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

### Why is this bad?
`Vec` already keeps its contents in a separate area on
the heap. So if you `Box` its contents, you just add another level of indirection.

### Known problems
Vec<Box<T: Sized>> makes sense if T is a large type (see [#3530](https://github.com/rust-lang/rust-clippy/issues/3530),
1st comment).

### Example
```
struct X {
    values: Vec<Box<i32>>,
}
```

Better:

```
struct X {
    values: Vec<i32>,
}
```