bug#63648: 29.0.90; project.el: with switch-use-entire-map, switch-project errors on non-project commands

[Juri Linkov]

>>>> I suggest you bring up this feature addition on emacs-devel, or otherwise
>>>> wait for a review from Eli, at least.
>>>>
>>>> It's not a big addition, but it's a distinct new feature (the
>>>> next-default-directory var).
>>>
>>> Indeed, such code addition better to be discussed on emacs-devel.
>>
>> Did this end up being discussed on emacs-devel?  I am still quite
>> interested in this feature.
>
> Oh, another thought (which maybe should be discussed on emacs-devel):
> maybe we don't need to make this specific next-default-directory var.
>
> Instead, maybe what we want is a way to bind a dynamic variable
> *without* changing the buffer-local value.  It would shadow the existing
> binding, but if we explicitly switched buffer we'd get back to the old
> value.  So we'd have:
>
> (special-let ((default-directory newval))
>   (assert default-directory newval))
>
> and
>
> (special-let ((default-directory newval))
>   (set-buffer (current-buffer))
>   (assert default-directory oldval))
>
> Ignore any complexities of implementing this and any complexities of the
> semantics which I haven't covered.  If we had this, would it work as an
> alternative to next-default-directory?

There is no code where to bind a dynamic variable, because its value
should be available for the next command in the command loop.
If you agree there is no other way to implement this than 
next-default-directory,
then I could bring up the discussion on emacs-devel.