bug#66464: Vc mode-line

[Juri Linkov]

>> It would be a pity not to add this handy feature.
>> So here is a small patch that joins the project name and vc status
>> on the mode line:
>
> Could you described the intended look?

Here is the screenshot how the mode line looks like:

> Two mode-line entries one right by another, without a space between?

The format is "project-branch" instead of "backend-branch".

> And with the backend name removed? Wouldn't you say we're losing some
> useful information this way? Or perhaps the backend name is not essential.

I'm sure that showing the backend name in all file buffers is useless
for most users and wastes the precious screen space.

But I don't propose to change the default.

> In any case, it seems like
>
>   (const :tag "Show project name and status" with-project)
>
> describes the option inaccurately, since VC's mode line doesn't show the
> project name.

Technically it's not vc-mode that shows the project name indeed.
I already tried such things as calling '(project-mode-line-format)'
from 'vc-mode-line-string'.  But it's an unnecessary complication.

> And if you customize 'vc-display-status' to 'with-project' but don't
> set project-mode-line to t, the project name won't be shown at all.

This is why the condition already handles this case:

  (and (eq vc-display-status 'with-project)
       (bound-and-true-p project-mode-line))