bug#60956: 27.2; project-try-vc considers every nonempty directory a root when vc-handled-backends is nil

[Dmitry Gutov]

Hi!

On 20/01/2023 00:45, Jason Orendorff wrote:
> I observed that `eglot' would happily start dozens of language server
> processes, but each one of them only seemed to know about a tiny
> fraction of my code. I tracked this down and found a minor bug in
> project.el.
>
> In `project-try-vc', when `vc-handled-backends' is nil, the value of
> `marker-re' computed here:
>
> https://git.savannah.gnu.org/cgit/emacs.git/tree/lisp/progmodes/project.el?id=207901457c018d94b1ce9e13a897d8241b1f3af2#n516
>  
> <https://git.savannah.gnu.org/cgit/emacs.git/tree/lisp/progmodes/project.el?id=207901457c018d94b1ce9e13a897d8241b1f3af2#n516>
>
> is the empty string.
>
> If no vc backends are enabled, no directory should be treated as a vc
> root. But the empty regexp matches everything, so *all* directories are
> treated as vc roots.
>
> Consequently, `eglot' spawned a lot of processes, because it starts one
> per project.
>
> The workaround is to set `vc-handled-backends' to any other value. (I
> suppose I configured it to nil long ago, when working in a huge
> Mercurial repository. Back then, commonplace hg commands in that repo
> were unreasonably slow.)

Thank you for this report.

Please try the attached patch.

project-marker-wildcard.diff
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