Avoid unnecessarily coping result inner value if it doesn't require ownership

crates/luaffi/src/future.rs

@@ -177,6 +177,15 @@ unsafe impl<F: Future<Output: IntoFfi> + 'static> IntoFfi for lua_future<F> {
         self
     }
 
+    fn require_owned() -> bool {
+        // future always requires full ownership of itself even if it's a "temporary", because we
+        // must yield a full cdata to the runtime not a cdata containing a pointer to the future. if
+        // this is set to false, postlude might receive a reference lua_future cdata instead of a
+        // full lua_future cdata, and the runtime might incorrectly read the pointer value as
+        // lua_future itself (it does not dereference it).
+        true
+    }
+
     fn postlude(ret: &str) -> impl Display {
         // When returning a future from Rust to Lua, yield it immediately to the runtime which will
         // poll it to completion in the background, then take the fulfilled value once the thread