From: Mattias Engdegård <mattiase@acm.org>
Date: Sun, 3 May 2020 12:22:50 +0000 (+0200)
Subject: Regexps cannot infloop; fix manual
X-Git-Tag: emacs-27.1.90~191
X-Git-Url: http://git.eshelyaron.com/gitweb/?a=commitdiff_plain;h=8ff5e346febf234b4d9152f636cda478c404948a;p=emacs.git

Regexps cannot infloop; fix manual

* doc/lispref/searching.texi (Regexp Special): Edit erroneous
statements about infinite looping in regexps.

(cherry picked from commit 63268253d21c57d991cba3f3b083d74f154a26fe)
---

diff --git a/doc/lispref/searching.texi b/doc/lispref/searching.texi
index 83c154938cd..c8a12bdd66b 100644
--- a/doc/lispref/searching.texi
+++ b/doc/lispref/searching.texi
@@ -338,16 +338,14 @@ first tries to match all three @samp{a}s; but the rest of the pattern is
 The next alternative is for @samp{a*} to match only two @samp{a}s.  With
 this choice, the rest of the regexp matches successfully.
 
-@strong{Warning:} Nested repetition operators can run for an
-indefinitely long time, if they lead to ambiguous matching.  For
+@strong{Warning:} Nested repetition operators can run for a very
+long time, if they lead to ambiguous matching.  For
 example, trying to match the regular expression @samp{\(x+y*\)*a}
 against the string @samp{xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxz} could
 take hours before it ultimately fails.  Emacs must try each way of
 grouping the @samp{x}s before concluding that none of them can work.
-Even worse, @samp{\(x*\)*} can match the null string in infinitely
-many ways, so it causes an infinite loop.  To avoid these problems,
-check nested repetitions carefully, to make sure that they do not
-cause combinatorial explosions in backtracking.
+In general, avoid expressions that can match the same string in
+multiple ways.
 
 @item @samp{+}
 @cindex @samp{+} in regexp