fix(streamdown-code): fall back to plain text for unknown/truncated language identifiers#434
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haydenbleasel merged 5 commits intovercel:mainfrom Mar 10, 2026
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…anguage identifiers When a code block's language identifier is unrecognised by Shiki (e.g. 'rus' from a network-truncated 'rust'), createHighlighter throws a ShikiError. Previously the .catch() block only logged the error and left subscribers hanging, causing a permanent React render-cycle stall. Fix: resolve the language to the 'text' fallback *before* calling getHighlighter() when the identifier is not in the bundledLanguages set. This prevents the exception entirely and ensures the code block renders with plain-text highlighting instead of breaking. Fixes vercel#433
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
`'text'` is a SpecialLanguage in Shiki, not a BundledLanguage, so the type annotations for getHighlighter and getHighlighterCacheKey need to accept both. Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
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Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
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great fix @sleitor appreciate it 🚀 |
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Fixes #433
Problem
When a code block language identifier is network-truncated during streaming (e.g.
rus`` beforerust`` is fully received), Shiki throws:The existing
.catch()handler only logs the error and cleans up subscribers — it doesn't provide a fallbackTokensResult. This leaves the render callback hanging, causing the React component tree to crash (blank screen).Fix
Before calling
getHighlighter(), check whether the resolved language name is in thelanguageNamesset. If it isn't recognized (truncated or unknown), substitute'text'so Shiki renders the block as plain uncolored text while the stream catches up.All existing tests pass.