Don't suggest changing explicit Clone impls if they have generics

clippy_lints/src/derive.rs

@@ -148,6 +148,13 @@ fn check_copy_clone<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, item: &Item, trait_ref
                         return;
                     }
                 }
+                for subst in substs {
+                    if let Some(subst) = subst.as_type() {
+                        if let ty::TyParam(_) = subst.sty {
+                            return;
+                        }
+                    }
+                }
             },
             _ => (),
         }

tests/ui/clone_on_copy_impl.rs

@@ -0,0 +1,22 @@
+use std::marker::PhantomData;
+use std::fmt;
+
+pub struct Key<T> {
+    #[doc(hidden)]
+    pub __name: &'static str,
+    #[doc(hidden)]
+    pub __phantom: PhantomData<T>,
+}
+
+impl<T> Copy for Key<T> {}
+
+impl<T> Clone for Key<T> {
+    fn clone(&self) -> Self {
+        Key {
+            __name: self.__name,
+            __phantom: self.__phantom,
+        }
+    }
+}
+
+fn main() {}