bug#61817: 30.0.50; Project.el finds incorrect project roots in git worktrees

[Dmitry Gutov]

On 27/02/2023 09:32, Arthur Miller wrote:
> Dmitry Gutov <dgutov@yandex.ru> writes:
>
> > On 26/02/2023 18:23, Arthur Miller wrote:
> > > What actions trigger the bug:
> > > Two different, unrelated repositories with emacs source code tree. My tree(s)
> > > looks like this:
> > > ~/repos/emsrc/emacs/
> > > ~/repos/enacs-tests/emacs/
> > > Where in both the last "emacs/" is the Emacs source tree from main git
> > > repository.
> > > ~/repos/emsrc/emacs/  is the one I use for my "everyday" Emacs. I build Emacs
> > > now
> > > and then once in a week or few weeks with a script, and I make each build in its
> > > own our-of-source worktree. The other one is one where I used to do some tests.
> > > It shouldn't matter since all worktrees are contained withing parent directory,
> > > which in one case is "emsrc" and in the other case "emacs-tests", but for some
> > > reason project.el sees the wrong one.
> > > 1. create two parent folders each one containing a copy of emacs sources
> > > 1. create out of source worktree for Emacs source under one of those
> > > 2. navigate to the worktree/lisp/progmodes
> > > 3. run M-: (project-known-project-roots)
> > > In my Emacs, I am in my currently installed emacs worktree, where git root is
> > > ~/repos/emsrc/emacs but project.el returns ("~/repos/emacs-tests/emacs/") as a
> > > result
> >
> > What does (project-root (project-current)) return? And which dirs you are
> > testing it in?
>
> It returns the current worktree folder:
>
> "/home/arthur/repos/emsrc/no-gtk-with-cairo-and-native-230226-061643/"
>
> which I guess is what project.el finds as root since it only uses .git as a
> marker, if I understand correctly what you write little further.
>
> > > I am not chasing the bug, but I don't see much code in project.el related
> > > to worktrees.
> >
> > Normally, there shouldn't be any need to handle worktree specially: it contains
> > a file called .git at the top which can serve as a marker just fine.
>
> Well define "normally" and "just fine" :). Anyway, when I read your reply it 
> seems
> like I have wrong expectation from project.el, so the fault is on my side. I
> thought it can deal with git projects in general, but as I understand it then,
> it only works with files in current directory.

We could change project-try-vc to follow the link to the parent repo, 
but how is the rest of it going to work?

If the project root is the parent repo, which set of files would 
(project-files pr) return? And how could that be implemented?

> > > The only place I see them mentioned is about submodules.I
> > > personally have used this one for quite some time, and it seems to correctly
> > > handle worktrees for me:
> >
> > You code looks like it can return the "actual git root" that can be a directory
> > residing somewhere else than the current directory tree.
>
> Git worktrees can be placed outside the main repository tree:
>
>      git worktree add ../my-new-shiny-emacs-patch
>
> as an example. The code will find correct git root both outside, or within the
> repo.

Exactly.

> But I think it should be done by actually asking git to list worktrees
> instead.
>
> >                                                           Is that what you
> > wanted?
>
> Yes that is what I wanted? :-).
>
> For automation purpose I need to find the project root, so I can pull sources to
> main, create a clean worktree from main, and switch Emacs to the new worktree
> interactively in one command, like M-x make-new-patch. Emacs asks me for a name
> and create a clean worktree from the main trunk for current project. Actually
> better variant is to ask which branch to patch, but the first one is slightly
> faster and works just fine in many cases.

It sounds like your code is Git-specific, not project-neutral.

But you still could find the worktree root using project.el, and then 
read the contents of .git, follow the link and do your automation stuff.