIRECTIVE_DEFINITION:
+                case $definition instanceof DirectiveDefinitionNode:
-                    $directiveDefs[] = $d;
+                    $directiveDefs[] = $definition;
                     break;
             }
         }
 
-        $operationTypes = $schemaDef
+        $operationTypes = $schemaDef !== null
             ? $this->getOperationTypes($schemaDef)
             : [
                 'query'        => isset($this->nodeMap['Query']) ? 'Query' : null,
@@ -154,9 +159,10 @@ class BuildSchema
         // If specified directives were not explicitly declared, add them.
         $skip = array_reduce(
             $directives,
-            static function ($hasSkip, $directive) {
+            static function (bool $hasSkip, Directive $directive) : bool {
                 return $hasSkip || $directive->name === 'skip';
-            }
+            },
+            false
         );
         if (! $skip) {
             $directives[] = Directive::skipDirective();
@@ -164,9 +170,10 @@ class BuildSchema
 
         $include = array_reduce(
             $directives,
-            static function ($hasInclude, $directive) {
+            static function (bool $hasInclude, Directive $directive) : bool {
                 return $hasInclude || $directive->name === 'include';
-            }
+            },
+            false
         );
         if (! $include) {
             $directives[] = Directive::includeDirective();
@@ -174,9 +181,10 @@ class BuildSchema
 
         $deprecated = array_reduce(
             $directives,
-            static function ($hasDeprecated, $directive) {
+            static function (bool $hasDeprecated, Directive $directive) : bool {
                 return $hasDeprecated || $directive->name === 'deprecated';
-            }
+            },
+            false
         );
         if (! $deprecated) {
             $directives[] = Directive::deprecatedDirective();

src/Utils/MixedStore.php

@@ -21,7 +21,7 @@ use function is_string;
  * Similar to PHP array, but allows any type of data to act as key (including arrays, objects, scalars)
  *
  * Note: unfortunately when storing array as key - access and modification is O(N)
- * (yet this should be really rare case and should be avoided when possible)
+ * (yet this should rarely be the case and should be avoided when possible)
  */
 class MixedStore implements ArrayAccess
 {

src/Utils/SchemaExtender.php

@@ -7,13 +7,16 @@ namespace GraphQL\Utils;
 use GraphQL\Error\Error;
 use GraphQL\Language\AST\DirectiveDefinitionNode;
 use GraphQL\Language\AST\DocumentNode;
+use GraphQL\Language\AST\EnumTypeExtensionNode;
+use GraphQL\Language\AST\InputObjectTypeExtensionNode;
+use GraphQL\Language\AST\InterfaceTypeExtensionNode;
 use GraphQL\Language\AST\Node;
-use GraphQL\Language\AST\NodeKind;
 use GraphQL\Language\AST\ObjectTypeExtensionNode;
 use GraphQL\Language\AST\SchemaDefinitionNode;
 use GraphQL\Language\AST\SchemaTypeExtensionNode;
 use GraphQL\Language\AST\TypeDefinitionNode;
 use GraphQL\Language\AST\TypeExtensionNode;
+use GraphQL\Language\AST\UnionTypeExtensionNode;
 use GraphQL\Type\Definition\CustomScalarType;
 use GraphQL\Type\Definition\Directive;
 use GraphQL\Type\Definition\EnumType;
@@ -75,8 +78,8 @@ class SchemaExtender
      */
     protected static function checkExtensionNode(Type $type, Node $node) : void
     {
-        switch ($node->kind) {
+        switch (true) {
-            case NodeKind::OBJECT_TYPE_EXTENSION:
+            case $node instanceof ObjectTypeExtensionNode:
                 if (! ($type instanceof ObjectType)) {
                     throw new Error(
                         'Cannot extend non-object type "' . $type->name . '".',
@@ -84,7 +87,7 @@ class SchemaExtender
                     );
                 }
                 break;
-            case NodeKind::INTERFACE_TYPE_EXTENSION:
+            case $node instanceof InterfaceTypeExtensionNode:
                 if (! ($type instanceof InterfaceType)) {
                     throw new Error(
                         'Cannot extend non-interface type "' . $type->name . '".',
@@ -92,7 +95,7 @@ class SchemaExtender
                     );
                 }
                 break;
-            case NodeKind::ENUM_TYPE_EXTENSION:
+            case $node instanceof EnumTypeExtensionNode:
                 if (! ($type instanceof EnumType)) {
                     throw new Error(
                         'Cannot extend non-enum type "' . $type->name . '".',
@@ -100,7 +103,7 @@ class SchemaExtender
                     );
                 }
                 break;
-            case NodeKind::UNION_TYPE_EXTENSION:
+            case $node instanceof UnionTypeExtensionNode:
                 if (! ($type instanceof UnionType)) {
                     throw new Error(
                         'Cannot extend non-union type "' . $type->name . '".',
@@ -108,7 +111,7 @@ class SchemaExtender
                     );
                 }
                 break;
-            case NodeKind::INPUT_OBJECT_TYPE_EXTENSION:
+            case $node instanceof InputObjectTypeExtensionNode:
                 if (! ($type instanceof InputObjectType)) {
                     throw new Error(
                         'Cannot extend non-input object type "' . $type->name . '".',
@@ -606,7 +609,9 @@ class SchemaExtender
         }
 
         $schemaExtensionASTNodes = count($schemaExtensions) > 0
-            ? ($schema->extensionASTNodes ? array_merge($schema->extensionASTNodes, $schemaExtensions) : $schemaExtensions)
+            ? ($schema->extensionASTNodes
+                ? array_merge($schema->extensionASTNodes, $schemaExtensions)
+                : $schemaExtensions)
             : $schema->extensionASTNodes;
 
         $types = array_merge(

src/Utils/SchemaPrinter.php

@@ -353,8 +353,8 @@ class SchemaPrinter
     private static function printObject(ObjectType $type, array $options) : string
     {
         $interfaces            = $type->getInterfaces();
-        $implementedInterfaces = ! empty($interfaces) ?
+        $implementedInterfaces = ! empty($interfaces)
-            ' implements ' . implode(
+            ? ' implements ' . implode(
                 ' & ',
                 array_map(
                     static function ($i) {
@@ -362,7 +362,8 @@ class SchemaPrinter
                     },
                     $interfaces
                 )
-            ) : '';
+            )
+            : '';
 
         return self::printDescription($options, $type) .
             sprintf("type %s%s {\n%s\n}", $type->name, $implementedInterfaces, self::printFields($options, $type));

src/Utils/TypeInfo.php

@@ -6,12 +6,21 @@ namespace GraphQL\Utils;
 
 use GraphQL\Error\InvariantViolation;
 use GraphQL\Error\Warning;
+use GraphQL\Language\AST\ArgumentNode;
+use GraphQL\Language\AST\DirectiveNode;
+use GraphQL\Language\AST\EnumValueNode;
 use GraphQL\Language\AST\FieldNode;
+use GraphQL\Language\AST\FragmentDefinitionNode;
+use GraphQL\Language\AST\InlineFragmentNode;
 use GraphQL\Language\AST\ListTypeNode;
+use GraphQL\Language\AST\ListValueNode;
 use GraphQL\Language\AST\NamedTypeNode;
 use GraphQL\Language\AST\Node;
-use GraphQL\Language\AST\NodeKind;
 use GraphQL\Language\AST\NonNullTypeNode;
+use GraphQL\Language\AST\ObjectFieldNode;
+use GraphQL\Language\AST\OperationDefinitionNode;
+use GraphQL\Language\AST\SelectionSetNode;
+use GraphQL\Language\AST\VariableDefinitionNode;
 use GraphQL\Type\Definition\CompositeType;
 use GraphQL\Type\Definition\Directive;
 use GraphQL\Type\Definition\EnumType;
@@ -254,13 +263,13 @@ class TypeInfo
         // any assumptions of a valid schema to ensure runtime types are properly
         // checked before continuing since TypeInfo is used as part of validation
         // which occurs before guarantees of schema and document validity.
-        switch ($node->kind) {
+        switch (true) {
-            case NodeKind::SELECTION_SET:
+            case $node instanceof SelectionSetNode:
                 $namedType               = Type::getNamedType($this->getType());
                 $this->parentTypeStack[] = Type::isCompositeType($namedType) ? $namedType : null;
                 break;
 
