Address comments and add requested tests

39 files changed, 511 insertions, 13 deletions

diff --git a/src/test/compile-fail/union-borrow-nested.rs b/src/test/compile-fail/borrowck/borrowck-union-borrow-nested.rs
index 19975d79b60..19975d79b60 100644
--- a/src/test/compile-fail/union-borrow-nested.rs
+++ b/src/test/compile-fail/borrowck/borrowck-union-borrow-nested.rs
diff --git a/src/test/compile-fail/union-borrow.rs b/src/test/compile-fail/borrowck/borrowck-union-borrow.rs
index e8989a3c2d4..e8989a3c2d4 100644
--- a/src/test/compile-fail/union-borrow.rs
+++ b/src/test/compile-fail/borrowck/borrowck-union-borrow.rs
diff --git a/src/test/compile-fail/union-move-assign.rs b/src/test/compile-fail/borrowck/borrowck-union-move-assign.rs
index d4d7bc6b0f7..d4d7bc6b0f7 100644
--- a/src/test/compile-fail/union-move-assign.rs
+++ b/src/test/compile-fail/borrowck/borrowck-union-move-assign.rs
diff --git a/src/test/compile-fail/union-move.rs b/src/test/compile-fail/borrowck/borrowck-union-move.rs
index 5320244cf43..5320244cf43 100644
--- a/src/test/compile-fail/union-move.rs
+++ b/src/test/compile-fail/borrowck/borrowck-union-move.rs
diff --git a/src/test/compile-fail/union-uninitialized.rs b/src/test/compile-fail/borrowck/borrowck-union-uninitialized.rs
index 36e062f8464..36e062f8464 100644
--- a/src/test/compile-fail/union-uninitialized.rs
+++ b/src/test/compile-fail/borrowck/borrowck-union-uninitialized.rs
diff --git a/src/test/compile-fail/privacy/union-field-privacy-1.rs b/src/test/compile-fail/privacy/union-field-privacy-1.rs
new file mode 100644
index 00000000000..4924fabafb0
--- /dev/null
+++ b/src/test/compile-fail/privacy/union-field-privacy-1.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.
+
+#![feature(pub_restricted)]
+#![feature(untagged_unions)]
+
+mod m {
+    pub union U {
+        pub a: u8,
+        pub(super) b: u8,
+        c: u8,
+    }
+}
+
+fn main() {
+    let u = m::U { a: 0 }; // OK
+    let u = m::U { b: 0 }; // OK
+    let u = m::U { c: 0 }; //~ ERROR field `c` of union `m::U` is private
+
+    let m::U { a } = u; // OK
+    let m::U { b } = u; // OK
+    let m::U { c } = u; //~ ERROR field `c` of union `m::U` is private
+}
diff --git a/src/test/compile-fail/privacy/union-field-privacy-2.rs b/src/test/compile-fail/privacy/union-field-privacy-2.rs
new file mode 100644
index 00000000000..7151538f412
--- /dev/null
+++ b/src/test/compile-fail/privacy/union-field-privacy-2.rs
@@ -0,0 +1,28 @@
+// 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.
+
+#![feature(pub_restricted)]
+#![feature(untagged_unions)]
+
+mod m {
+    pub union U {
+        pub a: u8,
+        pub(super) b: u8,
+        c: u8,
+    }
+}
+
+fn main() {
+    let u = m::U { a: 10 };
+
+    let a = u.a; // OK
+    let b = u.b; // OK
+    let c = u.c; //~ ERROR field `c` of struct `m::U` is private
+}
diff --git a/src/test/compile-fail/union-const-eval.rs b/src/test/compile-fail/union/union-const-eval.rs
index b2bf173c59c..b2bf173c59c 100644
--- a/src/test/compile-fail/union-const-eval.rs
+++ b/src/test/compile-fail/union/union-const-eval.rs
diff --git a/src/test/compile-fail/union-const-pat.rs b/src/test/compile-fail/union/union-const-pat.rs
index 3d168980ed2..3d168980ed2 100644
--- a/src/test/compile-fail/union-const-pat.rs
+++ b/src/test/compile-fail/union/union-const-pat.rs
diff --git a/src/test/compile-fail/union/union-copy.rs b/src/test/compile-fail/union/union-copy.rs
new file mode 100644
index 00000000000..6e08ae0074d
--- /dev/null
+++ b/src/test/compile-fail/union/union-copy.rs
@@ -0,0 +1,26 @@
+// 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.
+
+#![feature(untagged_unions)]
+
+union U {
+    a: u8
+}
+
+union W {
+    a: String
+}
+
+impl Clone for U { fn clone(&self) { panic!(); } }
+impl Clone for W { fn clone(&self) { panic!(); } }
+impl Copy for U {} // OK
+impl Copy for W {} //~ ERROR the trait `Copy` may not be implemented for this type
+
+fn main() {}
diff --git a/src/test/compile-fail/union-derive.rs b/src/test/compile-fail/union/union-derive.rs
index 0f78e96f640..0f78e96f640 100644
--- a/src/test/compile-fail/union-derive.rs
+++ b/src/test/compile-fail/union/union-derive.rs
diff --git a/src/test/compile-fail/union-empty.rs b/src/test/compile-fail/union/union-empty.rs
index ce5bbf60fee..ce5bbf60fee 100644
--- a/src/test/compile-fail/union-empty.rs
+++ b/src/test/compile-fail/union/union-empty.rs
diff --git a/src/test/compile-fail/union/union-feature-gate.rs b/src/test/compile-fail/union/union-feature-gate.rs
new file mode 100644
index 00000000000..abfc4d90921
--- /dev/null
+++ b/src/test/compile-fail/union/union-feature-gate.rs
@@ -0,0 +1,15 @@
+// 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.
+
+union U { //~ ERROR unions are unstable and possibly buggy
+    a: u8,
+}
+
+fn main() {}
diff --git a/src/test/compile-fail/union-fields.rs b/src/test/compile-fail/union/union-fields.rs
index 2bd1b8a7b32..a1721dda7de 100644
--- a/src/test/compile-fail/union-fields.rs
+++ b/src/test/compile-fail/union/union-fields.rs
@@ -24,11 +24,12 @@ fn main() {
     let u = U { ..u }; //~ ERROR union expressions should have exactly one field
                        //~^ ERROR functional record update syntax requires a struct
 
