[PATCH] c++: ICE with generic lambda and pack expansion [PR115425]

[Jason Merrill]

On 6/17/24 14:17, Marek Polacek wrote:
> Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk?

OK.

> -- >8 --
> In r13-272 we hardened the *_PACK_EXPANSION and *_ARGUMENT_PACK macros.
> That trips up here because make_pack_expansion returns error_mark_node
> and we access that with PACK_EXPANSION_LOCAL_P.
> 
> 	PR c++/115425
> 
> gcc/cp/ChangeLog:
> 
> 	* pt.cc (tsubst_pack_expansion): Return error_mark_node if
> 	make_pack_expansion doesn't work out.
> 
> gcc/testsuite/ChangeLog:
> 
> 	* g++.dg/cpp2a/lambda-generic12.C: New test.
> ---
>   gcc/cp/pt.cc                                  |  2 ++
>   gcc/testsuite/g++.dg/cpp2a/lambda-generic12.C | 25 +++++++++++++++++++
>   2 files changed, 27 insertions(+)
>   create mode 100644 gcc/testsuite/g++.dg/cpp2a/lambda-generic12.C
> 
> diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
> index 607753ae6b7..e676372f75b 100644
> --- a/gcc/cp/pt.cc
> +++ b/gcc/cp/pt.cc
> @@ -13775,6 +13775,8 @@ tsubst_pack_expansion (tree t, tree args, tsubst_flags_t complain,
>         else
>   	result = tsubst (pattern, args, complain, in_decl);
>         result = make_pack_expansion (result, complain);
> +      if (result == error_mark_node)
> +	return error_mark_node;
>         PACK_EXPANSION_LOCAL_P (result) = PACK_EXPANSION_LOCAL_P (t);
>         PACK_EXPANSION_SIZEOF_P (result) = PACK_EXPANSION_SIZEOF_P (t);
>         if (PACK_EXPANSION_AUTO_P (t))
> diff --git a/gcc/testsuite/g++.dg/cpp2a/lambda-generic12.C b/gcc/testsuite/g++.dg/cpp2a/lambda-generic12.C
> new file mode 100644
> index 00000000000..219529c7c32
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/cpp2a/lambda-generic12.C
> @@ -0,0 +1,25 @@
> +// PR c++/115425
> +// { dg-do compile { target c++20 } }
> +
> +using size_t = decltype(sizeof(0));
> +
> +template <int... I>
> +struct X {};
> +
> +template<int... Is>
> +void foo(X<Is...>);
> +
> +template<auto>
> +struct S;
> +
> +template<class T>
> +auto test() {
> +  constexpr static auto x = foo<X<__integer_pack (0)...>>(); // { dg-error "no matching function" }
> +  return []<size_t... Is>(X<Is...>) {
> +    (typename S<x[Is]>::type{}, ...);
> +  }(X<__integer_pack (0)...>{});
> +}
> +
> +int main() {
> +  test<int>();
> +}
> 
> base-commit: b63c7d92012f92e0517190cf263d29bbef8a06bf