Proposal to add Peekable::peek_mut

A "peekable" iterator has a `peek()`-method which provides an immutable reference to the next item. We currently do not have a method to modify that item, which we could easily add via a `peek_mut()`. See the test for a use-case (alike to my original use case), where a "pristine" iterator is passed on after modifying its state via `peek_mut()`.

If there is interest in this, I can expand on the tests and docs.

Document unsafety in core::slice::memchr

Contributes to #66219

Note sure if that's good enough, especially for the `align_to` call.
The docs only mention transmuting and I don't think that everything related to reference lifetimes and state validity mentioned in the [nomicon](https://doc.rust-lang.org/nomicon/transmutes.html) are relevant here.

driver: Only output ANSI logging if connected to a terminal

Fixes #78435.

See #78435 for more.

Cc `@RalfJung` `@oli-obk`

Update cargo

10 commits in 2af662e22177a839763ac8fb70d245a680b15214..bfca1cd22bf514d5f2b6c1089b0ded0ba7dfaa6e
2020-11-12 19:04:56 +0000 to 2020-11-24 16:33:21 +0000
- Shrink the progress bar, to give more space after it. (rust-lang/cargo#8892)
- Add some comments to the toml code (rust-lang/cargo#8887)
- Start searching git config at new path (rust-lang/cargo#8886)
- Fix documentation for CARGO_PRIMARY_PACKAGE. (rust-lang/cargo#8891)
- Bump to 0.51.0, update changelog (rust-lang/cargo#8894)
- Publish target's "doc" setting when emitting metadata (rust-lang/cargo#8869)
- Relaxes expectation of `cargo test` tests to accept test execution time (rust-lang/cargo#8884)
- Finish implementation of `-Zextra-link-arg`. (rust-lang/cargo#8441)
- Reproducible crate builds (rust-lang/cargo#8864)
- Allow resolver="1" to explicitly use the old resolver behavior. (rust-lang/cargo#8857)

Get rid of doctree::{ExternalCrate, ForeignItem, Trait, Function}

Closes #79314, closes #79331, closes #79332. Follow-up to #79264 and #79312, continues breaking up #78082.

r? `@GuillaumeGomez`

Rollup of 10 pull requests

Successful merges:

 - #76858 (Add exploit mitigations chapter to the rustc book)
 - #79310 (Make `fold_item_recur` non-nullable)
 - #79312 (Get rid of `doctree::Impl`)
 - #79321 (Accept '!' in intra-doc links)
 - #79346 (Allow using `-Z fewer-names=no` to retain value names)
 - #79351 (Fix typo in `keyword` docs for traits)
 - #79354 (BTreeMap: cut out the ceremony around BoxedNode)
 - #79358 (BTreeMap/BTreeSet: make public doc more consistent)
 - #79367 (Allow disabling TrapUnreachable via -Ztrap-unreachable=no)
 - #79374 (Add note to use nightly when using expr in const generics)

Failed merges:

r? `@ghost`
`@rustbot` modify labels: rollup

Add note to use nightly when using expr in const generics

As recommended by `@Icnr` in #73899 and in zulip, I've added a note saying that const expressions can be used in nightly.

```
error: generic parameters may not be used in const operations
  --> $DIR/issue-61935.rs:10:23
   |
 6 |         Self:FooImpl<{N==0}>
   |                       ^ cannot perform const operation using `N`
   |
   = help: const parameters may only be used as standalone arguments, i.e. `N`
   = note: use feature(const_generics) and feature(const_evaluatable_checked) to enable this

error: aborting due to previous error
```

I hope the note is well written 😅

Allow disabling TrapUnreachable via -Ztrap-unreachable=no

Currently this is only possible by defining a custom target, which is quite unwieldy.

This is useful for embedded targets where small code size is desired. For example, on my project (thumbv7em-none-eabi) this yields a 0.6% code size reduction: 132892 bytes -> 132122 bytes (770 bytes down).

BTreeMap/BTreeSet: make public doc more consistent

Tweaks #72876 and #73667 and propagate them to `BTreeSet`.

BTreeMap: cut out the ceremony around BoxedNode

The opposite direction of #79093.

r? ``@Mark-Simulacrum``

Fix typo in `keyword` docs for traits

This PR fixes a small typo in the `keyword_docs.rs` file, describing the differences between the 2015 and 2018 editions of traits.

Allow using `-Z fewer-names=no` to retain value names

Change `-Z fewer-names` into an optional boolean flag and allow using it
to either discard value names when true or retain them when false,
regardless of other settings.

Accept '!' in intra-doc links

This will allow linking to things like `Result<T, !>`.

*See <https://github.com/rust-lang/rust/pull/77832#discussion_r528409079>.*

r? ``@jyn514``

Get rid of `doctree::Impl`

Follow-up to https://github.com/rust-lang/rust/pull/79264, continues breaking up https://github.com/rust-lang/rust/pull/78082. At some point I want to introduce `MaybeInlined`, but I think I'll wait until I need `MaybeInlined::InlinedWithOriginal` because it's not very useful in other situations.

r? ``@GuillaumeGomez``

Make `fold_item_recur` non-nullable

This gets rid of a bunch of `unwrap()`s and makes it a little more clear
what's going on.

