Support LuaJIT cdata type (produced by ffi module)

src/lua.rs

@@ -26,7 +26,7 @@ use crate::table::Table;
 use crate::thread::Thread;
 use crate::types::{
     AppData, AppDataRef, AppDataRefMut, Callback, CallbackUpvalue, DestructedUserdata, Integer,
-    LightUserData, LuaRef, MaybeSend, Number, RegistryKey,
+    LightUserData, LuaRef, MaybeSend, Number, RegistryKey, SubtypeId,
 };
 use crate::userdata::{AnyUserData, MetaMethod, UserData, UserDataCell};
 use crate::userdata_impl::{UserDataProxy, UserDataRegistry};
@@ -2419,7 +2419,7 @@ impl Lua {
                         ffi::lua_pop(state, 1);
                         Nil
                     }
-                    _ => Value::UserData(AnyUserData(self.pop_ref(), 0)),
+                    _ => Value::UserData(AnyUserData(self.pop_ref(), SubtypeId::None)),
                 }
             }
 
@@ -2428,14 +2428,13 @@ impl Lua {
             #[cfg(feature = "luau")]
             ffi::LUA_TBUFFER => {
                 // Buffer is represented as a userdata type
-                Value::UserData(AnyUserData(self.pop_ref(), crate::types::BUFFER_SUBTYPE_ID))
+                Value::UserData(AnyUserData(self.pop_ref(), SubtypeId::Buffer))
             }
 
             #[cfg(feature = "luajit")]
             ffi::LUA_TCDATA => {
-                ffi::lua_pop(state, 1);
-                // TODO: Fix this in a next major release
-                panic!("cdata objects cannot be handled by mlua yet");
+                // CDATA is represented as a userdata type
+                Value::UserData(AnyUserData(self.pop_ref(), SubtypeId::CData))
             }
 
             _ => mlua_panic!("LUA_TNONE in pop_value"),
@@ -2520,7 +2519,7 @@ impl Lua {
                     }
                     _ => {
                         ffi::lua_xpush(state, self.ref_thread(), idx);
-                        Value::UserData(AnyUserData(self.pop_ref_thread(), 0))
+                        Value::UserData(AnyUserData(self.pop_ref_thread(), SubtypeId::None))
                     }
                 }
             }
@@ -2534,14 +2533,14 @@ impl Lua {
             ffi::LUA_TBUFFER => {
                 // Buffer is represented as a userdata type
                 ffi::lua_xpush(state, self.ref_thread(), idx);
-                let subtype_id = crate::types::BUFFER_SUBTYPE_ID;
-                Value::UserData(AnyUserData(self.pop_ref_thread(), subtype_id))
+                Value::UserData(AnyUserData(self.pop_ref_thread(), SubtypeId::Buffer))
             }
 
             #[cfg(feature = "luajit")]
             ffi::LUA_TCDATA => {
-                // TODO: Fix this in a next major release
-                panic!("cdata objects cannot be handled by mlua yet");
+                // CData is represented as a userdata type
+                ffi::lua_xpush(state, self.ref_thread(), idx);
+                Value::UserData(AnyUserData(self.pop_ref_thread(), SubtypeId::CData))
             }
 
             _ => mlua_panic!("LUA_TNONE in pop_value"),
@@ -3126,7 +3125,7 @@ impl Lua {
             ffi::lua_setuservalue(state, -2);
         }
 
-        Ok(AnyUserData(self.pop_ref(), 0))
+        Ok(AnyUserData(self.pop_ref(), SubtypeId::None))
     }
 
     #[cfg(not(feature = "luau"))]

src/scope.rs

@@ -10,7 +10,7 @@ use serde::Serialize;
 use crate::error::{Error, Result};
 use crate::function::Function;
 use crate::lua::Lua;
-use crate::types::{Callback, CallbackUpvalue, LuaRef, MaybeSend};
+use crate::types::{Callback, CallbackUpvalue, LuaRef, MaybeSend, SubtypeId};
 use crate::userdata::{
     AnyUserData, MetaMethod, UserData, UserDataCell, UserDataFields, UserDataMethods,
 };
@@ -511,7 +511,7 @@ impl<'lua, 'scope> Scope<'lua, 'scope> {
             #[cfg(not(feature = "luau"))]
             std::ptr::write(ud_ptr as _, UserDataCell::new(data));
             ffi::lua_setmetatable(state, -2);
-            let ud = AnyUserData(lua.pop_ref(), 0);
+            let ud = AnyUserData(lua.pop_ref(), SubtypeId::None);
             lua.register_raw_userdata_metatable(mt_ptr, None);
 
             #[cfg(any(feature = "lua51", feature = "luajit"))]

src/types.rs

@@ -29,9 +29,15 @@ pub type Integer = ffi::lua_Integer;
 /// Type of Lua floating point numbers.
 pub type Number = ffi::lua_Number;
 
-// LUA_TBUFFER subtype
-#[cfg(feature = "luau")]
-pub(crate) const BUFFER_SUBTYPE_ID: u8 = 1;
+// Represents different subtypes wrapped to AnyUserData
+#[derive(Debug, Copy, Clone, Eq, PartialEq)]
+pub(crate) enum SubtypeId {
+    None,
+    #[cfg(feature = "luau")]
+    Buffer,
+    #[cfg(feature = "luajit")]
+    CData,
+}
 
