Add Type::reset and Directive::reset methods

See #1424

This library uses a static cache for standard types and the internal directives.

While not ideal, this works fine. As long as you don't have a scenario where you want to change
them.

In my situation, we have 2 schema's with a custom ID type. They are not the same instance.
This still works fine, but as soon as we run our whole test suite at once, the static cache
is initialized in some test, and another test later expects something else.

While I think the better solution would be to remove these static caches completely, and store
them on an instance instead of statically. But that will be a much bigger task given the current
architecture.

With these 2 reset methods, we can manually reset the caches in our test suite.

It could also be used for people that run their GraphQL server in tools like RoadRunner
and FrankenPHP.

src/Type/Definition/Directive.php

@@ -33,7 +33,7 @@ class Directive
      *
      * @var array<string, Directive>
      */
-    protected static array $internalDirectives;
+    protected static array $internalDirectives = [];
 
     public string $name;
 
@@ -90,7 +90,11 @@ public static function includeDirective(): Directive
      */
     public static function getInternalDirectives(): array
     {
-        return self::$internalDirectives ??= [
+        if (self::$internalDirectives !== []) {
+            return self::$internalDirectives;
+        }
+
+        return self::$internalDirectives = [
             'include' => new self([
                 'name' => self::INCLUDE_NAME,
                 'description' => 'Directs the executor to include this field or fragment only when the `if` argument is true.',
@@ -162,4 +166,9 @@ public static function isSpecifiedDirective(Directive $directive): bool
     {
         return \array_key_exists($directive->name, self::getInternalDirectives());
     }
+
+    public static function reset(): void
+    {
+        self::$internalDirectives = [];
+    }
 }

src/Type/Definition/Type.php

@@ -31,7 +31,7 @@ abstract class Type implements \JsonSerializable
     ];
 
     /** @var array<string, ScalarType> */
-    protected static array $standardTypes;
+    protected static array $standardTypes = [];
 
     /**
      * @api
@@ -261,4 +261,9 @@ public function jsonSerialize(): string
     {
         return $this->toString();
     }
+
+    public static function reset(): void
+    {
+        static::$standardTypes = [];
+    }
 }

tests/Type/Definition/TypeTest.php

@@ -0,0 +1,19 @@
+<?php
+
+declare(strict_types=1);
+namespace GraphQL\Tests\Type\Definition;
+
+use GraphQL\Type\Definition\Type;
+use PHPUnit\Framework\TestCase;
+
+final class TypeTest extends TestCase
+{
+    public function testReset(): void
+    {
+        $stringType = Type::string();
+
+        Type::reset();
+
+        self::assertNotSame($stringType, Type::string());
+    }
+}

tests/Type/DirectiveTest.php

@@ -83,5 +83,14 @@ public function testDefinesADirectiveWithMultipleArgs(): void
         self::assertFalse($argumentBar->isDeprecated());
     }
 
+    public function testReset(): void
+    {
+        $directives = Directive::getInternalDirectives();
+
+        Directive::reset();
+
+        self::assertNotSame($directives, Directive::getInternalDirectives());
+    }
+
     // TODO implement all of https://github.com/graphql/graphql-js/blob/master/src/type/__tests__/directive-test.js
 }