-            case NodeKind::FIELD:
+            case $node instanceof FieldNode:
                 $parentType = $this->getParentType();
                 $fieldDef   = null;
                 if ($parentType) {
@@ -274,11 +283,11 @@ class TypeInfo
                 $this->typeStack[]     = Type::isOutputType($fieldType) ? $fieldType : null;
                 break;
 
-            case NodeKind::DIRECTIVE:
+            case $node instanceof DirectiveNode:
                 $this->directive = $schema->getDirective($node->name->value);
                 break;
 
-            case NodeKind::OPERATION_DEFINITION:
+            case $node instanceof OperationDefinitionNode:
                 $type = null;
                 if ($node->operation === 'query') {
                     $type = $schema->getQueryType();
@@ -290,22 +299,24 @@ class TypeInfo
                 $this->typeStack[] = Type::isOutputType($type) ? $type : null;
                 break;
 
-            case NodeKind::INLINE_FRAGMENT:
+            case $node instanceof InlineFragmentNode:
-            case NodeKind::FRAGMENT_DEFINITION:
+            case $node instanceof FragmentDefinitionNode:
                 $typeConditionNode = $node->typeCondition;
-                $outputType        = $typeConditionNode ? self::typeFromAST(
+                $outputType        = $typeConditionNode
-                    $schema,
+                    ? self::typeFromAST(
-                    $typeConditionNode
+                        $schema,
-                ) : Type::getNamedType($this->getType());
+                        $typeConditionNode
+                    )
+                    : Type::getNamedType($this->getType());
                 $this->typeStack[] = Type::isOutputType($outputType) ? $outputType : null;
                 break;
 
-            case NodeKind::VARIABLE_DEFINITION:
+            case $node instanceof VariableDefinitionNode:
                 $inputType              = self::typeFromAST($schema, $node->type);
                 $this->inputTypeStack[] = Type::isInputType($inputType) ? $inputType : null; // push
                 break;
 
-            case NodeKind::ARGUMENT:
+            case $node instanceof ArgumentNode:
                 $fieldOrDirective = $this->getDirective() ?: $this->getFieldDef();
                 $argDef           = $argType = null;
                 if ($fieldOrDirective) {
@@ -323,7 +334,7 @@ class TypeInfo
                 $this->inputTypeStack[] = Type::isInputType($argType) ? $argType : null;
                 break;
 
-            case NodeKind::LST:
+            case $node instanceof ListValueNode:
                 $listType               = Type::getNullableType($this->getInputType());
                 $itemType               = $listType instanceof ListOfType
                     ? $listType->getWrappedType()
@@ -331,7 +342,7 @@ class TypeInfo
                 $this->inputTypeStack[] = Type::isInputType($itemType) ? $itemType : null;
                 break;
 
-            case NodeKind::OBJECT_FIELD:
+            case $node instanceof ObjectFieldNode:
                 $objectType     = Type::getNamedType($this->getInputType());
                 $fieldType      = null;
                 $inputFieldType = null;
@@ -343,7 +354,7 @@ class TypeInfo
                 $this->inputTypeStack[] = Type::isInputType($inputFieldType) ? $inputFieldType : null;
                 break;
 
-            case NodeKind::ENUM:
+            case $node instanceof EnumValueNode:
                 $enumType  = Type::getNamedType($this->getInputType());
                 $enumValue = null;
                 if ($enumType instanceof EnumType) {
@@ -457,37 +468,37 @@ class TypeInfo
 
     public function leave(Node $node)
     {
-        switch ($node->kind) {
+        switch (true) {
-            case NodeKind::SELECTION_SET:
+            case $node instanceof SelectionSetNode:
                 array_pop($this->parentTypeStack);
                 break;
 
-            case NodeKind::FIELD:
+            case $node instanceof FieldNode:
                 array_pop($this->fieldDefStack);
                 array_pop($this->typeStack);
                 break;
 
-            case NodeKind::DIRECTIVE:
+            case $node instanceof DirectiveNode:
                 $this->directive = null;
                 break;
 
-            case NodeKind::OPERATION_DEFINITION:
+            case $node instanceof OperationDefinitionNode:
-            case NodeKind::INLINE_FRAGMENT:
+            case $node instanceof InlineFragmentNode:
-            case NodeKind::FRAGMENT_DEFINITION:
+            case $node instanceof FragmentDefinitionNode:
                 array_pop($this->typeStack);
                 break;
-            case NodeKind::VARIABLE_DEFINITION:
+            case $node instanceof VariableDefinitionNode:
                 array_pop($this->inputTypeStack);
                 break;
-            case NodeKind::ARGUMENT:
+            case $node instanceof ArgumentNode:
                 $this->argument = null;
                 array_pop($this->inputTypeStack);
                 break;
-            case NodeKind::LST:
+            case $node instanceof ListValueNode:
-            case NodeKind::OBJECT_FIELD:
+            case $node instanceof ObjectFieldNode:
                 array_pop($this->inputTypeStack);
                 break;
-            case NodeKind::ENUM:
+            case $node instanceof EnumValueNode:
                 $this->enumValue = null;
                 break;
         }

src/Utils/Value.php

@@ -199,7 +199,7 @@ class Value
                 }
 
                 $suggestions = Utils::suggestionList(
-                    $fieldName,
+                    (string) $fieldName,
                     array_keys($fields)
                 );
                 $didYouMean  = $suggestions

src/Validator/Rules/KnownArgumentNames.php

@@ -6,6 +6,8 @@ namespace GraphQL\Validator\Rules;
 
 use GraphQL\Error\Error;
 use GraphQL\Language\AST\ArgumentNode;
+use GraphQL\Language\AST\DirectiveNode;
+use GraphQL\Language\AST\FieldNode;
 use GraphQL\Language\AST\Node;
 use GraphQL\Language\AST\NodeKind;
 use GraphQL\Language\AST\NodeList;
@@ -34,7 +36,7 @@ class KnownArgumentNames extends ValidationRule
                 }
 
                 $argumentOf = $ancestors[count($ancestors) - 1];
-                if ($argumentOf->kind === NodeKind::FIELD) {
+                if ($argumentOf instanceof FieldNode) {
                     $fieldDef   = $context->getFieldDef();
                     $parentType = $context->getParentType();
                     if ($fieldDef && $parentType) {
@@ -56,7 +58,7 @@ class KnownArgumentNames extends ValidationRule
                             [$node]
                         ));
                     }
-                } elseif ($argumentOf->kind === NodeKind::DIRECTIVE) {
+                } elseif ($argumentOf instanceof DirectiveNode) {
                     $directive = $context->getDirective();
                     if ($directive) {
                         $context->reportError(new Error(

