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

[Dmitry Gutov <dgutov@yandex.ru>]

On 02.07.2020 20:41, Eli Zaretskii wrote:

>> The notion of current project is very common in most editors
> 
> But Emacs is more than just an IDE, it can be and is used for many
> other jobs.  For example, I customary take a break from my development
> work to read email, and when doing so I might issue some Grep command
> that I need for some email message I'm writing.  I don't think it's
> right for Emacs to assume that every Grep I do is necessarily related
> to the last project I was working on (which could be days in the past,
> btw).  This way, we would need a command to "get out of" (or "close")
> the project, which I think would be both a nuisance and absurd.

But it's for a default value (one you can insert using M-n, or not). 
Most users won't even notice this.

>> The use case is 'M-x xref-find-refereces' and xref backends which don't
>> override xref-backend-references. In which case this command searches
>> the current project using general purpose tools (one of semantic symref
>> tools, or Grep).
>>
>> But xref backend != current project. They're technically and
>> theoretically independent.
> 
> So you are saying that it might bring me the wrong references once in
> a while?  That's not good, is it?

If an xref backend doesn't define the xref-backend-references method, 
the alternative is no references at all.

Anything else we do, will be imprecise. But it's useful to have a 
default with "good enough" behavior, as you have probably noticed.

Whether the current implementation will give wrong results, and how 
often, is difficult for me to predict. It also depends on what we 
consider a "wrong reference". etags and elisp backends don't always give 
perfect results for "find definition" either.