GraphQL\Validator\ValidationContext::getRecursiveVariableUsages PHP Method

    function getRecursiveVariableUsages(OperationDefinitionNode $operation)
    {
        $usages = isset($this->recursiveVariableUsages[$operation]) ? $this->recursiveVariableUsages[$operation] : null;
        if (!$usages) {
            $usages = $this->getVariableUsages($operation);
            $fragments = $this->getRecursivelyReferencedFragments($operation);
            $tmp = [$usages];
            for ($i = 0; $i < count($fragments); $i++) {
                $tmp[] = $this->getVariableUsages($fragments[$i]);
            }
            $usages = call_user_func_array('array_merge', $tmp);
            $this->recursiveVariableUsages[$operation] = $usages;
        }
        return $usages;
    }

 public function __invoke(ValidationContext $context)
 {
     return [NodeKind::OPERATION_DEFINITION => ['enter' => function () {
         $this->varDefMap = [];
     }, 'leave' => function (OperationDefinitionNode $operation) use($context) {
         $usages = $context->getRecursiveVariableUsages($operation);
         foreach ($usages as $usage) {
             $node = $usage['node'];
             $type = $usage['type'];
             $varName = $node->name->value;
             $varDef = isset($this->varDefMap[$varName]) ? $this->varDefMap[$varName] : null;
             if ($varDef && $type) {
                 // A var type is allowed if it is the same or more strict (e.g. is
                 // a subtype of) than the expected type. It can be more strict if
                 // the variable type is non-null when the expected type is nullable.
                 // If both are list types, the variable item type can be more strict
                 // than the expected item type (contravariant).
                 $schema = $context->getSchema();
                 $varType = TypeInfo::typeFromAST($schema, $varDef->type);
                 if ($varType && !TypeInfo::isTypeSubTypeOf($schema, $this->effectiveType($varType, $varDef), $type)) {
                     $context->reportError(new Error(self::badVarPosMessage($varName, $varType, $type), [$varDef, $node]));
                 }
             }
         }
     }], NodeKind::VARIABLE_DEFINITION => function (VariableDefinitionNode $varDefNode) {
         $this->varDefMap[$varDefNode->variable->name->value] = $varDefNode;
     }];
 }