From: Jason Merrill <jason@redhat.com>
To: Jakub Jelinek <jakub@redhat.com>
Cc: gcc-patches@gcc.gnu.org
Subject: Re: [PATCH] c++: Implement DR2351 - void{} [PR102820]
Date: Wed, 27 Oct 2021 16:58:53 -0400 [thread overview]
Message-ID: <ccab13ba-1dd9-7db7-4d60-743b6d46fbdb@redhat.com> (raw)
In-Reply-To: <20211021084240.GE304296@tucnak>
On 10/21/21 04:42, Jakub Jelinek wrote:
> Hi!
>
> Here is an attempt to implement DR2351 - void{} - where void{} after
> pack expansion is considered valid and the same thing as void().
> For templates, dunno if we have some better way to check if a CONSTRUCTOR
> might be empty after pack expansion. Would that only if the constructor
> only contains EXPR_PACK_EXPANSION elements and nothing else, or something
> else too?
I think that's the only case. For template args there's the
pack_expansion_args_count function, but I don't think there's anything
similar for constructor elts; please feel free to add it.
> With the patch as is we wouldn't diagnose
> template <class ...T>
> void
> bar (T... t)
> {
> void{1, t...};
> }
> at parsing time, only at instantiation time, even when it will always
> expand to at least one CONSTRUCTOR elt.
>
> Bootstrapped/regtested on x86_64-linux and i686-linux.
>
> 2021-10-21 Jakub Jelinek <jakub@redhat.com>
>
> PR c++/102820
> * semantics.c (finish_compound_literal): Implement DR2351 - void{}.
> If type is cv void and compound_literal has no elements, return
> void_node. If type is cv void and compound_literal is instantiation
> dependent, handle it like other dependent compound literals.
>
> * g++.dg/cpp0x/dr2351.C: New test.
>
> --- gcc/cp/semantics.c.jj 2021-10-15 11:58:45.079131947 +0200
> +++ gcc/cp/semantics.c 2021-10-20 17:00:38.586705600 +0200
> @@ -3104,9 +3104,20 @@ 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;
> + else if (VOID_TYPE_P (type)
> + && processing_template_decl
> + && instantiation_dependent_expression_p (compound_literal))
> + /* If there are packs in compound_literal, it could
> + be void{} after pack expansion. */;
> + else
> + {
> + if (complain & tf_error)
> + error ("compound literal of non-object type %qT", type);
> + return error_mark_node;
> + }
> }
>
> if (template_placeholder_p (type))
> --- gcc/testsuite/g++.dg/cpp0x/dr2351.C.jj 2021-10-20 17:06:02.399162937 +0200
> +++ gcc/testsuite/g++.dg/cpp0x/dr2351.C 2021-10-20 17:05:54.294276511 +0200
> @@ -0,0 +1,36 @@
> +// DR2351
> +// { dg-do compile { target c++11 } }
> +
> +void
> +foo ()
> +{
> + void{};
> + void();
> +}
> +
> +template <class ...T>
> +void
> +bar (T... t)
> +{
> + void{t...};
> + void(t...);
> +}
> +
> +void
> +baz ()
> +{
> + bar ();
> +}
> +
> +template <class ...T>
> +void
> +qux (T... t)
> +{
> + void{t...}; // { dg-error "compound literal of non-object type" }
> +}
> +
> +void
> +corge ()
> +{
> + qux (1, 2);
> +}
>
> Jakub
>
next prev parent reply other threads:[~2021-10-27 20:58 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-10-21 8:42 Jakub Jelinek
2021-10-27 20:58 ` Jason Merrill [this message]
2021-10-28 11:26 ` [PATCH] c++, v2: " Jakub Jelinek
2021-10-28 12:01 ` Jason Merrill
2021-10-28 12:19 ` Jakub Jelinek
2021-10-28 14:56 ` Jason Merrill
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