Lifetime variance fixes for rustc
#97287 migrates rustc to a `Ty` type that is invariant over its lifetime `'tcx`, so I need to fix a bunch of places that assume that `Ty<'a>` and `Ty<'b>` can be unified by shortening both to some common lifetime.
This is doable, since many lifetimes are already `'tcx`, so all this PR does is be a bit more explicit that elided lifetimes are actually `'tcx`.
Split out from #97287 so the compiler team can review independently.
Document rounding for floating-point primitive operations and string parsing
The docs for floating point don't have much to say at present about either the precision of their results or rounding behaviour.
As I understand it[^1][^2], Rust doesn't support operating with non-default rounding directions, so we need only describe roundTiesToEven.
[^1]: https://github.com/rust-lang/rust/issues/41753#issuecomment-299322887
[^2]: https://github.com/llvm/llvm-project/issues/8472#issuecomment-980888781
This PR makes a start by documenting that for primitive operations and `from_str()`.
Use const initializer for LOCAL_PANIC_COUNT
This reduces the size of the __getit function for LOCAL_PANIC_COUNT and should speed up accesses of LOCAL_PANIC_COUNT a bit.
rustdoc: shrink GenericArgs/PathSegment with boxed slices
This PR also contains a few cleanup bits and pieces, but one of them is a broken intra-doc link, and the other is removing an unused Hash impl. The last commit is the one that matters.
Clarify slice and Vec iteration order
While already being inferable from the doc examples, it wasn't fully specified. This is the only logical way to do a slice iterator, so I think this should be uncontroversial. It also improves the `Vec::into_iter` example to better show the order and that the iterator returns owned values.
Change `NonNull::as_uninit_*` to take self by value (as opposed to reference), matching primitive pointers.
Copied from my comment on [#75402](https://github.com/rust-lang/rust/issues/75402#issuecomment-1100496823):
> I noticed that `as_uninit_*` on pointers take `self` by value (and pointers are `Copy`), e.g. see [`as_uninit_mut`](https://doc.rust-lang.org/core/primitive.pointer.html#method.as_uninit_mut).
>
> However, on `NonNull`, these functions take `self` by reference, e.g. see the function with the same name by for `NonNull`: [`as_uninit_mut`](https://doc.rust-lang.org/std/ptr/struct.NonNull.html#method.as_uninit_mut) takes `self` by mutable reference. Even more inconsistent, [`as_uninit_slice_mut`](https://doc.rust-lang.org/std/ptr/struct.NonNull.html#method.as_uninit_slice_mut) returns a mutable reference, but takes `self` by immutable reference.
>
> I think these methods should take `self` by value for consistency. The returned lifetime is unbounded anyways and not tied to the pointer/NonNull value anyways
I realized the change is trivial (if desired) so here I am creating my first PR. I think it's not a breaking change since (it's on nightly and) `NonNull` is `Copy`; all previous usages of these methods taking `self` by reference should continue to compile. However, it might cause warnings to appear on usages of `NonNull::as_uninit_mut`, which used to require the the `NonNull` variable be declared `mut`, but now it's not necessary.
Make write/print macros eagerly drop temporaries
This PR fixes the 2 regressions in #96434 (`println` and `eprintln`) and changes all the other similar macros (`write`, `writeln`, `print`, `eprint`) to match the old pre-#94868 behavior of `println` and `eprintln`.
argument position | before #94868 | after #94868 | after this PR
--- |:---:|:---:|:---:
`write!($tmp, "…", …)` | 😡 | 😡 | 😺
`write!(…, "…", $tmp)` | 😡 | 😡 | 😺
`writeln!($tmp, "…", …)` | 😡 | 😡 | 😺
`writeln!(…, "…", $tmp)` | 😡 | 😡 | 😺
`print!("…", $tmp)` | 😡 | 😡 | 😺
`println!("…", $tmp)` | 😺 | 😡 | 😺
`eprint!("…", $tmp)` | 😡 | 😡 | 😺
`eprintln!("…", $tmp)` | 😺 | 😡 | 😺
`panic!("…", $tmp)` | 😺 | 😺 | 😺
Example of code that is affected by this change:
```rust
use std::sync::Mutex;
fn main() {
let mutex = Mutex::new(0);
print!("{}", mutex.lock().unwrap()) /* no semicolon */
}
```
You can see several real-world examples like this in the Crater links at the top of #96434. This code failed to compile prior to this PR as follows, but works after this PR.
```console
error[E0597]: `mutex` does not live long enough
--> src/main.rs:5:18
|
5 | print!("{}", mutex.lock().unwrap()) /* no semicolon */
| ^^^^^^^^^^^^---------
| |
| borrowed value does not live long enough
| a temporary with access to the borrow is created here ...
6 | }
| -
| |
| `mutex` dropped here while still borrowed
| ... and the borrow might be used here, when that temporary is dropped and runs the `Drop` code for type `MutexGuard`
```
Stabilize `Ipv6Addr::to_ipv4_mapped`
CC https://github.com/rust-lang/rust/issues/27709 (tracking issue for the `ip` feature which contains more
functions)
The function `Ipv6Addr::to_ipv4` is bad because it also returns an IPv4
address for the IPv6 loopback address `::1`. Stabilize
`Ipv6Addr::to_ipv4_mapped` so we can recommend that function instead.
Move remaining tests with NLL differences to revisions
Based on #97206
I've already filed issues for any important differences that I've spotted: #97252#97253#97256#97267
There is a lot here, but each commit is self-contained as a separate directory. I can split into separate PRs as wanted or needed.
