Malformed queries trigger PHP warnings in the parser #574

Problem

When the lexer can't tokenize a query, the parser emits a series of PHP warnings before the driver throws Failed to parse the MySQL query. MySQL returns a single syntax error.

Reproduction

SELECT 'abc

The driver warnings alternate between these two:

Warning: Undefined array key 1 in .../src/parser/class-wp-parser.php on line 57
Warning: Attempt to read property "id" on null in .../src/parser/class-wp-parser.php on line 57

Any input that the lexer rejects does the same, for example SELECT x'ab01xyz'.

MySQL results are from MySQL 8.4. Driver results are from #573 at cd4384bc, with PHP 8.5.12 and SQLite 3.54.1.

Users see the warnings when WP_DEBUG is on. When an error handler turns warnings into exceptions, as PHPUnit does by default, the warning replaces the driver's own exception.

Cause

WP_MySQL_Lexer::remaining_tokens() stops at the invalid input and returns the tokens it has read so far, without an EOF token. The lookahead check in WP_Parser::parse_recursive() then reads $this->tokens[ $this->position ]->id past the end of the token list.

Direction

• Throw a syntax error when the lexer fails. For example, create_parser() could check that the lexer reached EOF and throw new_invalid_input_exception() ("MySQL query syntax error.").
• Reject odd-length X'…' literals in the lexer. MySQL rejects quoted hex literals with an odd number of digits, such as X'711', in its lexer with error 1064. Our lexer accepts them, so the query fails only when SQLite rejects the translated literal with unrecognized token: "X'711'". Once lexer failures are handled, both lexer copies (packages/mysql-on-sqlite and packages/mysql-parser) can reject them like MySQL does. testOddLengthQuotedHexadecimalLiteralsAreRejected from Support odd-length 0x hexadecimal literals #573 can then assert the syntax error.