The former wording only gave part of the picture, we want to be crystal
clear about this.

For a given code:

```rust
vec![0.0].iter().map(|s| s as i16).collect::<Vec<i16>>();
```

display:

```nocode
error: casting `&f64` as `i16` is invalid
 --> foo.rs:2:35
  |
2 |     vec![0.0].iter().map(|s| s as i16).collect::<Vec<i16>>();
  |                              -    ^^^ cannot cast `&f64` as `i16`
  |                              |
  |                              did you mean `*s`?
```

instead of:

```nocode
error: casting `&f64` as `i16` is invalid
 --> <anon>:2:30
  |
2 |     vec![0.0].iter().map(|s| s as i16).collect();
  |                              ^^^^^^^^
  |
  = help: cast through a raw pointer first
```

The change also adds the missing `SmallVec::truncate` method.

…ndturner

Provide hint when cast needs a dereference

For a given code:

``` rust
vec![0.0].iter().map(|s| s as i16).collect::<Vec<i16>>();
```

display:

``` nocode
error: casting `&f64` as `i16` is invalid
 --> file3.rs:2:35
  |
2 |     vec![0.0].iter().map(|s| s as i16).collect::<Vec<i16>>();
  |                              -    ^^^
  |                              |
  |                              did you mean `*s`?
```

instead of:

``` nocode
error: casting `&f64` as `i16` is invalid
 --> <anon>:2:30
  |
2 |     vec![0.0].iter().map(|s| s as i16).collect();
  |                              ^^^^^^^^
  |
  = help: cast through a raw pointer first
```

Fixes rust-lang#37338.

… r=arielb1

Type walker small vector

These two changes avoid allocations on some hot paths and speed up a few workloads (some from rustc-benchmarks, as well as the workload from rust-lang#36799) by 1--2%.

…ence-comment, r=GuillaumeGomez

Clarify the reference's status.

The former wording only gave part of the picture, we want to be crystal
clear about this.

/cc @petrochenkov, who had concerns about rust-lang#37820

Add a regression test for issue 23699.

This should close rust-lang#23699

Add missing examples for SocketAddrV4

r? @steveklabnik

cc @frewsxcv

…eklabnik

Add some internal docs links for Args/ArgsOs

In many places the docs link to other sections and I noticed it was lacking here. Not sure if there is a standard for if inter-linking is appropriate.

…es, r=eddyb

Move the myriad-closures.rs test case to run-pass-full test suite.

r? @eddyb

…ctors, r=nikomatsakis

ICH: Add test case for struct constructor expressions.

r? @nikomatsakis