mlua_codemp_patch/

state.rs

use std::any::TypeId;
use std::cell::RefCell;
use std::marker::PhantomData;
use std::ops::Deref;
use std::os::raw::{c_int, c_void};
use std::panic::Location;
use std::result::Result as StdResult;
use std::{fmt, mem, ptr};

use crate::chunk::{AsChunk, Chunk};
use crate::error::{Error, Result};
use crate::function::Function;
use crate::hook::Debug;
use crate::memory::MemoryState;
// use crate::scope::Scope;
use crate::stdlib::StdLib;
use crate::string::String;
use crate::table::Table;
use crate::thread::Thread;
use crate::types::{
    AppDataRef, AppDataRefMut, ArcReentrantMutexGuard, Integer, LightUserData, MaybeSend, Number,
    ReentrantMutex, ReentrantMutexGuard, RegistryKey, XRc, XWeak,
};
use crate::userdata::{AnyUserData, UserData, UserDataProxy, UserDataRegistry, UserDataVariant};
use crate::util::{assert_stack, check_stack, push_string, push_table, rawset_field, StackGuard};
use crate::value::{FromLua, FromLuaMulti, IntoLua, IntoLuaMulti, MultiValue, Nil, Value};

#[cfg(not(feature = "luau"))]
use crate::hook::HookTriggers;

#[cfg(any(feature = "luau", doc))]
use crate::{chunk::Compiler, types::VmState};

#[cfg(feature = "async")]
use std::future::{self, Future};

#[cfg(feature = "serialize")]
use serde::Serialize;

pub(crate) use extra::ExtraData;
pub use raw::RawLua;
use util::{callback_error_ext, StateGuard};

/// Top level Lua struct which represents an instance of Lua VM.
#[derive(Clone)]
pub struct Lua {
    pub(self) raw: XRc<ReentrantMutex<RawLua>>,
    // Controls whether garbage collection should be run on drop
    pub(self) collect_garbage: bool,
}

#[derive(Clone)]
pub(crate) struct WeakLua(XWeak<ReentrantMutex<RawLua>>);

pub(crate) struct LuaGuard(ArcReentrantMutexGuard<RawLua>);

/// Mode of the Lua garbage collector (GC).
///
/// In Lua 5.4 GC can work in two modes: incremental and generational.
/// Previous Lua versions support only incremental GC.
///
/// More information can be found in the Lua [documentation].
///
/// [documentation]: https://www.lua.org/manual/5.4/manual.html#2.5
#[derive(Clone, Copy, Debug, PartialEq, Eq)]
pub enum GCMode {
    Incremental,
    /// Requires `feature = "lua54"`
    #[cfg(feature = "lua54")]
    #[cfg_attr(docsrs, doc(cfg(feature = "lua54")))]
    Generational,
}

/// Controls Lua interpreter behavior such as Rust panics handling.
#[derive(Clone, Debug)]
#[non_exhaustive]
pub struct LuaOptions {
    /// Catch Rust panics when using [`pcall`]/[`xpcall`].
    ///
    /// If disabled, wraps these functions and automatically resumes panic if found.
    /// Also in Lua 5.1 adds ability to provide arguments to [`xpcall`] similar to Lua >= 5.2.
    ///
    /// If enabled, keeps [`pcall`]/[`xpcall`] unmodified.
    /// Panics are still automatically resumed if returned to the Rust side.
    ///
    /// Default: **true**
    ///
    /// [`pcall`]: https://www.lua.org/manual/5.4/manual.html#pdf-pcall
    /// [`xpcall`]: https://www.lua.org/manual/5.4/manual.html#pdf-xpcall
    pub catch_rust_panics: bool,

    /// Max size of thread (coroutine) object pool used to execute asynchronous functions.
    ///
    /// It works on Lua 5.4 and Luau, where [`lua_resetthread`] function
    /// is available and allows to reuse old coroutines after resetting their state.
    ///
    /// Default: **0** (disabled)
    ///
    /// [`lua_resetthread`]: https://www.lua.org/manual/5.4/manual.html#lua_resetthread
    #[cfg(feature = "async")]
    #[cfg_attr(docsrs, doc(cfg(feature = "async")))]
    pub thread_pool_size: usize,
}

impl Default for LuaOptions {
    fn default() -> Self {
        const { LuaOptions::new() }
    }
}

impl LuaOptions {
    /// Returns a new instance of `LuaOptions` with default parameters.
    pub const fn new() -> Self {
        LuaOptions {
            catch_rust_panics: true,
            #[cfg(feature = "async")]
            thread_pool_size: 0,
        }
    }

    /// Sets [`catch_rust_panics`] option.
    ///
    /// [`catch_rust_panics`]: #structfield.catch_rust_panics
    #[must_use]
    pub const fn catch_rust_panics(mut self, enabled: bool) -> Self {
        self.catch_rust_panics = enabled;
        self
    }

    /// Sets [`thread_pool_size`] option.
    ///
    /// [`thread_pool_size`]: #structfield.thread_pool_size
    #[cfg(feature = "async")]
    #[cfg_attr(docsrs, doc(cfg(feature = "async")))]
    #[must_use]
    pub const fn thread_pool_size(mut self, size: usize) -> Self {
        self.thread_pool_size = size;
        self
    }
}

impl Drop for Lua {
    fn drop(&mut self) {
        if self.collect_garbage {
            let _ = self.gc_collect();
        }
    }
}

impl fmt::Debug for Lua {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        write!(f, "Lua({:p})", self.lock().state())
    }
}

impl Default for Lua {
    #[inline]
    fn default() -> Self {
        Lua::new()
    }
}

impl Lua {
    /// Creates a new Lua state and loads the **safe** subset of the standard libraries.
    ///
    /// # Safety
    /// The created Lua state would have _some_ safety guarantees and would not allow to load unsafe
    /// standard libraries or C modules.
    ///
    /// See [`StdLib`] documentation for a list of unsafe modules that cannot be loaded.
    ///
    /// [`StdLib`]: crate::StdLib
    pub fn new() -> Lua {
        mlua_expect!(
            Self::new_with(StdLib::ALL_SAFE, LuaOptions::default()),
            "Cannot create a Lua state"
        )
    }

    /// Creates a new Lua state and loads all the standard libraries.
    ///
    /// # Safety
    /// The created Lua state would not have safety guarantees and would allow to load C modules.
    pub unsafe fn unsafe_new() -> Lua {
        Self::unsafe_new_with(StdLib::ALL, LuaOptions::default())
    }

