bug#31492: 26.1; query-replace-regexp undo fails in regexps w/o printable chars

[Tino Calancha]

emacs -Q

< C-M-% \b RET foo RET TAB TAB TAB
U ; undo all replacements
;; Nothing is undid :-(

--8<-----------------------------cut here---------------start------------->8---
commit f1ee02d0c0bef4534c895559eb53b1ac0ecfb752
Author: Tino Calancha <tino.calancha@gmail.com>
Date:   Fri May 18 22:19:18 2018 +0900

    Fix corner case in query-replace-regexp undo
    
    * lisp/replace.el (perform-replace): Handle the case of a regexp
    not having printable characters (Bug#31492).
    
    * test/lisp/replace-tests.el (query-replace-undo-bug31492): Add test.

diff --git a/lisp/replace.el b/lisp/replace.el
index 3503b656d9..526a40d230 100644
--- a/lisp/replace.el
+++ b/lisp/replace.el
@@ -2692,7 +2692,9 @@ perform-replace
                                    (setq real-match-data
                                          (save-excursion
                                            (goto-char (match-beginning 0))
-                                           (looking-at search-string)
+                                           (if (/= (match-beginning 0) 
(match-end 0))
+                                              (looking-at search-string)
+                                            (looking-back search-string (- 
(point) (length search-string))))
                                            (match-data t (nth 2 elt)))
                                          noedit
                                          (replace-match-maybe-edit
diff --git a/test/lisp/replace-tests.el b/test/lisp/replace-tests.el
index 40a1a31cf7..5c0ec2aa1c 100644
--- a/test/lisp/replace-tests.el
+++ b/test/lisp/replace-tests.el
@@ -399,5 +399,25 @@ replace-tests--query-replace-undo
       ;; 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
--8<-----------------------------cut here---------------end--------------->8---

In GNU Emacs 26.1 (build 6, x86_64-pc-linux-gnu, GTK+ Version 3.22.11)
 of 2018-05-18 built on calancha-pc
Repository revision: 73bc6f8693fcbb98b41ee67ab35a4dd8c3940355