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Mark the trailing unclosed fenced code block's <pre> with data-streaming so custom pre components can defer highlighting until the fence closes. The site's CodeBlock now reads the flag instead of a 180ms settle debounce.
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Deploying streamdown with
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| Preview URL: | https://f562bffc.streamdown-6nu.pages.dev |
| Branch Preview URL: | https://feat-streaming-fence-flag.streamdown-6nu.pages.dev |
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| return inFence ? lang : null; | ||
| }; | ||
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| const FENCE_OPEN_RE = /^[\t >]*(`{3,}|~{3,})/; |
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When a trailing indented code block begins with four or more spaces followed by backticks, such as ```js\n const x = 1, Markdown parses it as an indented <pre>, not a fenced block. This regex nevertheless accepts unlimited leading whitespace, so the block receives data-streaming and consumers may wait indefinitely for a closing fence that does not apply. Restrict fence indentation to the Markdown-supported range rather than accepting arbitrary spaces or tabs.
Useful? React with 👍 / 👎.
| const lastNewline = source.lastIndexOf('\n'); | ||
| if (lastNewline === -1) return true; |
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For Markdown using CR-only line endings, such as `````js\rconst x = 1\r``` ``, the parser recognizes a complete fenced block, but lastIndexOf('\n') returns `-1` and this function unconditionally classifies it as unclosed. The resulting `
` remains marked `data-streaming`, preventing consumers such as the site highlighter from upgrading the completed block; handle `\r` line boundaries as well as `\n`.Useful? React with 👍 / 👎.
Summary
rehypeStreamingFence: marks the trailing unclosed fenced code block's<pre>withdata-streaming, so customprecomponents can skip highlighting / diagram rendering until the fence closes.Streamdown, ahead of user rehype plugins.CodeBlockreads the flag instead of the 180msuseSettleddebounce; also stops briefly showing a stale highlight after a stream restart.Why
Browser trace (production build, ~200 cps, 120-line TS fence): a
precomponent that re-highlights with shiki on every reveal commit spent 880ms in shiki vs 57ms total markdown parse — 43% of main-thread busy time, growing quadratically with fence length. Markdown re-parsing itself stays ~1% of wall time and is not the bottleneck.Notes
Streamdownhas no end-of-stream signal.Test plan
vitest run— 208 passed (13 new cases for the flag)tscfor lib and site