bug#35238: 27.0.50; Clarify eventp behaviour with booleans

[Basil L. Contovounesios]

Severity: minor
Tags: patch

As mentioned in a past commit[1], nil is not an event.
Since the car of a mouse click event is considered its type,
shouldn't (nil) also be rejected as an event?

  (eventp '(nil)) ; => t

Should t be counted as an event?

  (eventp t)    ; => t
  (eventp '(t)) ; => t

If not, would the following change be welcome?

diff --git a/lisp/subr.el b/lisp/subr.el
index bdf98979c4..8c4df5bc6c 100644
--- a/lisp/subr.el
+++ b/lisp/subr.el
@@ -1227,12 +1227,14 @@ listify-key-sequence
                          c)))
            key)))
 
-(defun eventp (obj)
-  "True if the argument is an event object."
-  (when obj
-    (or (integerp obj)
-        (and (symbolp obj) obj (not (keywordp obj)))
-        (and (consp obj) (symbolp (car obj))))))
+(defun eventp (object)
+  "Return non-nil if OBJECT is an input event or event object."
+  (or (integerp object)
+      (and (symbolp (if (consp object)
+                        (setq object (car object))
+                      object))
+           (not (booleanp object))
+           (not (keywordp object)))))
 
 (defun event-modifiers (event)
   "Return a list of symbols representing the modifier keys in event EVENT.

[1: e18941095a]: * lisp/term/x-win.el (x-menu-bar-open): ...
  2012-08-10 10:47:12 -0400
  
https://git.savannah.gnu.org/cgit/emacs.git/commit/?id=e18941095a56075d6eb908a65aafcd1697fea2ae

Thanks,

-- 
Basil

In GNU Emacs 27.0.50 (build 9, x86_64-pc-linux-gnu, X toolkit, Xaw3d scroll 
bars)
 of 2019-04-11 built on thunk
Repository revision: 0627a8d7bc6ffa29d7a503fd36e760778ecb9fa1
Repository branch: master
Windowing system distributor 'The X.Org Foundation', version 11.0.12003000
System Description: Debian GNU/Linux buster/sid