We used to make the upvar types in the closure `==` but that was
stronger than we needed. Subtyping suffices, since we are copying the
upvar value into the closure field. This in turn allows us to infer
smaller lifetimes in captured values in some cases (like the example
here), avoiding errors.

But leave closure substs alone.

Rollup of 17 pull requests

- Successful merges: #46518, #48810, #48834, #48902, #49004, #49092, #49096, #49099, #49104, #49125, #49139, #49152, #49157, #49161, #49166, #49176, #49184
- Failed merges:

Stabilize slice patterns without `..`

And merge `feature(advanced_slice_patterns)` into `feature(slice_patterns)`.

The detailed description can be found in https://github.com/rust-lang/rust/issues/48836.

Slice patterns were unstable for long time since before 1.0 due to many bugs in the implementation, now this stabilization is possible primarily due to work of @arielb1 who [wrote the new MIR-based implementation of slice patterns](https://github.com/rust-lang/rust/pull/32202) and @mikhail-m1 who [fixed one remaining class of codegen issues](https://github.com/rust-lang/rust/pull/47926).

Reference PR https://github.com/rust-lang-nursery/reference/pull/259
cc https://github.com/rust-lang/rust/issues/23121
fixes #48836

Update beta to version with fixed FreeBSD support from #49023.

Fixes #42681

r? @alexcrichton

config.toml.example: thinlto bootstrap was removed

 It was removed in ff227c4a so remove the option that no longer works (we did not notice because it was commented out by default).

#49133 - Reworded the Error message: "`pub` not needed here" message

Docs: fix incorrect copy-paste for new `X?` in formatting strings

Do not suggest `.into()` in `const`s

Fix #49100.

Fix events handling in rustdoc

Fixes #49075.

Merge `feature(advanced_slice_patterns)` into `feature(slice_patterns)`

Add BufReader::buffer

This subsumes the need for an explicit is_empty function, and provides
access to the buffered data itself which has been requested from time to
time.

We could call this `buf` to match `fill_buf`, but I think I'd prefer `fill_buffer` anyways in hindsight.

rustbuild: Ship libsynchronization

Hot on the heels of #49044 comes similar issue with libsynchronization. Discovered while building clippy:
```
<skipped>
Compiling serde_derive v1.0.33
error: linking with `gcc` failed: exit code: 1
<skipped>
  = note: ld: cannot find -lsynchronization
```

r? @nikomatsakis

improve error message of inner attribute syntax

Fixes #49040

Use associated consts for GenericRadix base and prefix

The trait being private, this does not imply an API change.

Update rustfmt to 0.4.1

Replace many of the last references to readmes

In particular, this removes the dep track readme, so it should not be merged before https://github.com/rust-lang-nursery/rustc-guide/pull/92

Fix #47935

cc #48478

r? @nikomatsakis

Cache the specialization_graph query

Fixes #48987

r? @michaelwoerister

refactor the `BorrowckErrors` trait to take `fn(self)`

Fixes #48783

Suggest removing `&`s

This implements the error message discussed in #47744.
We check whether removing each `&` yields a type that satisfies the requested obligation.
Also, it was created a new `NodeId` field in `ObligationCause` in order to iterate through the `&`s. The way it's implemented now, it iterates through the obligation snippet and counts the number of `&`.

r? @estebank

Implement Integer methods for Wrapping

Wrapping<T> now implements:

count_ones, count_zeros, leading_zeros,
trailing_zeros, rotate_left, rotate_right, swap_bytes, from_be,
from_le, to_be, to_le, and pow

where T is:

u8, u16, u32, u64, usize, i8, i16, i32, i64, or isize.

Docs were written for all these methods, as well as examples. The
examples mirror the ones on u8, u16, etc... for consistency.

Closes #32463

Improve documentation for Borrow

This is the first step in improving the documentation for all the reference conversion traits. It proposes new text for the trait documentation of `Borrow`. Since I feel it is a somewhat radical rewrite and includes a stricter contract for `Borrow` then the previous text—namely that *all* shared traits need to behave the same, not just a select few—, I wanted to get some feedback before continuing.

Apart from the ‘normative’ description, the new text also includes a fairly extensive explanation of how the trait is used in the examples section. I included it because every time I look at how `HashMap` uses the trait, I need to think for a while as the use is a bit twisted. So, I thought having this thinking written down as part of the trait itself might be useful. One could argue that this should go into The Book, and, while I really like having everything important in the docs, I can see the text moved there, too.

So, before I move on: is this new text any good? Do we feel it is correct, useful, comprehensive, and understandable?

(This PR is in response to #44868 and #24140.)

Pin, Unpin, PinBox

Implementing rust-lang/rfcs#2349 (do not merge until RFC is merged)

@bors r? @cramertj

Fixes #42681

config.toml.example: thinlto bootstrap was removed in ff227c4a so remove the option.

Cleanup metadata and incremental cache processing of constants

fixes #49033
fixes #49081

we really need tests for this. do we have any cross compilation tests? I couldn't find any

Remove or hide deprecated unstable SipHasher{13,24}

Deprecated since Rust 1.13.0.

Wrapping<T> now implements:

count_ones, count_zeros, leading_zeros,
trailing_zeros, rotate_left, rotate_right, swap_bytes, from_be,
from_le, to_be, to_le, and pow

where T is:

u8, u16, u32, u64, usize, i8, i16, i32, i64, or isize.

Docs were written for all these methods, as well as examples. The
examples mirror the ones on u8, u16, etc... for consistency.

Closes #32463