Currently, the compiler requires `T` to also be `Send`.  There is no reason for
that.  `&Rw{Read,Write}LockGuard` only provides a shared referenced to `T`, sending
that across threads is safe if `T` is `Sync`.

…aught

…c=abort

The Dist Step is not ran in that case so we would end up trying to
install something that we didn't dist.

Signed-off-by: Marc-Antoine Perennou <[email protected]>

It's currently linking to a page that says it's on the page I'm changing the link too.

also modify the order crate attributes are applied, to have a better
order of how things can override lints, either per-crate or per-test

When pretty printing a cast expression occuring on the LHS of a '<'
or '<<' expression, we should add parens around the cast. Otherwise,
the '<'/'<<' gets interpreted as the beginning of the generics for
the type on the RHS of the cast.

When there's a lifetime mismatch between an argument with an anonymous
lifetime being returned in a method with a return type that has a named
lifetime, show specialized lifetime error pointing at argument with a
hint to give it an explicit lifetime matching the return type.

```
error[E0621]: explicit lifetime required in the type of `other`
  --> file2.rs:21:21
   |
17 |     fn bar(&self, other: Foo) -> Foo<'a> {
   |                   ----- consider changing the type of `other` to `Foo<'a>`
...
21 |                     other
   |                     ^^^^^ lifetime `'a` required
```

Follow up to rust-lang#44124 and rust-lang#42669.

before:

```
> rustc --emit foo
error: unknown emission type: `foo`
```

after:

```
> rustc --emit foo
error: unknown emission type: `foo` - expected one of: `llvm-bc`, `asm`, `llvm-ir`, `mir`, `obj`, `metadata`, `link`, `dep-info`
```

…=QuietMisdreavus

add missing docs for MetadataExt

r? @rust-lang/docs

rustbuild: don't try to install rls if ToolState is not Testing

We already do that for the Dist Step so we would end up trying to install something that we didn't dist.

RwLock guards are Sync if T is

Currently, the compiler requires `T` to also be `Send`.  There is no reason for
that.  `&Rw{Read,Write}LockGuard` only provides a shared referenced to `T`, sending
that across threads is safe if `T` is `Sync`.

Cc @oconnor663

Update the std::thread docs and clarify that panics can nowadays be caught

Handle anon lifetime arg being returned with named lifetime return type

When there's a lifetime mismatch between an argument with an anonymous
lifetime being returned in a method with a return type that has a named
lifetime, show specialized lifetime error pointing at argument with a
hint to give it an explicit lifetime matching the return type.

```
error[E0621]: explicit lifetime required in the type of `other`
  --> file2.rs:21:21
   |
17 |     fn bar(&self, other: Foo) -> Foo<'a> {
   |                   ----- consider changing the type of `other` to `Foo<'a>`
...
21 |                     other
   |                     ^^^^^ lifetime `'a` required
```

Follow up to rust-lang#44124 and rust-lang#42669. Fix rust-lang#44684.

…ts, r=GuillaumeGomez

rustdoc: add #[allow(unused)] to every doctest

More information in rust-lang#45750 - this is behavior that was documented but not actually implemented.

I also reordered how outer attributes are applied to doctests. Previously, attributes from `#![doc(test(attr(...)))]` would be applied *after* attributes from within the test itself, meaning if a doctest tried to override lints that would be set crate-wide, it wouldn't work at all. This gives a better scope of how lints can be applied.

Closes rust-lang#45750

Update reference link in doc's 404

It's currently linking to a page that says it's on the page I'm changing the link too.

…s, r=manishearth

Display all emission types in error msg if user inputs invalid option.

before:

```
> rustc --emit foo
error: unknown emission type: `foo`
```

after:

```
> rustc --emit foo
error: unknown emission type: `foo` - expected one of: `llvm-bc`, `asm`, `llvm-ir`, `mir`, `obj`, `metadata`, `link`, `dep-info`
```

…t, r=kennytm

Pretty print parens around casts on the LHS of `<`/`<<`

When pretty printing a cast expression occuring on the LHS of a `<` or `<<` expression, we should add parens around the cast. Otherwise, the `<`/`<<` gets interpreted as the beginning of the generics for the type on the RHS of the cast.

Consider:

    $ cat parens_cast.rs
    macro_rules! negative {
        ($e:expr) => { $e < 0 }
    }

    fn main() {
        negative!(1 as i32);
    }

Before this PR, the output of the following is not valid Rust:

    $ rustc -Z unstable-options --pretty=expanded parens_cast.rs
    #![feature(prelude_import)]
    #![no_std]
    #[prelude_import]
    use std::prelude::v1::*;
    #[macro_use]
    extern crate std as std;
    macro_rules! negative(( $ e : expr ) => { $ e < 0 });

    fn main() { 1 as i32 < 0; }

After this PR, the output of the following is valid Rust:

    $ rustc -Z unstable-options --pretty=expanded parens_cast.rs
    #![feature(prelude_import)]
    #![no_std]
    #[prelude_import]
    use std::prelude::v1::*;
    #[macro_use]
    extern crate std as std;
    macro_rules! negative(( $ e : expr ) => { $ e < 0 });

    fn main() { (1 as i32) < 0; }

I've gone through several README/wiki style documents but I'm still not sure where to test this though. I'm not even sure if this sort of thing is tested...