From 4db6fa83605de5f9a994ca1c1d8e28fc762624a5 Mon Sep 17 00:00:00 2001
From: Moonchild <moonchild@palemoon.org>
Date: Wed, 21 Dec 2022 18:53:25 +0100
Subject: [PATCH] Issue #1279 - Implement regular expressions lookbehind (v3)

Based on d10e8a5b with the addition of chromium issue 570241.
---
 js/src/irregexp/RegExpEngine.cpp | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/js/src/irregexp/RegExpEngine.cpp b/js/src/irregexp/RegExpEngine.cpp
index 4ed61fd364..42787dc0f0 100644
--- a/js/src/irregexp/RegExpEngine.cpp
+++ b/js/src/irregexp/RegExpEngine.cpp
@@ -4860,6 +4860,9 @@ TextNode::GetQuickCheckDetails(QuickCheckDetails* details,
                                int characters_filled_in,
                                bool not_at_start)
 {
+    // Do not collect any quick check details if the text node reads backward,
+    // since it reads in the opposite direction than we use for quick checks.
+    if (read_backward()) return;
     MOZ_ASSERT(characters_filled_in < details->characters());
     int characters = details->characters();
     int char_mask = MaximumCharacter(compiler->ascii());
@@ -5016,7 +5019,7 @@ QuickCheckDetails::Clear()
 void
 QuickCheckDetails::Advance(int by, bool ascii)
 {
-    if (by >= characters_) {
+    if (by >= characters_ || by < 0) {
         Clear();
         return;
     }