    /// Creates a new Lua state and loads the specified safe subset of the standard libraries.
    ///
    /// Use the [`StdLib`] flags to specify the libraries you want to load.
    ///
    /// # Safety
    /// The created Lua state would have _some_ safety guarantees and would not allow to load unsafe
    /// standard libraries or C modules.
    ///
    /// See [`StdLib`] documentation for a list of unsafe modules that cannot be loaded.
    ///
    /// [`StdLib`]: crate::StdLib
    pub fn new_with(libs: StdLib, options: LuaOptions) -> Result<Lua> {
        #[cfg(not(feature = "luau"))]
        if libs.contains(StdLib::DEBUG) {
            return Err(Error::SafetyError(
                "The unsafe `debug` module can't be loaded using safe `new_with`".to_string(),
            ));
        }
        #[cfg(feature = "luajit")]
        if libs.contains(StdLib::FFI) {
            return Err(Error::SafetyError(
                "The unsafe `ffi` module can't be loaded using safe `new_with`".to_string(),
            ));
        }

        let lua = unsafe { Self::inner_new(libs, options) };

        if libs.contains(StdLib::PACKAGE) {
            mlua_expect!(lua.disable_c_modules(), "Error disabling C modules");
        }
        unsafe { lua.lock().set_safe() };

        Ok(lua)
    }

    /// Creates a new Lua state and loads the specified subset of the standard libraries.
    ///
    /// Use the [`StdLib`] flags to specify the libraries you want to load.
    ///
    /// # Safety
    /// The created Lua state will not have safety guarantees and allow to load C modules.
    ///
    /// [`StdLib`]: crate::StdLib
    pub unsafe fn unsafe_new_with(libs: StdLib, options: LuaOptions) -> Lua {
        // Workaround to avoid stripping a few unused Lua symbols that could be imported
        // by C modules in unsafe mode
        let mut _symbols: Vec<*const extern "C-unwind" fn()> =
            vec![ffi::lua_isuserdata as _, ffi::lua_tocfunction as _];

        #[cfg(not(feature = "luau"))]
        _symbols.extend_from_slice(&[
            ffi::lua_atpanic as _,
            ffi::luaL_loadstring as _,
            ffi::luaL_openlibs as _,
        ]);
        #[cfg(any(feature = "lua54", feature = "lua53", feature = "lua52"))]
        {
            _symbols.push(ffi::lua_getglobal as _);
            _symbols.push(ffi::lua_setglobal as _);
            _symbols.push(ffi::luaL_setfuncs as _);
        }

        Self::inner_new(libs, options)
    }

    /// Creates a new Lua state with required `libs` and `options`
    unsafe fn inner_new(libs: StdLib, options: LuaOptions) -> Lua {
        let lua = Lua {
            raw: RawLua::new(libs, options),
            collect_garbage: true,
        };

        #[cfg(feature = "luau")]
        mlua_expect!(lua.configure_luau(), "Error configuring Luau");

        lua
    }

    /// Constructs a new Lua instance from an existing raw state.
    ///
    /// Once called, a returned Lua state is cached in the registry and can be retrieved
    /// by calling this function again.
    #[allow(clippy::missing_safety_doc)]
    #[inline]
    pub unsafe fn init_from_ptr(state: *mut ffi::lua_State) -> Lua {
        Lua {
            raw: RawLua::init_from_ptr(state, false),
            collect_garbage: true,
        }
    }

    /// FIXME: Deprecated load_from_std_lib

    /// Loads the specified subset of the standard libraries into an existing Lua state.
    ///
    /// Use the [`StdLib`] flags to specify the libraries you want to load.
    pub fn load_std_libs(&self, libs: StdLib) -> Result<()> {
        unsafe { self.lock().load_std_libs(libs) }
    }

    /// Loads module `modname` into an existing Lua state using the specified entrypoint
    /// function.
    ///
    /// Internally calls the Lua function `func` with the string `modname` as an argument,
    /// sets the call result to `package.loaded[modname]` and returns copy of the result.
    ///
    /// If `package.loaded[modname]` value is not nil, returns copy of the value without
    /// calling the function.
    ///
    /// If the function does not return a non-nil value then this method assigns true to
    /// `package.loaded[modname]`.
    ///
    /// Behavior is similar to Lua's [`require`] function.
    ///
    /// [`require`]: https://www.lua.org/manual/5.4/manual.html#pdf-require
    pub fn load_from_function<T>(&self, modname: &str, func: Function) -> Result<T>
    where
        T: FromLua,
    {
        let lua = self.lock();
        let state = lua.state();
        let loaded = unsafe {
            let _sg = StackGuard::new(state);
            check_stack(state, 2)?;
            protect_lua!(state, 0, 1, fn(state) {
                ffi::luaL_getsubtable(state, ffi::LUA_REGISTRYINDEX, cstr!("_LOADED"));
            })?;
            Table(lua.pop_ref())
        };

        let modname = unsafe { lua.create_string(modname)? };
        let value = match loaded.raw_get(&modname)? {
            Value::Nil => {
                let result = match func.call(&modname)? {
                    Value::Nil => Value::Boolean(true),
                    res => res,
                };
                loaded.raw_set(modname, &result)?;
                result
            }
            res => res,
        };
        T::from_lua(value, self)
    }

    /// Unloads module `modname`.
    ///
    /// Removes module from the [`package.loaded`] table which allows to load it again.
    /// It does not support unloading binary Lua modules since they are internally cached and can be
    /// unloaded only by closing Lua state.
    ///
    /// [`package.loaded`]: https://www.lua.org/manual/5.4/manual.html#pdf-package.loaded
    pub fn unload(&self, modname: &str) -> Result<()> {
        let lua = self.lock();
        let state = lua.state();
        let loaded = unsafe {
            let _sg = StackGuard::new(state);
            check_stack(state, 2)?;
            protect_lua!(state, 0, 1, fn(state) {
                ffi::luaL_getsubtable(state, ffi::LUA_REGISTRYINDEX, cstr!("_LOADED"));
            })?;
            Table(lua.pop_ref())
        };

        loaded.raw_set(modname, Nil)
    }

    // Executes module entrypoint function, which returns only one Value.
    // The returned value then pushed onto the stack.
    #[doc(hidden)]
    #[cfg(not(tarpaulin_include))]
    pub unsafe fn entrypoint<F, A, R>(state: *mut ffi::lua_State, func: F) -> c_int
    where
        F: FnOnce(&Lua, A) -> Result<R>,
        A: FromLuaMulti,
        R: IntoLua,
    {
        // Make sure that Lua is initialized
        let mut lua = Self::init_from_ptr(state);
        lua.collect_garbage = false;
        // `Lua` is no longer needed and must be dropped at this point to avoid possible memory leak
        // in case of possible longjmp (lua_error) below
        drop(lua);

        callback_error_ext(state, ptr::null_mut(), move |extra, nargs| {
            let rawlua = (*extra).raw_lua();
            let _guard = StateGuard::new(rawlua, state);
            let args = A::from_stack_args(nargs, 1, None, rawlua)?;
            func(rawlua.lua(), args)?.push_into_stack(rawlua)?;
            Ok(1)
        })
    }