src/Validator/Rules/KnownDirectives.php

@@ -7,10 +7,31 @@ namespace GraphQL\Validator\Rules;
 use GraphQL\Error\Error;
 use GraphQL\Language\AST\DirectiveDefinitionNode;
 use GraphQL\Language\AST\DirectiveNode;
+use GraphQL\Language\AST\EnumTypeDefinitionNode;
+use GraphQL\Language\AST\EnumTypeExtensionNode;
+use GraphQL\Language\AST\EnumValueDefinitionNode;
+use GraphQL\Language\AST\FieldDefinitionNode;
+use GraphQL\Language\AST\FieldNode;
+use GraphQL\Language\AST\FragmentDefinitionNode;
+use GraphQL\Language\AST\FragmentSpreadNode;
+use GraphQL\Language\AST\InlineFragmentNode;
 use GraphQL\Language\AST\InputObjectTypeDefinitionNode;
+use GraphQL\Language\AST\InputObjectTypeExtensionNode;
+use GraphQL\Language\AST\InputValueDefinitionNode;
+use GraphQL\Language\AST\InterfaceTypeDefinitionNode;
+use GraphQL\Language\AST\InterfaceTypeExtensionNode;
 use GraphQL\Language\AST\Node;
 use GraphQL\Language\AST\NodeKind;
 use GraphQL\Language\AST\NodeList;
+use GraphQL\Language\AST\ObjectTypeDefinitionNode;
+use GraphQL\Language\AST\ObjectTypeExtensionNode;
+use GraphQL\Language\AST\OperationDefinitionNode;
+use GraphQL\Language\AST\ScalarTypeDefinitionNode;
+use GraphQL\Language\AST\ScalarTypeExtensionNode;
+use GraphQL\Language\AST\SchemaDefinitionNode;
+use GraphQL\Language\AST\SchemaTypeExtensionNode;
+use GraphQL\Language\AST\UnionTypeDefinitionNode;
+use GraphQL\Language\AST\UnionTypeExtensionNode;
 use GraphQL\Language\DirectiveLocation;
 use GraphQL\Validator\ValidationContext;
 use function array_map;
@@ -96,8 +117,8 @@ class KnownDirectives extends ValidationRule
     private function getDirectiveLocationForASTPath(array $ancestors)
     {
         $appliedTo = $ancestors[count($ancestors) - 1];
-        switch ($appliedTo->kind) {
+        switch (true) {
-            case NodeKind::OPERATION_DEFINITION:
+            case $appliedTo instanceof OperationDefinitionNode:
                 switch ($appliedTo->operation) {
                     case 'query':
                         return DirectiveLocation::QUERY;
@@ -107,40 +128,40 @@ class KnownDirectives extends ValidationRule
                         return DirectiveLocation::SUBSCRIPTION;
                 }
                 break;
-            case NodeKind::FIELD:
+            case $appliedTo instanceof FieldNode:
                 return DirectiveLocation::FIELD;
-            case NodeKind::FRAGMENT_SPREAD:
+            case $appliedTo instanceof FragmentSpreadNode:
                 return DirectiveLocation::FRAGMENT_SPREAD;
-            case NodeKind::INLINE_FRAGMENT:
+            case $appliedTo instanceof InlineFragmentNode:
                 return DirectiveLocation::INLINE_FRAGMENT;
-            case NodeKind::FRAGMENT_DEFINITION:
+            case $appliedTo instanceof FragmentDefinitionNode:
                 return DirectiveLocation::FRAGMENT_DEFINITION;
-            case NodeKind::SCHEMA_DEFINITION:
+            case $appliedTo instanceof SchemaDefinitionNode:
-            case NodeKind::SCHEMA_EXTENSION:
+            case $appliedTo instanceof SchemaTypeExtensionNode:
                 return DirectiveLocation::SCHEMA;
-            case NodeKind::SCALAR_TYPE_DEFINITION:
+            case $appliedTo instanceof ScalarTypeDefinitionNode:
-            case NodeKind::SCALAR_TYPE_EXTENSION:
+            case $appliedTo instanceof ScalarTypeExtensionNode:
                 return DirectiveLocation::SCALAR;
-            case NodeKind::OBJECT_TYPE_DEFINITION:
+            case $appliedTo instanceof ObjectTypeDefinitionNode:
-            case NodeKind::OBJECT_TYPE_EXTENSION:
+            case $appliedTo instanceof ObjectTypeExtensionNode:
                 return DirectiveLocation::OBJECT;
-            case NodeKind::FIELD_DEFINITION:
+            case $appliedTo instanceof FieldDefinitionNode:
                 return DirectiveLocation::FIELD_DEFINITION;
-            case NodeKind::INTERFACE_TYPE_DEFINITION:
+            case $appliedTo instanceof InterfaceTypeDefinitionNode:
-            case NodeKind::INTERFACE_TYPE_EXTENSION:
+            case $appliedTo instanceof InterfaceTypeExtensionNode:
                 return DirectiveLocation::IFACE;
-            case NodeKind::UNION_TYPE_DEFINITION:
+            case $appliedTo instanceof UnionTypeDefinitionNode:
-            case NodeKind::UNION_TYPE_EXTENSION:
+            case $appliedTo instanceof UnionTypeExtensionNode:
                 return DirectiveLocation::UNION;
-            case NodeKind::ENUM_TYPE_DEFINITION:
+            case $appliedTo instanceof EnumTypeDefinitionNode:
-            case NodeKind::ENUM_TYPE_EXTENSION:
+            case $appliedTo instanceof EnumTypeExtensionNode:
                 return DirectiveLocation::ENUM;
-            case NodeKind::ENUM_VALUE_DEFINITION:
+            case $appliedTo instanceof EnumValueDefinitionNode:
                 return DirectiveLocation::ENUM_VALUE;
-            case NodeKind::INPUT_OBJECT_TYPE_DEFINITION:
+            case $appliedTo instanceof InputObjectTypeDefinitionNode:
-            case NodeKind::INPUT_OBJECT_TYPE_EXTENSION:
+            case $appliedTo instanceof InputObjectTypeExtensionNode:
                 return DirectiveLocation::INPUT_OBJECT;
-            case NodeKind::INPUT_VALUE_DEFINITION:
+            case $appliedTo instanceof InputValueDefinitionNode:
                 $parentNode = $ancestors[count($ancestors) - 3];
 
                 return $parentNode instanceof InputObjectTypeDefinitionNode

src/Validator/Rules/LoneAnonymousOperation.php

@@ -30,7 +30,7 @@ class LoneAnonymousOperation extends ValidationRule
                 $tmp = Utils::filter(
                     $node->definitions,
                     static function (Node $definition) {
-                        return $definition->kind === NodeKind::OPERATION_DEFINITION;
+                        return $definition instanceof OperationDefinitionNode;
                     }
                 );
 

src/Validator/Rules/LoneSchemaDefinition.php

@@ -19,12 +19,14 @@ class LoneSchemaDefinition extends ValidationRule
     public function getVisitor(ValidationContext $context)
     {
         $oldSchema      = $context->getSchema();
-        $alreadyDefined = $oldSchema !== null ? (
+        $alreadyDefined = $oldSchema !== null
-            $oldSchema->getAstNode() ||
+            ? (
-            $oldSchema->getQueryType() ||
+                $oldSchema->getAstNode() ||
-            $oldSchema->getMutationType() ||
+                $oldSchema->getQueryType() ||
-            $oldSchema->getSubscriptionType()
+                $oldSchema->getMutationType() ||
-        ) : false;
+                $oldSchema->getSubscriptionType()
+            )
+            : false;
 
         $schemaDefinitionsCount = 0;
 

src/Validator/Rules/OverlappingFieldsCanBeMerged.php

@@ -473,24 +473,24 @@ class OverlappingFieldsCanBeMerged extends ValidationRule
     private function doTypesConflict(OutputType $type1, OutputType $type2)
     {
         if ($type1 instanceof ListOfType) {
-            return $type2 instanceof ListOfType ?
+            return $type2 instanceof ListOfType
-                $this->doTypesConflict($type1->getWrappedType(), $type2->getWrappedType()) :
+                ? $this->doTypesConflict($type1->getWrappedType(), $type2->getWrappedType())
-                true;
+                : true;
         }
         if ($type2 instanceof ListOfType) {
-            return $type1 instanceof ListOfType ?
+            return $type1 instanceof ListOfType
-                $this->doTypesConflict($type1->getWrappedType(), $type2->getWrappedType()) :
+                ? $this->doTypesConflict($type1->getWrappedType(), $type2->getWrappedType())
-                true;
+                : true;
         }
         if ($type1 instanceof NonNull) {
-            return $type2 instanceof NonNull ?
+            return $type2 instanceof NonNull
-                $this->doTypesConflict($type1->getWrappedType(), $type2->getWrappedType()) :
+                ? $this->doTypesConflict($type1->getWrappedType(), $type2->getWrappedType())
-                true;
+                : true;
         }
         if ($type2 instanceof NonNull) {
-            return $type1 instanceof NonNull ?
+            return $type1 instanceof NonNull
-                $this->doTypesConflict($type1->getWrappedType(), $type2->getWrappedType()) :
+                ? $this->doTypesConflict($type1->getWrappedType(), $type2->getWrappedType())
-                true;
+                : true;
         }
         if (Type::isLeafType($type1) || Type::isLeafType($type2)) {
             return $type1 !== $type2;

src/Validator/Rules/ProvidedRequiredArgumentsOnDirectives.php

@@ -66,13 +66,15 @@ class ProvidedRequiredArgumentsOnDirectives extends ValidationRule
             }
 
