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Clarify str::from_utf8_unchecked's invariants #95895

Merged
merged 1 commit into from
Apr 12, 2022
Merged

Clarify str::from_utf8_unchecked's invariants #95895

merged 1 commit into from
Apr 12, 2022

Commits on Apr 10, 2022

  1. Clarify str::from_utf8_unchecked's invariants 

    Specifically, make it clear that it is immediately UB to pass ill-formed UTF-8 into the function. The previous wording left space to interpret that the UB only occurred when calling another function, which "assumes that `&str`s are valid UTF-8."

This does not change whether str being UTF-8 is a safety or a validity invariant. (As per previous discussion, it is a safety invariant, not a validity invariant.) It just makes it clear that valid UTF-8 is a precondition of str::from_utf8_unchecked, and that emitting an Abstract Machine fault (e.g. UB or a sanitizer error) on invalid UTF-8 is a valid thing to do.

If user code wants to create an unsafe `&str` pointing to ill-formed UTF-8, it must be done via transmutes. Also, just, don't.
    @CAD97
    CAD97 authored Apr 10, 2022
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