### What it does
Checks for `let _ = <expr>`
where expr has a type that implements `Drop`

### Why is this bad?
This statement immediately drops the initializer
expression instead of extending its lifetime to the end of the scope, which
is often not intended. To extend the expression's lifetime to the end of the
scope, use an underscore-prefixed name instead (i.e. _var). If you want to
explicitly drop the expression, `std::mem::drop` conveys your intention
better and is less error-prone.

### Example
```
{
    let _ = DroppableItem;
    //                   ^ dropped here
    /* more code */
}
```

Use instead:
```
{
    let _droppable = DroppableItem;
    /* more code */
    // dropped at end of scope
}
```