src/Language/Parser.php
private function parseUnionMemberTypes()
    {
        $types = [];
        if ($this->skip(Token::EQUALS)) {
            // Optional leading pipe
            $this->skip(Token::PIPE);
            do {
                $types[] = $this->parseNamedType();
            } while ($this->skip(Token::PIPE));
        }

        return $types;
    }
private function parseUnionMemberTypes()
    {
        $types = [];
        if ($this->skip(Token::EQUALS)) {
            // Optional leading pipe
            $this->skip(Token::PIPE);
            do {
                $types[] = $this->parseNamedType();
            } while ($this->skip(Token::PIPE));
        }

        return $types;
    }
UnionMemberTypes :
- = `|`? NamedType
- UnionMemberTypes | NamedType

@return NamedTypeNode[]