Re: obscure compilation error with cl-defstruct &aux boa constructor

[Madhu]

* Stefan Monnier <jwvtuarzrem.fsf-monnier+emacs @gnu.org> :
Wrote on Sun, 17 Apr 2022 11:16:30 -0400:
> Madhu [2022-04-16 22:16:18] wrote:
[...]
>> (stack (make-list (1+ (car ppss)) nil))) 0 4)
>
> It looks like some frames are missing between these two.

I think I posted the full backtrace, but there was other cruft on HEAD,
so it is not the same error you'd get on master with the single
indicated change. which would be

#+begin_example
Loading /dev/shm/emacs/lisp/progmodes/prog-mode.el (source)...
Loading /dev/shm/emacs/lisp/emacs-lisp/lisp-mode.el (source)...
Eager macro-expansion failure: (void-function cl-subseq)
Eager macro-expansion failure: (void-function cl-subseq)
Symbol’s function definition is void: cl-subseq
make[1]: *** [Makefile:912: bootstrap-emacs.pdmp] Error 255
#+end_example

>> The error goes away if I remove the &aux (and thus make all the
>> arguments optional)
>
> I must say that seeing your backtrace I can't understand why your code
> doesn't work or rather why our code works (the call to `cl-subseq`
> depends on the presence of `&aux` which is already present in our code).
>
>> Might this be a bug from a recent change? (I've not looked at the
>> changes yet, so this is a note to self)
>
> The bootstrap is delicate and ad-hoc.
> Sometimes innocuous changes can break it.

I see it isn't a recent error. to compile the indicated form I had a
workaround in loadup.el that defined cl-subseq (after loading "simple"),
since around 2019-03-14. (somehow I'd lost that workaround this time
around)