Closes: rust-lang#57977

Stabilize `std::{rc,sync}::Weak::{weak_count, strong_count}`

* Original PR: rust-lang#56696
* Tracking issue: rust-lang#57977

Closes: rust-lang#57977

Supporting comments:

> Although these were added for testing, it is occasionally useful to have a way to probe optimistically for whether a weak pointer has become dangling, without actually taking the overhead of manipulating atomics. Are there any plans to stabilize this?

_Originally posted by @bdonlan in rust-lang#57977 (comment)

> Having this stabilized would help. Currently, the only way to check if a weak pointer has become dangling is to call `upgrade`, which is by far expensive.

_Originally posted by @glebpom in rust-lang#57977 (comment)

Not sure if stabilizing these warrants a full RFC, so throwing this out here as a start for now.

Note: per CONTRIBUTING.md, I ran the tidy checks, but they seem to be failing on unchanged files (primarily in `src/stdsimd`).

Update cargo, books

Update nomicon, cargo, reference, book, rust-by-example, embedded-book

## nomicon

2 commits in 041c46e692a2592853aeca132c8dfe8eb5a79a9e..8be35b201f9cf0a4c3fcc96c83ac21671dcf3112
2019-11-20 16:46:45 +0100 to 2019-12-01 13:02:12 -0500
- Update unwinding.md
- ci: remove needless rust-docs component

## cargo

15 commits in 626f0f40efd32e6b3dbade50cd53fdfaa08446ba..5a139f7e6d67fd8a416a3f19d8e01581d24c0333
2019-12-03 16:53:04 +0000 to 2019-12-10 20:17:50 +0000
- Bump cargo-platform version. (rust-lang/cargo#7693)
- Add a test for `cargo locate-project` (rust-lang/cargo#7690)
- Emit error on [target.'cfg(debug_assertions)'.dependencies] and similar (rust-lang/cargo#7660)
- Update the layout of `Cargo Commands` in doc (rust-lang/cargo#7687)
- Features and dependencies can't have the same name (rust-lang/cargo#7682)
- Fix some typos in doc (rust-lang/cargo#7672)
- Add test for `NAME` environment variable when `cargo new` (rust-lang/cargo#7667)
- Add test for `GIT_COMMITTER_EMAIL` when `cargo new` (rust-lang/cargo#7666)
- document support for Bitbucket Pipelines badges (rust-lang/cargo#7663)
- Add cargo-vendor to the list of cargo commands in doc (rust-lang/cargo#7659)
- Fix typo in section 'Caching the Cargo home in CI' (rust-lang/cargo#7661)
- Docs: Add an appendix on git authentication. (rust-lang/cargo#7658)
- Remove --offline empty index error. (rust-lang/cargo#7655)
- Change the link destination of cargo book contribution (rust-lang/cargo#7657)
- Add a --offline hint. (rust-lang/cargo#7654)

## reference

2 commits in 9e843ae..787e8d8
2019-11-24 17:44:04 +0100 to 2019-12-10 10:01:29 -0800
- Update for visibility syntax changes. (rust-lang/reference#722)
- document `bind_by_move_pattern_guards` (rust-lang/reference#720)

## book

2 commits in 81ebaa2a3f88d4d106516c489682e64cacba4f60..ef8bb568035ded8ddfa30a9309026638cc3c8136
2019-11-15 08:30:04 -0800 to 2019-11-28 11:00:04 -0600
- Remove optional commas from match arms in ch18-03 (rust-lang/book#2176)
- Remove call_box() from ch20-03 (rust-lang/book#2177)

## rust-by-example

1 commits in 4835e025826729827a94fdeb7cb85fed288d08bb..b7ac1bc76b7d02a43c83b3a931d226f708aa1ff4
2019-11-14 09:20:43 -0300 to 2019-12-02 11:38:43 -0300
- Make TryFrom & TryInto example editable (rust-lang/rust-by-example#1297)

## embedded-book

1 commits in 5ca585c4a7552efb546e7681c3de0712f4ae4fdc..c26234930282210849256e4ecab925f0f2daf3be
2019-08-27 13:39:14 +0000 to 2019-12-07 17:25:11 +0000
- Fix `impl Gpio` -> `impl GpioConfig`  (rust-embedded/book#216)

…type-parameter, r=estebank

Indicate origin of where type parameter for uninferred types

Based on rust-lang#65951 (which is not merge yet), fixes rust-lang#67277.

This PR improves a little the diagnostic for code like:

```
 async fn foo() {
     bar().await;
}

 async fn bar<T>() -> () {}
```

by showing:
```
error[E0698]: type inside `async fn` body must be known in this context
 --> unresolved_type_param.rs:9:5
  |
9 |     bar().await;
  |     ^^^ cannot infer type for type parameter `T` declared on the function `bar`
  |
...
```
(The
```
declared on the function `bar`
```
part is new)

A small side note: `Vec` and `slice` seem to resist this change, because querying `item_name()` panics, and `get_opt_name()` returns `None`.

r? @estebank

fix type_name_of_val doc comment

.