On Thu, Oct 28, 2021 at 08:01:27AM -0400, Jason Merrill wrote:
> > --- gcc/cp/semantics.c.jj 2021-10-27 09:16:41.161600606 +0200
> > +++ gcc/cp/semantics.c 2021-10-28 13:06:59.325791588 +0200
> > @@ -3079,6 +3079,24 @@ finish_unary_op_expr (location_t op_loc,
> > return result;
> > }
> > +/* Return true if CONSTRUCTOR EXPR after pack expansion could have no
> > + elements. */
> > +
> > +static bool
> > +maybe_zero_constructor_nelts (tree expr)
> > +{
> > + if (CONSTRUCTOR_NELTS (expr) == 0)
> > + return true;
> > + if (!processing_template_decl)
> > + return false;
> > + unsigned int i;
> > + tree val;
> > + FOR_EACH_CONSTRUCTOR_VALUE (CONSTRUCTOR_ELTS (expr), i, val)
>
> Let's use
>
> for (constructor_elt &elt : CONSTRUCTOR_ELTS (t))
Ok, will do.
> > @@ -3104,9 +3122,20 @@ finish_compound_literal (tree type, tree
> > if (!TYPE_OBJ_P (type))
> > {
> > - if (complain & tf_error)
> > - error ("compound literal of non-object type %qT", type);
> > - return error_mark_node;
> > + /* DR2351 */
> > + if (VOID_TYPE_P (type) && CONSTRUCTOR_NELTS (compound_literal) == 0)
> > + return void_node;
>
> This test now seems redundant with the one below (if you remove the &&
> processing_template_decl).
It is not redundant, for the maybe case it doesn't return void_node, but
falls through into if (processing_template_decl), which, because
compound_literal is necessarily instantiation_dependent_expression_p
(it contains packs) will just create CONSTRUCTOR_IS_DEPENDENT CONSTRUCTOR
and we'll get here back during instantiation.
For the CONSTRUCTOR_NELTS == 0 case even in templates we know
compound_literal isn't dependent (it doesn't contain anything) and type
isn't either, so we can return void_node right away (and when
!processing_template_decl we have to do that).
Jakub
