Argument type for mutable with_metadata_of (#75091)

The method takes two pointer arguments: one `self` supplying the pointer
value, and a second pointer supplying the metadata.

The new parameter type more clearly reflects the actual requirements.
The provenance of the metadata parameter is disregarded completely.
Using a mutable pointer in the call site can be coerced to a const
pointer while the reverse is not true.

An example of the current use:

```rust
// Manually taking an unsized object from a `ManuallyDrop` into another allocation.
let val: &core::mem::ManuallyDrop<T> = …;

let ptr = val as *const _ as *mut T;
let ptr = uninit.as_ptr().with_metadata_of(ptr);
```

This could then instead be simplified to:

```rust
// Manually taking an unsized object from a `ManuallyDrop` into another allocation.
let val: &core::mem::ManuallyDrop<T> = …;

let ptr = uninit.as_ptr().with_metadata_of(&**val);
```

0 files changed, 0 insertions, 0 deletions