bug#40859: Clicking the wrap-prefix string inside a button causes an error

["Clément Pit-Claudel" <cpitclaudel@gmail.com>]

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On 26/04/2020 12.44, Clément Pit-Claudel wrote:
> On 26/04/2020 09.43, Eli Zaretskii wrote:
>>> From: Clément Pit-Claudel <cpitclaudel@gmail.com>
>>> Date: Sat, 25 Apr 2020 23:40:38 -0400
>>>
>>> The following snippet inserts a button with a long label and a wrap-prefix.  Clicking the prefix causes an error, whose backtrace is shown below.
>>
>> Isn't that a cockpit error?
> 
> Here's a tentative patch, but I can't claim to understand the button.el code well :/

A slightly revised version.


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From fd57a05b6598de77dbf9a7ba66a15dc1cd9568a2 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Cl=C3=A9ment=20Pit-Claudel?= <clement.pitclaudel@live.com>
Date: Sun, 26 Apr 2020 12:41:42 -0400
Subject: [PATCH] Only treat display strings as buttons if they have a 'button
 property

* lisp/button.el (push-button): Use posn-point instead of posn-string
if the string doesn't have a 'button property (Bug#40859).
---
 lisp/button.el | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/lisp/button.el b/lisp/button.el
index b3afc4eca2..3a6a6de774 100644
--- a/lisp/button.el
+++ b/lisp/button.el
@@ -469,10 +469,12 @@ push-button
       ;; POS is a mouse event; switch to the proper window/buffer
       (let ((posn (event-start pos)))
 	(with-current-buffer (window-buffer (posn-window posn))
-	  (if (posn-string posn)
-	      ;; mode-line, header-line, or display string event.
-	      (button-activate (posn-string posn) t)
-	    (push-button (posn-point posn) t))))
+          (let* ((str (posn-string posn))
+                 (str-button (and str (get-text-property (cdr str) 'button (car str)))))
+	    (if str-button
+	        ;; mode-line, header-line, or display string event.
+	        (button-activate str t)
+	      (push-button (posn-point posn) t)))))
     ;; POS is just normal position
     (let ((button (button-at (or pos (point)))))
       (when button
-- 
2.17.1