This line is too long; maybe you could factor out the error message to a static like

```rust
fn check_raw_pointer_deriving(...) {
    static MSG: &'static str = "use of `#[deriving]` with a raw pointer";

    fn check_struct_def(...) {
         /* ... */
                 ast::TyPtr(..) => cx.span_lint(RawPointerDeriving, field.span, MSG)
         /* ... */
     }
     /* ... */
}
```

(Even with this factored out the line below will be too long, you can break it over multiple lines via
```rust
ast::TyPtr(..) => {
    cx.span_lint(RawPointerDeriving, variant.span, MSG);
}
```