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

[Dmitry Gutov <dmitry@gutov.dev>]

On 30/08/2023 19:27, Juri Linkov wrote:
>>> 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.
>> Before we dive into all that, why not try advice on 'command-execute'? For
>> the PoC code at least. It's in Lisp since 2013.
> Thanks for bringing up 'command-execute'.  I forgot it was moved from C to Lisp,
> so the change is simpler and not needed to discuss on emacs-devel.  Then advice
> on 'command-execute' will be required to support older Emacs versions in project.el.
> But for Emacs 30 I modified my previous patch, and the next version is below:
> 
>> The comment in its body does say "Called directly from the C code", but I'm
>> not sure if that has any direct implications for us.
> Also interesting how 'command-execute' handles 'debug-on-next-call'
> similar to 'next-default-directory'.

I've tried the patch a little bit, some more impressions:

- Unfortunately, using default-directory instead of the specialized 
variable which we added lately (project-current-directory-override) 
brings back the bug it was added for: https://debbugs.gnu.org/58784. The 
switch to a different design didn't fix the problem of the temporary 
binding for d-d in the buffer which is current when the command is 
executed. So adding the next-default-directory variable might not be the 
best idea after all. But the advice thingy can set a binding for any 
variable, including the *-override one.

- I also managed to get into some transient state where some chars were 
doing one thing (their usual bindings), and some - invoked project 
commands instead, with no apparent method of quitting that state. Maybe 
I'll document it next time I see it.

- Using (project--keymap-prompt) for just a message call is cute, but I 
personally like the "guardrails": if I accidentally type a wrong char 
when choosing the command, I won't have to choose the other project 
again. This is debatable, but both modes of operation are probably worth 
keeping available (opinions welcome).

- Either way, with method with the advice should be useful for other 
things, like project--other-place-command.