#![feature(stmt_expr_attributes)] #![allow(clippy::let_unit_value, invalid_value)] use std::mem::MaybeUninit; union MyOwnMaybeUninit { value: u8, uninit: (), } fn main() { let _: usize = unsafe { MaybeUninit::uninit().assume_init() }; //~^ ERROR: this call for this type may be undefined behavior //~| NOTE: `#[deny(clippy::uninit_assumed_init)]` on by default // This is OK, because ZSTs do not contain data. let _: () = unsafe { MaybeUninit::uninit().assume_init() }; // This is OK, because `MaybeUninit` allows uninitialized data. let _: MaybeUninit<usize> = unsafe { MaybeUninit::uninit().assume_init() }; // This is OK, because all constituent types are uninit-compatible. let _: (MaybeUninit<usize>, MaybeUninit<bool>) = unsafe { MaybeUninit::uninit().assume_init() }; // This is OK, because all constituent types are uninit-compatible. let _: (MaybeUninit<usize>, [MaybeUninit<bool>; 2]) = unsafe { MaybeUninit::uninit().assume_init() }; // This is OK, because our own MaybeUninit is just as fine as the one from core. let _: MyOwnMaybeUninit = unsafe { MaybeUninit::uninit().assume_init() }; // This is OK, because empty arrays don't contain data. let _: [u8; 0] = unsafe { MaybeUninit::uninit().assume_init() }; // Was a false negative. let _: usize = unsafe { MaybeUninit::uninit().assume_init() }; //~^ ERROR: this call for this type may be undefined behavior polymorphic::<()>(); polymorphic_maybe_uninit_array::<10>(); polymorphic_maybe_uninit::<u8>(); fn polymorphic<T>() { // We are conservative around polymorphic types. let _: T = unsafe { MaybeUninit::uninit().assume_init() }; //~^ ERROR: this call for this type may be undefined behavior } fn polymorphic_maybe_uninit_array<const N: usize>() { // While the type is polymorphic, MaybeUninit<u8> is not. let _: [MaybeUninit<u8>; N] = unsafe { MaybeUninit::uninit().assume_init() }; } fn polymorphic_maybe_uninit<T>() { // The entire type is polymorphic, but it's wrapped in a MaybeUninit. let _: MaybeUninit<T> = unsafe { MaybeUninit::uninit().assume_init() }; } }