On Fri, Jul 5, 2024 at 12:18 PM Patrick Palka <ppa...@redhat.com> wrote:
>
> Bootstrapped and regtested on x86_64-pc-linux-gnu, does this look OK
> for trunk/14 and perhaps 13?
>
> Alternatively we can set current_template_parms from weakly_subsumes
> instead, who has only one caller anyway.
Ping.
>
> -- >8 --
>
> Here we normalize the constraint same_as<auto, bool> for the first
> time during constraint subsumption checking of B / TT as part of ttp
> coercion. During this normalization the set of in-scope template
> parameters i.e. current_template_parms is empty, which tricks the
> satisfaction cache into thinking that the satisfaction value of the
> constraint is independent of its template parameters, and we incorrectly
> conflate the satisfaction value with auto = bool vs auto = long and
> accept the specialization A<long, B>.
>
> This patch fixes this by setting current_template_parms appropirately
> during subsumption checking.
>
> PR c++/115656
>
> gcc/cp/ChangeLog:
>
> * pt.cc (is_compatible_template_arg): Set current_template_parms
> around the call to weakly_subsumes.
>
> gcc/testsuite/ChangeLog:
>
> * g++.dg/cpp2a/concepts-ttp7.C: New test.
> ---
> gcc/cp/pt.cc | 4 ++++
> gcc/testsuite/g++.dg/cpp2a/concepts-ttp7.C | 12 ++++++++++++
> 2 files changed, 16 insertions(+)
> create mode 100644 gcc/testsuite/g++.dg/cpp2a/concepts-ttp7.C
>
> diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
> index 017cc7fd0ab..1f6553790a5 100644
> --- a/gcc/cp/pt.cc
> +++ b/gcc/cp/pt.cc
> @@ -8493,6 +8493,10 @@ is_compatible_template_arg (tree parm, tree arg, tree
> args)
> return false;
> }
>
> + /* Normalization needs to know the effective set of in-scope
> + template parameters. */
> + auto ctp = make_temp_override (current_template_parms,
> + DECL_TEMPLATE_PARMS (arg));
> return weakly_subsumes (parm_cons, arg);
> }
>
> diff --git a/gcc/testsuite/g++.dg/cpp2a/concepts-ttp7.C
> b/gcc/testsuite/g++.dg/cpp2a/concepts-ttp7.C
> new file mode 100644
> index 00000000000..bc123ecf75e
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/cpp2a/concepts-ttp7.C
> @@ -0,0 +1,12 @@
> +// PR c++/115656
> +// { dg-do compile { target c++20 } }
> +
> +template<class T, class U> concept same_as = __is_same(T, U);
> +
> +template<same_as<bool> U, template<same_as<bool>> class TT>
> +struct A { };
> +
> +template<same_as<bool>> class B;
> +
> +A<bool, B> a1;
> +A<long, B> a2; // { dg-error "constraint failure" }
> --
> 2.45.2.746.g06e570c0df
>
