Auto merge of #25123 - arielb1:self-inhibiting-error, r=nikomatsakis

Fix #25076.

r? @nikomatsakis

src/test/compile-fail/issue-23966.rs

@@ -9,6 +9,5 @@
 // except according to those terms.
 
 fn main() {
-    "".chars().fold(|_, _| (), ());
-    //~^ ERROR cannot determine a type for this expression: unconstrained type
+    "".chars().fold(|_, _| (), ()); //~ ERROR is not implemented for the type `()`
 }

src/test/compile-fail/issue-25076.rs

@@ -0,0 +1,21 @@
+// Copyright 2015 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+struct S;
+
+trait InOut<T> { type Out; }
+
+fn do_fold<B, F: InOut<B, Out=B>>(init: B, f: F) {}
+
+fn bot<T>() -> T { loop {} }
+
+fn main() {
+    do_fold(bot(), ()); //~ ERROR is not implemented for the type `()`
+}