This will print a diagnostic for crates which are mentioned as `--extern`
arguments on the command line, but are never referenced from the source.

This diagnostic is controlled by `-Wunused-crate-dependencies` or
`#![warn(unused_crate_dependencies)]` and is "allow" by default.

There are cases where certain crates need to be linked in but are not
directly referenced - for example if they are providing symbols for C
linkage. In this case the warning can be suppressed with
`use needed_crate as _;`.

Thanks to @petrochenkov for simplified core.

Resolves issue rust-lang#57274

…file with other functions

add a lint against references to packed fields

Creating a reference to an insufficiently aligned packed field is UB and should be disallowed, both inside and outside of `unsafe` blocks. However, currently there is no stable alternative (rust-lang#64490) so all we do right now is have a future incompatibility warning when doing this outside `unsafe` (rust-lang#46043).

This adds an allow-by-default lint. @retep998 suggested this can help early adopters avoid issues. It also means we can then do a crater run where this is deny-by-default as suggested by @joshtriplett.

I guess the main thing to bikeshed is the lint name. I am not particularly happy with "packed_references" as it sounds like the packed field has reference type. I chose this because it is similar to "safe_packed_borrows". What about "reference_to_packed" or "unaligned_reference" or so?

JS cleanup

The goal here is just to improve the source code a bit. I recommend to review one commit at a time, otherwise it might not make much sense. :)

The biggest commit is the second one: to prevent to have "global" variables declared in `main.js` (and thus prevent name conflict or overwriting), I moved such code into anonymous functions.

r? @kinnison

cc @rust-lang/rustdoc

Warn about unused crate deps

Implements rust-lang#57274 by adding -Wunused-crate-dependencies. This will warn about any `--extern` option on the command line which isn't referenced by the crate source either via `use` or `extern crate`.

Crates which are added for some side effect but are otherwise unreferenced - such as for symbols they define - the warning can be suppressed with `use somecrate as _;`.

If a crate has multiple aliases (eg using `foo = { package = "bar" }` in `Cargo.toml`), then it will warn about each unused alias.

This does not consider crate added by some other means than `--extern`, including the standard library. It also doesn't consider any crate without `add_prelude` set (though I'm not sure about this).

Unfortunately this probably [does not yet work well with Cargo](rust-lang#57274 (comment)) as it will over-specify crates, causing spurious warnings. As a result, this lint is "allow" by default and must be explicitly enabled either via `#![warn(unused_crate_deps)]` or with `-Wunused-crate-deps`.

Use correct function for detecting `const fn` in unsafety checking

Resolves rust-lang#72394.

…eled-block, r=davidtwco

Allow unlabeled breaks from desugared `?` in labeled blocks

`?` is desugared into a `break` targeting the innermost `try` scope in which it resides. The `break` however will not have a label. https://github.com/rust-lang/rust/blob/master/src/librustc_ast_lowering/expr.rs#L1560

Since the `target` of the `break` is known, the compiler should not complain about an unlabeled jump for `break`s desugared from `?`.

Closes rust-lang#72483

Update books

## reference

7 commits in 892b928b565e35d25b6f9c47faee03b94bc41489..becdca9477c9eafa96a4eea5156fe7a2730d9dd2
2020-05-11 11:13:51 -0700 to 2020-05-21 21:08:02 +0100
- Update tuple index token. (rust-lang/reference#814)
- Fixes minor errors (rust-lang/reference#818)
- Update that macros can be deprecated. (rust-lang/reference#813)
- work on char/str descriptions (rust-lang/reference#809)
- cfg_attr needs a valid predicate (rust-lang/reference#812)
- Account for removal of UB in float-to-int casts (rust-lang/reference#810)
- Fix stray plus signs. (rust-lang/reference#811)

## book

6 commits in 6247be15a7f7509559f7981ee2209b9e0cc121df..e8a4714a9d8a6136a59b8e63544e149683876e36
2020-05-03 10:55:09 -0500 to 2020-05-25 10:29:27 -0500
- code is 1024 now, not 512
- Clean up install a bit
- We don't need build.sh anymore
- Fix CI status in README
- Port to github actions (rust-lang/book#2337)
- operating system -> allocator

## rust-by-example

5 commits in ab072b14393cbd9e8a1d1d75879bf51e27217bbb..7aa82129aa23e7e181efbeb8da03a2a897ef6afc
2020-05-09 08:46:39 -0300 to 2020-05-25 14:54:26 -0300
- Person of age 0 is alive (rust-lang/rust-by-example#1348)
- Gramatical fix in std/rc.md (rust-lang/rust-by-example#1347)
- Capture example should use String (rust-lang/rust-by-example#1331)
- Fix empty bound examples (rust-lang/rust-by-example#1343)
- Fix an inline comment in macros/repeat.md (rust-lang/rust-by-example#1344)

## edition-guide

1 commits in 49270740c7a4bff2763e6bc730b191d45b7d5167..0a8ab5046829733eb03df0738c4fafaa9b36b348
2020-05-11 08:50:29 -0500 to 2020-05-18 08:34:23 -0500
- Changes for Rust 1.32 & setup for edition-next (rust-lang/edition-guide#213)

## embedded-book

3 commits in 366c50a03bed928589771eba8a6f18e0c0c01d23..5555a97f04ad7974ac6fb8fb47c267c4274adf4a
2020-05-07 09:04:42 +0000 to 2020-05-25 18:00:51 +0000
- Remove reference to const-fn feature of cortex-m. Closes rust-embedded/book#242.  (rust-embedded/book#243)
- Spelling: Appplication -> Application  (rust-embedded/book#241)
- QEMU debugging updates  (rust-embedded/book#239)