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Panic on invalid usages of MaybeUninit::uninit().assume_init() #100423

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Panic on invalid usages of MaybeUninit::uninit().assume_init() #100423

wants to merge 1 commit into from

Commits on Feb 22, 2023

  1. Add new CheckMaybeUninit MIR transform 

    This MIR transform inserts the same validity checks from
`mem::{uninitialized,zeroed}` to `MaybeUninit::{uninit,zeroed}().assume_init()`.

We have been panicking in `mem::uninit` on invalid values for quite some
time now, and it has helped to get people off the unsound API and
towards using `MaybeUninit<T>`.

While correct usage of `MaybeUninit<T>` is clearly documented, some
people still use it incorrectly and simply replaced their wrong
`mem::uninit` usage with `MaybeUninit::uninit().assume_init()`. This
is not any more correct than the old version, and we should still emit
panics in these cases. As this can't be done in the library only, we
need this MIR pass to insert the calls.

For now, it only detects direct usages of
`MaybeUninit::uninit().assume_init()` but it could be extended in the
future to do more advanced dataflow analysis.
    @Noratrieb
    Noratrieb committed Feb 22, 2023
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