    // A simple module entrypoint without arguments
    #[doc(hidden)]
    #[cfg(not(tarpaulin_include))]
    pub unsafe fn entrypoint1<F, R>(state: *mut ffi::lua_State, func: F) -> c_int
    where
        F: FnOnce(&Lua) -> Result<R>,
        R: IntoLua,
    {
        Self::entrypoint(state, move |lua, _: ()| func(lua))
    }

    /// Skips memory checks for some operations.
    #[doc(hidden)]
    #[cfg(feature = "module")]
    pub fn skip_memory_check(&self, skip: bool) {
        let lua = self.lock();
        unsafe { (*lua.extra.get()).skip_memory_check = skip };
    }

    /// Enables (or disables) sandbox mode on this Lua instance.
    ///
    /// This method, in particular:
    /// - Set all libraries to read-only
    /// - Set all builtin metatables to read-only
    /// - Set globals to read-only (and activates safeenv)
    /// - Setup local environment table that performs writes locally and proxies reads to the global
    ///   environment.
    ///
    /// # Examples
    ///
    /// ```
    /// # use mlua::{Lua, Result};
    /// # fn main() -> Result<()> {
    /// let lua = Lua::new();
    ///
    /// lua.sandbox(true)?;
    /// lua.load("var = 123").exec()?;
    /// assert_eq!(lua.globals().get::<u32>("var")?, 123);
    ///
    /// // Restore the global environment (clear changes made in sandbox)
    /// lua.sandbox(false)?;
    /// assert_eq!(lua.globals().get::<Option<u32>>("var")?, None);
    /// # Ok(())
    /// # }
    /// ```
    ///
    /// Requires `feature = "luau"`
    #[cfg(any(feature = "luau", docsrs))]
    #[cfg_attr(docsrs, doc(cfg(feature = "luau")))]
    pub fn sandbox(&self, enabled: bool) -> Result<()> {
        let lua = self.lock();
        unsafe {
            if (*lua.extra.get()).sandboxed != enabled {
                let state = lua.main_state;
                check_stack(state, 3)?;
                protect_lua!(state, 0, 0, |state| {
                    if enabled {
                        ffi::luaL_sandbox(state, 1);
                        ffi::luaL_sandboxthread(state);
                    } else {
                        // Restore original `LUA_GLOBALSINDEX`
                        ffi::lua_xpush(lua.ref_thread(), state, ffi::LUA_GLOBALSINDEX);
                        ffi::lua_replace(state, ffi::LUA_GLOBALSINDEX);
                        ffi::luaL_sandbox(state, 0);
                    }
                })?;
                (*lua.extra.get()).sandboxed = enabled;
            }
            Ok(())
        }
    }

    /// Sets a 'hook' function that will periodically be called as Lua code executes.
    ///
    /// When exactly the hook function is called depends on the contents of the `triggers`
    /// parameter, see [`HookTriggers`] for more details.
    ///
    /// The provided hook function can error, and this error will be propagated through the Lua code
    /// that was executing at the time the hook was triggered. This can be used to implement a
    /// limited form of execution limits by setting [`HookTriggers.every_nth_instruction`] and
    /// erroring once an instruction limit has been reached.
    ///
    /// This method sets a hook function for the current thread of this Lua instance.
    /// If you want to set a hook function for another thread (coroutine), use
    /// [`Thread::set_hook()`] instead.
    ///
    /// Please note you cannot have more than one hook function set at a time for this Lua instance.
    ///
    /// # Example
    ///
    /// Shows each line number of code being executed by the Lua interpreter.
    ///
    /// ```
    /// # use mlua::{Lua, HookTriggers, Result};
    /// # fn main() -> Result<()> {
    /// let lua = Lua::new();
    /// lua.set_hook(HookTriggers::EVERY_LINE, |_lua, debug| {
    ///     println!("line {}", debug.curr_line());
    ///     Ok(())
    /// });
    ///
    /// lua.load(r#"
    ///     local x = 2 + 3
    ///     local y = x * 63
    ///     local z = string.len(x..", "..y)
    /// "#).exec()
    /// # }
    /// ```
    ///
    /// [`HookTriggers`]: crate::HookTriggers
    /// [`HookTriggers.every_nth_instruction`]: crate::HookTriggers::every_nth_instruction
    #[cfg(not(feature = "luau"))]
    #[cfg_attr(docsrs, doc(cfg(not(feature = "luau"))))]
    pub fn set_hook<F>(&self, triggers: HookTriggers, callback: F)
    where
        F: Fn(&Lua, Debug) -> Result<()> + MaybeSend + 'static,
    {
        let lua = self.lock();
        unsafe { lua.set_thread_hook(lua.state(), triggers, callback) };
    }

    /// Removes any hook previously set by [`Lua::set_hook()`] or [`Thread::set_hook()`].
    ///
    /// This function has no effect if a hook was not previously set.
    #[cfg(not(feature = "luau"))]
    #[cfg_attr(docsrs, doc(cfg(not(feature = "luau"))))]
    pub fn remove_hook(&self) {
        let lua = self.lock();
        unsafe {
            let state = lua.state();
            ffi::lua_sethook(state, None, 0, 0);
            match crate::util::get_main_state(lua.main_state) {
                Some(main_state) if !ptr::eq(state, main_state) => {
                    // If main_state is different from state, remove hook from it too
                    ffi::lua_sethook(main_state, None, 0, 0);
                }
                _ => {}
            };
            (*lua.extra.get()).hook_callback = None;
            (*lua.extra.get()).hook_thread = ptr::null_mut();
        }
    }

