bug#66317: Project mode-line

[Eli Zaretskii <eliz@gnu.org>]

> Date: Thu, 5 Oct 2023 23:23:17 +0300
> Cc: 66317@debbugs.gnu.org, me@eshelyaron.com
> From: Dmitry Gutov <dmitry@gutov.dev>
> 
> On 04/10/2023 09:18, Juri Linkov wrote:
> > diff --git a/lisp/bindings.el b/lisp/bindings.el
> > index 207adb3a2a4..70e4087e131 100644
> > --- a/lisp/bindings.el
> > +++ b/lisp/bindings.el
> > @@ -682,6 +682,7 @@ mode-line-end-spaces
> >   	     'mode-line-buffer-identification
> >   	     "   "
> >   	     'mode-line-position
> > +	     '(project-mode-line project-mode-line-format)
> >   	     '(vc-mode vc-mode)
> >   	     "  "
> >   	     'mode-line-modes
> 
> Speaking of this change from the first patch, do we want to have 
> project-mode-line automatically supported in Emacs <= 29, when they 
> install the new version from ELPA? Can we safely do that?
> 
> Simply altering mode-line-format, as in the original patch, might mess 
> up the custom mode-line the user had set up (or installed). How to only 
> change the default mode-line is less obvious, but perhaps checking that 
> the current value is equal to (get 'mode-line-format 'standard-value) 
> would mean altering is okay.
> 
> Or otherwise we should say something in the docstring of 
> project-mode-line: that it's only directly supported in Emacs 30, and in 
> older versions the user need to add the corresponding entry to the 
> mode-line-format by hand.

I think supporting it in Emacs 30 is fine.  It's a very minor feature,
after all, so let's not invest too much effort in it.