Re: [PATCH] c++: CWG 2229, cv-qualified unnamed bit-fields [PR123935]

[Andrew Pinski]

On Tue, Feb 3, 2026 at 2:12 PM Marek Polacek <pola...@redhat.com> wrote:
>
> Bootstrapped/regtested on ppc64le-pc-linux-gnu, ok for 17.0?
>
> -- >8 --
> This implements [class.bit]/2: An unnamed bit-field shall not be
> declared with a cv-qualified type.  This was clarified in DR 2229.
>
>         DR 2229
>         PR c++/123935
>
> gcc/cp/ChangeLog:
>
>         * decl2.cc (grokbitfield): Disallow cv-qualified unnamed bit-fields.
>
> gcc/testsuite/ChangeLog:
>
>         * g++.dg/DRs/dr2229.C: New test.
> ---
>  gcc/cp/decl2.cc                   |  9 +++++++++
>  gcc/testsuite/g++.dg/DRs/dr2229.C | 12 ++++++++++++
>  2 files changed, 21 insertions(+)
>  create mode 100644 gcc/testsuite/g++.dg/DRs/dr2229.C
>
> diff --git a/gcc/cp/decl2.cc b/gcc/cp/decl2.cc
> index 20ee662eea2..eb2294fffd0 100644
> --- a/gcc/cp/decl2.cc
> +++ b/gcc/cp/decl2.cc
> @@ -1635,6 +1635,15 @@ grokbitfield (const cp_declarator *declarator,
>        return NULL_TREE;
>      }
>
> +  /* [class.bit]/2 "An unnamed bit-field shall not be declared with
> +     a cv-qualified type."  */
> +  if (!DECL_NAME (value) && TYPE_QUALS (type) != TYPE_UNQUALIFIED)
> +    {
> +      error_at (DECL_SOURCE_LOCATION (value),
> +               "unnamed bit-field cannot be cv-qualified");
> +      return NULL_TREE;
> +    }
> +
>    int flags = LOOKUP_IMPLICIT;
>    if (init && DIRECT_LIST_INIT_P (init))
>      flags = LOOKUP_NORMAL;
> diff --git a/gcc/testsuite/g++.dg/DRs/dr2229.C 
> b/gcc/testsuite/g++.dg/DRs/dr2229.C
> new file mode 100644
> index 00000000000..32548071090
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/DRs/dr2229.C
> @@ -0,0 +1,12 @@
> +// DR 2229, Volatile unnamed bit-fields
> +// PR c++/123935
> +
> +struct S {
> +  const unsigned : 1; // { dg-error "unnamed bit-field cannot be 
> cv-qualified" }
> +  volatile unsigned : 1; // { dg-error "unnamed bit-field cannot be 
> cv-qualified" }
> +  const volatile unsigned : 1; // { dg-error "unnamed bit-field cannot be 
> cv-qualified" }
> +  unsigned : 1;
> +  const unsigned i1 : 1;
> +  volatile unsigned i2 : 1;
> +  const volatile unsigned i3 : 1;
> +};

Maybe one more test would be a typedef to a qualifier type.
Like:
```
typedef const int ci;
struct S1 {
  ci : 1; // { dg-error "unnamed bit-field cannot be cv-qualified" }
  ci ci1 : 1;
};
```

Thanks,
Andrew Pinski

>
> base-commit: 7197d0cce705254d0779a81bdad82d5a71b7f63b
> --
> 2.52.0
>