-    let U {} = u; //~ ERROR union patterns without `..` should have at least one field
+    let U {} = u; //~ ERROR union patterns should have exactly one field
     let U { a } = u; // OK
-    let U { a, b } = u; //~ ERROR union patterns can have at most one field
-    let U { a, b, c } = u; //~ ERROR union patterns can have at most one field
+    let U { a, b } = u; //~ ERROR union patterns should have exactly one field
+    let U { a, b, c } = u; //~ ERROR union patterns should have exactly one field
                            //~^ ERROR union `U` does not have a field named `c`
-    let U { .. } = u; // OK
-    let U { a, .. } = u; // OK
+    let U { .. } = u; //~ ERROR union patterns should have exactly one field
+                      //~^ ERROR `..` cannot be used in union patterns
+    let U { a, .. } = u; //~ ERROR `..` cannot be used in union patterns
 }
diff --git a/src/test/compile-fail/union/union-generic.rs b/src/test/compile-fail/union/union-generic.rs
new file mode 100644
index 00000000000..e6586b0fb7f
--- /dev/null
+++ b/src/test/compile-fail/union/union-generic.rs
@@ -0,0 +1,24 @@
+// 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.
+
+#![feature(untagged_unions)]
+
+use std::rc::Rc;
+
+union U<T: Copy> {
+    a: T
+}
+
+fn main() {
+    let u = U { a: Rc::new(0u32) };
+    //~^ ERROR  the trait bound `std::rc::Rc<u32>: std::marker::Copy` is not satisfied
+    let u = U::<Rc<u32>> { a: Default::default() };
+    //~^ ERROR  the trait bound `std::rc::Rc<u32>: std::marker::Copy` is not satisfied
+}
diff --git a/src/test/compile-fail/union-nonrepresentable.rs b/src/test/compile-fail/union/union-nonrepresentable.rs
index cb4683c2a0e..cb4683c2a0e 100644
--- a/src/test/compile-fail/union-nonrepresentable.rs
+++ b/src/test/compile-fail/union/union-nonrepresentable.rs
diff --git a/src/test/compile-fail/union/union-repr-c.rs b/src/test/compile-fail/union/union-repr-c.rs
new file mode 100644
index 00000000000..d7dfb126c93
--- /dev/null
+++ b/src/test/compile-fail/union/union-repr-c.rs
@@ -0,0 +1,29 @@
+// 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.
+
+#![feature(untagged_unions)]
+#![allow(unused)]
+#![deny(improper_ctypes)]
+
+#[repr(C)]
+union U {
+    a: u8,
+}
+
+union W {
+    a: u8,
+}
+
+extern "C" {
+    static FOREIGN1: U; // OK
+    static FOREIGN2: W; //~ ERROR found union without foreign-function-safe representation
+}
+
+fn main() {}
diff --git a/src/test/compile-fail/union/union-suggest-field.rs b/src/test/compile-fail/union/union-suggest-field.rs
new file mode 100644
index 00000000000..b05e9b6e273
--- /dev/null
+++ b/src/test/compile-fail/union/union-suggest-field.rs
@@ -0,0 +1,29 @@
+// 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.
+
+#![feature(untagged_unions)]
+
+union U {
+    principal: u8,
+}
+
+impl U {
+    fn calculate(&self) {}
+}
+
+fn main() {
+    let u = U { principle: 0 }; //~ ERROR union `U` has no field named `principle`
+                                //~^ HELP did you mean `principal`?
+    let w = u.principial; //~ ERROR attempted access of field `principial` on type `U`
+                          //~^ HELP did you mean `principal`?
+
+    let y = u.calculate; //~ ERROR attempted to take value of method `calculate` on type `U`
+                         //~^ HELP maybe a `()` to call it is missing?
+}
diff --git a/src/test/compile-fail/union-unsafe.rs b/src/test/compile-fail/union/union-unsafe.rs
index 762ac5d8751..97e1ec2cba8 100644
--- a/src/test/compile-fail/union-unsafe.rs
+++ b/src/test/compile-fail/union/union-unsafe.rs
@@ -15,9 +15,10 @@ union U {
 }
 
