bug#47799: 28.0.50; Default `project-files' implementation doesn't work with quoted filenames

[Dmitry Gutov <dgutov@yandex.ru>]

On 19.04.2021 23:48, Dmitry Gutov wrote:
> And how will we explain anyway that xref-matches-in-files, when called 
> without the new ROOT argument, doesn't handle remote or quoted file names?

The above is probably the only real blocker I see. Else we would need to 
document it to explicitly only take relative file names, I think. Do we 
have a precedent in the core library for this?

Other than that, an exploration into an API working with relative files 
names sounds good, actually. It could further speed up file listing, 
eliminating some concatenations in project--vc-list-files (in the big 
project I referred to, that takes it from 1s down to 0.75s).

If you have the time, patches welcome, even rough ones.

> So if you can fix this to avoid performance loss in the general case, 
> that would be a good improvement for now.

In the meantime, I've changed the fix to use the plan explained previously.

Downsides: either all files should be quoted, or none (is that a 
reasonable assumption?), and, of course, users which which do have 
directories making use of quoting still pay the performance overhead.