Markdown: double underscores inside emphasis can truncate the span
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Description
Prettier 3.9.6
--parser markdown
Input:
*a__b__c*
Output:
_a__b_\_c_
Expected output:
*a__b__c*
Why?
The entire identifier should remain emphasized; equivalent delimiter choices are fine. CommonMark 0.31.2 renders the input as <em>a__b__c</em>, but the output as <em>a__b</em>_c_. The emphasized key__x__value sentence also fails; the corresponding key__xy__value control preserves meaning.
Also reproduced on development commit 891accaaab6dab0fbb5eba6748fbb1f5ac4809b5. Related #3834 concerns word-leading underscores inside strong text; this example uses intraword underscores inside emphasis and introduces an escape despite a correct input AST.
GPT-6 Astra assisted; I manually reviewed this report.
Contributor guide
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Research direction
Reproduce the report with the supplied markdown input and the Markdown parser, then trace the emphasis delimiter handling that turns *a__b__c* into a truncated span with an escape. Done means the formatter preserves the input's meaning and produces the expected equivalent output, with regression coverage for this case and the mentioned key__x__value example.
Written by the indexing model from the issue text.
Assessment
- Tech stack
- javascript, markdown
- Domain
- tooling
- Issue type
- Bug
- Difficulty
- 3/5
- Estimated time
- 1-2 days
- Activity status
- Active
- Clarity
- Mostly clear
- Newbie friendliness
- 68/100