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

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?

Jason