1 files changed, 33 insertions, 0 deletions
diff --git a/tests/ui/structs-enums/enum-clike-ffi-as-int.rs b/tests/ui/structs-enums/enum-clike-ffi-as-int.rs
new file mode 100644
index 000000000..e2b2b43de
--- /dev/null
+++ b/tests/ui/structs-enums/enum-clike-ffi-as-int.rs
@@ -0,0 +1,33 @@
+// run-pass
+#![allow(dead_code)]
+
+/*!
+ * C-like enums have to be represented as LLVM ints, not wrapped in a
+ * struct, because it's important for the FFI that they interoperate
+ * with C integers/enums, and the ABI can treat structs differently.
+ * For example, on i686-linux-gnu, a struct return value is passed by
+ * storing to a hidden out parameter, whereas an integer would be
+ * returned in a register.
+ *
+ * This test just checks that the ABIs for the enum and the plain
+ * integer are compatible, rather than actually calling C code.
+ * The unused parameter to `foo` is to increase the likelihood of
+ * crashing if something goes wrong here.
+ */
+
+#[repr(u32)]
+enum Foo {
+    A = 0,
+    B = 23
+}
+
+#[inline(never)]
+extern "C" fn foo(_x: usize) -> Foo { Foo::B }
+
+pub fn main() {
+    unsafe {
+        let f: extern "C" fn(usize) -> u32 =
+            ::std::mem::transmute(foo as extern "C" fn(usize) -> Foo);
+        assert_eq!(f(0xDEADBEEF), Foo::B as u32);
+    }
+}