1 files changed, 30 insertions, 0 deletions
diff --git a/src/test/ui/impl-trait/nested-return-type2.rs b/src/test/ui/impl-trait/nested-return-type2.rs
new file mode 100644
index 000000000..39928d543
--- /dev/null
+++ b/src/test/ui/impl-trait/nested-return-type2.rs
@@ -0,0 +1,30 @@
+// check-pass
+
+trait Duh {}
+
+impl Duh for i32 {}
+
+trait Trait {
+    type Assoc: Duh;
+}
+
+// the fact that `R` is the `::Output` projection on `F` causes
+// an intermediate inference var to be generated which is then later
+// compared against the actually found `Assoc` type.
+impl<R: Duh, F: FnMut() -> R> Trait for F {
+    type Assoc = R;
+}
+
+// The `impl Send` here is then later compared against the inference var
+// created, causing the inference var to be set to `impl Send` instead of
+// the hidden type. We already have obligations registered on the inference
+// var to make it uphold the `: Duh` bound on `Trait::Assoc`. The opaque
+// type does not implement `Duh`, even if its hidden type does.
+// Lazy TAIT would error out, but we inserted a hack to make it work again,
+// keeping backwards compatibility.
+fn foo() -> impl Trait<Assoc = impl Send> {
+    || 42
+}
+
+fn main() {
+}