The spans for "trait bound not satisfied" errors in trivial trait bounds referenced the entire item (fn, impl, struct) before.
Now they only reference the obligation itself (`String: Copy`)

Address rust-lang#90869

Co-authored-by: Yuki Okushi <jtitor@2k36.org>

warn on must_use use on async fn's

As referenced in rust-lang#78149

This only works on `async` fn's for now, I can also look into if I can get `Box<dyn Future>` and `impl Future` working at this level (hir)

…ostics, r=estebank

Improve diagnostics when a static lifetime is expected

Makes progress towards rust-lang#90600

The diagnostics here were previously entirely removed due to giving a misleading suggestion but if we instead provide an informative label in that same location it should better help the user understand the situation.

I included the example from the issue as it demonstrates an area where the diagnostics are still lacking.
Happy to remove that if its just adding noise atm.

Permit const panics in stable const contexts in stdlib

Without this change, it is not possible to use `panic!` and similar (including `assert!`) in stable const contexts inside of stdlib. See rust-lang#89542 for a real-world case that currently fails for this reason. This does _not_ affect any user code.

For example, this snippet currently fails to compile:

```rust
#[stable(feature = "foo", since = "1.0.0")]
#[rustc_const_stable(feature = "foo", since = "1.0.0")]
const fn foo() {
    assert!(false);
    assert!(false, "foo");
}
```

With the addition of `#[rustc_const_unstable]` to `core::panicking::panic`, the error no longer occurs. This snippet has been added verbatim in this PR as a UI test.

To avoid needing to add `#![feature(core_panic)]` to libcore, the two instances of direct calls to `core::panicking::panic` have been switched to use the `panic!` macro.

I am requesting prioritization because this is holding up other stabilizations such as rust-lang#89542 (which is otherwise ready to merge and succeeds with this change)

…shtriplett

Add Vec::retain_mut

This is to continue the discussion started in rust-lang#83218.

Original comment was:

> Take 2 of rust-lang#34265, since I needed this today.

The reason I think why we should add `retain_mut` is for coherency and for discoverability. For example we have `chunks` and `chunks_mut` or `get` and `get_mut` or `iter` and `iter_mut`, etc. When looking for mutable `retain`, I would expect `retain_mut` to exist. It took me a while to find out about `drain_filter`. So even if it provides an API close to `drain_filter`, just for the discoverability, I think it's worth it.

cc ``````@m-ou-se`````` ``````@jonas-schievink`````` ``````@Mark-Simulacrum``````

Print escaped string if char literal has multiple characters, but only one printable character

Fixes rust-lang#90857

I'm not sure about the error message here, it could get rather long and *maybe* using the names of characters would be better? That wouldn't help the length any, though.

…und, r=estebank

Fix span for non-satisfied trivial trait bounds

The spans for "trait bound not satisfied" errors in trivial trait bounds referenced the entire item (fn, impl, struct) before.
Now they only reference the obligation itself (`String: Copy`)

Address rust-lang#90869

Remove workaround for the forward progress handling in LLVM

this workaround was only needed for LLVM < 12 and the minimum LLVM version was updated to 12 in rust-lang#90175

…estebank

Improve ManuallyDrop suggestion

closes rust-lang#90585
* Fixes the recommended change to use ManuallyDrop as per the issue
* Changes the note to a help
* improves the span so it only points at the type.