    /// Sets an 'interrupt' function that will periodically be called by Luau VM.
    ///
    /// Any Luau code is guaranteed to call this handler "eventually"
    /// (in practice this can happen at any function call or at any loop iteration).
    ///
    /// The provided interrupt function can error, and this error will be propagated through
    /// the Luau code that was executing at the time the interrupt was triggered.
    /// Also this can be used to implement continuous execution limits by instructing Luau VM to
    /// yield by returning [`VmState::Yield`].
    ///
    /// This is similar to [`Lua::set_hook`] but in more simplified form.
    ///
    /// # Example
    ///
    /// Periodically yield Luau VM to suspend execution.
    ///
    /// ```
    /// # use std::sync::{Arc, atomic::{AtomicU64, Ordering}};
    /// # use mlua::{Lua, Result, ThreadStatus, VmState};
    /// # fn main() -> Result<()> {
    /// let lua = Lua::new();
    /// let count = Arc::new(AtomicU64::new(0));
    /// lua.set_interrupt(move |_| {
    ///     if count.fetch_add(1, Ordering::Relaxed) % 2 == 0 {
    ///         return Ok(VmState::Yield);
    ///     }
    ///     Ok(VmState::Continue)
    /// });
    ///
    /// let co = lua.create_thread(
    ///     lua.load(r#"
    ///         local b = 0
    ///         for _, x in ipairs({1, 2, 3}) do b += x end
    ///     "#)
    ///     .into_function()?,
    /// )?;
    /// while co.status() == ThreadStatus::Resumable {
    ///     co.resume(())?;
    /// }
    /// # Ok(())
    /// # }
    /// ```
    #[cfg(any(feature = "luau", docsrs))]
    #[cfg_attr(docsrs, doc(cfg(feature = "luau")))]
    pub fn set_interrupt<F>(&self, callback: F)
    where
        F: Fn(&Lua) -> Result<VmState> + MaybeSend + 'static,
    {
        use std::rc::Rc;

        unsafe extern "C-unwind" fn interrupt_proc(state: *mut ffi::lua_State, gc: c_int) {
            if gc >= 0 {
                // We don't support GC interrupts since they cannot survive Lua exceptions
                return;
            }
            let result = callback_error_ext(state, ptr::null_mut(), move |extra, _| {
                let interrupt_cb = (*extra).interrupt_callback.clone();
                let interrupt_cb = mlua_expect!(interrupt_cb, "no interrupt callback set in interrupt_proc");
                if Rc::strong_count(&interrupt_cb) > 2 {
                    return Ok(VmState::Continue); // Don't allow recursion
                }
                let _guard = StateGuard::new((*extra).raw_lua(), state);
                interrupt_cb((*extra).lua())
            });
            match result {
                VmState::Continue => {}
                VmState::Yield => {
                    ffi::lua_yield(state, 0);
                }
            }
        }

        // Set interrupt callback
        let lua = self.lock();
        unsafe {
            (*lua.extra.get()).interrupt_callback = Some(Rc::new(callback));
            (*ffi::lua_callbacks(lua.main_state)).interrupt = Some(interrupt_proc);
        }
    }

    /// Removes any 'interrupt' previously set by `set_interrupt`.
    ///
    /// This function has no effect if an 'interrupt' was not previously set.
    #[cfg(any(feature = "luau", docsrs))]
    #[cfg_attr(docsrs, doc(cfg(feature = "luau")))]
    pub fn remove_interrupt(&self) {
        let lua = self.lock();
        unsafe {
            (*lua.extra.get()).interrupt_callback = None;
            (*ffi::lua_callbacks(lua.main_state)).interrupt = None;
        }
    }

    /// Sets the warning function to be used by Lua to emit warnings.
    ///
    /// Requires `feature = "lua54"`
    #[cfg(feature = "lua54")]
    #[cfg_attr(docsrs, doc(cfg(feature = "lua54")))]
    pub fn set_warning_function<F>(&self, callback: F)
    where
        F: Fn(&Lua, &str, bool) -> Result<()> + MaybeSend + 'static,
    {
        use std::ffi::CStr;
        use std::os::raw::c_char;
        use std::string::String as StdString;

        unsafe extern "C-unwind" fn warn_proc(ud: *mut c_void, msg: *const c_char, tocont: c_int) {
            let extra = ud as *mut ExtraData;
            callback_error_ext((*extra).raw_lua().state(), extra, |extra, _| {
                let cb = mlua_expect!(
                    (*extra).warn_callback.as_ref(),
                    "no warning callback set in warn_proc"
                );
                let msg = StdString::from_utf8_lossy(CStr::from_ptr(msg).to_bytes());
                cb((*extra).lua(), &msg, tocont != 0)
            });
        }

        let lua = self.lock();
        let state = lua.main_state;
        unsafe {
            (*lua.extra.get()).warn_callback = Some(Box::new(callback));
            ffi::lua_setwarnf(state, Some(warn_proc), lua.extra.get() as *mut c_void);
        }
    }

    /// Removes warning function previously set by `set_warning_function`.
    ///
    /// This function has no effect if a warning function was not previously set.
    ///
    /// Requires `feature = "lua54"`
    #[cfg(feature = "lua54")]
    #[cfg_attr(docsrs, doc(cfg(feature = "lua54")))]
    pub fn remove_warning_function(&self) {
        let lua = self.lock();
        unsafe {
            (*lua.extra.get()).warn_callback = None;
            ffi::lua_setwarnf(lua.main_state, None, ptr::null_mut());
        }
    }

    /// Emits a warning with the given message.
    ///
    /// A message in a call with `incomplete` set to `true` should be continued in
    /// another call to this function.
    ///
    /// Requires `feature = "lua54"`
    #[cfg(feature = "lua54")]
    #[cfg_attr(docsrs, doc(cfg(feature = "lua54")))]
    pub fn warning(&self, msg: impl AsRef<str>, incomplete: bool) {
        let msg = msg.as_ref();
        let mut bytes = vec![0; msg.len() + 1];
        bytes[..msg.len()].copy_from_slice(msg.as_bytes());
        let real_len = bytes.iter().position(|&c| c == 0).unwrap();
        bytes.truncate(real_len);
        let lua = self.lock();
        unsafe {
            ffi::lua_warning(lua.state(), bytes.as_ptr() as *const _, incomplete as c_int);
        }
    }

