Use variables to store marking state

Bug#78967.

(calendar-mode): Init new variables with user options.
* lisp/calendar/calendar.el (calendar-generate-window)
(calendar-unmark):
* lisp/calendar/diary-lib.el (diary-mark-entries)
(diary-redraw-calendar):
* lisp/calendar/holidays.el (calendar-mark-holidays): Use new
variables.
* etc/NEWS: Document the change.

1 files changed, 8 insertions, 0 deletions

diff --git a/etc/NEWS b/etc/NEWS
index a34a3d73292..80b461ddadf 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -2451,6 +2451,14 @@ modifier, it scrolls by year.
 The month and year navigation key bindings 'M-}', 'M-{', 'C-x ]' and
 'C-x [' now have the alternative keys '}', '{', ']' and '['.
 
+---
+*** Avoid modifying user options.
+The user options `calendar-mark-holidays-flag' and
+`calendar-mark-diary-entries-flag' are not modified anymore when
+changing the marking state in the calendar buffer.  We now use variables
+that are reset to the user option values whenever we generate a new
+calendar.
+
 ** Calc
 
 *** New user option 'calc-string-maximum-character'.