             $requiredArgsMap[$def->name->value] = Utils::keyMap(
-                $arguments ? array_filter($arguments, static function (Node $argument) : bool {
+                $arguments
-                    return $argument instanceof NonNullTypeNode &&
+                    ? array_filter($arguments, static function (Node $argument) : bool {
-                        (
+                        return $argument instanceof NonNullTypeNode &&
-                            ! isset($argument->defaultValue) ||
+                            (
-                            $argument->defaultValue === null
+                                ! isset($argument->defaultValue) ||
-                        );
+                                $argument->defaultValue === null
-                }) : [],
+                            );
+                    })
+                    : [],
                 static function (NamedTypeNode $argument) : string {
                     return $argument->name->value;
                 }

src/Validator/Rules/QueryComplexity.php

@@ -110,9 +110,8 @@ class QueryComplexity extends QuerySecurityRule
 
     private function nodeComplexity(Node $node, $complexity = 0)
     {
-        switch ($node->kind) {
+        switch (true) {
-            case NodeKind::FIELD:
+            case $node instanceof FieldNode:
-                /** @var FieldNode $node */
                 // default values
                 $args         = [];
                 $complexityFn = FieldDefinition::DEFAULT_COMPLEXITY_FN;
@@ -143,16 +142,14 @@ class QueryComplexity extends QuerySecurityRule
                 $complexity += call_user_func_array($complexityFn, [$childrenComplexity, $args]);
                 break;
 
-            case NodeKind::INLINE_FRAGMENT:
+            case $node instanceof InlineFragmentNode:
-                /** @var InlineFragmentNode $node */
                 // node has children?
                 if (isset($node->selectionSet)) {
                     $complexity = $this->fieldComplexity($node, $complexity);
                 }
                 break;
 
-            case NodeKind::FRAGMENT_SPREAD:
+            case $node instanceof FragmentSpreadNode:
-                /** @var FragmentSpreadNode $node */
                 $fragment = $this->getFragment($node);
 
                 if ($fragment !== null) {

src/Validator/Rules/QueryDepth.php

@@ -5,6 +5,9 @@ declare(strict_types=1);
 namespace GraphQL\Validator\Rules;
 
 use GraphQL\Error\Error;
+use GraphQL\Language\AST\FieldNode;
+use GraphQL\Language\AST\FragmentSpreadNode;
+use GraphQL\Language\AST\InlineFragmentNode;
 use GraphQL\Language\AST\Node;
 use GraphQL\Language\AST\NodeKind;
 use GraphQL\Language\AST\OperationDefinitionNode;
@@ -57,9 +60,8 @@ class QueryDepth extends QuerySecurityRule
 
     private function nodeDepth(Node $node, $depth = 0, $maxDepth = 0)
     {
-        switch ($node->kind) {
+        switch (true) {
-            case NodeKind::FIELD:
+            case $node instanceof FieldNode:
-                /** @var FieldNode $node */
                 // node has children?
                 if ($node->selectionSet !== null) {
                     // update maxDepth if needed
@@ -70,16 +72,14 @@ class QueryDepth extends QuerySecurityRule
                 }
                 break;
 
-            case NodeKind::INLINE_FRAGMENT:
+            case $node instanceof InlineFragmentNode:
-                /** @var InlineFragmentNode $node */
                 // node has children?
                 if ($node->selectionSet !== null) {
                     $maxDepth = $this->fieldDepth($node, $depth, $maxDepth);
                 }
                 break;
 
-            case NodeKind::FRAGMENT_SPREAD:
+            case $node instanceof FragmentSpreadNode:
-                /** @var FragmentSpreadNode $node */
                 $fragment = $this->getFragment($node);
 
                 if ($fragment !== null) {

src/Validator/Rules/QuerySecurityRule.php

@@ -9,7 +9,6 @@ use GraphQL\Language\AST\FieldNode;
 use GraphQL\Language\AST\FragmentDefinitionNode;
 use GraphQL\Language\AST\FragmentSpreadNode;
 use GraphQL\Language\AST\InlineFragmentNode;
-use GraphQL\Language\AST\NodeKind;
 use GraphQL\Language\AST\SelectionSetNode;
 use GraphQL\Type\Definition\Type;
 use GraphQL\Type\Introspection;
@@ -114,8 +113,8 @@ abstract class QuerySecurityRule extends ValidationRule
         $_astAndDefs           = $astAndDefs ?: new ArrayObject();
 
         foreach ($selectionSet->selections as $selection) {
-            switch ($selection->kind) {
+            switch (true) {
-                case NodeKind::FIELD:
+                case $selection instanceof FieldNode:
                     /** @var FieldNode $selection */
                     $fieldName = $selection->name->value;
                     $fieldDef  = null;
@@ -142,7 +141,7 @@ abstract class QuerySecurityRule extends ValidationRule
                     // create field context
                     $_astAndDefs[$responseName][] = [$selection, $fieldDef];
                     break;
-                case NodeKind::INLINE_FRAGMENT:
+                case $selection instanceof InlineFragmentNode:
                     /** @var InlineFragmentNode $selection */
                     $_astAndDefs = $this->collectFieldASTsAndDefs(
                         $context,
@@ -152,7 +151,7 @@ abstract class QuerySecurityRule extends ValidationRule
                         $_astAndDefs
                     );
                     break;
-                case NodeKind::FRAGMENT_SPREAD:
+                case $selection instanceof FragmentSpreadNode:
                     /** @var FragmentSpreadNode $selection */
                     $fragName = $selection->name->value;
 

src/Validator/ValidationContext.php

@@ -199,7 +199,7 @@ class ValidationContext
 
                 for ($i = 0, $selectionCount = count($set->selections); $i < $selectionCount; $i++) {
                     $selection = $set->selections[$i];
-                    if ($selection->kind === NodeKind::FRAGMENT_SPREAD) {
+                    if ($selection instanceof FragmentSpreadNode) {
                         $spreads[] = $selection;
                     } elseif ($selection->selectionSet) {
                         $setsToVisit[] = $selection->selectionSet;
@@ -223,7 +223,7 @@ class ValidationContext
         if (! $fragments) {
             $fragments = [];
             foreach ($this->getDocument()->definitions as $statement) {
-                if ($statement->kind !== NodeKind::FRAGMENT_DEFINITION) {
+                if (! ($statement instanceof FragmentDefinitionNode)) {
                     continue;
                 }
 

tests/Exception/InvalidArgumentTest.php

@@ -0,0 +1,18 @@
+<?php
+
+declare(strict_types=1);
+
+namespace GraphQL\Tests\Exception;
+
+use GraphQL\Exception\InvalidArgument;
+use PHPUnit\Framework\TestCase;
+
+final class InvalidArgumentTest extends TestCase
+{
+    public function testFromExpectedTypeAndArgument() : void
+    {
+        $exception = InvalidArgument::fromExpectedTypeAndArgument('bool|int', 'stringValue');
+
+        self::assertSame('Expected type "bool|int", got "string"', $exception->getMessage());
+    }
+}

tests/Executor/DeferredFieldsTest.php

@@ -109,10 +109,10 @@ class DeferredFieldsTest extends TestCase
             'fields' => [
                 'title'  => [
                     'type'    => Type::string(),
-                    'resolve' => function ($entry, $args, $context, ResolveInfo $info) {
+                    'resolve' => function ($story, $args, $context, ResolveInfo $info) {
                         $this->paths[] = $info->path;
 
-                        return $entry['title'];
+                        return $story['title'];
                     },
                 ],
                 'author' => [
@@ -185,7 +185,7 @@ class DeferredFieldsTest extends TestCase
             'fields' => [
                 'topStories'       => [
                     'type'    => Type::listOf($this->storyType),
-                    'resolve' => function ($val, $args, $context, ResolveInfo $info) {
+                    'resolve' => function ($rootValue, $args, $context, ResolveInfo $info) {
                         $this->paths[] = $info->path;
 
                         return Utils::filter(
@@ -198,7 +198,7 @@ class DeferredFieldsTest extends TestCase
                 ],
                 'featuredCategory' => [
                     'type'    => $this->categoryType,
-                    'resolve' => function ($val, $args, $context, ResolveInfo $info) {
+                    'resolve' => function ($rootValue, $args, $context, ResolveInfo $info) {
                         $this->paths[] = $info->path;
 
                         return $this->categoryDataSource[0];
@@ -206,7 +206,7 @@ class DeferredFieldsTest extends TestCase
                 ],
                 'categories'       => [
                     'type'    => Type::listOf($this->categoryType),
-                    'resolve' => function ($val, $args, $context, ResolveInfo $info) {
+                    'resolve' => function ($rootValue, $args, $context, ResolveInfo $info) {
                         $this->paths[] = $info->path;
 
                         return $this->categoryDataSource;
@@ -401,7 +401,7 @@ class DeferredFieldsTest extends TestCase
                 return [
                     'sync'         => [
                         'type'    => Type::string(),
-                        'resolve' => function ($v, $a, $c, ResolveInfo $info) {
+                        'resolve' => function ($complexType, $args, $context, ResolveInfo $info) {
                             $this->paths[] = $info->path;
 