    /// Gets information about the interpreter runtime stack.
    ///
    /// This function returns [`Debug`] structure that can be used to get information about the
    /// function executing at a given level. Level `0` is the current running function, whereas
    /// level `n+1` is the function that has called level `n` (except for tail calls, which do
    /// not count in the stack).
    ///
    /// [`Debug`]: crate::hook::Debug
    pub fn inspect_stack(&self, level: usize) -> Option<Debug> {
        let lua = self.lock();
        unsafe {
            let mut ar: ffi::lua_Debug = mem::zeroed();
            let level = level as c_int;
            #[cfg(not(feature = "luau"))]
            if ffi::lua_getstack(lua.state(), level, &mut ar) == 0 {
                return None;
            }
            #[cfg(feature = "luau")]
            if ffi::lua_getinfo(lua.state(), level, cstr!(""), &mut ar) == 0 {
                return None;
            }
            Some(Debug::new_owned(lua, level, ar))
        }
    }

    /// Returns the amount of memory (in bytes) currently used inside this Lua state.
    pub fn used_memory(&self) -> usize {
        let lua = self.lock();
        unsafe {
            match MemoryState::get(lua.main_state) {
                mem_state if !mem_state.is_null() => (*mem_state).used_memory(),
                _ => {
                    // Get data from the Lua GC
                    let used_kbytes = ffi::lua_gc(lua.main_state, ffi::LUA_GCCOUNT, 0);
                    let used_kbytes_rem = ffi::lua_gc(lua.main_state, ffi::LUA_GCCOUNTB, 0);
                    (used_kbytes as usize) * 1024 + (used_kbytes_rem as usize)
                }
            }
        }
    }

    /// Sets a memory limit (in bytes) on this Lua state.
    ///
    /// Once an allocation occurs that would pass this memory limit,
    /// a `Error::MemoryError` is generated instead.
    /// Returns previous limit (zero means no limit).
    ///
    /// Does not work in module mode where Lua state is managed externally.
    pub fn set_memory_limit(&self, limit: usize) -> Result<usize> {
        let lua = self.lock();
        unsafe {
            match MemoryState::get(lua.main_state) {
                mem_state if !mem_state.is_null() => Ok((*mem_state).set_memory_limit(limit)),
                _ => Err(Error::MemoryLimitNotAvailable),
            }
        }
    }

    /// Returns true if the garbage collector is currently running automatically.
    ///
    /// Requires `feature = "lua54/lua53/lua52/luau"`
    #[cfg(any(feature = "lua54", feature = "lua53", feature = "lua52", feature = "luau"))]
    pub fn gc_is_running(&self) -> bool {
        let lua = self.lock();
        unsafe { ffi::lua_gc(lua.main_state, ffi::LUA_GCISRUNNING, 0) != 0 }
    }

    /// Stop the Lua GC from running
    pub fn gc_stop(&self) {
        let lua = self.lock();
        unsafe { ffi::lua_gc(lua.main_state, ffi::LUA_GCSTOP, 0) };
    }

    /// Restarts the Lua GC if it is not running
    pub fn gc_restart(&self) {
        let lua = self.lock();
        unsafe { ffi::lua_gc(lua.main_state, ffi::LUA_GCRESTART, 0) };
    }

    /// Perform a full garbage-collection cycle.
    ///
    /// It may be necessary to call this function twice to collect all currently unreachable
    /// objects. Once to finish the current gc cycle, and once to start and finish the next cycle.
    pub fn gc_collect(&self) -> Result<()> {
        let lua = self.lock();
        unsafe {
            check_stack(lua.main_state, 2)?;
            protect_lua!(lua.main_state, 0, 0, fn(state) ffi::lua_gc(state, ffi::LUA_GCCOLLECT, 0))
        }
    }

    /// Steps the garbage collector one indivisible step.
    ///
    /// Returns true if this has finished a collection cycle.
    pub fn gc_step(&self) -> Result<bool> {
        self.gc_step_kbytes(0)
    }

    /// Steps the garbage collector as though memory had been allocated.
    ///
    /// if `kbytes` is 0, then this is the same as calling `gc_step`. Returns true if this step has
    /// finished a collection cycle.
    pub fn gc_step_kbytes(&self, kbytes: c_int) -> Result<bool> {
        let lua = self.lock();
        unsafe {
            check_stack(lua.main_state, 3)?;
            protect_lua!(lua.main_state, 0, 0, |state| {
                ffi::lua_gc(state, ffi::LUA_GCSTEP, kbytes) != 0
            })
        }
    }

    /// Sets the 'pause' value of the collector.
    ///
    /// Returns the previous value of 'pause'. More information can be found in the Lua
    /// [documentation].
    ///
    /// For Luau this parameter sets GC goal
    ///
    /// [documentation]: https://www.lua.org/manual/5.4/manual.html#2.5
    pub fn gc_set_pause(&self, pause: c_int) -> c_int {
        let lua = self.lock();
        unsafe {
            #[cfg(not(feature = "luau"))]
            return ffi::lua_gc(lua.main_state, ffi::LUA_GCSETPAUSE, pause);
            #[cfg(feature = "luau")]
            return ffi::lua_gc(lua.main_state, ffi::LUA_GCSETGOAL, pause);
        }
    }

    /// Sets the 'step multiplier' value of the collector.
    ///
    /// Returns the previous value of the 'step multiplier'. More information can be found in the
    /// Lua [documentation].
    ///
    /// [documentation]: https://www.lua.org/manual/5.4/manual.html#2.5
    pub fn gc_set_step_multiplier(&self, step_multiplier: c_int) -> c_int {
        let lua = self.lock();
        unsafe { ffi::lua_gc(lua.main_state, ffi::LUA_GCSETSTEPMUL, step_multiplier) }
    }

    /// Changes the collector to incremental mode with the given parameters.
    ///
    /// Returns the previous mode (always `GCMode::Incremental` in Lua < 5.4).
    /// More information can be found in the Lua [documentation].
    ///
    /// [documentation]: https://www.lua.org/manual/5.4/manual.html#2.5.1
    pub fn gc_inc(&self, pause: c_int, step_multiplier: c_int, step_size: c_int) -> GCMode {
        let lua = self.lock();
        let state = lua.main_state;

