POSIX bracket expressions ([:name:], [.x.], [=x=]) are only valid nested
inside another character class in std::regex. The three predicates now
additionally require that at position `start` we are inside an outer
character class, approximated by requiring more non-escaped `[` than
non-escaped `]` before `start`. A well-formed POSIX bracket contributes
one `[` and one `]` at/after `start`, so the check is unaffected by
earlier POSIX brackets.
Also stop emitting individual charSetTokens for characters inside a
POSIX bracket (`inAnyPosixBracket` guard), which removes the spurious
`[RegExpCharacterRange] :]-z` on [[:alpha:]-z].
Post-fix, unnested `[:digit:]`, `[:alpha:]`, and `a[🅱️]c` are correctly
parsed as ordinary character classes / literal sequences rather than
`RegExpNamedCharacterProperty`; and the [[:alpha:]-z] range no longer
crosses the POSIX bracket boundary.
Bundle: github/codeql-action codeql-bundle-v2.26.1 (CodeQL CLI 2.26.1).
bfb7b1d046