Re: [PATCH] c++: CTAD for class tmpl defined inside partial spec [PR104294]

[Jason Merrill <jason@redhat.com>]

On 1/31/22 11:14, Patrick Palka wrote:
> On Mon, Jan 31, 2022 at 11:07 AM Patrick Palka <ppalka@redhat.com> wrote:
>>
>> Here during deduction guide generation for the nested class template
>> B<char(int)>::C, the computation of outer_targs yields the template
>> arguments relative to the primary template for B (i.e. {char(int)})
>> but what we really what is those relative to the enclosing scope, the
>> partial specialization of B (i.e. {char, int}).
>>
>> Bootstrapped and regtested on x86_64-pc-linux-gnu, does this look OK for
>> trunk?
>>
>>          PR c++/104294
>>
>> gcc/cp/ChangeLog:
>>
>>          * pt.cc (ctor_deduction_guides_for): Correct computation of
>>          outer_targs.
>>
>> gcc/testsuite/ChangeLog:
>>
>>          * g++.dg/cpp1z/class-deduction106.C: New test.
>> ---
>>   gcc/cp/pt.cc                                  |  4 +++-
>>   .../g++.dg/cpp1z/class-deduction106.C         | 19 +++++++++++++++++++
>>   2 files changed, 22 insertions(+), 1 deletion(-)
>>   create mode 100644 gcc/testsuite/g++.dg/cpp1z/class-deduction106.C
>>
>> diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
>> index f46a7ad6655..0fe0ad4e44e 100644
>> --- a/gcc/cp/pt.cc
>> +++ b/gcc/cp/pt.cc
>> @@ -29568,7 +29568,9 @@ ctor_deduction_guides_for (tree tmpl, tsubst_flags_t complain)
>>     if (DECL_CLASS_SCOPE_P (tmpl)
>>         && CLASSTYPE_TEMPLATE_INSTANTIATION (DECL_CONTEXT (tmpl)))
>>       {
>> -      outer_args = CLASSTYPE_TI_ARGS (DECL_CONTEXT (tmpl));
>> +      outer_args = copy_node (CLASSTYPE_TI_ARGS (type));
>> +      gcc_assert (TMPL_ARGS_HAVE_MULTIPLE_LEVELS (outer_args));
> 
> Whoops, this assert should be slightly stronger: TMPL_ARGS_DEPTH
> (outer_args) > 1. Consider that fixed (pending another
> bootstrap/regtest cycle).

OK.

>> +      --TREE_VEC_LENGTH (outer_args);
>>         type = TREE_TYPE (most_general_template (tmpl));
>>       }
>>
>> diff --git a/gcc/testsuite/g++.dg/cpp1z/class-deduction106.C b/gcc/testsuite/g++.dg/cpp1z/class-deduction106.C
>> new file mode 100644
>> index 00000000000..382f6b70ef5
>> --- /dev/null
>> +++ b/gcc/testsuite/g++.dg/cpp1z/class-deduction106.C
>> @@ -0,0 +1,19 @@
>> +// PR c++/104294
>> +// { dg-do compile { target c++17 } }
>> +
>> +template<class>
>> +struct B;
>> +
>> +template <class R, class... Args>
>> +struct B<R(Args...)> {
>> +  template<class T>
>> +  struct C { C(T); };
>> +
>> +  C(decltype(nullptr)) -> C<void*>;
>> +};
>> +
>> +using ty1 = decltype(B<char(int)>::C{0});
>> +using ty1 = B<char(int)>::C<int>;
>> +
>> +using ty2 = decltype(B<char(int)>::C{nullptr});
>> +using ty2 = B<char(int)>::C<void*>;
>> --
>> 2.35.0
>>
>