                             return 'sync';
@@ -409,7 +409,7 @@ class DeferredFieldsTest extends TestCase
                     ],
                     'deferred'     => [
                         'type'    => Type::string(),
-                        'resolve' => function ($v, $a, $c, ResolveInfo $info) {
+                        'resolve' => function ($complexType, $args, $context, ResolveInfo $info) {
                             $this->paths[] = $info->path;
 
                             return new Deferred(function () use ($info) {
@@ -421,7 +421,7 @@ class DeferredFieldsTest extends TestCase
                     ],
                     'nest'         => [
                         'type'    => $complexType,
-                        'resolve' => function ($v, $a, $c, ResolveInfo $info) {
+                        'resolve' => function ($complexType, $args, $context, ResolveInfo $info) {
                             $this->paths[] = $info->path;
 
                             return [];
@@ -429,7 +429,7 @@ class DeferredFieldsTest extends TestCase
                     ],
                     'deferredNest' => [
                         'type'    => $complexType,
-                        'resolve' => function ($v, $a, $c, ResolveInfo $info) {
+                        'resolve' => function ($complexType, $args, $context, ResolveInfo $info) {
                             $this->paths[] = $info->path;
 
                             return new Deferred(function () use ($info) {

tests/Executor/ExecutorSchemaTest.php

@@ -75,7 +75,7 @@ class ExecutorSchemaTest extends TestCase
                 'article' => [
                     'type'    => $BlogArticle,
                     'args'    => ['id' => ['type' => Type::id()]],
-                    'resolve' => function ($_, $args) {
+                    'resolve' => function ($rootValue, $args) {
                         return $this->article($args['id']);
                     },
                 ],

tests/Executor/ExecutorTest.php

@@ -273,7 +273,7 @@ class ExecutorTest extends TestCase
                 'fields' => [
                     'test' => [
                         'type'    => Type::string(),
-                        'resolve' => static function ($val, $args, $ctx, $_info) use (&$info) {
+                        'resolve' => static function ($test, $args, $ctx, $_info) use (&$info) {
                             $info = $_info;
                         },
                     ],

tests/Executor/TestClasses/Adder.php

@@ -16,7 +16,7 @@ class Adder
     {
         $this->num = $num;
 
-        $this->test = function ($source, $args, $context) {
+        $this->test = function ($objectValue, $args, $context) {
             return $this->num + $args['addend1'] + $context['addend2'];
         };
     }

tests/Experimental/Executor/CollectorTest.php

@@ -362,7 +362,7 @@ class CollectorTest extends TestCase
             $operationName = null;
             foreach ($documentNode->definitions as $definitionNode) {
                 /** @var Node $definitionNode */
-                if ($definitionNode->kind === NodeKind::OPERATION_DEFINITION) {
+                if ($definitionNode instanceof OperationDefinitionNode) {
                     /** @var OperationDefinitionNode $definitionNode */
                     self::assertNotNull($definitionNode->name);
                     $operationName = $definitionNode->name->value;

tests/GraphQLTest.php

@@ -30,7 +30,7 @@ class GraphQLTest extends TestCase
                                         'type' => Type::nonNull(Type::string()),
                                     ],
                                 ],
-                                'resolve' => static function ($value, $args) use ($promiseAdapter) {
+                                'resolve' => static function ($rootValue, $args) use ($promiseAdapter) {
                                     return $promiseAdapter->createFulfilled(sprintf('Hi %s!', $args['name']));
                                 },
                             ],

tests/Language/VisitorTest.php

@@ -70,7 +70,12 @@ class VisitorTest extends ValidatorTestCase
         /** @var Node $node */
         [$node, $key, $parent, $path, $ancestors] = $args;
 
-        $parentArray = $parent && ! is_array($parent) ? ($parent instanceof NodeList ? iterator_to_array($parent) : $parent->toArray()) : $parent;
+        $parentArray = $parent && ! is_array($parent)
+            ? ($parent instanceof NodeList
+                ? iterator_to_array($parent)
+                : $parent->toArray()
+            )
+            : $parent;
 
         self::assertInstanceOf(Node::class, $node);
         self::assertContains($node->kind, array_keys(NodeKind::$classMap));
@@ -114,7 +119,9 @@ class VisitorTest extends ValidatorTestCase
     {
         $result = $ast;
         foreach ($path as $key) {
-            $resultArray = $result instanceof NodeList ? iterator_to_array($result) : $result->toArray();
+            $resultArray = $result instanceof NodeList
+                ? iterator_to_array($result)
+                : $result->toArray();
             self::assertArrayHasKey($key, $resultArray);
             $result = $resultArray[$key];
         }
@@ -384,7 +391,7 @@ class VisitorTest extends ValidatorTestCase
                     $this->checkVisitorFnArgs($ast, func_get_args());
                     $visited[] = ['leave', $node->kind, $node->value ?? null];
 
-                    if ($node->kind === NodeKind::NAME && $node->value === 'x') {
+                    if ($node instanceof NameNode && $node->value === 'x') {
                         return Visitor::stop();
                     }
                 },

tests/Regression/Issue396Test.php

@@ -0,0 +1,156 @@
+<?php
+
+declare(strict_types=1);
+
+namespace GraphQL\Tests\Regression;
+
+use GraphQL\GraphQL;
+use GraphQL\Type\Definition\InterfaceType;
+use GraphQL\Type\Definition\ObjectType;
+use GraphQL\Type\Definition\ResolveInfo;
+use GraphQL\Type\Definition\Type;
+use GraphQL\Type\Definition\UnionType;
+use GraphQL\Type\Schema;
+use PHPUnit\Framework\TestCase;
+use function stristr;
+
+/**
+ * @see https://github.com/webonyx/graphql-php/issues/396
+ */
+class Issue396Test extends TestCase
+{
+    public function testUnionResolveType()
+    {
+        $a = new ObjectType(['name' => 'A', 'fields' => ['name' => Type::string()]]);
+        $b = new ObjectType(['name' => 'B', 'fields' => ['name' => Type::string()]]);
+        $c = new ObjectType(['name' => 'C', 'fields' => ['name' => Type::string()]]);
+
+        $log = [];
+
+        $unionResult = new UnionType([
+            'name' => 'UnionResult',
+            'types' => [$a, $b, $c],
+            'resolveType' => static function ($result, $value, ResolveInfo $info) use ($a, $b, $c, &$log) : Type {
+                $log[] = [$result, $info->path];
+                if (stristr($result['name'], 'A')) {
+                    return $a;
+                }
+                if (stristr($result['name'], 'B')) {
+                    return $b;
+                }
+                if (stristr($result['name'], 'C')) {
+                    return $c;
+                }
+            },
+        ]);
+
+        $exampleType = new ObjectType([
+            'name' => 'Example',
+            'fields' => [
+                'field' => [
+                    'type' => Type::nonNull(Type::listOf(Type::nonNull($unionResult))),
+                    'resolve' => static function () : array {
+                        return [
+                            ['name' => 'A 1'],
+                            ['name' => 'B 2'],
+                            ['name' => 'C 3'],
+                        ];
+                    },
+                ],
+            ],
+        ]);
+
+        $schema = new Schema(['query' => $exampleType]);
+
+        $query = '
+            query {
+                field {
+                    ... on A {
+                        name
+                    }
+                    ... on B {
+                        name
+                    }
+                    ... on C {
+                        name
+                    }
+                }
+            }
+        ';
+
+        GraphQL::executeQuery($schema, $query);
+
+        $expected = [
+            [['name' => 'A 1'], ['field', 0]],
+            [['name' => 'B 2'], ['field', 1]],
+            [['name' => 'C 3'], ['field', 2]],
+        ];
+        self::assertEquals($expected, $log);
+    }
+
+    public function testInterfaceResolveType()
+    {
+        $log = [];
+
+        $interfaceResult = new InterfaceType([
+            'name' => 'InterfaceResult',
+            'fields' => [
+                'name' => Type::string(),
+            ],
+            'resolveType' => static function ($result, $value, ResolveInfo $info) use (&$a, &$b, &$c, &$log) : Type {
+                $log[] = [$result, $info->path];
+                if (stristr($result['name'], 'A')) {
+                    return $a;
+                }
+                if (stristr($result['name'], 'B')) {
+                    return $b;
+                }
+                if (stristr($result['name'], 'C')) {
+                    return $c;
+                }
+            },
+        ]);
+
+        $a = new ObjectType(['name' => 'A', 'fields' => ['name' => Type::string()], 'interfaces' => [$interfaceResult]]);
+        $b = new ObjectType(['name' => 'B', 'fields' => ['name' => Type::string()], 'interfaces' => [$interfaceResult]]);
+        $c = new ObjectType(['name' => 'C', 'fields' => ['name' => Type::string()], 'interfaces' => [$interfaceResult]]);
+
+        $exampleType = new ObjectType([
+            'name' => 'Example',
+            'fields' => [
+                'field' => [
+                    'type' => Type::nonNull(Type::listOf(Type::nonNull($interfaceResult))),
+                    'resolve' => static function () : array {
+                        return [
+                            ['name' => 'A 1'],
+                            ['name' => 'B 2'],
+                            ['name' => 'C 3'],
+                        ];
+                    },
+                ],
+            ],
+        ]);
+
+        $schema = new Schema([
+            'query' => $exampleType,
+            'types' => [$a, $b, $c],
+        ]);
+
+        $query = '
+            query {
+                field {
+                    name
+                }
+            }
+        ';
+
+        GraphQL::executeQuery($schema, $query);
+
+        $expected = [
+            [['name' => 'A 1'], ['field', 0]],
+            [['name' => 'B 2'], ['field', 1]],
+            [['name' => 'C 3'], ['field', 2]],
+        ];
+        self::assertEquals($expected, $log);
+    }
+}

