Support unions here and there

clippy_lints/src/derive.rs

@@ -140,8 +140,10 @@ fn check_copy_clone<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, item: &Item, trait_ref
             return; // ty is not Copy
         }
 
-        // Some types are not Clone by default but could be cloned `by hand` if necessary
         match ty.sty {
+            TypeVariants::TyUnion(..) => return,
+
+            // Some types are not Clone by default but could be cloned “by hand” if necessary
             TypeVariants::TyEnum(def, substs) |
             TypeVariants::TyStruct(def, substs) => {
                 for variant in &def.variants {

clippy_lints/src/len_zero.rs

@@ -209,7 +209,8 @@ fn has_is_empty(cx: &LateContext, expr: &Expr) -> bool {
         }
         ty::TyProjection(_) => ty.ty_to_def_id().map_or(false, |id| has_is_empty_impl(cx, &id)),
         ty::TyEnum(id, _) |
-        ty::TyStruct(id, _) => has_is_empty_impl(cx, &id.did),
+        ty::TyStruct(id, _) |
+        ty::TyUnion(id, _) => has_is_empty_impl(cx, &id.did),
         ty::TyArray(..) | ty::TyStr => true,
         _ => false,
     }

tests/compile-fail/derive.rs

@@ -1,6 +1,8 @@
 #![feature(plugin)]
 #![plugin(clippy)]
 
+#![feature(untagged_unions)]
+
 #![deny(warnings)]
 #![allow(dead_code)]
 
@@ -45,6 +47,20 @@ impl Clone for Qux {
     fn clone(&self) -> Self { Qux }
 }
 
+// looks like unions don't support deriving Clone for now
+#[derive(Copy)]
+union Union {
+    a: u8,
+}
+
+impl Clone for Union {
+    fn clone(&self) -> Self {
+        Union {
+            a: 42,
+        }
+    }
+}
+
 // See #666
 #[derive(Copy)]
 struct Lt<'a> {

tests/compile-fail/no_effect.rs

@@ -4,6 +4,7 @@
 #![deny(no_effect, unnecessary_operation)]
 #![allow(dead_code)]
 #![allow(path_statements)]
+#![feature(untagged_unions)]
 
 struct Unit;
 struct Tuple(i32);
@@ -15,6 +16,11 @@ enum Enum {
     Struct { field: i32 },
 }
 
+union Union {
+    a: u8,
+    b: f64,
+}
+
 fn get_number() -> i32 { 0 }
 fn get_struct() -> Struct { Struct { field: 0 } }
 
@@ -30,6 +36,7 @@ fn main() {
     Tuple(0); //~ERROR statement with no effect
     Struct { field: 0 }; //~ERROR statement with no effect
     Struct { ..s }; //~ERROR statement with no effect
+    Union { a: 0 }; //~ERROR statement with no effect
     Enum::Tuple(0); //~ERROR statement with no effect
     Enum::Struct { field: 0 }; //~ERROR statement with no effect
     5 + 6; //~ERROR statement with no effect