Add a guarded "C++ 26 extensions" block (cpp_no_cpp26) covering new
lexical surface introduced since C++23:
- [[ ... ]] attributes as a region, so P3394 annotations carrying a
value expression (eg [[=foo{1}]]) no longer trip cErrInBracket on
their braces/parens. A \w\@1<! look-behind keeps it from matching a
subscripted immediately-invoked lambda (arr[[]{...}()]).
- ^^ reflection operator (P2996).
- [: :] splice brackets (P2996).
- contract_assert keyword (P2900).
Add input/cpp_cpp26.cpp exercising these constructs with screendumps,
and update dumps/cpp_noreturn_00.dump for the new [[ ]] attribute
delimiter highlighting.
closes: #20577
Signed-off-by: Gareth Lloyd <gareth@ignition-web.co.uk>
Signed-off-by: Christian Brabandt <cb@256bit.org>
