bug#12812: defsetf with third argument = t

[Stefan Monnier]

>>> In Emacs 24.2 and earlier, defsetf was documented [1] to accept a third
>>> argument = t, with the same meaning as gv-define-simple-setter's
>>> optional FIX-RETURN argument. This behaviour no longer works.
>> Indeed, thanks, fixed.
> Still fails for me as originally described.
> I think it's gv-define-simple-setter that's broken now, by #12813.
> The FIX-RETURN case... doesn't.

Indeed, I fix it and broke it right away.  Should be fixed for good
this time.

> PS gv, cl-lib etc all looks like very nice stuff.

Thanks.  I'm particularly proud of gv.el ;-)

> Just reporting these issues while trying to figure out how to document
> some of it.

Tank you for doing that.  FWIW, I think the third arg of defsetf should
be undocumented.  I hesitated whether to fix it or not since AFAIK the
only users of that feature were in cl-macs.el and now use
gv-define-simple-setter instead.  The only reason why I installed the
fix is that it was such a trivial change to make.


        Stefan