Originally I wanted to make `fold_item` non-nullable too, which would
have been a lot nicer to work with, but unfortunately `stripper` does
actually return `None` in some places. I might make a follow-up moving
stripper to be special and not a pass so that passes can be
non-nullable.

Found while working on https://github.com/rust-lang/rust/issues/76998.

Add exploit mitigations chapter to the rustc book

This section documents the exploit mitigations applicable to the Rust compiler when building programs for the Linux operating system on the AMD64 architecture and equivalent. This was done for a project I'm currently working on, and I hope it'll also be helpful to others.

resolve: Do not put macros into `module.unexpanded_invocations` unless necessary

Macro invocations in modules <sup>(*)</sup> need to be tracked because they can produce named items when expanded.
We cannot give definite answer to queries like "does this module declare name `n`?" until all macro calls in that module are expanded.

Previously we marked too many macros as potentially producing named items.
E.g. in this example
```rust
mod m {
    const C: u32 = line!();
}
```
`line!()` cannot emit any items into module `m`, but it was still marked.
This PR fixes that and marks macro calls as "unexpanded in module" only if they can actually emit named items into that module.

Diagnostics in UI test outputs have different order now because this change affects macro expansion order.

<sup>*</sup> Any containers for named items are called modules in resolve (that includes blocks, traits and enums in addition to `mod` items).

Update Clippy

Biweekly Clippy update

r? `@Manishearth`

This section documents the exploit mitigations applicable to the Rust
compiler when building programs for the Linux operating system on the
AMD64 architecture and equivalent.

Add Metadata in std::os::fortanix_sgx::io::FromRawFd

Needed for https://github.com/fortanix/rust-sgx/pull/291

cc `@jethrogb`

Add PartialEq<char> for proc_macro::Punct

`punct.as_char() == '░'` is pervasive when parsing anything involving punct. I think `punct == '░'` is sufficiently unambiguous that it makes sense to provide the impl.

https://github.com/rust-lang/rust/blob/1899c489d4c30b2640d30b77ac04f0a548834d81/library/proc_macro/src/quote.rs#L79
https://github.com/rust-lang/rust/blob/1899c489d4c30b2640d30b77ac04f0a548834d81/library/proc_macro/src/quote.rs#L83
https://github.com/rust-lang/rust/blob/1899c489d4c30b2640d30b77ac04f0a548834d81/src/test/ui/suggestions/auxiliary/issue-61963.rs#L26
https://github.com/rust-lang/rust/blob/1899c489d4c30b2640d30b77ac04f0a548834d81/src/test/ui/proc-macro/auxiliary/three-equals.rs#L23

This is useful for embedded targets where small code size is desired.
For example, on my project (thumbv7em-none-eabi) this yields a 0.6% code size reduction.

Qualify `panic!` as `core::panic!` in non-built-in `core` macros

Fixes #78333.

-----

Otherwise code like this

    #![no_implicit_prelude]

    fn main() {
        ::std::todo!();
        ::std::unimplemented!();
    }

will fail to compile, which is unfortunate and presumably unintended.

This changes many invocations of `panic!` in a `macro_rules!` definition
to invocations of `$crate::panic!`, which makes the invocations hygienic.

Note that this does not make the built-in macro `assert!` hygienic.

* Switch a couple links over to intra-doc links
* Clean up some formatting/typography

Otherwise code like this

    #![no_implicit_prelude]

    fn main() {
        ::std::todo!();
        ::std::unimplemented!();
    }

will fail to compile, which is unfortunate and presumably unintended.

This changes many invocations of `panic!` in a `macro_rules!` definition
to invocations of `$crate::panic!`, which makes the invocations hygienic.

Note that this does not make the built-in macro `assert!` hygienic.

Drop support for all cloudabi targets

`cloudabi` is a tier-3 target, and [it is no longer being maintained upstream][no].

This PR drops supports for cloudabi targets. Those targets are:
* aarch64-unknown-cloudabi
* armv7-unknown-cloudabi
* i686-unknown-cloudabi
* x86_64-unknown-cloudabi

Since this drops supports for a target, I'd like somebody to tag `relnotes` label to this PR.

Some other issues:
* The tidy exception for `cloudabi` crate is still remained because
  * `parking_lot v0.9.0` and `parking_lot v0.10.2` depends on `cloudabi v0.0.3`.
  * `parking_lot v0.11.0` depends on `cloudabi v0.1.0`.

[no]: https://github.com/NuxiNL/cloudabi#note-this-project-is-unmaintained

Rollup of 10 pull requests

Successful merges:

 - #76829 (stabilize const_int_pow)
 - #79080 (MIR visitor: Don't treat debuginfo field access as a use of the struct)
 - #79236 (const_generics: assert resolve hack causes an error)
 - #79287 (Allow using generic trait methods in `const fn`)
 - #79324 (Use Option::and_then instead of open-coding it)
 - #79325 (Reduce boilerplate with the `?` operator)
 - #79330 (Fix typo in comment)
 - #79333 (doc typo)
 - #79337 (Use Option::map instead of open coding it)
 - #79343 (Add my (`@flip1995)` work mail to the mailmap)

Failed merges:

r? `@ghost`
`@rustbot` modify labels: rollup