Inline most of the code paths for conversions with boxed slices
This helps with the specific problem described in #49541, obviously without making any large change to how inlining works in the general case.
Everything involved in the conversions is made `#[inline]`, except for the `<Vec<T>>::into_boxed_slice` entry point which is made `#[inline(always)]` after checking that duplicating the function mentioned in the issue prevented its inlining if I only annotate it with
`#[inline]`.
For the record, that function was:
```rust
pub fn foo() -> Box<[u8]> {
vec![0].into_boxed_slice()
}
```
To help the inliner's job, we also hoist a `self.capacity() != self.len` check in `<Vec<T>>::shrink_to_fit` and mark it as `#[inline]` too.
Some modules were still using the deprecated `allocator` module, use the
`alloc` module instead.
Some modules were using `super` while it's not needed.
Some modules were more or less ordering them, and other not, so the
latter have been modified to match the others.
94d1970bba moved the alloc::allocator
module to core::heap, moving e.g. Alloc and Layout out of the alloc
crate. While alloc::heap reexports them, it's better to use them from
where they really come from.
This helps with the specific problem described in #49541, obviously without
making any large change to how inlining works in the general case.
Everything involved in the conversions is made `#[inline]`, except for the
`<Vec<T>>::into_boxed_slice` entry point which is made `#[inline(always)]`
after checking that duplicating the function mentioned in the issue prevented
its inlining if I only annotate it with `#[inline]`.
For the record, that function was:
```rust
pub fn foo() -> Box<[u8]> {
vec![0].into_boxed_slice()
}
```
To help the inliner's job, we also hoist a `self.capacity() != self.len` check
in `<Vec<T>>::shrink_to_fit` and mark it as `#[inline]` too.
FusedIterator is a marker trait that promises that the implementing
iterator continues to return `None` from `.next()` once it has returned
`None` once (and/or `.next_back()`, if implemented).
The effects of FusedIterator are already widely available through
`.fuse()`, but with stable `FusedIterator`, stable Rust users can
implement this trait for their iterators when appropriate.
Make core::ops::Place an unsafe trait
Consumers of `Place` would reasonably expect that the `pointer` function returns a valid pointer to memory that can actually be written to.
Thew `_raw` prefix is included because the fact that `Box`’s ownership
semantics are "dissolved" or recreated seem more important than the exact
parameter type or return type.
Add Box::leak<'a>(Box<T>) -> &'a mut T where T: 'a
Adds:
```rust
impl<T: ?Sized> Box<T> {
pub fn leak<'a>(b: Box<T>) -> &'a mut T where T: 'a {
unsafe { &mut *Box::into_raw(b) }
}
}
```
which is useful for when you just want to put some stuff on the heap and then have a reference to it for the remainder of the program.
r? @sfackler
cc @durka
