1 files changed, 32 insertions, 0 deletions
diff --git a/tests/ui/coercion/codegen-smart-pointer-with-alias.rs b/tests/ui/coercion/codegen-smart-pointer-with-alias.rs
new file mode 100644
index 00000000000..a68952bb70a
--- /dev/null
+++ b/tests/ui/coercion/codegen-smart-pointer-with-alias.rs
@@ -0,0 +1,32 @@
+//@ build-pass
+
+// Regression test for <https://github.com/rust-lang/rust/issues/139812>.
+
+// Make sure that the unsize coercion we collect in mono for `Signal<i32> -> Signal<dyn Any>`
+// doesn't choke on the fact that the inner unsized field of `Signal<T>` is a (trivial) alias.
+// This exercises a normalize call that is necessary since we're getting a type from the type
+// system, which isn't guaranteed to be normalized after substitution.
+
+#![feature(coerce_unsized)]
+
+use std::ops::CoerceUnsized;
+
+trait Mirror {
+    type Assoc: ?Sized;
+}
+impl<T: ?Sized> Mirror for T {
+    type Assoc = T;
+}
+
+trait Any {}
+impl<T> Any for T {}
+
+struct Signal<'a, T: ?Sized>(<&'a T as Mirror>::Assoc);
+
+// This `CoerceUnsized` impl isn't special; it's a bit more restricted than we'd see in the wild,
+// but this ICE also reproduces if we were to make it general over `Signal<T> -> Signal<U>`.
+impl<'a> CoerceUnsized<Signal<'a, dyn Any>> for Signal<'a, i32> {}
+
+fn main() {
+    Signal(&1i32) as Signal<dyn Any>;
+}