Fix emphasis multiple-of-3 rule mis-rendering (e.g. *foo***bar*)#458
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lepture merged 1 commit intoJun 26, 2026
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CommonMark rules 9 and 10 require the multiple-of-3 delimiter test to use the lengths of the original delimiter runs, not the lengths remaining after a run has been partially consumed. mistune mutated _Delimiter.length as it consumed markers and then reused that mutated value in the mod-3 test, so the leftover of a partially consumed run (e.g. the ** left after *a* closes in '*a***a*') could no longer match a later delimiter. Track the original run length on _Delimiter and use it in _can_match_emphasis_delimiters. Fixes cases such as '*a***a*' and '*foo***bar*', which two CommonMark reference implementations (markdown-it-py, commonmark.py) render as <em>a</em>*<em>a</em> and <em>foo</em>*<em>bar</em>. Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Codecov Report✅ All modified and coverable lines are covered by tests. Additional details and impacted files@@ Coverage Diff @@
## main #458 +/- ##
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Coverage 91.01% 91.02%
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Files 34 34
Lines 3395 3398 +3
Branches 670 670
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+ Hits 3090 3093 +3
Misses 184 184
Partials 121 121
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The emphasis "multiple of 3" rule misuses the remaining delimiter run length, so
*foo***bar*renders incorrectly. This is a regression from the new inline engine (commit 5de41fb). Triangulated against markdown-it-py and commonmark.py; 738 tests pass and a differential fuzz drops from 26 mismatches to 0.