I believe the previous code was calling `ops::Add::add` instead of the
`+` operator to get this behavior.

LinkedList::remove() removes the element at the specified index and returns it.

Signed-off-by: Bijan Tabatabai <bijan311@yahoo.com>

Add LinkedList::remove()

LinkedList::remove() removes the element at the specified index and returns it.

I added this because I think having a remove function would be useful to have, and similar functions are in other containers, like Vec and HashMap.

I'm not sure if adding a feature like this requires an RFC or not, so I'm sorry if this PR is premature.

…albertodt

Stabilize Once::is_completed

Closes rust-lang#54890

This function has been around for some time. I haven't seen anyone raise any objections to it. I've personally found it useful myself. It would be nice to finally stabilize it and

…-obk

Make integer exponentiation methods unstably const

cc rust-lang#53718

This makes the following inherent methods on integer primitives into unstable `const fn`:
- `pow`
- `checked_pow`
- `wrapping_pow`
- `overflowing_pow`
- `saturating_pow`
- `next_power_of_two`
- `checked_next_power_of_two`
- `wrapping_next_power_of_two`

Only two changes were made to the implementation of these methods. First, I had to switch from the `?` operator, which is not yet implemented in a const context, to a `try_opt` macro. Second, `next_power_of_two` was using `ops::Add::add` (see the first commit) to "get overflow checks", so I switched to `#[rustc_inherit_overflow_checks]`. I'm not quite sure why the attribute wasn't used in the first place.

…iser

Fix race condition when allocating source files in SourceMap

This makes allocating address space in the source map an atomic operation. `rustc` does not currently do this in parallel, so this bug can't trigger, but parsing files in parallel could trigger it, and that is something we want to do.

Fixes rust-lang#69261.

r? @wesleywiser

…-DPC

Clean up E0317 explanation

r? @Dylan-DPC