Re: project.el: git submodules?

[Dmitry Gutov]

On 14.05.2020 20:57, Stefan Monnier wrote:
> > > > I even have a patch, but here's another thought: wouldn't this mistakenly
> > > > punish people who keep their $HOME as a Git repository to sync
> > > > between machines?
> > > Depends if the Git worktrees within their $HOME use the same repository
> > > as the one used for $HOME.
> > Not 'git worktrees' (to be clear), just random other work directories, for
> > work/hobby/etc projects.
>
> Yes, I make "work trees" in a generic sense not just in the `git worktree` 
> sense.
>
> > Yes, a user option (inrended for dir-locals) is likely in order, but users
> > such as described above would have to set it in _all_ of their
> > work directories.
>
> Not if the repository they use for $HOME is different than the one they
> use for ~/work, ~/my/hobby/, ...

Then they'll only have to set it in ~/.dir-locals.el? Is that what you mean?

Here's the patch I made according to your description:

diff --git a/lisp/progmodes/project.el b/lisp/progmodes/project.el
index ac56537b97..bf737e821a 100644
--- a/lisp/progmodes/project.el
+++ b/lisp/progmodes/project.el
@@ -266,11 +266,18 @@ project-try-vc
   (let* ((backend (ignore-errors (vc-responsible-backend dir)))
          (root
           (pcase backend
-            ('Git
+            (`(or ,'Git ,'Hg)
              ;; Don't stop at submodule boundary.
-             (or (vc-file-getprop dir 'project-git-root)
-                 (vc-file-setprop dir 'project-git-root
-                                  (vc-find-root dir ".git/"))))
+             (or (vc-file-getprop dir 'project-vc-root)
+                 (let* ((default-directory dir)
+                        (root (vc-root-dir))
+                        (parent (file-name-directory
+                                 (directory-file-name root))))
+                   (vc-file-setprop dir 'project-vc-root
+                                    (or
+                                     (let ((default-directory parent))
+                                       (vc-root-dir))
+                                     root)))))
             ('nil nil)
             (_ (ignore-errors (vc-call-backend backend 'root dir))))))
     (and root (cons 'vc root))))