This was mentioned during the discussion of LWG 3827 but looks like it didn't make it into the issue.

It was mentioned in cplusplus/nbballot#502

It doesn't really matter now, because if it was supposed to be present in older standards, it's gone now anyway. I don't think we want a compatibility note saying that something which was never in the standard is gone now.

Oh wait, they're not gone, we only deprecated them for now. Sigh.

I suppose we could add __alignof_is_defined to Annex D. I find it hard to care. Nobody should ever try to use that macro in C++.

What's unclear about this specification in [stdalign.h.syn] ?

The contents of the C++ header <stdalign.h> are the same as the C standard library header <stdalign.h>, with the following changes: The header <stdalign.h> does not define a macro named alignas.
See also: ISO/IEC 9899:2018, 7.15

Our normative reference is to C17, so if this has a macro in <stdalign.h>, then C++23 has this macro as well.

What exactly is the problem? Do you want index entries for the macros?

We explicitly deprecated __alignas_is_defined in C++23, it would be silly to leave __alignof_is_defined there, un-deprecated. It would conflict with the clear direction of an NB comment.

Ah, ok, we're simply missing an entry for __alignof_is_defined in [depr.c.macros].

@jwakely , do you feel we should do that editorially, or is that an LWG matter? Strictly speaking, it's normatively deprecating a macro whose status quo is that it's not deprecated.

Yeah I think we should probably do it as an LWG issue. I don't know why it was never listed in the contents of <cstdalign>, if it had been there, we'd have deprecated it as part of LWG 3827.

Hmm... I'm tried to submit an LWG issue but not sure whether it is wanted (it's possibly too late). Since C++26 will probably refer to C23 and thus should get __alignas_is_defined/__alignof_is_defined removed.

That's now LWG4036.

Should be fixed by #6915.