        #[cfg(any(
            feature = "lua53",
            feature = "lua52",
            feature = "lua51",
            feature = "luajit",
            feature = "luau"
        ))]
        unsafe {
            if pause > 0 {
                #[cfg(not(feature = "luau"))]
                ffi::lua_gc(state, ffi::LUA_GCSETPAUSE, pause);
                #[cfg(feature = "luau")]
                ffi::lua_gc(state, ffi::LUA_GCSETGOAL, pause);
            }

            if step_multiplier > 0 {
                ffi::lua_gc(state, ffi::LUA_GCSETSTEPMUL, step_multiplier);
            }

            #[cfg(feature = "luau")]
            if step_size > 0 {
                ffi::lua_gc(state, ffi::LUA_GCSETSTEPSIZE, step_size);
            }
            #[cfg(not(feature = "luau"))]
            let _ = step_size; // Ignored

            GCMode::Incremental
        }

        #[cfg(feature = "lua54")]
        let prev_mode = unsafe { ffi::lua_gc(state, ffi::LUA_GCINC, pause, step_multiplier, step_size) };
        #[cfg(feature = "lua54")]
        match prev_mode {
            ffi::LUA_GCINC => GCMode::Incremental,
            ffi::LUA_GCGEN => GCMode::Generational,
            _ => unreachable!(),
        }
    }

    /// Changes the collector to generational mode with the given parameters.
    ///
    /// Returns the previous mode. More information about the generational GC
    /// can be found in the Lua 5.4 [documentation][lua_doc].
    ///
    /// Requires `feature = "lua54"`
    ///
    /// [lua_doc]: https://www.lua.org/manual/5.4/manual.html#2.5.2
    #[cfg(feature = "lua54")]
    #[cfg_attr(docsrs, doc(cfg(feature = "lua54")))]
    pub fn gc_gen(&self, minor_multiplier: c_int, major_multiplier: c_int) -> GCMode {
        let lua = self.lock();
        let state = lua.main_state;
        let prev_mode = unsafe { ffi::lua_gc(state, ffi::LUA_GCGEN, minor_multiplier, major_multiplier) };
        match prev_mode {
            ffi::LUA_GCGEN => GCMode::Generational,
            ffi::LUA_GCINC => GCMode::Incremental,
            _ => unreachable!(),
        }
    }

    /// Sets a default Luau compiler (with custom options).
    ///
    /// This compiler will be used by default to load all Lua chunks
    /// including via `require` function.
    ///
    /// See [`Compiler`] for details and possible options.
    ///
    /// Requires `feature = "luau"`
    #[cfg(any(feature = "luau", doc))]
    #[cfg_attr(docsrs, doc(cfg(feature = "luau")))]
    pub fn set_compiler(&self, compiler: Compiler) {
        let lua = self.lock();
        unsafe { (*lua.extra.get()).compiler = Some(compiler) };
    }

    /// Toggles JIT compilation mode for new chunks of code.
    ///
    /// By default JIT is enabled. Changing this option does not have any effect on
    /// already loaded functions.
    #[cfg(any(feature = "luau-jit", doc))]
    #[cfg_attr(docsrs, doc(cfg(feature = "luau-jit")))]
    pub fn enable_jit(&self, enable: bool) {
        let lua = self.lock();
        unsafe { (*lua.extra.get()).enable_jit = enable };
    }

    /// Sets Luau feature flag (global setting).
    ///
    /// See https://github.com/luau-lang/luau/blob/master/CONTRIBUTING.md#feature-flags for details.
    #[cfg(feature = "luau")]
    #[doc(hidden)]
    #[allow(clippy::result_unit_err)]
    pub fn set_fflag(name: &str, enabled: bool) -> StdResult<(), ()> {
        if let Ok(name) = std::ffi::CString::new(name) {
            if unsafe { ffi::luau_setfflag(name.as_ptr(), enabled as c_int) != 0 } {
                return Ok(());
            }
        }
        Err(())
    }

    /// Returns Lua source code as a `Chunk` builder type.
    ///
    /// In order to actually compile or run the resulting code, you must call [`Chunk::exec`] or
    /// similar on the returned builder. Code is not even parsed until one of these methods is
    /// called.
    ///
    /// [`Chunk::exec`]: crate::Chunk::exec
    #[track_caller]
    pub fn load<'a>(&self, chunk: impl AsChunk<'a>) -> Chunk<'a> {
        let caller = Location::caller();
        Chunk {
            lua: self.weak(),
            name: chunk.name().unwrap_or_else(|| caller.to_string()),
            env: chunk.environment(self),
            mode: chunk.mode(),
            source: chunk.source(),
            #[cfg(feature = "luau")]
            compiler: unsafe { (*self.lock().extra.get()).compiler.clone() },
        }
    }

    /// Create and return an interned Lua string. Lua strings can be arbitrary `[u8]` data including
    /// embedded nulls, so in addition to `&str` and `&String`, you can also pass plain `&[u8]`
    /// here.
    #[inline]
    pub fn create_string(&self, s: impl AsRef<[u8]>) -> Result<String> {
        unsafe { self.lock().create_string(s) }
    }

    /// Create and return a Luau [buffer] object from a byte slice of data.
    ///
    /// Requires `feature = "luau"`
    ///
    /// [buffer]: https://luau-lang.org/library#buffer-library
    #[cfg(feature = "luau")]
    pub fn create_buffer(&self, buf: impl AsRef<[u8]>) -> Result<AnyUserData> {
        use crate::types::SubtypeId;

        let lua = self.lock();
        let state = lua.state();
        unsafe {
            if lua.unlikely_memory_error() {
                crate::util::push_buffer(lua.ref_thread(), buf.as_ref(), false)?;
                return Ok(AnyUserData(lua.pop_ref_thread(), SubtypeId::Buffer));
            }

            let _sg = StackGuard::new(state);
            check_stack(state, 4)?;
            crate::util::push_buffer(state, buf.as_ref(), true)?;
            Ok(AnyUserData(lua.pop_ref(), SubtypeId::Buffer))
        }
    }

    /// Creates and returns a new empty table.
    pub fn create_table(&self) -> Result<Table> {
        self.create_table_with_capacity(0, 0)
    }

    /// Creates and returns a new empty table, with the specified capacity.
    /// `narr` is a hint for how many elements the table will have as a sequence;
    /// `nrec` is a hint for how many other elements the table will have.
    /// Lua may use these hints to preallocate memory for the new table.
    pub fn create_table_with_capacity(&self, narr: usize, nrec: usize) -> Result<Table> {
        unsafe { self.lock().create_table_with_capacity(narr, nrec) }
    }