tests/Regression/Issue467Test.php

@@ -0,0 +1,45 @@
+<?php
+
+declare(strict_types=1);
+
+namespace GraphQL\Tests\Regression;
+
+use GraphQL\GraphQL;
+use GraphQL\Utils\BuildSchema;
+use PHPUnit\Framework\TestCase;
+
+/**
+ * @see https://github.com/webonyx/graphql-php/issues/467
+ */
+class Issue467Test extends TestCase
+{
+    public function testInputObjectValidation()
+    {
+        $schemaStr = '
+input MsgInput {
+  msg: String
+}
+
+type Query {
+  echo(msg: MsgInput): String
+}
+
+schema {
+    query: Query
+}
+';
+
+        $query     = '
+query echo ($msg: MsgInput) {
+          echo (msg: $msg)
+}';
+        $variables = ['msg' => ['my message']];
+
+        $schema = BuildSchema::build($schemaStr);
+        $result = GraphQL::executeQuery($schema, $query, null, null, $variables);
+
+        $expectedError = 'Variable "$msg" got invalid value ["my message"]; Field "0" is not defined by type MsgInput.';
+        self::assertCount(1, $result->errors);
+        self::assertEquals($expectedError, $result->errors[0]->getMessage());
+    }
+}

tests/Server/ServerTestCase.php

@@ -25,13 +25,13 @@ abstract class ServerTestCase extends TestCase
                 'fields' => [
                     'f1'                      => [
                         'type'    => Type::string(),
-                        'resolve' => static function ($root, $args, $context, $info) {
+                        'resolve' => static function ($rootValue, $args, $context, $info) {
                             return $info->fieldName;
                         },
                     ],
                     'fieldWithPhpError'       => [
                         'type'    => Type::string(),
-                        'resolve' => static function ($root, $args, $context, $info) {
+                        'resolve' => static function ($rootValue, $args, $context, $info) {
                             trigger_error('deprecated', E_USER_DEPRECATED);
                             trigger_error('notice', E_USER_NOTICE);
                             trigger_error('warning', E_USER_WARNING);
@@ -55,8 +55,8 @@ abstract class ServerTestCase extends TestCase
                     ],
                     'testContextAndRootValue' => [
                         'type'    => Type::string(),
-                        'resolve' => static function ($root, $args, $context, $info) {
+                        'resolve' => static function ($rootValue, $args, $context, $info) {
-                            $context->testedRootValue = $root;
+                            $context->testedRootValue = $rootValue;
 
                             return $info->fieldName;
                         },
@@ -68,7 +68,7 @@ abstract class ServerTestCase extends TestCase
                                 'type' => Type::nonNull(Type::string()),
                             ],
                         ],
-                        'resolve' => static function ($root, $args) {
+                        'resolve' => static function ($rootValue, $args) {
                             return $args['arg'];
                         },
                     ],
@@ -79,7 +79,7 @@ abstract class ServerTestCase extends TestCase
                                 'type' => Type::nonNull(Type::int()),
                             ],
                         ],
-                        'resolve' => static function ($root, $args, $context) {
+                        'resolve' => static function ($rootValue, $args, $context) {
                             $context['buffer']($args['num']);
 
                             return new Deferred(static function () use ($args, $context) {

tests/StarWarsSchema.php

@@ -273,7 +273,7 @@ class StarWarsSchema
                             'type'        => $episodeEnum,
                         ],
                     ],
-                    'resolve' => static function ($root, $args) {
+                    'resolve' => static function ($rootValue, $args) {
                         return StarWarsData::getHero($args['episode'] ?? null);
                     },
                 ],
@@ -286,7 +286,7 @@ class StarWarsSchema
                             'type'        => Type::nonNull(Type::string()),
                         ],
                     ],
-                    'resolve' => static function ($root, $args) {
+                    'resolve' => static function ($rootValue, $args) {
                         $humans = StarWarsData::humans();
 
                         return $humans[$args['id']] ?? null;
@@ -301,7 +301,7 @@ class StarWarsSchema
                             'type'        => Type::nonNull(Type::string()),
                         ],
                     ],
-                    'resolve' => static function ($root, $args) {
+                    'resolve' => static function ($rootValue, $args) {
                         $droids = StarWarsData::droids();
 
                         return $droids[$args['id']] ?? null;

tests/Type/EnumTypeTest.php

@@ -74,7 +74,7 @@ class EnumTypeTest extends TestCase
                         'fromInt'    => ['type' => Type::int()],
                         'fromString' => ['type' => Type::string()],
                     ],
-                    'resolve' => static function ($value, $args) {
+                    'resolve' => static function ($rootValue, $args) {
                         if (isset($args['fromInt'])) {
                             return $args['fromInt'];
                         }
@@ -92,7 +92,7 @@ class EnumTypeTest extends TestCase
                         'fromName'  => ['type' => Type::string()],
                         'fromValue' => ['type' => Type::string()],
                     ],
-                    'resolve' => static function ($value, $args) {
+                    'resolve' => static function ($rootValue, $args) {
                         if (isset($args['fromName'])) {
                             return $args['fromName'];
                         }
@@ -107,7 +107,7 @@ class EnumTypeTest extends TestCase
                         'fromEnum' => ['type' => $ColorType],
                         'fromInt'  => ['type' => Type::int()],
                     ],
-                    'resolve' => static function ($value, $args) {
+                    'resolve' => static function ($rootValue, $args) {
                         if (isset($args['fromInt'])) {
                             return $args['fromInt'];
                         }
@@ -132,7 +132,7 @@ class EnumTypeTest extends TestCase
                             'type' => Type::boolean(),
                         ],
                     ],
-                    'resolve' => static function ($value, $args) use ($Complex2) {
+                    'resolve' => static function ($rootValue, $args) use ($Complex2) {
                         if (! empty($args['provideGoodValue'])) {
                             // Note: this is one of the references of the internal values which
                             // ComplexEnum allows.
@@ -156,7 +156,7 @@ class EnumTypeTest extends TestCase
                 'favoriteEnum' => [
                     'type'    => $ColorType,
                     'args'    => ['color' => ['type' => $ColorType]],
-                    'resolve' => static function ($value, $args) {
+                    'resolve' => static function ($rootValue, $args) {
                         return $args['color'] ?? null;
                     },
                 ],
@@ -169,7 +169,7 @@ class EnumTypeTest extends TestCase
                 'subscribeToEnum' => [
                     'type'    => $ColorType,
                     'args'    => ['color' => ['type' => $ColorType]],
-                    'resolve' => static function ($value, $args) {
+                    'resolve' => static function ($rootValue, $args) {
                         return $args['color'] ?? null;
                     },
                 ],

tests/Type/IntrospectionTest.php

@@ -1049,7 +1049,7 @@ class IntrospectionTest extends TestCase
                 'field' => [
                     'type'    => Type::string(),
                     'args'    => ['complex' => ['type' => $TestInputObject]],
-                    'resolve' => static function ($_, $args) {
+                    'resolve' => static function ($testType, $args) {
                         return json_encode($args['complex']);
                     },
                 ],

tests/Type/QueryPlanTest.php

@@ -5,6 +5,8 @@ declare(strict_types=1);
 namespace GraphQL\Tests\Type;
 
 use GraphQL\GraphQL;
+use GraphQL\Tests\Executor\TestClasses\Dog;
+use GraphQL\Type\Definition\InterfaceType;
 use GraphQL\Type\Definition\ObjectType;
 use GraphQL\Type\Definition\QueryPlan;
 use GraphQL\Type\Definition\ResolveInfo;
@@ -295,6 +297,117 @@ final class QueryPlanTest extends TestCase
         self::assertFalse($queryPlan->hasType('Test'));
     }
 
