Vec::push invalidates interior references even when it does not reallocate · Issue #60847 · rust-lang/rust (original) (raw)

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Description

To my knowledge, the following code is intended to be legal:

fn main() { let mut v = Vec::with_capacity(10); v.push(0); let v0 = unsafe { &*(&v[0] as *const _) }; // laundering the lifetime -- we take care that v does not reallocate, so that's okay. v.push(1); let _val = *v0; }

However, Miri currently flags this as UB. The reason is that Vec::push implicitly (through auto-deref) calls deref_mut to create a &mut [T] covering all elements in the vector, which overlaps with our reference v0 in the example code above. Overlapping shared and mutable references are prohibited by Stacked Borrows.