Rollup merge of #57045 - RalfJung:kill-more-uninit, r=SimonSapin

Kill remaining uses of mem::uninitialized in libcore, liballoc

Kill remaining uses of mem::uninitialized in libcore and liballoc, and enable a lint that will warn when uses are added again in the future.

To avoid casting raw pointers around (which is always very dangerous because it is not typechecked at all -- it doesn't even get the "same size" sanity check that `transmute` gets), I also added two new functions to `MaybeUninit`:

```rust
    /// Get a pointer to the first contained values.
    pub fn first_ptr(this: &[MaybeUninit<T>]) -> *const T {
        this as *const [MaybeUninit<T>] as *const T
    }

    /// Get a mutable pointer to the first contained values.
    pub fn first_mut_ptr(this: &mut [MaybeUninit<T>]) -> *mut T {
        this as *mut [MaybeUninit<T>] as *mut T
    }
```

I changed some of the existing code to use array-of-`MaybeUninit` instead of `MaybeUninit`-of-array, successfully removing raw pointer casts there as well.

0 files changed, 0 insertions, 0 deletions