### What it does
Checks for calls to `std::mem::drop` with a value
that derives the Copy trait

### Why is this bad?
Calling `std::mem::drop` [does nothing for types that
implement Copy](https://doc.rust-lang.org/std/mem/fn.drop.html), since the
value will be copied and moved into the function on invocation.

### Example
```
let x: i32 = 42; // i32 implements Copy
std::mem::drop(x) // A copy of x is passed to the function, leaving the
                  // original unaffected
```