bug#44861: 27.1; [PATCH] signal in `replace-regexp-in-string'

["Mattias Engdegård" <mattiase@acm.org>]

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forcemerge 15107 44861
stop

Suggested patch attached. A small test suite for replace-regexp-in-string has already been pushed to master -- very rudimentary, but better than nothing -- and the patch amends it with some new relevant cases that didn't work before.

It is basically your patch but slightly optimised; it turned out that the function call and allocation overhead of the original patch made it a tad too expensive (a pity, because it was very neat). Now performance is about the same as before when the pattern contains no submatches, and slightly above (< 10% slower) with one submatch. It seems worth the correctness.


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From 9bc8dc80be5cee517fa53e6b8f37881d4220f162 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Mattias=20Engdeg=C3=A5rd?= <mattiase@acm.org>
Date: Wed, 25 Nov 2020 15:32:08 +0100
Subject: [PATCH] Fix replace-regexp-in-string substring match data translation

For certain patterns, re-matching the same regexp on the matched
substring does not produce correctly translated match data
(bug#15107 and bug#44861).

Reported by Kevin Ryde and Shigeru Fukaya.

* lisp/subr.el (replace-regexp-in-string): Translate the match data
by explicit manipulation instead of trusting a call to string-match on
the matched string to do the job.
* test/lisp/subr-tests.el (subr-replace-regexp-in-string):
Add test cases.
---
 lisp/subr.el            | 17 ++++++++++++-----
 test/lisp/subr-tests.el |  6 +++++-
 2 files changed, 17 insertions(+), 6 deletions(-)

diff --git a/lisp/subr.el b/lisp/subr.el
index 1fb0f9ab7e..0ee2199933 100644
--- a/lisp/subr.el
+++ b/lisp/subr.el
@@ -4537,7 +4537,7 @@ replace-regexp-in-string
   ;; might be reasonable to do so for long enough STRING.]
   (let ((l (length string))
 	(start (or start 0))
-	matches str mb me)
+	matches str mb me md)
     (save-match-data
       (while (and (< start l) (string-match regexp string start))
 	(setq mb (match-beginning 0)
@@ -4546,10 +4546,17 @@ replace-regexp-in-string
 	(when (= me mb) (setq me (min l (1+ mb))))
 	;; Generate a replacement for the matched substring.
 	;; Operate on only the substring to minimize string consing.
-	;; Set up match data for the substring for replacement;
-	;; presumably this is likely to be faster than munging the
-	;; match data directly in Lisp.
-	(string-match regexp (setq str (substring string mb me)))
+
+        ;; Translate the match data so that it applies to the matched substring.
+        (setq md (match-data nil md t))  ; Reuse list from previous match.
+        (let ((m md))
+          (while m
+            (when (car m)
+              (setcar m (- (car m) mb)))
+            (setq m (cdr m)))
+          (set-match-data md))
+
+        (setq str (substring string mb me))
 	(setq matches
 	      (cons (replace-match (if (stringp rep)
 				       rep
diff --git a/test/lisp/subr-tests.el b/test/lisp/subr-tests.el
index c77be511dc..67f7fc9749 100644
--- a/test/lisp/subr-tests.el
+++ b/test/lisp/subr-tests.el
@@ -545,7 +545,11 @@ subr-replace-regexp-in-string
                             (match-beginning 1) (match-end 1)))
                   "babbcaacabc")
                  "b<abbc,0,4,1,3>a<ac,0,2,1,1><abc,0,3,1,2>"))
-  )
+  ;; anchors (bug#15107, bug#44861)
+  (should (equal (replace-regexp-in-string "a\\B" "b" "a aaaa")
+                 "a bbba"))
+  (should (equal (replace-regexp-in-string "\\`\\|x" "z" "--xx--")
+                 "z--zz--")))
 
 (provide 'subr-tests)
 ;;; subr-tests.el ends here
-- 
2.21.1 (Apple Git-122.3)