Re: [PATCH] c++: requires-expr in pack expansion using pack [PR103105]

[Jason Merrill <jason@redhat.com>]

On 4/12/22 12:17, Patrick Palka wrote:
> Here after dependent substitution of {Ts...} into the alias 'wrap',
> since we never partially instantiate a requires-expr, we end up with a
> requires-expr whose REQUIRES_EXPR_EXTRA_ARGS contains an
> ARGUMENT_PACK_SELECT (which just resolves to the parameter pack Ts).
> Then when looking up the resulting dependent specialization of A, we
> crash from iterative_hash_template_arg since it deliberately doesn't
> handle ARGUMENT_PACK_SELECT.
> 
> Like with r12-7102-gdb5f1c17031ad8, it seems the right fix here is to
> resolve ARGUMENT_PACK_SELECT arguments before storing them into an
> extra args tree (such as REQUIRES_EXPR).
> 
> Bootstrapped and regtested on x86_64-pc-linux-gnu, does this look OK for
> trunk/11?  For 11, we'd need to backport r12-7102 as a prereq.

OK, that additional backport seems reasonable.

> 	PR c++/103105
> 	PR c++/103706
> 
> gcc/cp/ChangeLog:
> 
> 	* pt.cc (build_extra_args): Call preserve_args.
> 
> gcc/testsuite/ChangeLog:
> 
> 	* g++.dg/cpp2a/concepts-requires29.C: New test.
> 	* g++.dg/cpp2a/concepts-requires29a.C: New test.
> ---
>   gcc/cp/pt.cc                                  |  2 +-
>   .../g++.dg/cpp2a/concepts-requires29.C        | 18 +++++++++++++++
>   .../g++.dg/cpp2a/concepts-requires29a.C       | 23 +++++++++++++++++++
>   3 files changed, 42 insertions(+), 1 deletion(-)
>   create mode 100644 gcc/testsuite/g++.dg/cpp2a/concepts-requires29.C
>   create mode 100644 gcc/testsuite/g++.dg/cpp2a/concepts-requires29a.C
> 
> diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
> index 78519562953..84712e6fc2f 100644
> --- a/gcc/cp/pt.cc
> +++ b/gcc/cp/pt.cc
> @@ -13048,7 +13048,7 @@ build_extra_args (tree pattern, tree args, tsubst_flags_t complain)
>   {
>     /* Make a copy of the extra arguments so that they won't get changed
>        out from under us.  */
> -  tree extra = copy_template_args (args);
> +  tree extra = preserve_args (copy_template_args (args), /*cow_p=*/false);
>     if (local_specializations)
>       if (tree locals = extract_local_specs (pattern, complain))
>         extra = tree_cons (NULL_TREE, extra, locals);
> diff --git a/gcc/testsuite/g++.dg/cpp2a/concepts-requires29.C b/gcc/testsuite/g++.dg/cpp2a/concepts-requires29.C
> new file mode 100644
> index 00000000000..5118df978c9
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/cpp2a/concepts-requires29.C
> @@ -0,0 +1,18 @@
> +// PR c++/103105
> +// { dg-do compile { target c++20 } }
> +
> +template<bool> class A;
> +
> +template<class... Ts>
> +using wrap = A<1 != (0 + ... + requires { Ts(); })>;
> +
> +template<class... Ts> using type = wrap<Ts...>;
> +
> +using ty0 = type<>;
> +using ty0 = A<true>;
> +
> +using ty1 = type<int>;
> +using ty1 = A<false>;
> +
> +using ty2 = type<int, int>;
> +using ty2 = A<true>;
> diff --git a/gcc/testsuite/g++.dg/cpp2a/concepts-requires29a.C b/gcc/testsuite/g++.dg/cpp2a/concepts-requires29a.C
> new file mode 100644
> index 00000000000..c41c1e6d039
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/cpp2a/concepts-requires29a.C
> @@ -0,0 +1,23 @@
> +// PR c++/103105
> +// { dg-do compile { target c++20 } }
> +
> +template<class...> struct list;
> +template<bool> struct A;
> +
> +template<class T, class... Ts>
> +using wrap = A<1 != (0 + ... + requires { T() = Ts(); })>;
> +
> +template<class... Ts>
> +using type = list<wrap<Ts, Ts...>...>;
> +
> +using ty0 = type<>;
> +using ty0 = list<>;
> +
> +using ty1 = type<int>;
> +using ty1 = list<A<true>>;
> +
> +using ty2 = type<int, int>;
> +using ty2 = list<A<true>, A<true>>;
> +
> +using ty3 = type<int, int, int>;
> +using ty3 = list<A<true>, A<true>, A<true>>;