moonbitlang / core / 7020

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fix(regex): limit how deep groups can nest

The parser recurses once per level of group nesting, so a pattern that only
nests overflowed the stack instead of raising `ParserError`: between 150 and
200 levels on the wasm backend, between 400 and 1000 on wasm-gc and
JavaScript.

Groups nested more than 64 deep now raise. The limit is a counter in the
parser context and one check where a group body is parsed. 64 is less than
half the depth at which the wasm backend overflows, and patterns written by
hand nest a few levels.

4 of 4 new or added lines in 2 files covered. (100.0%)

16736 of 18709 relevant lines covered (89.45%)

377289.78 hits per line