bug#66317: Project mode-line

[Eshel Yaron via "Bug reports for GNU Emacs, the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>]

Juri Linkov <juri@linkov.net> writes:

>>>>>>> Agreed.  No need to support it in older versions.  Moreover,
>>>>>>> I'm trying to add another option to join project and vc indicators
>>>>>>> on the mode-line that won't be possible to support in older versions.
>>>>>> Then that needs to be explained in the docstring. project.el is installable
>>>>>> in older versions.
>>>>> Hopefully I explained this sufficiently well in the docstring
>>>>> both for users of older versions and users who customized the
>>>>> default mode line.
>>>> Not sure: I imagine that most users don't customize mode-line-format
>>>> themselves, and thus don't know which contents it has.
>>>>
>>>> I would append some clarification that in Emacs 30 the mode-line has that
>>>> element by default.
>>> I'm not sure if this helps because a user might run Emacs 30
>>> and still using some package that heavily modifies the mode line.
>>> This will puzzle the user: why it doesn't work in Emacs 30
>>> as documented.
>>
>> Hence "by default".
>>
>> Mode-line package authors might be helped out by this explanation as well.
>
> Maybe this would be sufficient:
>
> diff --git a/lisp/progmodes/project.el b/lisp/progmodes/project.el
> index 2475d7c403e..1d6c9c1cf1b 100644
> --- a/lisp/progmodes/project.el
> +++ b/lisp/progmodes/project.el
> @@ -2109,7 +2109,8 @@ project-uniquify-dirname-transform
>  (defcustom project-mode-line nil
>    "Show the current project name with the menu on the mode line.
>  This feature requires the presence of the following item in
> -`mode-line-format': `(project-mode-line project-mode-line-format)'."
> +`mode-line-format': `(project-mode-line project-mode-line-format)'
> +that already exists by default in Emacs 30."

To me, this description looks a bit too implementation-focused.  How
about the following?

    Show the name of the current project on the mode line.

    This option only works in Emacs 30 or later, for a similar effect in
    Emacs 29 or earlier add `project-mode-line-format' to your
    `mode-line-format' instead of using this option.