Auto merge of #782 - RalfJung:generator, r=RalfJung

add a failing test where an immovable generator gets moved

Test courtesy of @shepmaster

tests/compile-fail/generator-pinned-moved.rs

@@ -0,0 +1,44 @@
+#![feature(generators, generator_trait)]
+
+use std::{
+    ops::{Generator, GeneratorState},
+    pin::Pin,
+};
+
+fn firstn() -> impl Generator<Yield = u64, Return = ()> {
+    static move || {
+        let mut num = 0;
+        let num = &mut num;
+
+        yield *num;
+        *num += 1; //~ ERROR dangling pointer was dereferenced
+    }
+}
+
+struct GeneratorIteratorAdapter<G>(G);
+
+impl<G> Iterator for GeneratorIteratorAdapter<G>
+where
+    G: Generator<Return = ()>,
+{
+    type Item = G::Yield;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        let me = unsafe { Pin::new_unchecked(&mut self.0) };
+        match me.resume() {
+            GeneratorState::Yielded(x) => Some(x),
+            GeneratorState::Complete(_) => None,
+        }
+    }
+}
+
+fn main() {
+    let mut generator_iterator_2 = {
+        let mut generator_iterator = GeneratorIteratorAdapter(firstn());
+        generator_iterator.next(); // pin it
+
+        generator_iterator // move it
+    }; // *deallocate* generator_iterator
+
+    generator_iterator_2.next(); // and use moved value
+}