Also closures

compiler/rustc_hir_typeck/src/closure.rs

@@ -56,7 +56,9 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         // closure sooner rather than later, so first examine the expected
         // type, and see if can glean a closure kind from there.
         let (expected_sig, expected_kind) = match expected.to_option(self) {
-            Some(ty) => self.deduce_closure_signature(ty),
+            Some(ty) => {
+                self.deduce_closure_signature(self.try_structurally_resolve_type(expr_span, ty))
+            }
             None => (None, None),
         };
         let body = self.tcx.hir().body(closure.body);

tests/ui/traits/new-solver/deduce-closure-signature-after-normalization.rs

@@ -0,0 +1,12 @@
+// compile-flags: -Ztrait-solver=next
+// check-pass
+
+#![feature(return_position_impl_trait_in_trait)]
+
+trait Foo {
+    fn test() -> impl Fn(u32) -> u32 {
+        |x| x.count_ones()
+    }
+}
+
+fn main() {}