Fix crash when processing strikethrough

close https://github.com/markdown-it/markdown-it/issues/742

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.

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) {

lib/rules_inline/strikethrough.js

@@ -33,7 +33,7 @@ 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,
+      jump:   i / 2, // for `~~` 1 marker = 2 characters
       token:  state.tokens.length - 1,
       end:    -1,
       open:   scanned.can_open,

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>
+.