### What it does
Checks for use of `Box<T>` where T is a collection such as Vec anywhere in the code.
Check the [Box documentation](https://doc.rust-lang.org/std/boxed/index.html) for more information.

### Why is this bad?
Collections already keeps their contents in a separate area on
the heap. So if you `Box` them, you just add another level of indirection
without any benefit whatsoever.

### Example
```
struct X {
    values: Box<Vec<Foo>>,
}
```

Better:

```
struct X {
    values: Vec<Foo>,
}
```