1 files changed, 41 insertions, 0 deletions
diff --git a/src/test/ui/lint/opaque-ty-ffi-normalization-cycle.rs b/src/test/ui/lint/opaque-ty-ffi-normalization-cycle.rs
new file mode 100644
index 000000000..c83bca4a4
--- /dev/null
+++ b/src/test/ui/lint/opaque-ty-ffi-normalization-cycle.rs
@@ -0,0 +1,41 @@
+#![feature(type_alias_impl_trait)]
+#![allow(unused)]
+#![deny(improper_ctypes)]
+
+pub trait TraitA {
+    type Assoc;
+}
+
+impl TraitA for u32 {
+    type Assoc = u32;
+}
+
+pub trait TraitB {
+    type Assoc;
+}
+
+impl<T> TraitB for T
+where
+    T: TraitA,
+{
+    type Assoc = <T as TraitA>::Assoc;
+}
+
+type AliasA = impl TraitA<Assoc = u32>;
+
+type AliasB = impl TraitB;
+
+fn use_of_a() -> AliasA {
+    3
+}
+
+fn use_of_b() -> AliasB {
+    3
+}
+
+extern "C" {
+    fn lint_me() -> <AliasB as TraitB>::Assoc;
+    //~^ ERROR `extern` block uses type `AliasB`, which is not FFI-safe
+}
+
+fn main() {}