…s_conversion)

Example:
let _x: String = String::from("hello world").into();

It's also significantly easier to read.

Prefer using AES/SHA2 features directly.

This way, we can show the plus and minus buttons on screens, while voice
control will read off actual words "Collapse" and "Expand" instead of reading
"open brace minus close brace" and "open brace plus close brace".

Part of rust-lang#87059

…f start

…lnay

Add `core::stream::from_iter`

_Tracking issue: https://github.com/rust-lang/rust/issues/81798_

This_ PR implements `std::stream::from_iter`, as outlined in the _"Converting an Iterator to a Stream"_ section of the [Stream RFC](https://github.com/nellshamrell/rfcs/blob/add-async-stream-rfc/text/0000-async-stream.md#converting-an-iterator-to-a-stream). This function enables converting an `Iterator` to a `Stream` by wrapping each item in the iterator with a `Poll::Ready` instance.

r? `@tmandry`

cc/ `@rust-lang/libs` `@rust-lang/wg-async-foundations`

## Example

Being able to convert from an iterator into a stream is useful when refactoring from iterative loops into a more functional adapter-based style. This is fairly common when using more complex `filter` / `map` / `find` chains. In its basic form this conversion looks like this:

**before**
```rust
let mut output = vec![];
for item in my_vec {
    let out = do_io(item).await?;
    output.push(out);
}
```
**after**
```rust
use std::stream;

let output = stream::from_iter(my_vec.iter())
    .map(async |item| do_io(item).await)
    .collect()?;
```

Having a way to convert an `Iterator` to a `Stream` is essential in enabling this flow.

## Implementation Notes

This PR makes use of `unsafe {}` to pin an item. Currently we're having conversations on the libs stream in Zulip how to bring `pin-project` in as a dependency to `core` so we can omit the `unsafe {}`.

This PR also includes a documentation block which references `Stream::next` which currently doesn't exist in the stdlib (originally included in the RFC and PR, but later omitted because of an unresolved issue). `stream::from_iter` can't stabilize before `Stream` does, and there's still a chance we may stabilize `Stream` with a `next` method. So this PR includes documentation referencing that method, which we can remove as part of stabilization if by any chance we don't have `Stream::next`.

## Alternatives Considered

### `impl IntoStream for T: IntoIterator`

An obvious question would be whether we could make it so every iterator can automatically be converted into a stream by calling `into_stream` on it. The answer is: "perhaps, but it could cause type issues". Types like `std::collections` may want to opt to create manual implementations for `IntoStream` and `IntoIter`, which wouldn't be possible if it was implemented through a catch-all trait.

Possibly an alternative such as `impl IntoStream for T: Iterator` could work, but it feels somewhat restrictive. In the end, converting an iterator to a stream is likely to be a bit of a niche case. And even then, **adding a standalone function to convert an `Iterator` into a `Stream` would not be mutually exclusive with a blanket implementation**.

### Naming

The exact name can be debated in the period before stabilization. But I've chosen `stream::from_iter` rather than `stream::iter` because we are _creating a stream from an iterator_ rather than _iterating a stream_. We also expect to add a stream counterpart to `iter::from_fn` later on (blocked on async closures), and having `stream::from_fn` and `stream::from_iter` would feel like a consistent pair. It also has prior art in `async_std::stream::from_iter`.

## Future Directions
### Stream conversions for collections

This is a building block towards implementing `stream/stream_mut/into_stream` methods for `std::collections`, `std::vec`, and more. This would allow even quicker refactorings from using loops to using iterator adapters by omitting the import altogether:

**before**
```rust
use std::stream;

let output = stream::from_iter(my_vec.iter())
    .map(async |item| do_io(item).await)
    .collect()?;
```
**after**
```rust
let output = my_vec
    .stream()
    .map(async |item| do_io(item).await)
    .collect()?;
```

Remove space after negative sign in Literal to_string

Negative proc macro literal tokens used to be printed with a space between the minus sign and the magnitude. That's because `impl ToString for Literal` used to convert the Literal into a TokenStream, which splits the minus sign into a separate Punct token.

```rust
Literal::isize_unsuffixed(-10).to_string()  // "- 10"
```

This PR updates the ToString impl to directly use `rustc_ast::token::Lit`'s ToString, which matches the way Rust negative numbers are idiomatically written without a space.

```rust
Literal::isize_unsuffixed(-10).to_string()  // "-10"
```

…brace, r=notriddle

Rustdoc accessibility: use an icon for the [-]/[+] controls

This is a reopening of rust-lang#87207 with improvement for the way of generating the `background-image` CSS property.

I quote from the original PR:

> This way, we can show the plus and minus buttons on screens, while voice
> control will read off actual words "Collapse" and "Expand" instead of reading
> "open brace minus close brace" and "open brace plus close brace".

Part of rust-lang#87059

r? ``@notriddle``

don't use .into() to convert types to identical types (clippy::useless_conversion)

Example:
let _x: String = String::from("hello world").into();

Use .contains instead of manual reimplementation.

It's also significantly easier to read.

…=Amanieu

Remove the aarch64 `crypto` target_feature

The subfeatures `aes` or `sha2` should be used instead.

This can't yet be done for ARM targets as some LLVM intrinsics still require `crypto`.

Also update the runtime feature detection tests in `library/std` to mirror the updates in `stdarch`. This also helps rust-lang#86941

r? ``@Amanieu``

Update cargo

11 commits in d21c22870e58499d6c31f1bef3bf1255eb021666..cc17afbb0067b1f57d8882640f63b2168d5b7624
2021-07-26 20:23:21 +0000 to 2021-08-02 20:28:08 +0000
- Stabilize the rust-version field (rust-lang/cargo#9732)
- Remove nbsp characters. (rust-lang/cargo#9751)
- Update unstable documentation TOC. (rust-lang/cargo#9750)
- Some minor updates for package/publish package selection. (rust-lang/cargo#9749)
- Bump to 0.57.0, update changelog (rust-lang/cargo#9748)
- Stabilize `[env]` sections (rust-lang/cargo#9411)
- doc: Clarify [doc].browser docs, document PathAndArgs better (rust-lang/cargo#9747)
- Bump cargo-util version. (rust-lang/cargo#9745)
- Make clippy happy (rust-lang/cargo#9736)
- Fix typo in features doc (rust-lang/cargo#9737)
- doc test supports silent output (rust-lang/cargo#9730)

…Artichaut

Test dropping union fields more

Now that rust-lang#87403 is merged, a few more tests can be added for reads/writes to dropping union fields.

r? ``@LeSeulArtichaut``