BTreeMap: tougher checks on code using raw into_kv_pointers

r? `@Mark-Simulacrum`

Use probe-stack=inline-asm in LLVM 11+

Fixes (?) #74405, related to #43241

r? `@cuviper`

Rollup of 6 pull requests

Successful merges:

 - #77693 (Add test for #59352)
 - #80515 (Improve JS performance by storing length before comparing to it in loops)
 - #81030 (Update mdbook)
 - #81033 (Remove useless `clean::Variant` struct)
 - #81049 (inline: Round word-size cost estimates up)
 - #81054 (Drop a few unneeded borrows)

Failed merges:

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

Drop a few unneeded borrows

`@rustbot` modify labels +C-cleanup +T-compiler

inline: Round word-size cost estimates up

Remove useless `clean::Variant` struct

It had exactly one field and no special behavior, so there was no point in having it.

r? `@CraftSpider`

Update mdbook

Just a few small fixes and changes, see https://github.com/rust-lang/mdBook/blob/master/CHANGELOG.md#mdbook-046 for a list.

Improve JS performance by storing length before comparing to it in loops

Since https://github.com/rust-lang/rust/pull/79052 is quite complicated to review, I suggested to split into smaller parts. This first part is mostly about saving the array length into a variable (I tried to not change anything else as much as possible 😃 ).

r? `@jyn514`

Add test for #59352

Issue #59352 reported an optimization regression with rustc 1.32.0+. That regression could be tracked to a change that caused a function to miss the size limit of llvm's inlining, which results in an unreachable panicing branch being generated.
Enabling mir inline solves the issue, but is currently only done for `mir-opt-level>=2`.

This PR adds a test that can serve as a regression test for #59352, if/when mir inlining gets mature enough for opt-level 1, or some other optimization can remove the panic.

Remove DepKind::CrateMetadata and pre-allocation of DepNodes

Remove much of the special-case handling around crate metadata
dependency tracking by replacing `DepKind::CrateMetadata` and the
pre-allocation of corresponding `DepNodes` with on-demand invocation
of the `crate_hash` query.

There's no `Variant`, so it seems silly to have `Kind`.

It had exactly one field and no special behavior, so there was no point.

Update Miri

Fixes #80907.

r? `@RalfJung`

Co-authored-by: NRalf Jung <post@ralfj.de>

Update cargo

10 commits in 329895f5b52a358e5d9ecb26215708b5cb31d906..a73e5b7d567c3036b296fc6b33ed52c5edcd882e
2021-01-06 00:01:52 +0000 to 2021-01-12 23:45:39 +0000
- Sort available binaries when multiple (rust-lang/cargo#9066)
- Fix misspelling of environment variable (rust-lang/cargo#9067)
- Remove statement that opt-level 0 turns on debug (rust-lang/cargo#9070)
- Fix `links` vars showing up for testing packages (rust-lang/cargo#9065)
- Fix unit_for computation on proc-macros in shared workspace. (rust-lang/cargo#9059)
- Document `could not find the github team` error on `cargo owner --add` (rust-lang/cargo#9000)
- Unstable section of cargo/config.toml takes bools (rust-lang/cargo#9057)
- [doc] add note about empty environment variables for missing manifest keys (rust-lang/cargo#9053)
- another round of clippy lint fixes (rust-lang/cargo#9051)
- Updated display message of cargo metadata --help (rust-lang/cargo#9050)

Choose the version of python at runtime (portable version)

r? `@Mark-Simulacrum`

Fixed version of https://github.com/rust-lang/rust/pull/80585. The goal is to avoid giving 'error: python3 required' when downloading LLVM from CI and instead default to python3 where possible.

This has some minor overhead when you have `python` as python2, but almost nothing compared to actually running the build.

Rollup of 5 pull requests

Successful merges:

 - #80254 (Don't try to add nested predicate to Rustdoc auto-trait `ParamEnv`)
 - #80834 (Remove unreachable panics from VecDeque::{front/back}[_mut])
 - #80944 (Use Option::map_or instead of `.map(..).unwrap_or(..)`)
 - #81008 (Don't ICE when computing a layout of a generator tainted by errors)
 - #81023 (Remove doctree::Variant)

Failed merges:

 - #81033 (Remove useless `clean::Variant` struct)

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

Remove doctree::Variant

This was easy, probably was missed when whatever used it was removed

Don't ICE when computing a layout of a generator tainted by errors

Fixes #80998.

Use Option::map_or instead of `.map(..).unwrap_or(..)`

``@rustbot`` modify labels +C-cleanup +T-compiler

Remove unreachable panics from VecDeque::{front/back}[_mut]

`VecDeque`'s `front`, `front_mut`, `back` and `back_mut` methods are implemented in terms of the index operator, which causes these functions to contain [unreachable panic calls](https://rust.godbolt.org/z/MTnq1o).

This PR reimplements these methods in terms of `get[_mut]` instead.

Don't try to add nested predicate to Rustdoc auto-trait `ParamEnv`

Fixes #80233

We already have logic in `evaluate_predicates` that tries to add
unimplemented predicates to our `ParamEnv`. Trying to add a predicate
that already holds can lead to errors later on, since projection
will prefer trait candidates from the `ParamEnv` to predicates from an
impl.

Set tokens on AST node in `collect_tokens`

A new `HasTokens` trait is introduced, which is used to move logic from
the callers of `collect_tokens` into the body of `collect_tokens`.

In addition to reducing duplication, this paves the way for PR #80689,
which needs to perform additional logic during token collection.

Update RLS and Rustfmt

Fixes #80576

Updates Rustfmt to use `rustfmt-v1.4.31` branch. Both are updated (along with `racer`) in tandem to pull in the exact same version of rustc-ap-* libraries.

r? `@calebcartwright`

- Try `py -3` first for windows compatibility
- Fall back to `python3` if `py` doesn't work

Rollup of 17 pull requests

Successful merges:

 - #79982 (Add missing methods to unix ExitStatusExt)
 - #80017 (Suggest `_` and `..` if a pattern has too few fields)
 - #80169 (Recommend panic::resume_unwind instead of panicking.)
 - #80217 (Add a `std::io::read_to_string` function)
 - #80444 (Add as_ref and as_mut methods for Bound)
 - #80567 (Add Iterator::intersperse_with)
 - #80829 (Get rid of `DepConstructor`)
 - #80895 (Fix handling of malicious Readers in read_to_end)
 - #80966 (Deprecate atomic::spin_loop_hint in favour of hint::spin_loop)
 - #80969 (Use better ICE message when no MIR is available)
 - #80972 (Remove unstable deprecated Vec::remove_item)
 - #80973 (Update books)
 - #80980 (Fixed incorrect doc comment)
 - #80981 (Fix -Cpasses=list and llvm version print with -vV)
 - #80985 (Fix stabilisation version of slice_strip)
 - #80990 (llvm: Remove the unused context from CreateDebugLocation)
 - #80991 (Fix formatting specifiers doc links)

Failed merges:

 - #80944 (Use Option::map_or instead of `.map(..).unwrap_or(..)`)

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