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

[Juri Linkov]

> 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 didn't test yet the cases from bug#58784.  So this might require more changes.

> - 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.

It would be nice to have a reproducible test case.
But indeed chars in the project map invoke the project commands,
and all other chars fall back to local/global keybindings.

> - 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).

This is easy to do with something like in 'y-or-n-p-map'.

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

It's not recommended to use advice in the core packages,
maybe only for providing backward-compatibility with older versions.