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

[Juri Linkov]

> Thinking about it, I guess there's (roughly) two classes of commands
> which want different things from default-directory, classes 1 and 2:
>
> 1. wants whatever the current value of default-directory is (and gets
> this by just using default-directory as a variable)
>
> 2. wants the value of default-directory for some specific buffer X (and
> gets this either with buffer-local-value or by using
> with-current-buffer)
>
> If we could change 1 without changing 2, then we'd be happy.

I think we can't solve this logical paradox because it contains
self-contradictory requirements.  Here is the command that
illustrates this paradox.  What should this command print?

  C-x p p ... C-h v default-directory RET

Like Schrödinger's cat, it belongs simultaneously to both classes:

1. wants to print the new value of default-directory
   because 'C-h v' is the next command for which
   the value of default-directory was explicitly set.

2. wants to print the original value of default-directory
   because 'C-h v' was invoked in the buffer where
   the value of default-directory should stay unchanged.