bug#18357: 24.3.93; Calendar not fully displayed

[Stephen Berman]

On Sat, 30 Aug 2014 12:58:26 +0300 Eli Zaretskii <eliz@gnu.org> wrote:

>> From: Stephen Berman <stephen.berman@gmx.net>
>> Date: Fri, 29 Aug 2014 20:24:09 +0200
>> 
>> 0. emacs -Q
>>    (sanity check) M-x calendar => The Calendar is fully displayed in the
>>    lower fitted window.
>> 1. M-x customize-option RET calendar-week-start-day RET, set value to 1
>>    and save for current session.
>>    M-x customize-face RET mode-line RET, show all attributes, check
>>    `Overline' set its value to `On' and save for current session.
>> 2. M-x calendar => Only the last four lines of the Calendar are
>>    displayed in the lower fitted window.
>> 
>> It looks as if point is centered in the Calendar window, but if I type
>> `C-l', it displays the last five lines, not just the last four.  Also,
>> the date could be relevant, since point is on today's date, which is on
>> the last line of the displayed Calendar; if this changes on September 1,
>> I'll report back.
>> 
>> I'm not sure but I think I first observed this problem in my build of
>> 2014-08-20.  I don't remember seeing it in my previous build of
>> 2014-07-22, but if I do the above recipe with the executable from the
>> that build, I do see the problematic display, which suggests it is due
>> to a change in a non-pre-loaded lisp file, though nothing in the
>> ChangeLog looks relevant, so perhaps my memory of when this began is
>> failing me.
>> 
>> The Calendar display problem also happens in my 2014-08-21 build from
>> the trunk, but only when configured --without-toolkit-scroll-bars; a
>> trunk build with (GTK+) scroll bars (including the new horizontal scroll
>> bar) does not show the problem.  However, I just rebuilt the current
>> emacs-24 --without-toolkit-scroll-bars and still see the problem there.
>
> Sorry, I don't see any problem here: with the customized face of the
> mode line, the window showing the calendar buffer is not tall enough
> to show all of the buffer _and_ show the cursor on today's date (we
> don't allow point to be in a partially visible line).  So Emacs
> scrolls the display to make the line with point fully visible.  That's
> perfectly normal, not a problem.
[...]
>                                 Rather, I'm guessing that this is
> caused by the fact that today's date is on the last line of the
> buffer, which wasn't so before.
>
> You can customize calendar-minimum-window-height to work around "the
> problem".

Your analysis is convincing (and makes explicit what I vaguely suspected
about point being on the last line; moreover, I was mistaken in saying
that the amount scrolled was different from doing `C-l': it depends on
which line point is on when you type `C-l', of course).  In addition,
the workaround is acceptable, so I'm closing this bug.

Two questions remain for me: (i) Since I use the Calendar pretty much
daily and the triggering configuration comes up about every four weeks,
why don't I remember seeing this before? (This isn't a question I think
you can answer; I guess my memory just isn't good enough.) (ii) Why
doesn't "the problem" happen in the trunk build with toolkit scroll
bars?  Is this perhaps because Martin's window changes add an extra
pixel or two, leaving enough space?

Steve Berman