Phan\Analysis\PreOrderAnalysisVisitor::setReturnTypeOfGenerator PHP Method

    private function setReturnTypeOfGenerator(FunctionInterface $func, Node $node)
    {
        // Currently, there is no way to describe the types passed to
        // a Generator in phpdoc.
        // So, nothing bothers recording the types beyond \Generator.
        $func->setHasReturn(true);
        // Returns \Generator, technically
        $func->setHasYield(true);
        if ($func->getUnionType()->isEmpty()) {
            $func->setIsReturnTypeUndefined(true);
            $func->getUnionType()->addUnionType(Type::fromNamespaceAndName('\\', 'Generator')->asUnionType());
        }
        if (!$func->isReturnTypeUndefined()) {
            $func_return_type = $func->getUnionType();
            if (!$func_return_type->canCastToExpandedUnionType(Type::fromNamespaceAndName('\\', 'Generator')->asUnionType(), $this->code_base)) {
                // At least one of the documented return types must
                // be Generator, Iterable, or Traversable.
                // Check for the issue here instead of in visitReturn/visitYield so that
                // the check is done exactly once.
                $this->emitIssue(Issue::TypeMismatchReturn, $node->lineno ?? 0, '\\Generator', $func->getName(), (string) $func_return_type);
            }
        }
    }