 /// A "light" userdata value. Equivalent to an unmanaged raw pointer.
 #[derive(Debug, Copy, Clone, Eq, PartialEq)]

src/userdata.rs

@@ -22,7 +22,7 @@ use crate::function::Function;
 use crate::lua::Lua;
 use crate::string::String;
 use crate::table::{Table, TablePairs};
-use crate::types::{LuaRef, MaybeSend};
+use crate::types::{LuaRef, MaybeSend, SubtypeId};
 use crate::util::{check_stack, get_userdata, take_userdata, StackGuard};
 use crate::value::{FromLua, FromLuaMulti, IntoLua, IntoLuaMulti, Value};
 use crate::UserDataRegistry;
@@ -791,7 +791,7 @@ impl<T> Deref for UserDataVariant<T> {
 /// [`is`]: crate::AnyUserData::is
 /// [`borrow`]: crate::AnyUserData::borrow
 #[derive(Clone, Debug)]
-pub struct AnyUserData<'lua>(pub(crate) LuaRef<'lua>, pub(crate) u8);
+pub struct AnyUserData<'lua>(pub(crate) LuaRef<'lua>, pub(crate) SubtypeId);
 
 /// Owned handle to an internal Lua userdata.
 ///
@@ -801,7 +801,7 @@ pub struct AnyUserData<'lua>(pub(crate) LuaRef<'lua>, pub(crate) u8);
 #[cfg(feature = "unstable")]
 #[cfg_attr(docsrs, doc(cfg(feature = "unstable")))]
 #[derive(Clone, Debug)]
-pub struct OwnedAnyUserData(pub(crate) crate::types::LuaOwnedRef, pub(crate) u8);
+pub struct OwnedAnyUserData(pub(crate) crate::types::LuaOwnedRef, pub(crate) SubtypeId);
 
 #[cfg(feature = "unstable")]
 impl OwnedAnyUserData {
@@ -1112,9 +1112,12 @@ impl<'lua> AnyUserData<'lua> {
 
     /// Returns a type name of this `UserData` (from a metatable field).
     pub(crate) fn type_name(&self) -> Result<Option<StdString>> {
-        #[cfg(feature = "luau")]
-        if self.1 == crate::types::BUFFER_SUBTYPE_ID {
-            return Ok(Some("buffer".to_owned()));
+        match self.1 {
+            SubtypeId::None => {}
+            #[cfg(feature = "luau")]
+            SubtypeId::Buffer => return Ok(Some("buffer".to_owned())),
+            #[cfg(feature = "luajit")]
+            SubtypeId::CData => return Ok(Some("cdata".to_owned())),
         }
 
         let lua = self.0.lua;

src/value.rs

@@ -24,7 +24,7 @@ use crate::lua::Lua;
 use crate::string::String;
 use crate::table::Table;
 use crate::thread::Thread;
-use crate::types::{Integer, LightUserData, Number};
+use crate::types::{Integer, LightUserData, Number, SubtypeId};
 use crate::userdata::AnyUserData;
 use crate::util::{check_stack, StackGuard};
 
@@ -88,9 +88,11 @@ impl<'lua> Value<'lua> {
             Value::Table(_) => "table",
             Value::Function(_) => "function",
             Value::Thread(_) => "thread",
+            Value::UserData(AnyUserData(_, SubtypeId::None)) => "userdata",
             #[cfg(feature = "luau")]
-            Value::UserData(AnyUserData(_, crate::types::BUFFER_SUBTYPE_ID)) => "buffer",
-            Value::UserData(_) => "userdata",
+            Value::UserData(AnyUserData(_, SubtypeId::Buffer)) => "buffer",
+            #[cfg(feature = "luajit")]
+            Value::UserData(AnyUserData(_, SubtypeId::CData)) => "cdata",
             Value::Error(_) => "error",
         }
     }
@@ -419,7 +421,18 @@ impl<'lua> Value<'lua> {
     #[inline]
     pub fn is_buffer(&self) -> bool {
         self.as_userdata()
-            .map(|ud| ud.1 == crate::types::BUFFER_SUBTYPE_ID)
+            .map(|ud| ud.1 == SubtypeId::Buffer)
+            .unwrap_or_default()
+    }
+
+    /// Returns `true` if the value is a CData wrapped in [`AnyUserData`].
+    #[cfg(any(feature = "luajit", doc))]
+    #[cfg_attr(docsrs, doc(cfg(feature = "luajit")))]
+    #[doc(hidden)]
+    #[inline]
+    pub fn is_cdata(&self) -> bool {
+        self.as_userdata()
+            .map(|ud| ud.1 == SubtypeId::CData)
             .unwrap_or_default()
     }
 

tests/tests.rs

@@ -1325,10 +1325,10 @@ fn test_warnings() -> Result<()> {
 
 #[test]
 #[cfg(feature = "luajit")]
-#[should_panic]
-fn test_luajit_cdata() {
+fn test_luajit_cdata() -> Result<()> {
     let lua = unsafe { Lua::unsafe_new() };
-    let _v: Result<Value> = lua
+
+    let cdata = lua
         .load(
             r#"
         local ffi = require("ffi")
@@ -1341,7 +1341,12 @@ fn test_luajit_cdata() {
         return ptr
     "#,
         )
-        .eval();
+        .eval::<Value>()?;
+    assert!(cdata.is_userdata() && cdata.is_cdata());
+    assert_eq!(cdata.type_name(), "cdata");
+    assert!(cdata.to_string()?.starts_with("cdata<void *>:"));
+
+    Ok(())
 }
 
 #[test]