To clarify, GCC deliberately supports this as an extension in its default mode, which does not attempt to be a conforming ISO C++ implementation. So that isn't a bug in itself. The bug is that it fails to issue a diagnostic when the -pedantic option is used.

> On Jul 16, 2026, at 21:22, Nate Eldredge via Std-Discussion <std-discussion_at_[hidden]> wrote:
>
> Looks like this is a known bug in GCC: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=72751
>
>> On Jul 16, 2026, at 20:59, Russell Shaw via Std-Discussion <std-discussion_at_[hidden]> wrote:
>>
>> Hi,
>>
>> [class.union.anon] says "Nested types, anonymous unions, and functions
>> shall not be declared within an anonymous union."
>>
>> It seems pretty definite. Everywhere i read and g++ allows them.
>>
>> struct A {
>>
>> union {
>> union {
>> int x;
>> };
>> };
>>
>> A() {
>> int a = x;
>> }
>> };
>>
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>>
>
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