bug#36861: 27.0.50; display-fill-column-indicator-mode in log-edit-mode

[Ergus]

On Tue, Aug 06, 2019 at 05:59:28PM +0300, Eli Zaretskii wrote:
> > Date: Sun, 04 Aug 2019 22:30:05 +0200
> > CC: Eli Zaretskii <eliz@gnu.org>,36861@debbugs.gnu.org
> > From: Ergus <spacibba@aol.com>
> >
> > Dfci was not designed to be used in this way, and the mode initialization 
> > actually sets the character, but in the
> > future it could make many other dynamic tests/checks if needed. So I don't 
> > think we should modify it to work
> > the other way you suggest, because for menit is not general enough. But I will 
> > follow the Eli's suggestions in
> > this aspects more than my own opinion.
> > Any way, if you want to use the mode in this way (for now) you can/need to set 
> > the
> > display-fill-column-indicator-character to your desired value and it should 
> > work as it is now. But I can't promise
> > that it will work the same way in the future.
> > But again, probably Eli will suggest a better solution for your use case.
>
> I don't think I understand the problem.  Why doesn't just setting the
> characters and the mode variable work as expected?  AFAIU, one needs
> to call the mode function only if one wants Emacs to deduce the
> indicator character automatically.

Hi:

It should work as you say. But the default value for
display-fill-column-indicator-character is nil until the mode function
is executed (at least once).

I think that what they want is display-fill-column-indicator-character
to be non-nil without initialization; which we cannot set without some
checks.

Probably I'll need to reword the doc string about the default value to
specify that the value is really nil and it is initialized to the other
non-nil values in the mode function.

Does it makes sense?