bug#41821: 28.0.50; read-directory-name in vc commands should provide defaults from projects

[Juri Linkov]

>> > Why not have some relevant history in VC itself?
>>
>> Then like the project history currently is saved in ~/.emacs.d/projects
>> saving of a separate vc-directory history will be duplicated the same way
>> in e.g. ~/.emacs.d/vc-projects?
>
> Not necessarily duplicated, because no one said the projects I use
> will necessarily visit all (indeed, even one of) the VC roots that I
> will visit via VC commands.  And vice versa.
>
> IOW, please don't assume that, because project.el can use the VC
> backend, it will always use VC in the same directories.  If the roots
> are different, offering the same completion candidates will be
> confusing and even annoying.

OTOH, it would be confusing and annoying to have duplicate histories for
users who prefer project.el solely for handling vc repositories.

>> > Moreover, using a command such as "C-x v d" doesn't mean I want
>> > project.el record that, again because I might be using project.el
>> > commands for projects that aren't based on VC.
>>
>> Then project.el could have a customizable variable that will prevent
>> recording vc project history.
>
> What for? let every layer record its own history, and then use the
> relevant history in each layer.
>
>> > And if the history is collected by VC, it could be made available to
>> > project.el commands that call into VC, right?
>>
>> You mean to record an internal vc-history separately from project.el,
>> but still to save it in the same project file ~/.emacs.d/projects?
>
> No, I mean provide a possibility for project.el to access the history
> saved in ~/.emacs.d/vc-history, in addition to project.el's own
> history.  If the user wants that.

This is what I meant by a customizable variable mentioned above
to toggle recording of a separate vc history.