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add warning sign to UB examples #72431

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May 23, 2020
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add warning sign to UB examples #72431

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26 changes: 13 additions & 13 deletions src/libcore/mem/maybe_uninit.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -20,9 +20,9 @@ use crate::mem::ManuallyDrop;
/// # #![allow(invalid_value)]
/// use std::mem::{self, MaybeUninit};
///
/// let x: &i32 = unsafe { mem::zeroed() }; // undefined behavior!
/// let x: &i32 = unsafe { mem::zeroed() }; // undefined behavior! ⚠️
/// // The equivalent code with `MaybeUninit<&i32>`:
/// let x: &i32 = unsafe { MaybeUninit::zeroed().assume_init() }; // undefined behavior!
/// let x: &i32 = unsafe { MaybeUninit::zeroed().assume_init() }; // undefined behavior! ⚠️
/// ```
///
/// This is exploited by the compiler for various optimizations, such as eliding
Expand All @@ -35,9 +35,9 @@ use crate::mem::ManuallyDrop;
/// # #![allow(invalid_value)]
/// use std::mem::{self, MaybeUninit};
///
/// let b: bool = unsafe { mem::uninitialized() }; // undefined behavior!
/// let b: bool = unsafe { mem::uninitialized() }; // undefined behavior! ⚠️
/// // The equivalent code with `MaybeUninit<bool>`:
/// let b: bool = unsafe { MaybeUninit::uninit().assume_init() }; // undefined behavior!
/// let b: bool = unsafe { MaybeUninit::uninit().assume_init() }; // undefined behavior! ⚠️
/// ```
///
/// Moreover, uninitialized memory is special in that the compiler knows that
Expand All @@ -49,9 +49,9 @@ use crate::mem::ManuallyDrop;
/// # #![allow(invalid_value)]
/// use std::mem::{self, MaybeUninit};
///
/// let x: i32 = unsafe { mem::uninitialized() }; // undefined behavior!
/// let x: i32 = unsafe { mem::uninitialized() }; // undefined behavior! ⚠️
/// // The equivalent code with `MaybeUninit<i32>`:
/// let x: i32 = unsafe { MaybeUninit::uninit().assume_init() }; // undefined behavior!
/// let x: i32 = unsafe { MaybeUninit::uninit().assume_init() }; // undefined behavior! ⚠️
/// ```
/// (Notice that the rules around uninitialized integers are not finalized yet, but
/// until they are, it is advisable to avoid them.)
Expand Down Expand Up @@ -348,7 +348,7 @@ impl<T> MaybeUninit<T> {
/// let x = MaybeUninit::<(u8, NotZero)>::zeroed();
/// let x = unsafe { x.assume_init() };
/// // Inside a pair, we create a `NotZero` that does not have a valid discriminant.
/// // This is undefined behavior.
/// // This is undefined behavior. ⚠️
/// ```
#[stable(feature = "maybe_uninit", since = "1.36.0")]
#[inline]
Expand Down Expand Up @@ -400,7 +400,7 @@ impl<T> MaybeUninit<T> {
///
/// let x = MaybeUninit::<Vec<u32>>::uninit();
/// let x_vec = unsafe { &*x.as_ptr() };
/// // We have created a reference to an uninitialized vector! This is undefined behavior.
/// // We have created a reference to an uninitialized vector! This is undefined behavior. ⚠️
/// ```
///
/// (Notice that the rules around references to uninitialized data are not finalized yet, but
Expand Down Expand Up @@ -437,7 +437,7 @@ impl<T> MaybeUninit<T> {
///
/// let mut x = MaybeUninit::<Vec<u32>>::uninit();
/// let x_vec = unsafe { &mut *x.as_mut_ptr() };
/// // We have created a reference to an uninitialized vector! This is undefined behavior.
/// // We have created a reference to an uninitialized vector! This is undefined behavior. ⚠️
/// ```
///
/// (Notice that the rules around references to uninitialized data are not finalized yet, but
Expand Down Expand Up @@ -489,7 +489,7 @@ impl<T> MaybeUninit<T> {
///
/// let x = MaybeUninit::<Vec<u32>>::uninit();
/// let x_init = unsafe { x.assume_init() };
/// // `x` had not been initialized yet, so this last line caused undefined behavior.
/// // `x` had not been initialized yet, so this last line caused undefined behavior. ⚠️
/// ```
#[stable(feature = "maybe_uninit", since = "1.36.0")]
#[inline(always)]
Expand Down Expand Up @@ -553,7 +553,7 @@ impl<T> MaybeUninit<T> {
/// x.write(Some(vec![0,1,2]));
/// let x1 = unsafe { x.read() };
/// let x2 = unsafe { x.read() };
/// // We now created two copies of the same vector, leading to a double-free when
/// // We now created two copies of the same vector, leading to a double-free ⚠️ when
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Just to be clear, this ⚠︎ is supposed to be in the middle of the sentence, right?

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I added the warning sign next to the "dangerous noun". But if you think it'd be better to move it to the end of the sentence I can do that, too.

/// // they both get dropped!
/// ```
#[unstable(feature = "maybe_uninit_extra", issue = "63567")]
Expand Down Expand Up @@ -603,7 +603,7 @@ impl<T> MaybeUninit<T> {
///
/// let x = MaybeUninit::<Vec<u32>>::uninit();
/// let x_vec: &Vec<u32> = unsafe { x.get_ref() };
/// // We have created a reference to an uninitialized vector! This is undefined behavior.
/// // We have created a reference to an uninitialized vector! This is undefined behavior. ⚠️
/// ```
///
/// ```rust,no_run
Expand Down Expand Up @@ -686,7 +686,7 @@ impl<T> MaybeUninit<T> {
/// unsafe {
/// *b.get_mut() = true;
/// // We have created a (mutable) reference to an uninitialized `bool`!
/// // This is undefined behavior.
/// // This is undefined behavior. ⚠️
/// }
/// ```
///
Expand Down