Mark LightUserData as Send+Sync (send feature flag)

src/types.rs

@@ -41,6 +41,11 @@ pub(crate) enum SubtypeId {
 #[derive(Debug, Copy, Clone, Eq, PartialEq)]
 pub struct LightUserData(pub *mut c_void);
 
+#[cfg(feature = "send")]
+unsafe impl Send for LightUserData {}
+#[cfg(feature = "send")]
+unsafe impl Sync for LightUserData {}
+
 pub(crate) type Callback<'a> = Box<dyn Fn(&'a RawLua, c_int) -> Result<c_int> + 'static>;
 
 pub(crate) struct Upvalue<T> {

src/value.rs

@@ -934,6 +934,13 @@ pub trait FromLuaMulti: Sized {
 mod assertions {
     use super::*;
 
+    #[cfg(not(feature = "send"))]
     static_assertions::assert_not_impl_any!(Value: Send);
+    #[cfg(not(feature = "send"))]
     static_assertions::assert_not_impl_any!(MultiValue: Send);
+
+    #[cfg(feature = "send")]
+    static_assertions::assert_impl_all!(Value: Send, Sync);
+    #[cfg(feature = "send")]
+    static_assertions::assert_impl_all!(MultiValue: Send, Sync);
 }