inhibit enum layout optimizations under `#[repr(C)]` or `#[repr(u8)]`

Fixes #40029

1 files changed, 59 insertions, 0 deletions

diff --git a/src/test/run-pass/enum-layout-optimization.rs b/src/test/run-pass/enum-layout-optimization.rs
new file mode 100644
index 00000000000..a562761cab9
--- /dev/null
+++ b/src/test/run-pass/enum-layout-optimization.rs
@@ -0,0 +1,59 @@
+// 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.
+
+// Test that we will do various size optimizations to enum layout, but
+// *not* if `#[repr(u8)]` or `#[repr(C)]` is passed. See also #40029.
+
+#![allow(dead_code)]
+
+use std::mem;
+
+enum Nullable<T> {
+    Alive(T),
+    Dropped,
+}
+
+#[repr(u8)]
+enum NullableU8<T> {
+    Alive(T),
+    Dropped,
+}
+
+#[repr(C)]
+enum NullableC<T> {
+    Alive(T),
+    Dropped,
+}
+
+struct StructNewtype<T>(T);
+
+#[repr(C)]
+struct StructNewtypeC<T>(T);
+
+enum EnumNewtype<T> { Variant(T) }
+
+#[repr(u8)]
+enum EnumNewtypeU8<T> { Variant(T) }
+
+#[repr(C)]
+enum EnumNewtypeC<T> { Variant(T) }
+
+fn main() {
+    assert!(mem::size_of::<Box<i32>>() == mem::size_of::<Nullable<Box<i32>>>());
+    assert!(mem::size_of::<Box<i32>>() < mem::size_of::<NullableU8<Box<i32>>>());
+    assert!(mem::size_of::<Box<i32>>() < mem::size_of::<NullableC<Box<i32>>>());
+
+    assert!(mem::size_of::<i32>() == mem::size_of::<StructNewtype<i32>>());
+    assert!(mem::size_of::<i32>() == mem::size_of::<StructNewtypeC<i32>>());
+
+    assert!(mem::size_of::<i32>() == mem::size_of::<EnumNewtype<i32>>());
+    assert!(mem::size_of::<i32>() < mem::size_of::<EnumNewtypeU8<i32>>());
+    assert!(mem::size_of::<i32>() < mem::size_of::<EnumNewtypeC<i32>>());
+}