Make querying isOneOf optional in Introspection query (#1737)

Including it by default makes introspection fail on servers that do not support it:

```
Cannot query field "isOneOf" on type "__Type".
```

Thus, I added a configuration option `typeIsOneOf` which works analogous to `directiveIsRepeatable`.

Author: spawnia

CHANGELOG.md

@@ -9,6 +9,12 @@ You can find and compare releases at the [GitHub release page](https://github.co
 
 ## Unreleased
 
+## v15.21.3
+
+### Fixed
+
+- Make querying `isOneOf` optional in Introspection query https://github.com/webonyx/graphql-php/pull/1737
+
 ## v15.21.2
 
 ### Fixed

src/Type/Introspection.php

@@ -30,14 +30,18 @@
  * @phpstan-type IntrospectionOptions array{
  *     descriptions?: bool,
  *     directiveIsRepeatable?: bool,
+ *     typeIsOneOf?: bool,
  * }
  *
  * Available options:
  * - descriptions
- *   Whether to include descriptions in the introspection result.
+ *   Include descriptions in the introspection result?
  *   Default: true
  * - directiveIsRepeatable
- *   Whether to include `isRepeatable` flag on directives.
+ *   Include field `isRepeatable` for directives?
+ *   Default: false
+ * - typeIsOneOf
+ *   Include field `isOneOf` for types?
  *   Default: false
  *
  * @see \GraphQL\Tests\Type\IntrospectionTest
@@ -81,6 +85,7 @@ public static function getIntrospectionQuery(array $options = []): string
         $optionsWithDefaults = array_merge([
             'descriptions' => true,
             'directiveIsRepeatable' => false,
+            'typeIsOneOf' => false,
         ], $options);
 
         $descriptions = $optionsWithDefaults['descriptions']
@@ -89,6 +94,9 @@ public static function getIntrospectionQuery(array $options = []): string
         $directiveIsRepeatable = $optionsWithDefaults['directiveIsRepeatable']
             ? 'isRepeatable'
             : '';
+        $typeIsOneOf = $optionsWithDefaults['typeIsOneOf']
+            ? 'isOneOf'
+            : '';
 
         return <<<GRAPHQL
   query IntrospectionQuery {
@@ -115,7 +123,7 @@ public static function getIntrospectionQuery(array $options = []): string
     kind
     name
     {$descriptions}
-    isOneOf
+    {$typeIsOneOf}
     fields(includeDeprecated: true) {
       name
       {$descriptions}
@@ -210,7 +218,10 @@ enumValues(includeDeprecated: true) {
      */
     public static function fromSchema(Schema $schema, array $options = []): array
     {
-        $optionsWithDefaults = array_merge(['directiveIsRepeatable' => true], $options);
+        $optionsWithDefaults = array_merge([
+            'directiveIsRepeatable' => true,
+            'typeIsOneOf' => true,
+        ], $options);
 
         $result = GraphQL::executeQuery(
             $schema,

src/Utils/Utils.php

@@ -116,9 +116,7 @@ public static function chr(int $ord, string $encoding = 'UTF-8'): string
             return pack('N', $ord);
         }
 
-        $converted = mb_convert_encoding(self::chr($ord, 'UCS-4BE'), $encoding, 'UCS-4BE');
-
-        return $converted;
+        return mb_convert_encoding(self::chr($ord, 'UCS-4BE'), $encoding, 'UCS-4BE');
     }
 
     /** UTF-8 compatible ord(). */

tests/Type/IntrospectionTest.php

@@ -41,6 +41,7 @@ public function testExecutesAnIntrospectionQuery(): void
         $source = Introspection::getIntrospectionQuery([
             'descriptions' => false,
             'directiveIsRepeatable' => true,
+            'typeIsOneOf' => true,
         ]);
 
         $expected = [
@@ -1773,7 +1774,10 @@ public function testExecutesAnIntrospectionQueryWithoutCallingGlobalFieldResolve
         $schema = new Schema([
             'query' => $QueryRoot,
         ]);
-        $source = Introspection::getIntrospectionQuery(['directiveIsRepeatable' => true]);
+        $source = Introspection::getIntrospectionQuery([
+            'directiveIsRepeatable' => true,
+            'typeIsOneOf' => true,
+        ]);
 
         $calledForFields = [];
         $fieldResolver = static function ($value, array $args, $context, ResolveInfo $info) use (&$calledForFields) {

tests/Utils/BuildClientSchemaTest.php

@@ -26,7 +26,10 @@ final class BuildClientSchemaTest extends TestCase
      */
     protected static function assertCycleIntrospection(string $sdl): void
     {
-        $options = ['directiveIsRepeatable' => true];
+        $options = [
+            'directiveIsRepeatable' => true,
+            'typeIsOneOf' => true,
+        ];
 
         $serverSchema = BuildSchema::build($sdl);
         $initialIntrospection = Introspection::fromSchema($serverSchema, $options);

tests/Validator/QueryComplexityTest.php

@@ -164,7 +164,7 @@ public function testQueryWithCustomAndSkipDirective(): void
 
     public function testComplexityIntrospectionQuery(): void
     {
-        $this->assertIntrospectionQuery(188);
+        $this->assertIntrospectionQuery(187);
     }
 
     public function testIntrospectionTypeMetaFieldQuery(): void