In general, the I/O interface of hermit-abi is more POSIX-like
interface. Consequently, platform abstraction layer for HermitOS
has slightly adjusted and some inaccuracies remove.

`std::alloc` said that the default allocator is unspecified for all
crrate types except `cdylib` and `staticlib`. Adjust
`std::alloc::System` documentation to say the same.

Fixes rust-lang#125870.

Added the following (all unstable):

* Defaulted type pararameter `A: Allocator`.
* `UniqueRc::new_in()`.
* `T:  ?Sized` where possible.
* `impl CoerceUnsized for UniqueRc`.
* Drive-by doc polish: links and periods at the end of sentences.

These changes are motivated by supporting the implementation of unsized
`Rc::make_mut()` (PR rust-lang#116113), but are also intended to be obvious
generalizations of `UniqueRc` to support the things `Rc` does.

We don't build LLVM when using the precompiled version from the CI builder.

Signed-off-by: onur-ozkan <[email protected]>

This module contains tests not just of parse (FromStr) but also
to_string (Display) for literals.

Improve escaping of byte, byte str, and c str proc-macro literals

This PR changes the behavior of `proc_macro::Literal::byte_character` (rust-lang#115268), `byte_string`, and `c_string` (rust-lang#119750) to improve their choice of escape sequences. 3 categories of changes are made:

1. Never use `\x00`. Always prefer `\0`, which is supported in all the same places.

2. Never escape `\'` inside double quotes and `\"` inside single quotes.

3. Never use `\x` for valid UTF-8 in literals that permit `\u`.

The second commit adds tests covering these cases, asserting the **old** behavior.

The third commit implements the behavior change and simultaneously updates the tests to assert the **new** behavior.

…d-on-generics-2, r=fee1-dead

`E0229`: Suggest Moving Type Constraints to Type Parameter Declaration

Fixes rust-lang#113073

This PR suggests  `impl<T: Bound> Trait<T> for Foo` when finding `impl Trait<T: Bound> for Foo`. Tangentially, it also improves a handful of other error messages.

It accomplishes this in two steps:
1. Check if constrained arguments and parameter names appear in the same order and delay emitting "incorrect number of generic arguments" error because it can be confusing for the programmer to see `0 generic arguments provided` when there are `n` constrained generic arguments.

2. Inside `E0229`, suggest declaring the type parameter right after the `impl` keyword by finding the relevant impl block's span for type parameter declaration. This also handles lifetime declarations correctly.

Also, the multi part suggestion doesn't use the fluent error mechanism because translating all the errors to fluent style feels outside the scope of this PR. I will handle it in a separate PR if this gets approved.

add HermitOS support for vectored read/write operations

In general, the I/O interface of hermit-abi is revised and now a more POSIX-like interface. Consequently, platform abstraction layer for HermitOS has slightly adjusted and some inaccuracies remove.

Hermit is a tier 3 platform and this PR changes only files, wich are related to the tier 3 platform.

…r=jhpratt

Unify guarantees about the default allocator

`std::alloc` said that the default allocator is unspecified for all crrate types except `cdylib` and `staticlib`. Adjust `std::alloc::System` documentation to say the same.

Fixes rust-lang#125870.

`UniqueRc`: support allocators and `T: ?Sized`.

Added the following (all unstable):

* Defaulted type pararameter `A: Allocator`.
* `UniqueRc::new_in()`.
* `T:  ?Sized` where possible.
* `impl CoerceUnsized for UniqueRc`.

These changes are motivated by supporting the implementation of unsized `Rc::make_mut()` (PR rust-lang#116113), but are also intended to be obvious generalizations of `UniqueRc` to support the things `Rc` does.

r? ``````@the8472``````

extend the check for LLVM build

We don't build LLVM when using the precompiled version from the CI builder.

Closes rust-lang#126156

const validation: fix ICE on dangling ZST reference

Fixes rust-lang#126393
I'm not super happy with this fix but I can't think of a better one.

r? `@oli-obk`