Add a failing xcrate generator test

src/test/run-pass/generator/auxiliary/xcrate.rs

@@ -12,14 +12,16 @@
 
 use std::ops::Generator;
 
-fn bar() -> bool {
-    false
-}
-
 pub fn foo() -> impl Generator<Yield = (), Return = ()> {
     || {
-        if bar() {
+        if false {
             yield;
         }
     }
 }
+
+pub fn bar<T: 'static>(t: T) -> Box<Generator<Yield = T, Return = ()>> {
+    Box::new(|| {
+        yield t;
+    })
+}

src/test/run-pass/generator/xcrate.rs

@@ -23,4 +23,15 @@ fn main() {
         GeneratorState::Complete(()) => {}
         s => panic!("bad state: {:?}", s),
     }
+
+    let mut foo = xcrate::bar(3);
+
+    match foo.resume() {
+        GeneratorState::Yielded(4) => {}
+        s => panic!("bad state: {:?}", s),
+    }
+    match foo.resume() {
+        GeneratorState::Complete(()) => {}
+        s => panic!("bad state: {:?}", s),
+    }
 }