From c9dd942246f7dd991fb3c8fc86b42edcbce4d949 Mon Sep 17 00:00:00 2001
From: Alex Kocharin <alex@kocharin.ru>
Date: Mon, 14 Dec 2020 11:48:08 +0300
Subject: [PATCH] Fix crash when processing strikethrough

close https://github.com/markdown-it/markdown-it/issues/742
---
 CHANGELOG.md                                | 5 +++++
 lib/rules_inline/balance_pairs.js           | 4 ++++
 lib/rules_inline/strikethrough.js           | 4 ++--
 test/fixtures/markdown-it/strikethrough.txt | 7 +++++++
 4 files changed, 18 insertions(+), 2 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index ba066aea6..697e82468 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -6,6 +6,11 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
 
+## [12.0.4] - WIP
+### Fixed
+- Fix crash introduced in `12.0.3` when processing strikethrough (`~~`) and similar plugins, #742.
+
+
 ## [12.0.3] - 2020-12-07
 ### Fixed
 - `[](<foo<bar>)` is no longer a valid link.
diff --git a/lib/rules_inline/balance_pairs.js b/lib/rules_inline/balance_pairs.js
index 4278c8ec8..bd8355085 100644
--- a/lib/rules_inline/balance_pairs.js
+++ b/lib/rules_inline/balance_pairs.js
@@ -29,6 +29,10 @@ function processDelimiters(state, delimiters) {
     minOpenerIdx = openersBottom[closer.marker][closer.length % 3];
 
     openerIdx = closerIdx - closer.jump - 1;
+
+    // avoid crash if `closer.jump` is pointing outside of the array, see #742
+    if (openerIdx < -1) openerIdx = -1;
+
     newMinOpenerIdx = openerIdx;
 
     for (; openerIdx > minOpenerIdx; openerIdx -= opener.jump + 1) {
diff --git a/lib/rules_inline/strikethrough.js b/lib/rules_inline/strikethrough.js
index f3afe4a3d..cb8944fc3 100644
--- a/lib/rules_inline/strikethrough.js
+++ b/lib/rules_inline/strikethrough.js
@@ -32,8 +32,8 @@ module.exports.tokenize = function strikethrough(state, silent) {
 
     state.delimiters.push({
       marker: marker,
-      length: 0, // disable "rule of 3" length checks meant for emphasis
-      jump:   i,
+      length: 0,     // disable "rule of 3" length checks meant for emphasis
+      jump:   i / 2, // for `~~` 1 marker = 2 characters
       token:  state.tokens.length - 1,
       end:    -1,
       open:   scanned.can_open,
diff --git a/test/fixtures/markdown-it/strikethrough.txt b/test/fixtures/markdown-it/strikethrough.txt
index ec2678b9e..3e3b17ba6 100644
--- a/test/fixtures/markdown-it/strikethrough.txt
+++ b/test/fixtures/markdown-it/strikethrough.txt
@@ -127,3 +127,10 @@ Coverage: single tilde
 .
 <p>~a~</p>
 .
+
+Regression test for #742:
+.
+-~~~~;~~~~~~
+.
+<p>-<s><s>;</s></s>~~</p>
+.