On Fri, Jul 30, 2021 at 9:26 AM Jason Merrill via Gcc-patches
<gcc-patches@gcc.gnu.org> wrote:
>
> In discussion of jakub's patch for C++20 pointer-interconvertibility, it
> came up that we allow anonymous structs to have bases, but don't do anything
> usable with them. Let's reject it.
>
> The comment change is something I noticed while looking for the right place
> to diagnose this: finish_struct_anon does not actually check for anything
> invalid, so it shouldn't claim to.
This should fix PR 96636 by rejecting the code.
Thanks,
Andrew Pinski
>
> Tested x86_64-pc-linux-gnu, applying to trunk.
>
> gcc/cp/ChangeLog:
>
> * class.c (finish_struct_anon): Improve comment.
> * decl.c (fixup_anonymous_aggr): Reject anonymous struct
> with bases.
>
> gcc/testsuite/ChangeLog:
>
> * g++.dg/ext/anon-struct8.C: New test.
> ---
> gcc/cp/class.c | 3 +--
> gcc/cp/decl.c | 3 +++
> gcc/testsuite/g++.dg/ext/anon-struct8.C | 9 +++++++++
> 3 files changed, 13 insertions(+), 2 deletions(-)
> create mode 100644 gcc/testsuite/g++.dg/ext/anon-struct8.C
>
> diff --git a/gcc/cp/class.c b/gcc/cp/class.c
> index 14db06692dc..6f31700c06c 100644
> --- a/gcc/cp/class.c
> +++ b/gcc/cp/class.c
> @@ -3072,8 +3072,7 @@ finish_struct_anon_r (tree field)
> }
> }
>
> -/* Check for things that are invalid. There are probably plenty of other
> - things we should check for also. */
> +/* Fix up any anonymous union/struct members of T. */
>
> static void
> finish_struct_anon (tree t)
> diff --git a/gcc/cp/decl.c b/gcc/cp/decl.c
> index 01d64a16125..71308a06c63 100644
> --- a/gcc/cp/decl.c
> +++ b/gcc/cp/decl.c
> @@ -5084,6 +5084,9 @@ fixup_anonymous_aggr (tree t)
> {
> tree field, type;
>
> + if (BINFO_N_BASE_BINFOS (TYPE_BINFO (t)))
> + error_at (location_of (t), "anonymous struct with base classes");
> +
> for (field = TYPE_FIELDS (t); field; field = DECL_CHAIN (field))
> if (TREE_CODE (field) == FIELD_DECL)
> {
> diff --git a/gcc/testsuite/g++.dg/ext/anon-struct8.C
> b/gcc/testsuite/g++.dg/ext/anon-struct8.C
> new file mode 100644
> index 00000000000..f4e3f11b678
> --- /dev/null
> +++ b/gcc/testsuite/g++.dg/ext/anon-struct8.C
> @@ -0,0 +1,9 @@
> +// { dg-options "" }
> +
> +struct A { };
> +struct B {
> + struct: A { int i; }; // { dg-error "anonymous struct with
> base" }
> +};
> +union U {
> + struct: A { int i; }; // { dg-error "anonymous struct with
> base" }
> +};
>
> base-commit: 0ba2003cf306aa98b6ec91c9d849ab9bafcf17c2
> --
> 2.27.0
>
