Filter obtrusive events in help-read-key-sequence.

This fixes most of bug #29272.

* lisp/help.el (help-read-key-sequence): After a mouse event, pause for 0.01s,
discarding any events (such as <help-echo>) received in this time, before
polling for the double-click (etc.) events which may follow.  This fixes the
infinite loop which occurred whwn <help-echo> events triggered a sit-for
whilst handling menu events.

1 files changed, 11 insertions, 5 deletions

diff --git a/lisp/help.el b/lisp/help.el
index fbb9fc8cbe6..212e3679dad 100644
--- a/lisp/help.el
+++ b/lisp/help.el
@@ -728,11 +728,17 @@ with `mouse-movement' events."
 Describe the following key, mouse click, or menu item: "))
                 ((and (pred vectorp) (let `(,key0 . ,_) (aref key 0))
                       (guard (symbolp key0)) (let keyname (symbol-name key0)))
-                 (if no-mouse-movement
-                     (string-match "mouse-movement" keyname)
-                   (and (string-match "\\(mouse\\|down\\|click\\|drag\\)"
-                                      keyname)
-                        (not (sit-for (/ double-click-time 1000.0) t)))))))
+                 (or
+                  (and no-mouse-movement
+                       (string-match "mouse-movement" keyname))
+                  (and (string-match "\\(mouse\\|down\\|click\\|drag\\)"
+                                     keyname)
+                       (progn
+                         ;; Discard events (e.g. <help-echo>) which might
+                         ;; spuriously trigger the `sit-for'.
+                         (sleep-for 0.01)
+                         (while (read-event nil nil 0.01))
+                         (not (sit-for (/ double-click-time 1000.0) t))))))))
           (list
            key
            ;; If KEY is a down-event, read and include the