Re: [PATCH v2] c++: resolvedness of resolve_nondeduced_context result [PR126406]

On 7/30/26 4:07 PM, Patrick Palka wrote:
> 
>> On 7/30/26 3:00 PM, Patrick Palka wrote:
>>> Changes in v2:
>>>     - Outright revert r16-5967, and instead fix PR119343 more directly
>>>       for sake of backports.
>>>
>>> Bootstrapped and regtested on x86_64-pc-linux-gnu, does this look
>>> OK for trunk/16?
>>>
>>> -- >8 --
>>>
>>> In r16-5967-gbae0ed69e1862a we removed the mark_used call from
>>> resolve_nondeduced_context under the rationale that it should be
>>> the callers' responsiblity to do so.c
>>>
>>> Removing this call however now means that resolve_nondeduced_context
>>> could return a specialization whose type is not yet fully resolved
>>> (i.e. has an uninstantiated noexcept or undeduced return type), and
>>> callers that immediately inspect TREE_TYPE of the result (such as
>>> standard_conversion and build_conditional_expr) now misbehave.
>>>
>>> In light of such callers, this patch reverts r16-5967 and more
>>> directly fixes the PR119343 bug by just propagating error_mark_node
>>> from resolve_nondeduced_context during convert_to_void.
>>>
>>> @@ -1573,7 +1573,8 @@ convert_to_void (tree expr, impl_conv_void implicit,
>>> tsubst_flags_t complain)
>>>        default:;
>>>        }
>>>      expr = resolve_nondeduced_context (expr, complain);
>>> -  if (!mark_single_function (expr, complain))
>>> +  if (expr == error_mark_node
>>> +      || !mark_single_function (expr, complain))
>>
>> I still don't understand why this makes a difference, given that
>> mark_single_function has
>>
>>>    if (expr == error_mark_node)
>>>      return false;
>>
>> so for expr == error_mark_node it should return false, and we should already
>> return error_mark_node?
> 
> Ah indeed, I missed that Egas made mark_used and mark_single_function propagate
> error_mark_node as a follow-up.
> 
> -- >8 --
> 
> 
> Subject: [PATCH] c++: resolvedness of resolve_nondeduced_context result
>   [PR126406]
> 
> In r16-5967-gbae0ed69e1862a we removed the mark_used call from
> resolve_nondeduced_context under the rationale that it should be
> the caller's responsiblity to do so.
> 
> Removing this call however now means that resolve_nondeduced_context
> could return a specialization whose type is not yet fully resolved
> (i.e. has an uninstantiated noexcept or undeduced return type), and
> callers that immediately inspect TREE_TYPE of the result (such as
> standard_conversion and build_conditional_expr) now misbehave.
> 
> In light of such callers, this patch reverts r16-5967; it's not
> necessary to fix PR119343 because after r16-6276 convert_to_void
> now properly propagates an error_mark_node result from
> resolve_nondeduced_context.
> 
> 	PR c++/126406
> 	PR c++/119343
> 
> gcc/cp/ChangeLog:
> 
> 	* pt.cc (resolve_nondeduced_context): Revert r16-5967 change.

OK.

> gcc/testsuite/ChangeLog:
> 
> 	* g++.dg/cpp0x/cond2a.C: New test.
> 	* g++.dg/cpp1y/auto-fn67.C: New test.
> 	* g++.dg/cpp1z/noexcept-type29.C: New test.
> ---
>   gcc/cp/pt.cc                                 |  2 ++
>   gcc/testsuite/g++.dg/cpp0x/cond2a.C          | 17 +++++++++++++++++
>   gcc/testsuite/g++.dg/cpp1y/auto-fn67.C       | 11 +++++++++++
>   gcc/testsuite/g++.dg/cpp1z/noexcept-type29.C | 11 +++++++++++
>   4 files changed, 41 insertions(+)
>   create mode 100644 gcc/testsuite/g++.dg/cpp0x/cond2a.C
>   create mode 100644 gcc/testsuite/g++.dg/cpp1y/auto-fn67.C
>   create mode 100644 gcc/testsuite/g++.dg/cpp1z/noexcept-type29.C
> 
> diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
> index 6a081b838e06..1d22563bc586 100644
> --- a/gcc/cp/pt.cc
> +++ b/gcc/cp/pt.cc
> @@ -25653,6 +25653,8 @@ resolve_nondeduced_context (tree orig_expr, tsubst_flags_t complain)
>   	}
>         if (good == 1)
>   	{
> +	  if (!mark_used (goodfn, complain) && !(complain & tf_error))
> +	    return error_mark_node;
>   	  expr = goodfn;
>   	  if (baselink)
>   	    expr = build_baselink (BASELINK_BINFO (baselink),
> diff --git a/gcc/testsuite/g++.dg/cpp0x/cond2a.C b/gcc/testsuite/g++.dg/cpp0x/cond2a.C
> new file mode 100644
> index 000000000000..a42e198291b2
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/cpp0x/cond2a.C
> @@ -0,0 +1,17 @@
> +// PR c++/126406
> +// { dg-do compile { target c++14 } }
> +// A version of cond2.C where f has a deduced return type
> +// and g is instantiated.
> +
> +bool b;
> +
> +template < class T > auto f ()
> +{
> +}
> +
> +template < class T > auto g () -> decltype (b ? f < int > : throw 0)
> +{
> +  return b ? f<int> : throw 0;
> +}
> +
> +using type = decltype(g<int>());
> diff --git a/gcc/testsuite/g++.dg/cpp1y/auto-fn67.C b/gcc/testsuite/g++.dg/cpp1y/auto-fn67.C
> new file mode 100644
> index 000000000000..20ff86459c3d
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/cpp1y/auto-fn67.C
> @@ -0,0 +1,11 @@
> +// PR c++/126406
> +// { dg-do compile { target c++14 } }
> +
> +template<class T> auto g(T) { }
> +static_assert(g<int>);
> +
> +template<class T>
> +struct B {
> +  static auto g(T) { }
> +};
> +static_assert(B<int>::g);
> diff --git a/gcc/testsuite/g++.dg/cpp1z/noexcept-type29.C b/gcc/testsuite/g++.dg/cpp1z/noexcept-type29.C
> new file mode 100644
> index 000000000000..c620b180fc83
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/cpp1z/noexcept-type29.C
> @@ -0,0 +1,11 @@
> +// PR c++/126406
> +// { dg-do compile { target c++11 } }
> +
> +template<class T> void f(T) noexcept(noexcept(T())) { }
> +static_assert(f<int>);
> +
> +template<class T>
> +struct A {
> +  static void f(T) noexcept(noexcept(T())) { }
> +};
> +static_assert(A<int>::f);