bug#72309: propertized-buffer-identification with maximum width

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

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On Sunday, July 28th, 2024 at 12:05 AM, Eli Zaretskii <eliz@gnu.org> wrote:

> > Date: Sat, 27 Jul 2024 09:22:21 +0000
> > From: Heime heimeborgia@protonmail.com
> > Cc: 72309@debbugs.gnu.org
> > 
> > On Saturday, July 27th, 2024 at 5:48 PM, Eli Zaretskii eliz@gnu.org wrote:
> > 
> > > tags 72309 notabug
> > > thanks
> > > 
> > > > Date: Fri, 26 Jul 2024 19:04:14 +0000
> > > > From: Heime via "Bug reports for GNU Emacs,
> > > > the Swiss army knife of text editors" bug-gnu-emacs@gnu.org
> > > > 
> > > > propertized-buffer-identification could be improved so that when using a
> > > > maximum width there are three dots and a space at the end to indicate
> > > > that the buffer name has been truncated.
> > > 
> > > Emacs doesn't truncate the buffer name shown on the mode line, so no
> > > ellipsis should be needed, ever. IOW, the maximum width is basically
> > > infinity.
> > > 
> > > Where did you see the buffer name truncated on the mode line?
> > 
> > There is this construct
> > 
> > (width rest…)
> > 
> > which specifies truncation or padding of the results of rest.
> > 
> > If used on the buffer name it just truncates without specification
> > that truncation occurred.
> 
> 
> Where in the Emacs code did you see that? I cannot find anything like
> that in bindings.el, which is where we have the code used for
> displaying the buffer name on the mode line.

The last entry in "24.4.2 The Data Structure of the Mode Line".

I have tried it and setting a maximum width does work and the abrupt 
truncation in the buffer name does occur.