1 files changed, 23 insertions, 0 deletions
diff --git a/tests/ui/impl-trait/negative-reasoning.rs b/tests/ui/impl-trait/negative-reasoning.rs
new file mode 100644
index 00000000000..70e24a3a9d0
--- /dev/null
+++ b/tests/ui/impl-trait/negative-reasoning.rs
@@ -0,0 +1,23 @@
+// Tests that we cannot assume that an opaque type does *not* implement some
+// other trait
+#![feature(type_alias_impl_trait)]
+
+trait OpaqueTrait {}
+impl<T> OpaqueTrait for T {}
+type OpaqueType = impl OpaqueTrait;
+fn mk_opaque() -> OpaqueType {
+    ()
+}
+
+#[derive(Debug)]
+struct D<T>(T);
+
+trait AnotherTrait {}
+impl<T: std::fmt::Debug> AnotherTrait for T {}
+
+// This is in error, because we cannot assume that `OpaqueType: !Debug`
+impl AnotherTrait for D<OpaqueType> {
+    //~^ ERROR conflicting implementations of trait `AnotherTrait` for type `D<OpaqueType>`
+}
+
+fn main() {}