 fn main() {
-    let u = U { a: 10 }; // OK
+    let mut u = U { a: 10 }; // OK
     let a = u.a; //~ ERROR access to union field requires unsafe function or block
+    u.a = 11; //~ ERROR access to union field requires unsafe function or block
     let U { a } = u; //~ ERROR matching on union field requires unsafe function or block
-    if let U { a: 11 } = u {} //~ ERROR matching on union field requires unsafe function or block
-    let U { .. } = u; // OK
+    if let U { a: 12 } = u {} //~ ERROR matching on union field requires unsafe function or block
+    // let U { .. } = u; // OK
 }
diff --git a/src/test/compile-fail/union-unsized.rs b/src/test/compile-fail/union/union-unsized.rs
index 381122406d7..a238eaf0525 100644
--- a/src/test/compile-fail/union-unsized.rs
+++ b/src/test/compile-fail/union/union-unsized.rs
@@ -12,6 +12,12 @@
 
 union U {
     a: str, //~ ERROR the trait bound `str: std::marker::Sized` is not satisfied
+    b: u8,
+}
+
+union W {
+    a: u8,
+    b: str, //~ ERROR the trait bound `str: std::marker::Sized` is not satisfied
 }
 
 fn main() {}
diff --git a/src/test/compile-fail/union-with-drop-fields-lint.rs b/src/test/compile-fail/union/union-with-drop-fields-lint.rs
index 87a72efbe08..87a72efbe08 100644
--- a/src/test/compile-fail/union-with-drop-fields-lint.rs
+++ b/src/test/compile-fail/union/union-with-drop-fields-lint.rs
diff --git a/src/test/run-pass/auxiliary/union.rs b/src/test/run-pass/union/auxiliary/union.rs
index dc0ca7c81c0..dc0ca7c81c0 100644
--- a/src/test/run-pass/auxiliary/union.rs
+++ b/src/test/run-pass/union/auxiliary/union.rs
diff --git a/src/test/run-pass/union-backcomp.rs b/src/test/run-pass/union/union-backcomp.rs
index c1210dd6212..9394b618ddf 100644
--- a/src/test/run-pass/union-backcomp.rs
+++ b/src/test/run-pass/union/union-backcomp.rs
@@ -10,7 +10,11 @@
 
 #![feature(untagged_unions)]
 
