Add signature check to lua_pollable

crates/luajit/src/lib.rs

@@ -11,6 +11,7 @@ use std::{
     marker::PhantomData,
     ops::{Deref, DerefMut},
     os::raw::{c_char, c_int, c_void},
+    pin::Pin,
     process,
     ptr::{self, NonNull},
     rc::Rc,
@@ -981,26 +982,26 @@ impl Stack {
         loop {
             match self.resume(narg)? {
                 ResumeStatus::Ok => {
-                    let n = self.size() - base;
-                    break Ok(if nret == LUA_MULTRET {
-                        n
+                    if nret == LUA_MULTRET {
+                        break Ok(self.size() - base);
                     } else {
-                        self.resize(nret);
-                        nret
-                    });
+                        self.resize(base + nret);
+                        break Ok(nret);
+                    }
                 }
                 ResumeStatus::Suspended => {
+                    narg = 0;
                     self.resize(1);
-                    let value = self.slot(1);
-                    let ptr = value.cdata::<lua_pollable>().cast_mut();
-                    if ptr.is_null() {
-                        return Err(Error::InvalidType(
-                            "cdata<struct lua_pollable>",
-                            value.type_of().name(),
-                        ));
-                    } else {
-                        unsafe { (&mut *ptr).await }
-                        narg = 0;
+
+                    let ptr = self.slot(1).cdata::<lua_pollable>().cast_mut();
+                    if !ptr.is_null() {
+                        // SAFETY: rust futures boxed in cdata payloads are never moved by the GC so
+                        // we can safely make a Pin out of this pointer. see also comments in
+                        // `luaffi::future::lua_future<T>`.
+                        let fut = unsafe { Pin::new_unchecked(&mut *ptr) };
+                        if fut.is_valid() {
+                            fut.await;
+                        }
                     }
                 }
             }