bug#54228: 29.0.50; project.el: Support local projects

["Daniel Martín via Bug reports for GNU Emacs, the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>]

Manuel Uberti via "Bug reports for GNU Emacs, the Swiss army knife of
text editors" <bug-gnu-emacs@gnu.org> writes:

> Hi,
>
> I attached a small patch which simply adds to project.el some code I
> have been using for a while for projects that I do not intend to handle with Git.
>
> The gist of it is that adding a `.project` (empty) file to the root
> directory of your project make it possible for commands such as 'C-x p
> f' to work on it.
>
> Is this of any interest?
>

I use similar code in my config.  It's specially useful for monorepos,
where there is only one big .git folder, but multiple projects that you
want to handle separately.

If we want to contribute this to project.el, I wonder if it makes sense
to generalize it a little bit by making ".project" the default value of
a customization variable.  That'd avoid the name clash with some Eclipse
files.  We could also detect files from common build systems, but I
don't know if that would be out of scope for the rather minimalist
project.el (vs projectile.el, for example).