documenation -> documentation

As per the `FIXME` comment, it's an abstraction that makes the code
harder to read.

It was duplicated from the method above.

Because there is also a `MaybeTransmutableQuery<Dfa<...>, C>` impl, and
we don't need both.

It appears identically as a closure in two functions.

Also change its return type from `bool` to `Option<()>` so it can be
used with `?`.

Also sort them.

Co-authored-by: Josh Triplett <josh@joshtriplett.org>

LLVM still has trouble re-using discriminants sometimes when rebuilding a two-variant enum, so when we have the correct variant already built, just use it.

That's simpler in LLVM *and* in MIR, so might as well: <https://rust.godbolt.org/z/KhdE8eToW>

Attempt to describe the intent behind the `From` trait further

Inspired by the <https://internals.rust-lang.org/t/allow-use-as-and-try-as-for-from-and-tryfrom-traits/19240/26?u=scottmcm> thread.

`@rustbot` label +T-libs-api

add some docs to hooks/mod.rs

r? `@oli-obk`

Fix typo in attrs.rs

documenation -> documentation

…-obk

`rustc_transmute` cleanups

Just some things I found while poking around this code.

r? `@oli-obk`

…torino

Assorted small cleanups

r? `@spastorino`

Reuse existing `Some`s in `Option::(x)or`

LLVM still has trouble re-using discriminants sometimes when rebuilding a two-variant enum, so when we have the correct variant already built, just use it.

That's shorter in the Rust code, as well as simpler in MIR and the optimized LLVM, so might as well: <https://rust.godbolt.org/z/KhdE8eToW>

Thanks to `@veber-alex` for pointing out this opportunity in rust-lang#101210 (comment)

Minor doc clarification in Once::call_once