Prevent button.el from clearing help-echo strings

In order to fix one of the issues discussed in bug#61413, i.e.
'buttonize' clobbering the help-echo property set by
'icon-string'.

This is a reasonable interpretation of the button.el
docstrings - "if HELP-ECHO, use that as the `help-echo'
property"; conversely, if not HELP-ECHO, then do not do
anything, preserving existing values for that property.

* lisp/button.el (button--properties): Only add a help-echo
property if HELP-ECHO is non-nil.  Add an additional property
for bookkeeping.
(unbuttonize-region): Check for that bookkeeping property
before clearing help-echo.
* test/lisp/button-tests.el (button--preserve-help-echo):
Validate these changes.

1 files changed, 28 insertions, 0 deletions

diff --git a/test/lisp/button-tests.el b/test/lisp/button-tests.el
index 7f6a5bd52cd..b784cf02e28 100644
--- a/test/lisp/button-tests.el
+++ b/test/lisp/button-tests.el
@@ -101,4 +101,32 @@
       (setq button (insert-button "overlay" 'help-echo help))
       (should (equal (button--help-echo button) "overlay: x")))))
 
+(ert-deftest button--preserve-help-echo ()
+  "Ensure buttonizing functions preserve existing `help-echo' properties."
+  ;; buttonize.
+  (let* ((string (propertize "button text" 'help-echo "help text"))
+         (button (buttonize string #'ignore)))
+    (should (equal (get-text-property 0 'help-echo button)
+                   "help text")))
+  ;; buttonize-region.
+  (with-temp-buffer
+    (insert (propertize "button text" 'help-echo "help text"))
+    (buttonize-region (point-min) (point) #'ignore)
+    (should (equal (get-text-property (point-min) 'help-echo)
+                   "help text"))
+    ;; unbuttonize-region should not clear the property either.
+    (unbuttonize-region (point-min) (point))
+    (should (equal (get-text-property (point-min) 'help-echo)
+                   "help text")))
+  ;; unbuttonize-region should still clear properties applied with
+  ;; buttonize.
+  (with-temp-buffer
+    (insert "button text")
+    (buttonize-region (point-min) (point) #'ignore nil "help text")
+    (should (equal (get-text-property (point-min) 'help-echo)
+                   "help text"))
+    (unbuttonize-region (point-min) (point))
+    (should (equal (get-text-property (point-min) 'help-echo)
+                   nil))))
+
 ;;; button-tests.el ends here