Support deriving some traits for unions

src/libsyntax_ext/deriving/generic/mod.rs

@@ -410,9 +410,18 @@ impl<'a> TraitDef<'a> {
                     ast::ItemKind::Enum(ref enum_def, ref generics) => {
                         self.expand_enum_def(cx, enum_def, &item.attrs, item.ident, generics)
                     }
+                    ast::ItemKind::Union(ref struct_def, ref generics) => {
+                        if self.supports_unions {
+                            self.expand_struct_def(cx, &struct_def, item.ident, generics)
+                        } else {
+                            cx.span_err(mitem.span,
+                                        "this trait cannot be derived for unions");
+                            return;
+                        }
+                    }
                     _ => {
                         cx.span_err(mitem.span,
-                                    "`derive` may only be applied to structs and enums");
+                                    "`derive` may only be applied to structs, enums and unions");
                         return;
                     }
                 };

src/test/compile-fail/union-derive.rs

@@ -0,0 +1,30 @@
+// Copyright 2016 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+// Most traits cannot be derived for unions.
+
+#![feature(untagged_unions)]
+
+#[derive(
+    Clone, //~ ERROR this trait cannot be derived for unions
+    PartialEq, //~ ERROR this trait cannot be derived for unions
+    Eq, //~ ERROR this trait cannot be derived for unions
+    PartialOrd, //~ ERROR this trait cannot be derived for unions
+    Ord, //~ ERROR this trait cannot be derived for unions
+    Hash, //~ ERROR this trait cannot be derived for unions
+    Default, //~ ERROR this trait cannot be derived for unions
+    Debug, //~ ERROR this trait cannot be derived for unions
+)]
+union U {
+    a: u8,
+    b: u16,
+}
+
+fn main() {}

src/test/run-pass/union-derive.rs

@@ -0,0 +1,31 @@
+// Copyright 2016 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+// Some traits can be derived for unions.
+
+#![feature(untagged_unions)]
+
+#[derive(
+    Copy,
+)]
+union U {
+    a: u8,
+    b: u16,
+}
+
+impl Clone for U {
+    fn clone(&self) -> Self { *self }
+}
+
+fn main() {
+    let u = U { b: 0 };
+    let u1 = u;
+    let u2 = u.clone();
+}