SET parser: too permissive on invalid syntax — should produce empty result

[renecannao]

Problem

ProxySQL's regex-based SET parser (MySQL_Set_Stmt_Parser::parse1v2()) returns an empty map for syntactically invalid SET statements. This signals to ProxySQL that the statement is unparseable, causing it to forward the SET verbatim to the backend.

ParserSQL's SetParser is more lenient — it partially parses invalid statements and produces a non-empty result instead of failing. This causes ProxySQL to attempt to process variables that came from malformed SQL.

Failing test cases

These should all produce an empty map but instead produce partial results:

SET sql_mode='TRADITIONAL' , whatever
  Expected: {} (syntax error: trailing "whatever" with no assignment)
  Got:      {"sql_mode": ["TRADITIONAL"], "whatever": [""]}

SET sql_mode='TRADITIONAL' , whatever = 
  Expected: {} (syntax error: empty value after =)
  Got:      {"sql_mode": ["TRADITIONAL"], "whatever": [""]}

SET sql_mode=(SELECT CONCAT(@@sql_mode, ',PIPES_AS_CONCAT,NO_ENGINE_SUBSTITUTION')), time_zone = '+00:00', NAMES utf8mb4 COLLATE utf8mb4_unicode_ci
  Expected: 3 entries (this one actually works, but mismatched — subquery handling)

SET sql_mode=(SELECT CONCA(@@sql_mode, '...'))   -- misspelled function
  Expected: {}
  Got:      {"sql_mode": [...]}

SET sql_mode=(SELECT CONCAT(@@sql_mode, ',PIPES_AS_CONCAT[,NO_ENGINE_SUBSTITUTION'))   -- unmatched bracket
  Expected: {}
  Got:      {"sql_mode": [...]}

SET sql_mode=(SELCT CONCAT(@@sql_mode, '...'))   -- misspelled SELECT
  Expected: {}
  Got:      {"sql_mode": [...]}

SET sql_mode='TRADITIONAL' , whatever = , autocommit=1   -- empty assignment
  Expected: {}
  Got:      partial results

Suggested approach

The SetParser should validate that the entire input was consumed after parsing. If there are remaining unconsumed tokens after the SET statement, return ParseResult::ERROR or an empty AST. This matches the "parse everything or nothing" contract that the regex parser provides.

Context

Discovered during integration testing into ProxySQL. Test suite: setparser_test_common.h, test arrays Set1_v2[0], syntax_errors[0], syntax_errors[1], sql_mode[21], sql_mode[23-25].