On 11/9/23 14:58, Marek Polacek wrote:
Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk?
-- >8 --
Here we are wrongly parsing
int y(auto(42));
which uses the C++23 cast-to-prvalue feature, and initializes y to 42.
However, we were treating the auto as an implicit template parameter.
Fixing the auto{42} case is easy, but when auto is followed by a (,
I found the fix to be much more involved. For instance, we cannot
use cp_parser_expression, because that can give hard errors. It's
also necessary to disambiguate 'auto(i)' as 'auto i', not a cast.
auto(), auto(int), auto(f)(int), auto(*), auto(i[]), auto(...), etc.
are all function declarations. We have to look at more than one
token to decide.
Yeah, this is a most vexing parse problem. The code is synthesizing
template parameters before we've resolved whether the auto is a
decl-specifier or not.
In this fix, I'm (ab)using cp_parser_declarator, with member_p=false
so that it doesn't commit. But it handles even more complicated
cases as
int fn (auto (*const **&f)(int) -> char);
But it doesn't seem to handle the extremely vexing
struct A {
A(int,int);
};
int main()
{
int a;
A b(auto(a), 42);
}
I think we need to stop synthesizing immediately when we see RID_AUTO,
and instead go back after we successfully parse a declaration and
synthesize for any autos we saw along the way. :/
Jason