+    public function testQueryPlanOnInterface() : void
+    {
+        $petType = new InterfaceType([
+            'name'   => 'Pet',
+            'fields' => static function () {
+                return [
+                    'name' => ['type' => Type::string()],
+                ];
+            },
+        ]);
+
+        $dogType = new ObjectType([
+            'name'       => 'Dog',
+            'interfaces' => [$petType],
+            'isTypeOf'   => static function ($obj) {
+                return $obj instanceof Dog;
+            },
+            'fields' => static function () {
+                return [
+                    'name'  => ['type' => Type::string()],
+                    'woofs' => ['type' => Type::boolean()],
+                ];
+            },
+        ]);
+
+        $query = 'query Test {
+          pets {
+            name
+            ... on Dog {
+              woofs
+            }
+          }
+        }';
+
+        $expectedQueryPlan = [
+            'woofs'  => [
+                'type' => Type::boolean(),
+                'fields' => [],
+                'args' => [],
+            ],
+            'name'   => [
+                'type' => Type::string(),
+                'args' => [],
+                'fields' => [],
+            ],
+        ];
+
+        $expectedReferencedTypes = [
+            'Dog',
+            'Pet',
+        ];
+
+        $expectedReferencedFields = [
+            'woofs',
+            'name',
+        ];
+
+        /** @var QueryPlan $queryPlan */
+        $queryPlan = null;
+        $hasCalled = false;
+
+        $petsQuery = new ObjectType([
+            'name'   => 'Query',
+            'fields' => [
+                'pets' => [
+                    'type'    => Type::listOf($petType),
+                    'resolve' => static function (
+                        $value,
+                        $args,
+                        $context,
+                        ResolveInfo $info
+                    ) use (
+                        &$hasCalled,
+                        &$queryPlan
+) {
+                        $hasCalled = true;
+                        $queryPlan = $info->lookAhead();
+
+                        return [];
+                    },
+                ],
+            ],
+        ]);
+
+        $schema = new Schema([
+            'query' => $petsQuery,
+            'types'      => [$dogType],
+            'typeLoader' => static function ($name) use ($dogType, $petType) {
+                switch ($name) {
+                    case 'Dog':
+                        return $dogType;
+                    case 'Pet':
+                        return $petType;
+                }
+            },
+        ]);
+        GraphQL::executeQuery($schema, $query)->toArray();
+
+        self::assertTrue($hasCalled);
+        self::assertEquals($expectedQueryPlan, $queryPlan->queryPlan());
+        self::assertEquals($expectedReferencedTypes, $queryPlan->getReferencedTypes());
+        self::assertEquals($expectedReferencedFields, $queryPlan->getReferencedFields());
+        self::assertEquals(['woofs'], $queryPlan->subFields('Dog'));
+
+        self::assertTrue($queryPlan->hasField('name'));
+        self::assertFalse($queryPlan->hasField('test'));
+
+        self::assertTrue($queryPlan->hasType('Dog'));
+        self::assertFalse($queryPlan->hasType('Test'));
+    }
+
     public function testMergedFragmentsQueryPlan() : void
     {
         $image = new ObjectType([

tests/Type/ScalarSerializationTest.php

@@ -13,9 +13,9 @@ class ScalarSerializationTest extends TestCase
 {
     // Type System: Scalar coercion
     /**
-     * @see it('serializes output int')
+     * @see it('serializes output as Int')
      */
-    public function testSerializesOutputInt() : void
+    public function testSerializesOutputAsInt() : void
     {
         $intType = Type::int();
 
@@ -114,9 +114,9 @@ class ScalarSerializationTest extends TestCase
     }
 
     /**
-     * @see it('serializes output float')
+     * @see it('serializes output as Float')
      */
-    public function testSerializesOutputFloat() : void
+    public function testSerializesOutputAsFloat() : void
     {
         $floatType = Type::float();
 
@@ -149,9 +149,9 @@ class ScalarSerializationTest extends TestCase
     }
 
     /**
-     * @see it('serializes output strings')
+     * @see it('serializes output as String')
      */
-    public function testSerializesOutputStrings() : void
+    public function testSerializesOutputAsString() : void
     {
         $stringType = Type::string();
 
@@ -181,23 +181,27 @@ class ScalarSerializationTest extends TestCase
     }
 
     /**
-     * @see it('serializes output boolean')
+     * @see it('serializes output as Boolean')
      */
-    public function testSerializesOutputBoolean() : void
+    public function testSerializesOutputAsBoolean() : void
     {
         $boolType = Type::boolean();
 
-        self::assertTrue($boolType->serialize('string'));
-        self::assertFalse($boolType->serialize(''));
-        self::assertTrue($boolType->serialize('1'));
-        self::assertTrue($boolType->serialize(1));
-        self::assertFalse($boolType->serialize(0));
         self::assertTrue($boolType->serialize(true));
+        self::assertTrue($boolType->serialize(1));
+        self::assertTrue($boolType->serialize('1'));
+        self::assertTrue($boolType->serialize('string'));
+
         self::assertFalse($boolType->serialize(false));
-        // TODO: how should it behave on '0'?
+        self::assertFalse($boolType->serialize(0));
+        self::assertFalse($boolType->serialize('0'));
+        self::assertFalse($boolType->serialize(''));
     }
 
-    public function testSerializesOutputID() : void
+    /**
+     * @see it('serializes output as ID')
+     */
+    public function testSerializesOutputAsID() : void
     {
         $idType = Type::id();
 