    /// Creates a table and fills it with values from an iterator.
    pub fn create_table_from<K, V, I>(&self, iter: I) -> Result<Table>
    where
        K: IntoLua,
        V: IntoLua,
        I: IntoIterator<Item = (K, V)>,
    {
        let lua = self.lock();
        let state = lua.state();
        unsafe {
            let _sg = StackGuard::new(state);
            check_stack(state, 6)?;

            let iter = iter.into_iter();
            let lower_bound = iter.size_hint().0;
            let protect = !lua.unlikely_memory_error();
            push_table(state, 0, lower_bound, protect)?;
            for (k, v) in iter {
                lua.push(k)?;
                lua.push(v)?;
                if protect {
                    protect_lua!(state, 3, 1, fn(state) ffi::lua_rawset(state, -3))?;
                } else {
                    ffi::lua_rawset(state, -3);
                }
            }

            Ok(Table(lua.pop_ref()))
        }
    }

    /// Creates a table from an iterator of values, using `1..` as the keys.
    pub fn create_sequence_from<T, I>(&self, iter: I) -> Result<Table>
    where
        T: IntoLua,
        I: IntoIterator<Item = T>,
    {
        unsafe { self.lock().create_sequence_from(iter) }
    }

    /// Wraps a Rust function or closure, creating a callable Lua function handle to it.
    ///
    /// The function's return value is always a `Result`: If the function returns `Err`, the error
    /// is raised as a Lua error, which can be caught using `(x)pcall` or bubble up to the Rust code
    /// that invoked the Lua code. This allows using the `?` operator to propagate errors through
    /// intermediate Lua code.
    ///
    /// If the function returns `Ok`, the contained value will be converted to one or more Lua
    /// values. For details on Rust-to-Lua conversions, refer to the [`IntoLua`] and
    /// [`IntoLuaMulti`] traits.
    ///
    /// # Examples
    ///
    /// Create a function which prints its argument:
    ///
    /// ```
    /// # use mlua::{Lua, Result};
    /// # fn main() -> Result<()> {
    /// # let lua = Lua::new();
    /// let greet = lua.create_function(|_, name: String| {
    ///     println!("Hello, {}!", name);
    ///     Ok(())
    /// });
    /// # let _ = greet;    // used
    /// # Ok(())
    /// # }
    /// ```
    ///
    /// Use tuples to accept multiple arguments:
    ///
    /// ```
    /// # use mlua::{Lua, Result};
    /// # fn main() -> Result<()> {
    /// # let lua = Lua::new();
    /// let print_person = lua.create_function(|_, (name, age): (String, u8)| {
    ///     println!("{} is {} years old!", name, age);
    ///     Ok(())
    /// });
    /// # let _ = print_person;    // used
    /// # Ok(())
    /// # }
    /// ```
    ///
    /// [`IntoLua`]: crate::IntoLua
    /// [`IntoLuaMulti`]: crate::IntoLuaMulti
    pub fn create_function<F, A, R>(&self, func: F) -> Result<Function>
    where
        F: Fn(&Lua, A) -> Result<R> + MaybeSend + 'static,
        A: FromLuaMulti,
        R: IntoLuaMulti,
    {
        (self.lock()).create_callback(Box::new(move |rawlua, nargs| unsafe {
            let args = A::from_stack_args(nargs, 1, None, rawlua)?;
            func(rawlua.lua(), args)?.push_into_stack_multi(rawlua)
        }))
    }

    /// Wraps a Rust mutable closure, creating a callable Lua function handle to it.
    ///
    /// This is a version of [`create_function`] that accepts a FnMut argument. Refer to
    /// [`create_function`] for more information about the implementation.
    ///
    /// [`create_function`]: #method.create_function
    pub fn create_function_mut<F, A, R>(&self, func: F) -> Result<Function>
    where
        F: FnMut(&Lua, A) -> Result<R> + MaybeSend + 'static,
        A: FromLuaMulti,
        R: IntoLuaMulti,
    {
        let func = RefCell::new(func);
        self.create_function(move |lua, args| {
            (*func.try_borrow_mut().map_err(|_| Error::RecursiveMutCallback)?)(lua, args)
        })
    }

    /// Wraps a C function, creating a callable Lua function handle to it.
    ///
    /// # Safety
    /// This function is unsafe because provides a way to execute unsafe C function.
    pub unsafe fn create_c_function(&self, func: ffi::lua_CFunction) -> Result<Function> {
        let lua = self.lock();
        ffi::lua_pushcfunction(lua.ref_thread(), func);
        Ok(Function(lua.pop_ref_thread()))
    }

    /// Wraps a Rust async function or closure, creating a callable Lua function handle to it.
    ///
    /// While executing the function Rust will poll the Future and if the result is not ready,
    /// call `yield()` passing internal representation of a `Poll::Pending` value.
    ///
    /// The function must be called inside Lua coroutine ([`Thread`]) to be able to suspend its
    /// execution. An executor should be used to poll [`AsyncThread`] and mlua will take a
    /// provided Waker in that case. Otherwise noop waker will be used if try to call the
    /// function outside of Rust executors.
    ///
    /// The family of `call_async()` functions takes care about creating [`Thread`].
    ///
    /// Requires `feature = "async"`
    ///
    /// # Examples
    ///
    /// Non blocking sleep:
    ///
    /// ```
    /// use std::time::Duration;
    /// use mlua::{Lua, Result};
    ///
    /// async fn sleep(_lua: Lua, n: u64) -> Result<&'static str> {
    ///     tokio::time::sleep(Duration::from_millis(n)).await;
    ///     Ok("done")
    /// }
    ///
    /// #[tokio::main]
    /// async fn main() -> Result<()> {
    ///     let lua = Lua::new();
    ///     lua.globals().set("sleep", lua.create_async_function(sleep)?)?;
    ///     let res: String = lua.load("return sleep(...)").call_async(100).await?; // Sleep 100ms
    ///     assert_eq!(res, "done");
    ///     Ok(())
    /// }
    /// ```
    ///
    /// [`Thread`]: crate::Thread
    /// [`AsyncThread`]: crate::AsyncThread
    #[cfg(feature = "async")]
    #[cfg_attr(docsrs, doc(cfg(feature = "async")))]
    pub fn create_async_function<F, A, FR, R>(&self, func: F) -> Result<Function>
    where
        F: Fn(Lua, A) -> FR + MaybeSend + 'static,
        A: FromLuaMulti,
        FR: Future<Output = Result<R>> + MaybeSend + 'static,
        R: IntoLuaMulti,
    {
        // In future we should switch to async closures when they are stable to capture `&Lua`
        // See https://rust-lang.github.io/rfcs/3668-async-closures.html
        (self.lock()).create_async_callback(Box::new(move |rawlua, nargs| unsafe {
            let args = match A::from_stack_args(nargs, 1, None, rawlua) {
                Ok(args) => args,
                Err(e) => return Box::pin(future::ready(Err(e))),
            };
            let lua = rawlua.lua();
            let fut = func(lua.clone(), args);
            Box::pin(async move { fut.await?.push_into_stack_multi(lua.raw_lua()) })
        }))
    }

