From d5a54a962786e4b1761d36e305ded66f5c1cfc79 Mon Sep 17 00:00:00 2001
From: Niko Matsakis <niko@alum.mit.edu>
Date: Thu, 9 Nov 2017 17:00:36 -0500
Subject: [PATCH] add a compile-fail test for cyclic generators being forbidden

---
 .../generator-yielding-or-returning-itself.rs | 45 +++++++++++++++++++
 1 file changed, 45 insertions(+)
 create mode 100644 src/test/compile-fail/generator-yielding-or-returning-itself.rs

diff --git a/src/test/compile-fail/generator-yielding-or-returning-itself.rs b/src/test/compile-fail/generator-yielding-or-returning-itself.rs
new file mode 100644
index 0000000000000..13abdf616b29b
--- /dev/null
+++ b/src/test/compile-fail/generator-yielding-or-returning-itself.rs
@@ -0,0 +1,45 @@
+// Copyright 2016 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.
+
+#![feature(generator_trait)]
+#![feature(generators)]
+
+// Test that we cannot create a generator that returns a value of its
+// own type.
+
+use std::ops::Generator;
+
+pub fn want_cyclic_generator_return<T>(_: T)
+    where T: Generator<Yield = (), Return = T>
+{
+}
+
+fn supply_cyclic_generator_return() {
+    want_cyclic_generator_return(|| {
+        //~^ ERROR type mismatch
+        if false { yield None.unwrap(); }
+        None.unwrap()
+    })
+}
+
+pub fn want_cyclic_generator_yield<T>(_: T)
+    where T: Generator<Yield = T, Return = ()>
+{
+}
+
+fn supply_cyclic_generator_yield() {
+    want_cyclic_generator_yield(|| {
+        //~^ ERROR type mismatch
+        if false { yield None.unwrap(); }
+        None.unwrap()
+    })
+}
+
+fn main() { }