+fn union() {}
+
 fn main() {
+    union();
+
     let union = 10;
 
     union;
diff --git a/src/test/run-pass/union-basic.rs b/src/test/run-pass/union/union-basic.rs
index 1651aa901b9..1651aa901b9 100644
--- a/src/test/run-pass/union-basic.rs
+++ b/src/test/run-pass/union/union-basic.rs
diff --git a/src/test/run-pass/union/union-c-interop.rs b/src/test/run-pass/union/union-c-interop.rs
new file mode 100644
index 00000000000..a9f97620ebd
--- /dev/null
+++ b/src/test/run-pass/union/union-c-interop.rs
@@ -0,0 +1,47 @@
+// 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.
+
+#![feature(untagged_unions)]
+
+#[derive(Copy)]
+#[repr(C)]
+struct LARGE_INTEGER_U {
+    LowPart: u32,
+    HighPart: u32,
+}
+
+#[derive(Copy)]
+#[repr(C)]
+union LARGE_INTEGER {
+  __unnamed__: LARGE_INTEGER_U,
+  u: LARGE_INTEGER_U,
+  QuadPart: u64,
+}
+
+impl Clone for LARGE_INTEGER_U { fn clone(&self) -> Self { *self } }
+impl Clone for LARGE_INTEGER { fn clone(&self) -> Self { *self } }
+
+#[link(name = "rust_test_helpers")]
+extern "C" {
+    fn increment_all_parts(_: LARGE_INTEGER) -> LARGE_INTEGER;
+}
+
+fn main() {
+    unsafe {
+        let mut li = LARGE_INTEGER { QuadPart: 0 };
+        let li_c = increment_all_parts(li);
+        li.__unnamed__.LowPart += 1;
+        li.__unnamed__.HighPart += 1;
+        li.u.LowPart += 1;
+        li.u.HighPart += 1;
+        li.QuadPart += 1;
+        assert_eq!(li.QuadPart, li_c.QuadPart);
+    }
+}
diff --git a/src/test/run-pass/union-const-trans.rs b/src/test/run-pass/union/union-const-trans.rs
index bdae1a0eaf8..bdae1a0eaf8 100644
--- a/src/test/run-pass/union-const-trans.rs
+++ b/src/test/run-pass/union/union-const-trans.rs
diff --git a/src/test/run-pass/union-derive.rs b/src/test/run-pass/union/union-derive.rs
index b71c23990a4..b71c23990a4 100644
--- a/src/test/run-pass/union-derive.rs
+++ b/src/test/run-pass/union/union-derive.rs
diff --git a/src/test/run-pass/union-drop-assign.rs b/src/test/run-pass/union/union-drop-assign.rs
index 0da68e43f32..0da68e43f32 100644
--- a/src/test/run-pass/union-drop-assign.rs
+++ b/src/test/run-pass/union/union-drop-assign.rs
diff --git a/src/test/run-pass/union-drop.rs b/src/test/run-pass/union/union-drop.rs
index 2ca68dc3b6e..2ca68dc3b6e 100644
--- a/src/test/run-pass/union-drop.rs
+++ b/src/test/run-pass/union/union-drop.rs
diff --git a/src/test/run-pass/union/union-generic.rs b/src/test/run-pass/union/union-generic.rs
new file mode 100644
index 00000000000..9293805edbf
--- /dev/null
+++ b/src/test/run-pass/union/union-generic.rs
@@ -0,0 +1,43 @@
+// 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.
+
+#![feature(untagged_unions)]
+
+union MaybeItem<T: Iterator> {
+    elem: T::Item,
+    none: (),
+}
+
+union U<A, B> {
+    a: A,
+    b: B,
+}
+
+unsafe fn union_transmute<A, B>(a: A) -> B {
+    U { a: a }.b
+}
+
+fn main() {
+    unsafe {
+        let u = U::<String, Vec<u8>> { a: String::from("abcd") };
+
+        assert_eq!(u.b.len(), 4);
+        assert_eq!(u.b[0], b'a');
+
+        let b = union_transmute::<(u8, u8), u16>((1, 1));
+        assert_eq!(b, (1 << 8) + 1);
+
+        let v: Vec<u8> = vec![1, 2, 3];
+        let mut i = v.iter();
+        i.next();
+        let mi = MaybeItem::<std::slice::Iter<_>> { elem: i.next().unwrap() };
+        assert_eq!(*mi.elem, 2);
+    }
+}
diff --git a/src/test/compile-fail/union-field-privacy.rs b/src/test/run-pass/union/union-inherent-method.rs
index d1f2bbbc3d0..adea27bd254 100644
--- a/src/test/compile-fail/union-field-privacy.rs
+++ b/src/test/run-pass/union/union-inherent-method.rs
@@ -10,12 +10,15 @@
 
