Fix UB: replace unsafe String::from_utf8_unchecked#7781
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Manishearth merged 1 commit intounicode-org:mainfrom Mar 16, 2026
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Fix UB: replace unsafe String::from_utf8_unchecked#7781Manishearth merged 1 commit intounicode-org:mainfrom
Manishearth merged 1 commit intounicode-org:mainfrom
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…rsion A panic in a CustomTransliterator can unwind through Insertable's Drop impl without fully restoring UTF-8 validity, causing into_string() to produce undefined behavior via from_utf8_unchecked. Use checked from_utf8().expect() so this becomes a clean panic instead. Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
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Manishearth
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Good call.
In general for ICU4X I would prefer us to be much more careful about unchecked indexing, it's really not worth it in most cases.
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with checked conversion
A panic in a CustomTransliterator can unwind through Insertable's Drop impl without fully restoring UTF-8 validity, causing into_string() to produce undefined behavior via from_utf8_unchecked. Use checked from_utf8().expect() so this becomes a clean panic instead.
This one seemed correct to me (process: hammer on Claude until it gets a good patch). Maybe there is a better way, but I think this one is ok.
Changelog
icu_experimental/transliterator: Fix UB caused in partially-written unwind states by using checked UTF-8 conversion instead of
from_utf8_unchecked