This patch adds the `core::stream` submodule and implements `core::stream::Stream` in accordance with RFC2996.

Add feedback from @camelid

…res when feature capture_disjoint_fields is enabled

This is a temporary change only, as we wait to resolve dynamic dispatch issues. The `Stream::next` method and corresponding documentation are expected to be fully restored once we have a path to proceed.

Ref: rust-lang/rfcs#2996 (comment)

update docs

Co-authored-by: Oli Scherer <github35764891676564198441@oli-obk.de>

Previously, the HTML output format was represented by both
`Some(OutputFormat::Html)` and `None` so there's no need to have an
optional. Instead, `OutputFormat::Html` is explicitly the default and we
no longer have a "tri-state enum".

Replacing with equal number of values does not increase the length of the vec.

Reference: https://stackoverflow.com/a/62559271/3990767

This commit makes cfg(version) treat the nightlies
for version 1.n.0 as 1.n.0, even though that nightly
version might not have all stabilizations and features
of the released 1.n.0. This is done for greater
convenience for people who want to test a newly
stabilized feature on nightly.

For users who wish to pin nightlies, this commit adds
a -Z assume-incomplete-release option that they can
enable if there are any issues due to this change.

parentesized -> parenthesized

Before, it could print this error if no toolchain was configured:

```
error: no default toolchain configured
error: backtrace:
error: stack backtrace:
   0: error_chain::backtrace::imp::InternalBacktrace::new
   1: rustup::config::Cfg::toolchain_for_dir
   2: rustup_init::run_rustup_inner
   3: rustup_init::main
   4: std::rt::lang_start::{{closure}}
   5: main
   6: __libc_start_main
   7: _start
```

Previously, `downloading_llvm` would check `self.build` while it was
still an empty string, and think it was always false. This fixes the
check.

This seems right, given that conceptually bools are unsigned, but the
implications of this change may have more action at distance that I'm
not sure how to exhaustively consider.

For instance there are a number of cases where code attaches range
metadata if `scalar.is_bool()` holds. Supposedly it would no longer be
attached to the `repr(i8)` enums? Though I'm not sure why booleans are
being special-cased here in the first place...

Fixes rust-lang#80556

Add `core::stream::Stream`

[[Tracking issue: rust-lang#79024](rust-lang#79024)]

This patch adds the `core::stream` submodule and implements `core::stream::Stream` in accordance with [RFC2996](rust-lang/rfcs#2996). The RFC hasn't been merged yet, but as requested by the libs team in rust-lang/rfcs#2996 (comment) I'm filing this PR to get the ball rolling.

## Documentatation

The docs in this PR have been adapted from [`std::iter`](https://doc.rust-lang.org/std/iter/index.html), [`async_std::stream`](https://docs.rs/async-std/1.7.0/async_std/stream/index.html), and [`futures::stream::Stream`](https://docs.rs/futures/0.3.8/futures/stream/trait.Stream.html). Once this PR lands my plan is to follow this up with PRs to add helper methods such as `stream::repeat` which can be used to document more of the concepts that are currently missing. That will allow us to cover concepts such as "infinite streams" and "laziness" in more depth.

## Feature gate

The feature gate for `Stream` is `stream_trait`. This matches the `#[lang = "future_trait"]` attribute name. The intention is that only the APIs defined in RFC2996 will use this feature gate, with future additions such as `stream::repeat` using their own feature gates. This is so we can ensure a smooth path towards stabilizing the `Stream` trait without needing to stabilize all the APIs in `core::stream` at once. But also don't start expanding the API until _after_ stabilization, as was the case with `std::future`.

__edit:__ the feature gate has been changed to `async_stream` to match the feature gate proposed in the RFC.

## Conclusion

This PR introduces `core::stream::{Stream, Next}` and re-exports it from `std` as `std::stream::{Stream, Next}`. Landing `Stream` in the stdlib has been a mult-year process; and it's incredibly exciting for this to finally happen!

---

r? `````@KodrAus`````
cc/ `````@rust-lang/wg-async-foundations````` `````@rust-lang/libs`````

…=eddyb

Consider Scalar to be a bool only if its unsigned

This seems right, given that conceptually bools are unsigned, but the
implications of this change may have more action at distance that I'm
not sure how to exhaustively consider.

For instance there are a number of cases where code attaches range
metadata if `scalar.is_bool()` holds. Supposedly it would no longer be
attached to the `repr(i8)` enums? Though I'm not sure why booleans are
being special-cased here in the first place...

Fixes rust-lang#80556

cc `@eddyb`

…-ou-se

Stabilize raw ref macros

This stabilizes `raw_ref_macros` (rust-lang#73394), which is possible now that rust-lang#74355 is fixed.

However, as I already said in rust-lang#73394 (comment), I am not particularly happy with the current names of the macros. So I propose we also change them, which means I am proposing to stabilize the following in `core::ptr`:
```rust
pub macro const_addr_of($e:expr) {
    &raw const $e
}

pub macro mut_addr_of($e:expr) {
    &raw mut $e
}
```

The macro name change means we need another round of FCP. Cc `````@rust-lang/libs`````
Fixes rust-lang#73394

… r=m-ou-se

Stabilize `unsigned_abs`

Resolves rust-lang#74913.

This PR stabilizes the `i*::unsigned_abs()` method, which returns the absolute value of an integer _as its unsigned equivalent_. This has the advantage that it does not overflow on `i*::MIN`.

