Guard against custom rule not incrementing pos

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).
 
 
+## [13.1.0] - WIP
+### Changed
+- Throw an error if 3rd party plugin doesn't increment `line` or `pos` counters
+  (previously, markdown-it would likely go into infinite loop instead), #847.
+
 ## [13.0.1] - 2022-05-03
 ### Fixed
 - Bumped `linkify-it` to 4.0.1. That should fix some hangs, caused by wrong
@@ -616,6 +621,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Renamed presets folder (configs -> presets).
 
 
+[13.1.0]: https://github.com/markdown-it/markdown-it/compare/13.0.1...13.1.0
 [13.0.1]: https://github.com/markdown-it/markdown-it/compare/13.0.0...13.0.1
 [13.0.0]: https://github.com/markdown-it/markdown-it/compare/12.3.2...13.0.0
 [12.3.2]: https://github.com/markdown-it/markdown-it/compare/12.3.1...12.3.2

lib/parser_block.js

@@ -46,7 +46,7 @@ function ParserBlock() {
 // Generate tokens for input range
 //
 ParserBlock.prototype.tokenize = function (state, startLine, endLine) {
-  var ok, i,
+  var ok, i, prevLine,
       rules = this.ruler.getRules(''),
       len = rules.length,
       line = startLine,
@@ -74,12 +74,21 @@ ParserBlock.prototype.tokenize = function (state, startLine, endLine) {
     // - update `state.line`
     // - update `state.tokens`
     // - return true
+    prevLine = state.line;
 
     for (i = 0; i < len; i++) {
       ok = rules[i](state, line, endLine, false);
-      if (ok) { break; }
+      if (ok) {
+        if (prevLine >= state.line) {
+          throw new Error("block rule didn't increment state.line");
+        }
+        break;
+      }
     }
 
+    // this can only happen if user disables paragraph rule
+    if (!ok) throw new Error('none of the block rules matched');
+
     // set state.tight if we had an empty line before current tag
     // i.e. latest empty line should not count
     state.tight = !hasEmptyLines;

lib/parser_inline.js

@@ -99,7 +99,10 @@ ParserInline.prototype.skipToken = function (state) {
       ok = rules[i](state, true);
       state.level--;
 
-      if (ok) { break; }
+      if (ok) {
+        if (pos >= state.pos) { throw new Error("inline rule didn't increment state.pos"); }
+        break;
+      }
     }
   } else {
     // Too much nesting, just skip until the end of the paragraph.
@@ -124,7 +127,7 @@ ParserInline.prototype.skipToken = function (state) {
 // Generate tokens for input range
 //
 ParserInline.prototype.tokenize = function (state) {
-  var ok, i,
+  var ok, i, prevPos,
       rules = this.ruler.getRules(''),
       len = rules.length,
       end = state.posMax,
@@ -137,11 +140,15 @@ ParserInline.prototype.tokenize = function (state) {
     // - update `state.pos`
     // - update `state.tokens`
     // - return true
+    prevPos = state.pos;
 
     if (state.level < maxNesting) {
       for (i = 0; i < len; i++) {
         ok = rules[i](state, false);
-        if (ok) { break; }
+        if (ok) {
+          if (prevPos >= state.pos) { throw new Error("inline rule didn't increment state.pos"); }
+          break;
+        }
       }
     }
 

test/misc.js

@@ -169,6 +169,45 @@ describe('API', function () {
 });
 
 
+describe('Plugins', function () {
+
+  it('should not loop infinitely if all rules are disabled', function () {
+    var md = markdownit();
+
+    md.inline.ruler.enableOnly([]);
+    md.inline.ruler2.enableOnly([]);
+    md.block.ruler.enableOnly([]);
+
+    assert.throws(() => md.render(' - *foo*\n - `bar`'), /none of the block rules matched/);
+  });
+
+  it('should not loop infinitely if inline rule doesn\'t increment pos', function () {
+    var md = markdownit();
+
+    md.inline.ruler.after('text', 'custom', function (state/*, silent*/) {
+      if (state.src.charCodeAt(state.pos) !== 0x40/* @ */) return false;
+      return true;
+    });
+
+    assert.throws(() => md.render('foo@bar'), /inline rule didn't increment state.pos/);
+    assert.throws(() => md.render('[foo@bar]()'), /inline rule didn't increment state.pos/);
+  });
+
+  it('should not loop infinitely if block rule doesn\'t increment pos', function () {
+    var md = markdownit();
+
+    md.block.ruler.before('paragraph', 'custom', function (state, startLine/*, endLine, silent*/) {
+      var pos = state.bMarks[startLine] + state.tShift[startLine];
+      if (state.src.charCodeAt(pos) !== 0x40/* @ */) return false;
+      return true;
+    }, { alt: [ 'paragraph' ] });
+
+    assert.throws(() => md.render('foo\n@bar\nbaz'), /block rule didn't increment state.line/);
+    assert.throws(() => md.render('foo\n\n@bar\n\nbaz'), /block rule didn't increment state.line/);
+  });
+});
+
+
 describe('Misc', function () {
 
   it('Should replace NULL characters', function () {