1 files changed, 34 insertions, 0 deletions
diff --git a/src/test/ui/box/thin_zst.rs b/src/test/ui/box/thin_zst.rs
new file mode 100644
index 000000000..77c400d17
--- /dev/null
+++ b/src/test/ui/box/thin_zst.rs
@@ -0,0 +1,34 @@
+#![feature(thin_box)]
+// run-pass
+use std::boxed::ThinBox;
+use std::error::Error;
+use std::{fmt, mem};
+use std::ops::DerefMut;
+
+const EXPECTED: &str = "boooo!";
+
+fn main() {
+    let thin_error: ThinBox<dyn Error> = ThinBox::new_unsize(Foo);
+    assert_eq!(mem::size_of::<*const i32>(), mem::size_of_val(&thin_error));
+    let msg = thin_error.to_string();
+    assert_eq!(EXPECTED, msg);
+
+    let mut thin_concrete_error: ThinBox<Foo> = ThinBox::new(Foo);
+    assert_eq!(mem::size_of::<*const i32>(), mem::size_of_val(&thin_concrete_error));
+    let msg = thin_concrete_error.to_string();
+    assert_eq!(EXPECTED, msg);
+    let inner = thin_concrete_error.deref_mut();
+    let msg = inner.to_string();
+    assert_eq!(EXPECTED, msg);
+}
+
+#[derive(Debug)]
+struct Foo;
+
+impl fmt::Display for Foo {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(f, "{}", EXPECTED)
+    }
+}
+
+impl Error for Foo {}