 #![feature(untagged_unions)]
 
-mod m {
-    pub union U {
-        a: u8
-    }
+union U {
+    a: u8,
+}
+
+impl U {
+    fn method(&self) -> u8 { unsafe { self.a } }
 }
 
 fn main() {
-    let u = m::U { a: 0 }; //~ ERROR field `a` of union `m::U` is private
+    let u = U { a: 10 };
+    assert_eq!(u.method(), 10);
 }
diff --git a/src/test/run-pass/union/union-macro.rs b/src/test/run-pass/union/union-macro.rs
new file mode 100644
index 00000000000..a23fbc3be9e
--- /dev/null
+++ b/src/test/run-pass/union/union-macro.rs
@@ -0,0 +1,33 @@
+// 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.
+
+#![feature(untagged_unions)]
+
+macro_rules! duplicate {
+   ($i: item) => {
+        mod m1 {
+            $i
+        }
+        mod m2 {
+            $i
+        }
+   }
+}
+
+duplicate! {
+    pub union U {
+        pub a: u8
+    }
+}
+
+fn main() {
+    let u1 = m1::U { a: 0 };
+    let u2 = m2::U { a: 0 };
+}
diff --git a/src/test/run-pass/union/union-overwrite.rs b/src/test/run-pass/union/union-overwrite.rs
new file mode 100644
index 00000000000..9389a6237bc
--- /dev/null
+++ b/src/test/run-pass/union/union-overwrite.rs
@@ -0,0 +1,80 @@
+// 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.
+
+#![feature(untagged_unions)]
+
+#[repr(C)]
+struct Pair<T, U>(T, U);
+#[repr(C)]
+struct Triple<T>(T, T, T);
+
+#[repr(C)]
+union U<A, B> {
+    a: Pair<A, A>,
+    b: B,
+}
+
+#[repr(C)]
+union W<A, B> {
+    a: A,
+    b: B,
+}
+
+#[cfg(target_endian = "little")]
+unsafe fn check() {
+    let mut u = U::<u8, u16> { b: 0xDE_DE };
+    u.a.0 = 0xBE;
+    assert_eq!(u.b, 0xDE_BE);
+
+    let mut u = U::<u16, u32> { b: 0xDEAD_DEAD };
+    u.a.0 = 0xBEEF;
+    assert_eq!(u.b, 0xDEAD_BEEF);
+
+    let mut u = U::<u32, u64> { b: 0xDEADBEEF_DEADBEEF };
+    u.a.0 = 0xBAADF00D;
+    assert_eq!(u.b, 0xDEADBEEF_BAADF00D);
+
+    let mut w = W::<Pair<Triple<u8>, u8>, u32> { b: 0xDEAD_DEAD };
+    w.a.0 = Triple(0, 0, 0);
+    assert_eq!(w.b, 0xDE00_0000);
+
+    let mut w = W::<Pair<u8, Triple<u8>>, u32> { b: 0xDEAD_DEAD };
+    w.a.1 = Triple(0, 0, 0);
+    assert_eq!(w.b, 0x0000_00AD);
+}
+
+#[cfg(target_endian = "big")]
+unsafe fn check() {
+    let mut u = U::<u8, u16> { b: 0xDE_DE };
+    u.a.0 = 0xBE;
+    assert_eq!(u.b, 0xBE_DE);
+
+    let mut u = U::<u16, u32> { b: 0xDEAD_DEAD };
+    u.a.0 = 0xBEEF;
+    assert_eq!(u.b, 0xBEEF_DEAD);
+
+    let mut u = U::<u32, u64> { b: 0xDEADBEEF_DEADBEEF };
+    u.a.0 = 0xBAADF00D;
+    assert_eq!(u.b, 0xBAADF00D_DEADBEEF);
+
+    let mut w = W::<Pair<Triple<u8>, u8>, u32> { b: 0xDEAD_DEAD };
+    w.a.0 = Triple(0, 0, 0);
+    assert_eq!(w.b, 0x0000_00AD);
+
+    let mut w = W::<Pair<u8, Triple<u8>>, u32> { b: 0xDEAD_DEAD };
+    w.a.1 = Triple(0, 0, 0);
+    assert_eq!(w.b, 0xDE00_0000);
+}
+
+fn main() {
+    unsafe {
+        check();
+    }
+}
diff --git a/src/test/run-pass/union-packed.rs b/src/test/run-pass/union/union-packed.rs
