make-text-button no longer modifies its string arg

* etc/NEWS: Mention this.
* lisp/apropos.el (apropos-library-button):
* lisp/ibuf-ext.el (ibuffer-old-saved-filters-warning):
There’s no longer a need copy make-text-button’s string arg.
* lisp/button.el (make-text-button): Return a copy of a string arg.
Delay making the copy until after error-checking.

1 files changed, 5 insertions, 0 deletions

diff --git a/etc/NEWS b/etc/NEWS
index 27e511047e6..edad5b37d6c 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -476,6 +476,11 @@ are 'eq'.  To compare contents, use 'compare-window-configurations'
 instead.  This change helps fix a bug in 'sxhash-equal', which returned
 incorrect hashes for window configurations and some other objects.
 
+** When its first argument is a string, 'make-text-button' no longer
+modifies the string's text properties; instead, it uses and returns
+a copy of the string.  This helps avoid trouble when strings are
+shared or constants.
+
 ---
 ** The obsolete function 'thread-alive-p' has been removed.