Fix corner case in query-replace-regexp undo

This commit fixes Bug#31492.
* lisp/replace.el (replace-match-maybe-edit): Preserve match data.

* test/lisp/replace-tests.el (query-replace-undo-bug31492): Add test.

2 files changed, 24 insertions, 0 deletions

diff --git a/lisp/replace.el b/lisp/replace.el
index 3503b656d9c..a17dd19b0d3 100644
--- a/lisp/replace.el
+++ b/lisp/replace.el
@@ -2214,6 +2214,10 @@ passed in.  If LITERAL is set, no checking is done, anyway."
             noedit nil)))
   (set-match-data match-data)
   (replace-match newtext fixedcase literal)
+  ;; `query-replace' undo feature needs the beginning of the match position,
+  ;; but `replace-match' may change it, for instance, with a regexp like "^".
+  ;; Ensure that this function preserves the match data (Bug#31492).
+  (set-match-data match-data)
   ;; `replace-match' leaves point at the end of the replacement text,
   ;; so move point to the beginning when replacing backward.
   (when backward (goto-char (nth 0 match-data)))
diff --git a/test/lisp/replace-tests.el b/test/lisp/replace-tests.el
index 40a1a31cf7c..40ee838e679 100644
--- a/test/lisp/replace-tests.el
+++ b/test/lisp/replace-tests.el
@@ -399,5 +399,25 @@ Each element has the format:
       ;; After undo text must be the same.
       (should (string= text (buffer-string))))))
 
+(ert-deftest query-replace-undo-bug31492 ()
+  "Test for https://debbugs.gnu.org/31492 ."
+  (let ((text "a\nb\nc\n")
+        (count 0)
+        (inhibit-message t))
+    (with-temp-buffer
+      (insert text)
+      (goto-char 1)
+      (cl-letf (((symbol-function 'read-event)
+                 (lambda (&rest args)
+                   (cl-incf count)
+                   (let ((val (pcase count
+                                ((or 1 2) ?\s) ; replace current and go next
+                                (3 ?U) ; undo-all
+                                (_ ?q)))) ; exit
+                     val))))
+        (perform-replace "^\\|\b\\|$" "foo" t t nil))
+      ;; After undo text must be the same.
+      (should (string= text (buffer-string))))))
+
 
 ;;; replace-tests.el ends here