bug#11260: 24.1.50; `holiday-sexp' may create entry twice

[Michael Heerdegen <michael_heerdegen@web.de>]

Hi,

the following happens also in Emacs 23.  Recipe:

1. emacs -Q
2. M-x calendar RET
3. evaluate: (require 'holidays)
4. evaluate:
   (add-to-list
    'calendar-holidays
    '(holiday-sexp
      '(list 4 17 2012)
      "April 17th 2012"))

5. In the calendar, move point to April 17th 2012 and hit h.

You'll see that "April 17th 2012" appears twice.

I've debugged this.

`calendar-holiday-list' indeed returns two entries for this date.

The bug is in `holiday-sexp':

| (defun holiday-sexp (sexp string)
|   "Sexp holiday for dates in the calendar window.
| SEXP is an expression in variable `year' that is evaluated to
| give `date'.  STRING is an expression in `date' that evaluates to
| the holiday description of `date'.  If `date' is visible in the
| calendar window, the holiday STRING is on that date.  If date is
| nil, or if the date is not visible, there is no holiday."
|   (let ((m displayed-month)
|         (y displayed-year)
|         year date)
|     (calendar-increment-month m y -1)
|     (holiday-filter-visible-calendar
|      (list
|       (progn
|         (setq year y
|               date (eval sexp))
|         (list date (if date (eval string))))
|       (progn
|         (setq year (1+ y)
|               date (eval sexp))  ;; <------------------------------- 
|         (list date (if date (eval string))))))))


At the marked position, there is no check if `date' is in the
incremented year.


I see two possible fixes:

1.  Add such a check, and set date to nil when it fails.

2.  Add to the doc of `holiday-sexp' that a given sexp _must_ return
    either nil or a date which is in the year equal to the value of
    `year'.

I would prefer 1., because I don't see the need for such a
restriction.  But I'm not really familiar with calendar stuff.


Thanks,

Michael.


In GNU Emacs 24.1.50.1 (i486-pc-linux-gnu, GTK+ Version 3.2.3)
 of 2012-04-10 on zelenka, modified by Debian
 (emacs-snapshot package, version 2:20120410-1)
Windowing system distributor `The X.Org Foundation', version 11.0.11104000
Configured using:
 `configure '--build' 'i486-linux-gnu' '--host' 'i486-linux-gnu'
 '--prefix=/usr' '--sharedstatedir=/var/lib' '--libexecdir=/usr/lib'
 '--localstatedir=/var' '--infodir=/usr/share/info'
 '--mandir=/usr/share/man' '--with-pop=yes'
 '--enable-locallisppath=/etc/emacs-snapshot:/etc/emacs:/usr/local/share/emacs/24.1.50/site-lisp:/usr/local/share/emacs/site-lisp:/usr/share/emacs/24.1.50/site-lisp:/usr/share/emacs/site-lisp'
 '--without-compress-info' '--with-crt-dir=/usr/lib/i386-linux-gnu/'
 '--with-x=yes' '--with-x-toolkit=gtk3' '--with-imagemagick=yes'
 'build_alias=i486-linux-gnu' 'host_alias=i486-linux-gnu'
 'CFLAGS=-DDEBIAN -DSITELOAD_PURESIZE_EXTRA=5000 -g -O2''

Important settings:
  value of $LC_ALL: de_DE.utf8
  value of $LC_COLLATE: nil
  value of $LC_CTYPE: nil
  value of $LC_MESSAGES: nil
  value of $LC_MONETARY: nil
  value of $LC_NUMERIC: nil
  value of $LC_TIME: C
  value of $LANG: de_DE.utf8
  value of $XMODIFIERS: nil
  locale-coding-system: utf-8-unix
  default enable-multibyte-characters: t