1 files changed, 33 insertions, 0 deletions
diff --git a/tests/ui/type-alias-impl-trait/impl_trait_for_same_tait.rs b/tests/ui/type-alias-impl-trait/impl_trait_for_same_tait.rs
new file mode 100644
index 000000000..3f1a9d12b
--- /dev/null
+++ b/tests/ui/type-alias-impl-trait/impl_trait_for_same_tait.rs
@@ -0,0 +1,33 @@
+#![feature(type_alias_impl_trait)]
+
+trait Foo {}
+impl Foo for () {}
+impl Foo for i32 {}
+
+type Bar<T: Foo> = impl std::fmt::Debug;
+fn defining_use<T: Foo>() -> Bar<T> {
+    42
+}
+
+trait Bop {}
+
+impl Bop for Bar<()> {}
+
+// If the hidden type is the same, this is effectively a second impl for the same type.
+impl Bop for Bar<i32> {}
+//~^ ERROR conflicting implementations
+
+type Barr = impl std::fmt::Debug;
+fn defining_use2() -> Barr {
+    42
+}
+
+// Even completely different opaque types must conflict.
+impl Bop for Barr {}
+//~^ ERROR conflicting implementations
+
+// And obviously the hidden type must conflict, too.
+impl Bop for i32 {}
+//~^ ERROR conflicting implementations
+
+fn main() {}