tests/Type/ValidationTest.php

@@ -879,6 +879,144 @@ class ValidationTest extends TestCase
         );
     }
 
+    /**
+     * @see it('accepts an Input Object with breakable circular reference')
+     */
+    public function testAcceptsAnInputObjectWithBreakableCircularReference() : void
+    {
+        $schema = BuildSchema::build('
+      input AnotherInputObject {
+        parent: SomeInputObject
+      }
+      
+      type Query {
+        field(arg: SomeInputObject): String
+      }
+      
+      input SomeInputObject {
+        self: SomeInputObject
+        arrayOfSelf: [SomeInputObject]
+        nonNullArrayOfSelf: [SomeInputObject]!
+        nonNullArrayOfNonNullSelf: [SomeInputObject!]!
+        intermediateSelf: AnotherInputObject
+      }
+        ');
+        self::assertEquals([], $schema->validate());
+    }
+
+    /**
+     * @see it('rejects an Input Object with non-breakable circular reference')
+     */
+    public function testRejectsAnInputObjectWithNonBreakableCircularReference() : void
+    {
+        $schema = BuildSchema::build('
+      type Query {
+        field(arg: SomeInputObject): String
+      }
+      
+      input SomeInputObject {
+        nonNullSelf: SomeInputObject!
+      }
+        ');
+        $this->assertMatchesValidationMessage(
+            $schema->validate(),
+            [
+                [
+                    'message'   => 'Cannot reference Input Object "SomeInputObject" within itself through a series of non-null fields: "nonNullSelf".',
+                    'locations' => [['line' => 7, 'column' => 9]],
+                ],
+            ]
+        );
+    }
+
+    /**
+     * @see it('rejects Input Objects with non-breakable circular reference spread across them')
+     */
+    public function testRejectsInputObjectsWithNonBreakableCircularReferenceSpreadAcrossThem() : void
+    {
+        $schema = BuildSchema::build('
+      type Query {
+        field(arg: SomeInputObject): String
+      }
+      
+      input SomeInputObject {
+        startLoop: AnotherInputObject!
+      }
+      
+      input AnotherInputObject {
+        nextInLoop: YetAnotherInputObject!
+      }
+      
+      input YetAnotherInputObject {
+        closeLoop: SomeInputObject!
+      }
+        ');
+        $this->assertMatchesValidationMessage(
+            $schema->validate(),
+            [
+                [
+                    'message'   => 'Cannot reference Input Object "SomeInputObject" within itself through a series of non-null fields: "startLoop.nextInLoop.closeLoop".',
+                    'locations' => [
+                        ['line' => 7, 'column' => 9],
+                        ['line' => 11, 'column' => 9],
+                        ['line' => 15, 'column' => 9],
+                    ],
+                ],
+            ]
+        );
+    }
+
+    /**
+     * @see it('rejects Input Objects with multiple non-breakable circular reference')
+     */
+    public function testRejectsInputObjectsWithMultipleNonBreakableCircularReferences() : void
+    {
+        $schema = BuildSchema::build('
+      type Query {
+        field(arg: SomeInputObject): String
+      }
+      
+      input SomeInputObject {
+        startLoop: AnotherInputObject!
+      }
+      
+      input AnotherInputObject {
+        closeLoop: SomeInputObject!
+        startSecondLoop: YetAnotherInputObject!
+      }
+      
+      input YetAnotherInputObject {
+        closeSecondLoop: AnotherInputObject!
+        nonNullSelf: YetAnotherInputObject!
+      }
+        ');
+        $this->assertMatchesValidationMessage(
+            $schema->validate(),
+            [
+                [
+                    'message'   => 'Cannot reference Input Object "SomeInputObject" within itself through a series of non-null fields: "startLoop.closeLoop".',
+                    'locations' => [
+                        ['line' => 7, 'column' => 9],
+                        ['line' => 11, 'column' => 9],
+                    ],
+                ],
+                [
+                    'message'   => 'Cannot reference Input Object "AnotherInputObject" within itself through a series of non-null fields: "startSecondLoop.closeSecondLoop".',
+                    'locations' => [
+                        ['line' => 12, 'column' => 9],
+                        ['line' => 16, 'column' => 9],
+                    ],
+                ],
+                [
+                    'message'   => 'Cannot reference Input Object "YetAnotherInputObject" within itself through a series of non-null fields: "nonNullSelf".',
+                    'locations' => [
+                        ['line' => 17, 'column' => 9],
+                    ],
+                ],
+            ]
+        );
+    }
+
     /**
      * @see it('rejects an Input Object type with incorrectly typed fields')
      */

tests/Utils/AstFromValueTest.php

@@ -10,6 +10,7 @@ use GraphQL\Language\AST\FloatValueNode;
 use GraphQL\Language\AST\IntValueNode;
 use GraphQL\Language\AST\ListValueNode;
 use GraphQL\Language\AST\NameNode;
+use GraphQL\Language\AST\NodeList;
 use GraphQL\Language\AST\NullValueNode;
 use GraphQL\Language\AST\ObjectFieldNode;
 use GraphQL\Language\AST\ObjectValueNode;
@@ -179,18 +180,18 @@ class AstFromValueTest extends TestCase
     public function testConvertsArrayValuesToListASTs() : void
     {
         $value1 = new ListValueNode([
-            'values' => [
+            'values' => new NodeList([
                 new StringValueNode(['value' => 'FOO']),
                 new StringValueNode(['value' => 'BAR']),
-            ],
+            ]),
         ]);
         self::assertEquals($value1, AST::astFromValue(['FOO', 'BAR'], Type::listOf(Type::string())));
 
         $value2 = new ListValueNode([
-            'values' => [
+            'values' => new NodeList([
                 new EnumValueNode(['value' => 'HELLO']),
                 new EnumValueNode(['value' => 'GOODBYE']),
-            ],
+            ]),
         ]);
         self::assertEquals($value2, AST::astFromValue(['HELLO', 'GOODBYE'], Type::listOf($this->myEnum())));
     }
@@ -220,10 +221,10 @@ class AstFromValueTest extends TestCase
         ]);
 
         $expected = new ObjectValueNode([
-            'fields' => [
+            'fields' => new NodeList([
                 $this->objectField('foo', new IntValueNode(['value' => '3'])),
                 $this->objectField('bar', new EnumValueNode(['value' => 'HELLO'])),
-            ],
+            ]),
         ]);
 
         $data = ['foo' => 3, 'bar' => 'HELLO'];
@@ -259,9 +260,9 @@ class AstFromValueTest extends TestCase
 
         self::assertEquals(
             new ObjectValueNode([
-                'fields' => [
+                'fields' => new NodeList([
                     $this->objectField('foo', new NullValueNode([])),
-                ],
+                ]),
             ]),
             AST::astFromValue(['foo' => null], $inputObj)
         );

tests/Utils/BuildSchemaTest.php

@@ -51,7 +51,7 @@ class BuildSchemaTest extends TestCase
         ');
 
         $root = [
-            'add' => static function ($root, $args) {
+            'add' => static function ($rootValue, $args) {
                 return $args['x'] + $args['y'];
             },
         ];
@@ -437,7 +437,7 @@ type WorldTwo {
      */
     public function testSpecifyingUnionTypeUsingTypename() : void
     {
-        $schema   = BuildSchema::buildAST(Parser::parse('
+        $schema    = BuildSchema::buildAST(Parser::parse('
             type Query {
               fruits: [Fruit]
             }
@@ -452,7 +452,7 @@ type WorldTwo {
               length: Int
             }
         '));
-        $query    = '
+        $query     = '
             {
               fruits {
                 ... on Apple {
@@ -464,7 +464,7 @@ type WorldTwo {
               }
             }
         ';
-        $root     = [
+        $rootValue = [
             'fruits' => [
                 [
                     'color'      => 'green',
@@ -476,7 +476,7 @@ type WorldTwo {
                 ],
             ],
         ];
-        $expected = [
+        $expected  = [
             'data' => [
                 'fruits' => [
                     ['color' => 'green'],
@@ -485,7 +485,7 @@ type WorldTwo {
             ],
         ];
 
-        $result = GraphQL::executeQuery($schema, $query, $root);
+        $result = GraphQL::executeQuery($schema, $query, $rootValue);
         self::assertEquals($expected, $result->toArray(true));
     }
 
@@ -494,7 +494,7 @@ type WorldTwo {
      */
     public function testSpecifyingInterfaceUsingTypename() : void
     {
-        $schema   = BuildSchema::buildAST(Parser::parse('
+        $schema    = BuildSchema::buildAST(Parser::parse('
             type Query {
               characters: [Character]
             }
@@ -513,7 +513,7 @@ type WorldTwo {
               primaryFunction: String
             }
         '));
-        $query    = '
+        $query     = '
             {
               characters {
                 name
@@ -526,7 +526,7 @@ type WorldTwo {
               }
             }
         ';
-        $root     = [
+        $rootValue = [
             'characters' => [
                 [
                     'name'         => 'Han Solo',
@@ -540,7 +540,7 @@ type WorldTwo {
                 ],
             ],
         ];
-        $expected = [
+        $expected  = [
             'data' => [
                 'characters' => [
                     ['name' => 'Han Solo', 'totalCredits' => 10],
@@ -549,7 +549,7 @@ type WorldTwo {
             ],
         ];
 
-        $result = GraphQL::executeQuery($schema, $query, $root);
+        $result = GraphQL::executeQuery($schema, $query, $rootValue);
         self::assertEquals($expected, $result->toArray(true));
     }
 

tests/Utils/SchemaExtenderTest.php

@@ -219,7 +219,9 @@ class SchemaExtenderTest extends TestCase
     {
         $ast              = Parser::parse(SchemaPrinter::doPrint($extendedSchema));
         $ast->definitions = array_values(array_filter(
-            $ast->definitions instanceof NodeList ? iterator_to_array($ast->definitions->getIterator()) : $ast->definitions,
+            $ast->definitions instanceof NodeList
+                ? iterator_to_array($ast->definitions->getIterator())
+                : $ast->definitions,
             function (Node $node) : bool {
                 return ! in_array(Printer::doPrint($node), $this->testSchemaDefinitions, true);
             }

tools/gendocs.php

@@ -40,7 +40,9 @@ function renderClassMethod(ReflectionMethod $method) {
         $def = $type . '$' . $p->getName();
 
         if ($p->isDefaultValueAvailable()) {
-            $val = $p->isDefaultValueConstant() ? $p->getDefaultValueConstantName() : $p->getDefaultValue();
+            $val = $p->isDefaultValueConstant()
+                ? $p->getDefaultValueConstantName()
+                : $p->getDefaultValue();
             $def .= " = " . Utils::printSafeJson($val);
         }