The problem was is that in cp/pt.cc:find_template_parameter_info::found
compiler tried to get TEMPLATE_TEMPLATE_PARM tree from TEMPLATE_DECL tree by
DECL_INITIAL instead of TREE_TYPE(like for TYPE_DECL). Therefore, parm got
nullptr, because cp/pt.cc:process_template_parm doesn't assign anything to
DECL_INITIAL for both TYPE_DECL and TEMPLATE_DECL.
On Monday, March 25th, 2024 at 7:17 PM, centurion <centurion...@proton.me>
wrote:
> From b34312d82b236601c348382d30e625558f37d40c Mon Sep 17 00:00:00 2001
> From: centurion centurion...@proton.me
>
> Date: Mon, 25 Mar 2024 01:57:21 +0400
> Subject: [PATCH] c++: fix alias CTAD [PR114377]
>
> PR c++/114377
>
> gcc/cp/ChangeLog:
>
> PR c++/114377
> * pt.cc (find_template_parameter_info::found): Use TREE_TYPE for
> TEMPLATE_DECL instead of DECL_INITIAL.
>
> gcc/testsuite/ChangeLog:
>
> * g++.dg/cpp2a/class-deduction-alias19.C: New test.
> ---
> gcc/cp/pt.cc | 3 ++-
> .../g++.dg/cpp2a/class-deduction-alias19.C | 15 +++++++++++++++
> 2 files changed, 17 insertions(+), 1 deletion(-)
> create mode 100644 gcc/testsuite/g++.dg/cpp2a/class-deduction-alias19.C
>
> diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
> index 8cf0d5b7a8d..d8a02f1cd7f 100644
> --- a/gcc/cp/pt.cc
> +++ b/gcc/cp/pt.cc
> @@ -11032,7 +11032,8 @@ find_template_parameter_info::found (tree parm)
> {
> if (TREE_CODE (parm) == TREE_LIST)
> parm = TREE_VALUE (parm);
> - if (TREE_CODE (parm) == TYPE_DECL)
> + if (TREE_CODE (parm) == TYPE_DECL
> + || TREE_CODE(parm) == TEMPLATE_DECL)
> parm = TREE_TYPE (parm);
> else
> parm = DECL_INITIAL (parm);
> diff --git a/gcc/testsuite/g++.dg/cpp2a/class-deduction-alias19.C
> b/gcc/testsuite/g++.dg/cpp2a/class-deduction-alias19.C
> new file mode 100644
> index 00000000000..1ea79bd7691
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/cpp2a/class-deduction-alias19.C
> @@ -0,0 +1,15 @@
> +// PR c++/114377
> +// { dg-do compile { target c++20 } }
> +
> +template <template <typename> typename Iterator>
>
> +struct K {};
> +
> +template <typename C, typename IteratorPolicy>
>
> +class Foo {};
> +
> +template <typename C, template<typename> typename TTP>
>
> +using Bar = Foo<C, K<TTP>>;
>
> +
> +void s() {
> + Bar(1); // { dg-error "failed|no match" }
> +}
> --
> 2.44.0
