Add failing test for Manishearth#124

Signed-off-by: Anders Kaseorg <[email protected]>

gc/tests/resurrection.rs

@@ -0,0 +1,36 @@
+use gc::{force_collect, Finalize, Gc, GcCell};
+use gc_derive::{Finalize, Trace};
+
+#[derive(Finalize, Trace)]
+struct Foo {
+    bar: GcCell<Option<Gc<Bar>>>,
+}
+
+#[derive(Trace)]
+struct Bar {
+    string: String,
+    foo: Gc<Foo>,
+    this: GcCell<Option<Gc<Bar>>>,
+}
+
+impl Finalize for Bar {
+    fn finalize(&self) {
+        *self.foo.bar.borrow_mut() = self.this.borrow().clone();
+    }
+}
+
+#[test]
+fn resurrection_by_finalizer() {
+    let foo = Gc::new(Foo {
+        bar: GcCell::new(None),
+    });
+    let bar = Gc::new(Bar {
+        string: "Hello, world!".to_string(),
+        foo: foo.clone(),
+        this: GcCell::new(None),
+    });
+    *bar.this.borrow_mut() = Some(bar.clone());
+    drop(bar);
+    force_collect();
+    assert_eq!(foo.bar.borrow().as_ref().unwrap().string, "Hello, world!");
+}