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Assume::NOTHING doesn't check lifetimes #164246

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#164365
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Assume::NOTHING doesn't check lifetimes#164246
#164365
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C-bugCategory: This is a bug.

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@funsafemath
funsafemath
opened on Oct 13, 2026

I tried this code:

#![feature(transmutability)]

fn func(n: &i32) -> &'static i32 { 
    unsafe{ core::mem::TransmuteFrom::<_, { core::mem::Assume::NOTHING }>::transmute(n) }    
}

I expected to see this happen: code doesn't compile

Instead, this happened: code compiles

The code didn't compile before #161251, so it may be caused by #163946

https://play.rust-lang.org/?version=nightly&mode=debug&edition=2024&gist=b210e3e8210e93103d5780374ce126f9

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rustc 1.101.0-nightly 2026-10-12

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  1. funsafemath
    added
    C-bugCategory: This is a bug.
    on Oct 13, 2026
  2. rustbot
    added
    needs-triageThis issue may need triage. Remove when done. See docs forge.rust-lang.org/release/issue-triaging
    on Oct 13, 2026
  3. JonathanBrouwer
    added a commit that references this issue on Oct 16, 2026

    Rollup merge of rust-lang#164365 - lsunsi:avoid-erased-region-on-tran…

    e23a3da
  4. rust-bors
    closed this as completedin e23a3daon Oct 16, 2026
  5. rustbot
    removed
    needs-triageThis issue may need triage. Remove when done. See docs forge.rust-lang.org/release/issue-triaging
    on Oct 16, 2026
  6. rust-bors
    added a commit that references this issue on Oct 16, 2026

    Unrolled build for #164365 in rollup 164430

    6f523b3
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