Usually, references to the interior are only created by the `Deref` and
`DerefMut` impl of the guards `Ref` and `RefMut`. Note that `RefCell`
already has to cope with leaks of such guards which, when it occurs,
effectively makes it impossible to ever acquire a mutable guard or any
guard for `Ref` and `RefMut` respectively. It is already safe to use
this to create a reference to the inner of the ref cell that lives as
long as the reference to the `RefCell` itself, e.g.

```rust
fn leak(r: &RefCell<usize>) -> Option<&usize> {
    let guard = r.try_borrow().ok()?;
    let leaked = Box::leak(Box::new(guard));
    Some(&*leaked)
}
```

The newly added methods allow the same reference conversion without an
indirection over a leaked allocation and composing with both borrow and
try_borrow without additional method combinations.

This re-exports the primitive types from libcore at `core::primitive` to allow
macro authors to have a reliable location to use them from.

…tures

…olnay

Add primitive module to libcore

This re-exports the primitive types from libcore at `core::primitive` to allow
macro authors to have a reliable location to use them from.

Fixes rust-lang#44865

…tolnay

Add methods to 'leak' RefCell borrows as references with the lifetime of the original reference

Usually, references to the interior are only created by the `Deref` and
`DerefMut` impl of the guards `Ref` and `RefMut`. Note that `RefCell`
already has to cope with leaks of such guards which, when it occurs,
effectively makes it impossible to ever acquire a mutable guard or any
guard for `Ref` and `RefMut` respectively. It is already safe to use
this to create a reference to the inner of the ref cell that lives as
long as the reference to the `RefCell` itself, e.g.

```rust
fn leak(r: &RefCell<usize>) -> Option<&usize> {
    let guard = r.try_borrow().ok()?;
    let leaked = Box::leak(Box::new(guard));
    Some(&*leaked)
}
```

The newly added methods allow the same reference conversion without an
indirection over a leaked allocation. It's placed on the `Ref`/`RefMut` to
compose with both borrow and try_borrow directly.

…acrum

debug_assert a few more raw pointer methods

Fixes rust-lang#53871

…crum

Deduplicate identifier printing a bit

rust-lang#67010 introduced a couple more subtly different ways to print an identifier.
This PR attempts to restore the order.

The most basic identifier printing interface is `Formatter`-based now, so `String`s are not allocated unless required.

r? @Mark-Simulacrum

syntax: Remove `Nt(Impl,Trait,Foreign)Item`

Follow-up to rust-lang#69366.
r? @Centril

remove redundant clones and import

…bank

Minor refactoring of statement parsing

Extracted out of rust-lang#69445.

r? @estebank

…, r=Dylan-DPC

Clean up e0370 e0371

r? @Dylan-DPC