RE: trailing whitespace in calendar

[Drew Adams]

> > (add-hook 'today-visible-calendar-hook ...
> 
> That hook got renamed to calendar-today-visible-hook

Actually, it's not the problem that it was renamed.  The
problem is that the old name is no longer recognized.

The option was renamed in Emacs 23, but Emacs remained smart
enough and careful enough, through release 24.5, to continue
to respect the old name as well.  This respect (support) was
removed in Emacs 25.

Prior to Emacs 25, Emacs did the following just before the
defcustom for the new name, `calendar-today-visible-hook':

 (define-obsolete-variable-alias 'today-visible-calendar-hook
   'calendar-today-visible-hook "23.1")

As `C-h f define-obsolete-variable-alias' says:

 If CURRENT-NAME is a defcustom ... then the
 define-obsolete-variable-alias statement should be
 evaluated before the defcustom, if user customizations
 are to be respected.

IOW, `define-obsolete-variable-alias' is an easy way
to warn users about a name change but also continue to
support the old name.

It was decided in Emacs 25 that this user customization
(and others that were also deprecated in Emacs 23) is no
longer to be respected.

It is _good_ for users to use the new names.  Whether it
is good for them to be forced (silently) to use them is
a different question.  At any rate, that's the case now.

It might be better perhaps if the warning, which tells
you what the new name is, continued to be issued, even
after support was discontinued.

For example, after desupport the warning message could
perhaps be changed to an error (raised when the old name
is used), to let you know what the problem is.  Then
users like Luis would not need to wonder "Do you know
why this is not working now?"

Instead, Emacs just fails to recognize the old name now.