Re: [PATCH] c++: desig init in presence of list ctor [PR109871]

[Jason Merrill <jason@redhat.com>]

On 5/16/23 11:38, Patrick Palka wrote:
> add_list_candidates has logic to reject designated initialization of a
> non-aggregate type, but this is inadvertendly being suppressed if the type
> has a list constructor due to the order of case analysis, which in the
> below testcase leads to us incorrectly treating the list initializer as
> an ordinary non-designated one.  This patch fixes this by making us check
> for invalid designated initialization sooner.
> 
> Bootstrapped and regtested on x86_64-pc-linux-gnu, does this look OK for
> trunk and perhaps 13?  IIUC desig init is C++20 but we also accept it
> with a pedwarn in earlier dialects, so not sure if this'd be suitable
> for backporting.

OK.

> 	PR c++/109871
> 
> gcc/cp/ChangeLog:
> 
> 	* call.cc (add_list_candidates): Check for invalid
> 	designated initialization sooner, even for types that have
> 	a list constructor.
> 
> gcc/testsuite/ChangeLog:
> 
> 	* g++.dg/cpp0x/desig6.C: New test.
> ---
>   gcc/cp/call.cc                      | 16 ++++++++--------
>   gcc/testsuite/g++.dg/cpp0x/desig6.C | 16 ++++++++++++++++
>   2 files changed, 24 insertions(+), 8 deletions(-)
>   create mode 100644 gcc/testsuite/g++.dg/cpp0x/desig6.C
> 
> diff --git a/gcc/cp/call.cc b/gcc/cp/call.cc
> index 48611bb16a3..908374a43c9 100644
> --- a/gcc/cp/call.cc
> +++ b/gcc/cp/call.cc
> @@ -4129,6 +4129,14 @@ add_list_candidates (tree fns, tree first_arg,
>     if (CONSTRUCTOR_NELTS (init_list) == 0
>         && TYPE_HAS_DEFAULT_CONSTRUCTOR (totype))
>       ;
> +  else if (CONSTRUCTOR_IS_DESIGNATED_INIT (init_list)
> +	   && !CP_AGGREGATE_TYPE_P (totype))
> +    {
> +      if (complain & tf_error)
> +	error ("designated initializers cannot be used with a "
> +	       "non-aggregate type %qT", totype);
> +      return;
> +    }
>     /* If the class has a list ctor, try passing the list as a single
>        argument first, but only consider list ctors.  */
>     else if (TYPE_HAS_LIST_CTOR (totype))
> @@ -4140,14 +4148,6 @@ add_list_candidates (tree fns, tree first_arg,
>         if (any_strictly_viable (*candidates))
>   	return;
>       }
> -  else if (CONSTRUCTOR_IS_DESIGNATED_INIT (init_list)
> -	   && !CP_AGGREGATE_TYPE_P (totype))
> -    {
> -      if (complain & tf_error)
> -	error ("designated initializers cannot be used with a "
> -	       "non-aggregate type %qT", totype);
> -      return;
> -    }
>   
>     /* Expand the CONSTRUCTOR into a new argument vec.  */
>     vec<tree, va_gc> *new_args;
> diff --git a/gcc/testsuite/g++.dg/cpp0x/desig6.C b/gcc/testsuite/g++.dg/cpp0x/desig6.C
> new file mode 100644
> index 00000000000..8d4cf483176
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/cpp0x/desig6.C
> @@ -0,0 +1,16 @@
> +// PR c++/109871
> +// { dg-do compile { target c++11 } }
> +// { dg-options "" }
> +
> +#include <initializer_list>
> +
> +struct vector {
> +  vector(std::initializer_list<int>); // #1
> +  vector(int); // #2
> +};
> +
> +void f(vector);
> +
> +int main() {
> +  f({.blah = 42}); // { dg-error "designated" } previously incorrectly selected #2
> +}