Re: [PATCH] c++: mark_single_function and SFINAE [PR108282]

[Jason Merrill <jason@redhat.com>]

On 1/4/23 11:37, Patrick Palka wrote:
> We typically ignore mark_used failure when in a non-SFINAE context for
> sake of better error recovery.  But in mark_single_function we're
> instead ignoring mark_used failure in a SFINAE context, which ends up
> causing the second static_assert here to incorrectly fail.
> 
> Bootstrapped and regtested on x86_64-pc-linux-gnu, does this look OK for
> trunk/12?

OK.

> 	PR c++/108282
> 
> gcc/cp/ChangeLog:
> 
> 	* decl2.cc (mark_single_function): Ignore mark_used failure
> 	only in a non-SFINAE context rather than in a SFINAE one.
> 
> gcc/testsuite/ChangeLog:
> 
> 	* g++.dg/cpp2a/concepts-requires34.C: New test.
> ---
>   gcc/cp/decl2.cc                               |  2 +-
>   .../g++.dg/cpp2a/concepts-requires34.C        | 19 +++++++++++++++++++
>   2 files changed, 20 insertions(+), 1 deletion(-)
>   create mode 100644 gcc/testsuite/g++.dg/cpp2a/concepts-requires34.C
> 
> diff --git a/gcc/cp/decl2.cc b/gcc/cp/decl2.cc
> index f95529a5c9a..00ed64d1691 100644
> --- a/gcc/cp/decl2.cc
> +++ b/gcc/cp/decl2.cc
> @@ -5600,7 +5600,7 @@ mark_single_function (tree expr, tsubst_flags_t complain)
>   
>     if (is_overloaded_fn (expr) == 1
>         && !mark_used (expr, complain)
> -      && (complain & tf_error))
> +      && !(complain & tf_error))
>       return false;
>     return true;
>   }
> diff --git a/gcc/testsuite/g++.dg/cpp2a/concepts-requires34.C b/gcc/testsuite/g++.dg/cpp2a/concepts-requires34.C
> new file mode 100644
> index 00000000000..670a6dab31a
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/cpp2a/concepts-requires34.C
> @@ -0,0 +1,19 @@
> +// PR c++/108282
> +// { dg-do compile { target c++20 } }
> +
> +template<class T>
> +concept TEST = requires { T::TT; };
> +
> +struct C { };
> +
> +template<class AT>
> +struct B {
> +  static inline void TT() requires TEST<AT>;
> +};
> +
> +int main() {
> +  static_assert( !TEST<C> );
> +  static_assert( !TEST<B<C>> );
> +
> +  B<C>::TT();  // { dg-error "no match" }
> +}