index b1650ae3a7c..6a61280823e 100644
--- a/src/test/run-pass/union-packed.rs
+++ b/src/test/run-pass/union/union-packed.rs
@@ -71,4 +71,34 @@ fn main() {
     assert_eq!(align_of::<Up>(), 1);
     assert_eq!(align_of_val(&up), 1);
     assert_eq!(align_of_val(&CUP), 1);
+
+    hybrid::check_hybrid();
+}
+
+mod hybrid {
+    use std::mem::size_of;
+
+    #[repr(packed)]
+    struct S1 {
+        a: u16,
+        b: u8,
+    }
+
+    #[repr(packed)]
+    union U {
+        s: S1,
+        c: u16,
+    }
+
+    #[repr(packed)]
+    struct S2 {
+        d: u8,
+        u: U,
+    }
+
+    pub fn check_hybrid() {
+        assert_eq!(size_of::<S1>(), 3);
+        assert_eq!(size_of::<U>(), 3);
+        assert_eq!(size_of::<S2>(), 4);
+    }
 }
diff --git a/src/test/run-pass/union-pat-refutability.rs b/src/test/run-pass/union/union-pat-refutability.rs
index e6144f35f1d..e6144f35f1d 100644
--- a/src/test/run-pass/union-pat-refutability.rs
+++ b/src/test/run-pass/union/union-pat-refutability.rs
diff --git a/src/test/run-pass/union/union-trait-impl.rs b/src/test/run-pass/union/union-trait-impl.rs
new file mode 100644
index 00000000000..a5a2be0133a
--- /dev/null
+++ b/src/test/run-pass/union/union-trait-impl.rs
@@ -0,0 +1,27 @@
+// 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.
+
+#![feature(untagged_unions)]
+
+use std::fmt;
+
+union U {
+    a: u8
+}
+
+impl fmt::Display for U {
+    fn fmt(&self, f: &mut fmt::Formatter) -> Result<(), fmt::Error> {
+        unsafe { write!(f, "Oh hai {}", self.a) }
+    }
+}
+
+fn main() {
+    assert_eq!(U { a: 2 }.to_string(), "Oh hai 2");
+}
diff --git a/src/test/run-pass/union-transmute.rs b/src/test/run-pass/union/union-transmute.rs
index 4eb66268ab8..4eb66268ab8 100644
--- a/src/test/run-pass/union-transmute.rs
+++ b/src/test/run-pass/union/union-transmute.rs
diff --git a/src/test/run-pass/union/union-with-drop-fields-lint.rs b/src/test/run-pass/union/union-with-drop-fields-lint.rs
new file mode 100644
index 00000000000..5a1424830d0
--- /dev/null
+++ b/src/test/run-pass/union/union-with-drop-fields-lint.rs
@@ -0,0 +1,42 @@
+// 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.
+
+// ignore-pretty
+
+#![feature(untagged_unions)]
+#![allow(dead_code)]
+#![allow(unions_with_drop_fields)]
+
+union U {
+    a: u8, // OK
+}
+
+union W {
+    a: String, // OK
+    b: String, // OK
+}
+
+struct S(String);
+
+// `S` doesn't implement `Drop` trait, but still has non-trivial destructor
+union Y {
+    a: S, // OK
+}
+
+// We don't know if `T` is trivially-destructable or not until trans
+union J<T> {
+    a: T, // OK
+}
+
+union H<T: Copy> {
+    a: T, // OK
+}
+
+fn main() {}
diff --git a/src/test/run-pass/union-xcrate.rs b/src/test/run-pass/union/union-xcrate.rs
index 2a76c96ef25..2a76c96ef25 100644
--- a/src/test/run-pass/union-xcrate.rs
+++ b/src/test/run-pass/union/union-xcrate.rs