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emacs-28 0771d89: * etc/PROBLEMS: Mention problems with regexp matcher.
From: |
Stefan Kangas |
Subject: |
emacs-28 0771d89: * etc/PROBLEMS: Mention problems with regexp matcher. (Bug#18577) |
Date: |
Sun, 24 Oct 2021 17:57:34 -0400 (EDT) |
branch: emacs-28
commit 0771d8939adaacf0b9b41150be9c53e6b9519b04
Author: Stefan Kangas <stefan@marxist.se>
Commit: Stefan Kangas <stefan@marxist.se>
* etc/PROBLEMS: Mention problems with regexp matcher. (Bug#18577)
---
etc/PROBLEMS | 12 ++++++++++++
1 file changed, 12 insertions(+)
diff --git a/etc/PROBLEMS b/etc/PROBLEMS
index ede83a6..daff102 100644
--- a/etc/PROBLEMS
+++ b/etc/PROBLEMS
@@ -742,6 +742,18 @@ completed" message that tls.el relies upon, causing
affected Emacs
functions to hang. To work around the problem, use older or newer
versions of gnutls-cli, or use Emacs's built-in gnutls support.
+*** Stack overflow in regexp matcher.
+Due to fundamental limitations in the way Emacs' regular expression
+engine is designed, you might run into combinatorial explosions in
+backtracking with certain regexps.
+
+Avoid "\(...\(...\)*...\)*" and "\(...\)*\(...\)*". Look for a way to
+anchor your regular expression, to avoid matching the null string in
+infinite ways. The latter is what creates backtrack points, and
+eventual overflow in practice.
+
+(Also prefer "\(?:...\)" to "\(...\)" unless you need the latter.)
+
* Runtime problems related to font handling
** Characters are displayed as empty boxes or with wrong font under X.
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