1 files changed, 42 insertions, 0 deletions
diff --git a/tests/ui/traits/principal-less-objects.rs b/tests/ui/traits/principal-less-objects.rs
new file mode 100644
index 00000000000..62bad0d7d77
--- /dev/null
+++ b/tests/ui/traits/principal-less-objects.rs
@@ -0,0 +1,42 @@
+// run-pass
+// Check that trait objects without a principal codegen properly.
+
+use std::sync::atomic::{AtomicUsize, Ordering};
+use std::mem;
+
+// Array is to make sure the size is not exactly pointer-size, so
+// we can be sure we are measuring the right size in the
+// `size_of_val` test.
+struct SetOnDrop<'a>(&'a AtomicUsize, #[allow(unused_tuple_struct_fields)] [u8; 64]);
+impl<'a> Drop for SetOnDrop<'a> {
+    fn drop(&mut self) {
+        self.0.store(self.0.load(Ordering::Relaxed) + 1, Ordering::Relaxed);
+    }
+}
+
+trait TypeEq<V: ?Sized> {}
+impl<T: ?Sized> TypeEq<T> for T {}
+fn assert_types_eq<U: ?Sized, V: ?Sized>() where U: TypeEq<V> {}
+
+fn main() {
+    // Check that different ways of writing the same type are equal.
+    assert_types_eq::<dyn Sync, dyn Sync + Sync>();
+    assert_types_eq::<dyn Sync + Send, dyn Send + Sync>();
+    assert_types_eq::<dyn Sync + Send + Sync, dyn Send + Sync>();
+
+    // Check that codegen works.
+    //
+    // Using `AtomicUsize` here because `Cell<u32>` is not `Sync`, and
+    // so can't be made into a `Box<dyn Sync>`.
+    let c = AtomicUsize::new(0);
+    {
+        let d: Box<dyn Sync> = Box::new(SetOnDrop(&c, [0; 64]));
+
+        assert_eq!(mem::size_of_val(&*d),
+                   mem::size_of::<SetOnDrop>());
+        assert_eq!(mem::align_of_val(&*d),
+                   mem::align_of::<SetOnDrop>());
+        assert_eq!(c.load(Ordering::Relaxed), 0);
+    }
+    assert_eq!(c.load(Ordering::Relaxed), 1);
+}