I have gone ahead and used this in a couple locations throughout the repository.

…ional-record-update-syntax-error, r=nikomatsakis

Support FRU pattern with `[feature(capture_disjoint_fields)]`

In case of a functional record update syntax for creating a structure, `ExprUseVisitor` to only detect the precise use of some of the field in the `..x` part of the syntax. However, when we start building MIR, we
1. First, build the place for `x`
2. and then, add precise field projections so that only some parts of `x` end up getting read.

When `capture_disjoint_fields` is enabled, and FRU is used within a closure `x` won't be completely captured, and therefore the first step will fail. This PR updates `mir_build` to create a place builder in the first step and then create place from the builder only after applying the field projection.

Closes rust-lang/project-rfc-2229#32
r? ``````@nikomatsakis``````

Slight simplification of chars().count()

Slight simplification: No need to call len(), we can just count the number of non continuation bytes.

I can't see any reason not to do this, can you?

cfg(version): treat nightlies as complete

This PR makes cfg(version) treat the nightlies
for version 1.n.0 as 1.n.0, even though that nightly
version might not have all stabilizations and features
of the released 1.n.0. This is done for greater
convenience for people who want to test a newly
stabilized feature on nightly, or in other words,
give newly stabilized features as many eyeballs
as possible.

For users who wish to pin nightlies, this commit adds
a -Z assume-incomplete-release option that they can
enable if they run into any issues due to this change.
Implements the suggestion in rust-lang#64796 (comment)

Warn write-only fields

cc `@Boscop's` example in rust-lang#49256.

…nal, r=GuillaumeGomez

rustdoc: Remove unnecessary optional

Previously, the HTML output format was represented by both
`Some(OutputFormat::Html)` and `None` so there's no need to have an
optional. Instead, `OutputFormat::Html` is explicitly the default and we
no longer have a "tri-state enum".

r? `````@GuillaumeGomez`````

Updated Vec::splice documentation

Replacing with equal number of values does not increase the length of the vec.

Reference: https://stackoverflow.com/a/62559271/3990767

…anxiyn

update rustfmt to v1.4.34

Short summary: Various formatting fixes (several const generic related) and introduction of `imports_granularity` config option

Long summary copied from changelog:

#### Changed
- `merge_imports` configuration has been deprecated in favor of the new `imports_granularity` option. Any existing usage of `merge_imports` will be automatically mapped to the corresponding value on `imports_granularity` with a warning message printed to encourage users to update their config files.

#### Added
- New `imports_granularity` option has been added which succeeds `merge_imports`. This new option supports several additional variants which allow users to merge imports at different levels (crate or module), and even flatten imports to have a single use statement per item. ([PR rust-lang/rustfmt#4634](rust-lang/rustfmt#4634), [PR rust-lang/rustfmt#4639](rust-lang/rustfmt#4639))

See the section on the configuration site for more information
https://rust-lang.github.io/rustfmt/?version=v1.4.33&search=#imports_granularity

#### Fixed
- Fix erroneous removal of `const` keyword on const trait impl ([rust-lang/rustfmt#4084](rust-lang/rustfmt#4084))
- Fix incorrect span usage wit const generics in supertraits ([rust-lang/rustfmt#4204](rust-lang/rustfmt#4204))
- Use correct span for const generic params ([rust-lang/rustfmt#4263](rust-lang/rustfmt#4263))
- Correct span on const generics to include type bounds ([rust-lang/rustfmt#4310](rust-lang/rustfmt#4310))
- Idempotence issue on blocks containing only empty statements ([rust-lang/rustfmt#4627](rust-lang/rustfmt#4627) and [rust-lang#3868](rust-lang/rustfmt#3868))
- Fix issue with semicolon placement on required functions that have a trailing comment that ends in a line-style comment before the semicolon ([rust-lang/rustfmt#4646](rust-lang/rustfmt#4646))
- Avoid shared interned cfg_if symbol since rustfmt can re-initialize the rustc_ast globals on multiple inputs ([rust-lang/rustfmt#4656](rust-lang/rustfmt#4656))
- Don't insert trailing comma on (base-less) rest in struct literals within macros ([rust-lang/rustfmt#4675](rust-lang/rustfmt#4675))

…r=sanxiyn

`fn cold_path` doesn't need to be pub

Fixes rust-lang#81429

Note: this PR also fixes a small typo that I found

…c, r=bugadani

Add missing variants in match binding

cc `````@bugadani````` `````@CraftSpider`````
r? `````@camelid`````

Fix typo in pat.rs

parentesized -> parenthesized

…ulacrum

Don't print error output from rustup when detecting default build triple

Before, it could print this error if no toolchain was configured:

```
error: no default toolchain configured
error: backtrace:
error: stack backtrace:
   0: error_chain::backtrace::imp::InternalBacktrace::new
   1: rustup::config::Cfg::toolchain_for_dir
   2: rustup_init::run_rustup_inner
   3: rustup_init::main
   4: std::rt::lang_start::{{closure}}
   5: main
   6: __libc_start_main
   7: _start
```

Don't clone LLVM submodule when download-ci-llvm is set

Previously, `downloading_llvm` would check `self.build` while it was
still an empty string, and think it was always false. This fixes the
check.

This addresses the worst part of rust-lang#76653. There are still some large submodules being downloaded (in particular, `rustc-by-example` is 146 MB, and all the submodules combined are 311 MB), but this is a lot better than the whopping 1.4 GB before.