bug#54210: 27.1; appt-add checks for bad data only at end

[Robert Pluim <rpluim@gmail.com>]

>>>>> On Tue, 01 Mar 2022 13:54:47 +0100, Francesco Potortì <pot@potorti.it> said:

    Francesco> appt-add asks the user for three parameters:
    Francesco> - time (a time string)
    Francesco> - message (a string)
    Francesco> - minutes (a number)

    Francesco> if the time string is badly formatted (for example if it is "8" rather
    Francesco> than "8.00") appt-add barfs.  That's ok, but it barfs only after all
    Francesco> three parameters have been read.  It should barf immediately after
    Francesco> submitting the wrong parameter.

    Francesco> Maybe I'll find the time to look at it and propose a patch, but since
    Francesco> I don't know, I prefer reporting it now.

Aha, a learning opportunity (for me :-) )

How about this (I canʼt find a `read-time-of-day', unless org has one hidden
away somewhere):

diff --git a/lisp/calendar/appt.el b/lisp/calendar/appt.el
index ebdafb438e..6a3ea7c356 100644
--- a/lisp/calendar/appt.el
+++ b/lisp/calendar/appt.el
@@ -510,10 +510,12 @@ appt-add
 Optional argument WARNTIME is an integer (or string) giving the number
 of minutes before the appointment at which to start warning.
 The default is `appt-message-warning-time'."
-  (interactive "sTime (hh:mm[am/pm]): \nsMessage: \n\
-sMinutes before the appointment to start warning: ")
-  (unless (string-match appt-time-regexp time)
-    (user-error "Unacceptable time-string"))
+  (interactive (list (let ((time (read-string "Time (hh:mm[am/pm]): ")))
+                       (unless (string-match appt-time-regexp time)
+                         (user-error "Unacceptable time-string"))
+                       time)
+                     (read-string "Message: ")
+                     (read-string "Minutes before the appointment to start warning: ")))
   (and (stringp warntime)
        (setq warntime (unless (string-equal warntime "")
                         (string-to-number warntime))))