Add test for generator sizes with resume arguments

src/test/ui/generator/resume-arg-size.rs

@@ -0,0 +1,28 @@
+#![feature(generators)]
+
+// run-pass
+
+use std::mem::size_of_val;
+
+fn main() {
+    // Generator taking a `Copy`able resume arg.
+    let gen_copy = |mut x: usize| {
+        loop {
+            drop(x);
+            x = yield;
+        }
+    };
+
+    // Generator taking a non-`Copy` resume arg.
+    let gen_move = |mut x: Box<usize>| {
+        loop {
+            drop(x);
+            x = yield;
+        }
+    };
+
+    // Neither of these generators have the resume arg live across the `yield`, so they should be
+    // 4 Bytes in size (only storing the discriminant)
+    assert_eq!(size_of_val(&gen_copy), 4);
+    assert_eq!(size_of_val(&gen_move), 4);
+}