    /// Wraps a Lua function into a new thread (or coroutine).
    ///
    /// Equivalent to `coroutine.create`.
    pub fn create_thread(&self, func: Function) -> Result<Thread> {
        unsafe { self.lock().create_thread(&func) }
    }

    /// Creates a Lua userdata object from a custom userdata type.
    ///
    /// All userdata instances of the same type `T` shares the same metatable.
    #[inline]
    pub fn create_userdata<T>(&self, data: T) -> Result<AnyUserData>
    where
        T: UserData + MaybeSend + 'static,
    {
        unsafe { self.lock().make_userdata(UserDataVariant::new(data)) }
    }

    /// Creates a Lua userdata object from a custom serializable userdata type.
    ///
    /// Requires `feature = "serialize"`
    #[cfg(feature = "serialize")]
    #[cfg_attr(docsrs, doc(cfg(feature = "serialize")))]
    #[inline]
    pub fn create_ser_userdata<T>(&self, data: T) -> Result<AnyUserData>
    where
        T: UserData + Serialize + MaybeSend + 'static,
    {
        unsafe { self.lock().make_userdata(UserDataVariant::new_ser(data)) }
    }

    /// Creates a Lua userdata object from a custom Rust type.
    ///
    /// You can register the type using [`Lua::register_userdata_type()`] to add fields or methods
    /// _before_ calling this method.
    /// Otherwise, the userdata object will have an empty metatable.
    ///
    /// All userdata instances of the same type `T` shares the same metatable.
    #[inline]
    pub fn create_any_userdata<T>(&self, data: T) -> Result<AnyUserData>
    where
        T: MaybeSend + 'static,
    {
        unsafe { self.lock().make_any_userdata(UserDataVariant::new(data)) }
    }

    /// Creates a Lua userdata object from a custom serializable Rust type.
    ///
    /// See [`Lua::create_any_userdata()`] for more details.
    ///
    /// Requires `feature = "serialize"`
    #[cfg(feature = "serialize")]
    #[cfg_attr(docsrs, doc(cfg(feature = "serialize")))]
    #[inline]
    pub fn create_ser_any_userdata<T>(&self, data: T) -> Result<AnyUserData>
    where
        T: Serialize + MaybeSend + 'static,
    {
        unsafe { (self.lock()).make_any_userdata(UserDataVariant::new_ser(data)) }
    }

    /// Registers a custom Rust type in Lua to use in userdata objects.
    ///
    /// This methods provides a way to add fields or methods to userdata objects of a type `T`.
    pub fn register_userdata_type<T: 'static>(&self, f: impl FnOnce(&mut UserDataRegistry<T>)) -> Result<()> {
        let mut registry = const { UserDataRegistry::new() };
        f(&mut registry);

        let lua = self.lock();
        unsafe {
            // Deregister the type if it already registered
            let type_id = TypeId::of::<T>();
            if let Some(&table_id) = (*lua.extra.get()).registered_userdata.get(&type_id) {
                ffi::luaL_unref(lua.state(), ffi::LUA_REGISTRYINDEX, table_id);
            }

            // Register the type
            lua.register_userdata_metatable(registry)?;
        }
        Ok(())
    }

    /// Create a Lua userdata "proxy" object from a custom userdata type.
    ///
    /// Proxy object is an empty userdata object that has `T` metatable attached.
    /// The main purpose of this object is to provide access to static fields and functions
    /// without creating an instance of type `T`.
    ///
    /// You can get or set uservalues on this object but you cannot borrow any Rust type.
    ///
    /// # Examples
    ///
    /// ```
    /// # use mlua::{Lua, Result, UserData, UserDataFields, UserDataMethods};
    /// # fn main() -> Result<()> {
    /// # let lua = Lua::new();
    /// struct MyUserData(i32);
    ///
    /// impl UserData for MyUserData {
    ///     fn add_fields<F: UserDataFields<Self>>(fields: &mut F) {
    ///         fields.add_field_method_get("val", |_, this| Ok(this.0));
    ///     }
    ///
    ///     fn add_methods<M: UserDataMethods<Self>>(methods: &mut M) {
    ///         methods.add_function("new", |_, value: i32| Ok(MyUserData(value)));
    ///     }
    /// }
    ///
    /// lua.globals().set("MyUserData", lua.create_proxy::<MyUserData>()?)?;
    ///
    /// lua.load("assert(MyUserData.new(321).val == 321)").exec()?;
    /// # Ok(())
    /// # }
    /// ```
    #[inline]
    pub fn create_proxy<T>(&self) -> Result<AnyUserData>
    where
        T: UserData + 'static,
    {
        let ud = UserDataProxy::<T>(PhantomData);
        unsafe { self.lock().make_userdata(UserDataVariant::new(ud)) }
    }

    /// Sets the metatable for a Luau builtin vector type.
    #[cfg(any(feature = "luau", doc))]
    #[cfg_attr(docsrs, doc(cfg(feature = "luau")))]
    pub fn set_vector_metatable(&self, metatable: Option<Table>) {
        let lua = self.lock();
        let state = lua.state();
        unsafe {
            let _sg = StackGuard::new(state);
            assert_stack(state, 2);

            #[cfg(not(feature = "luau-vector4"))]
            ffi::lua_pushvector(state, 0., 0., 0.);
            #[cfg(feature = "luau-vector4")]
            ffi::lua_pushvector(state, 0., 0., 0., 0.);
            match metatable {
                Some(metatable) => lua.push_ref(&metatable.0),
                None => ffi::lua_pushnil(state),
            };
            ffi::lua_setmetatable(state, -2);
        }
    }

    /// Returns a handle to the global environment.
    pub fn globals(&self) -> Table {
        let lua = self.lock();
        let state = lua.state();
        unsafe {
            let _sg = StackGuard::new(state);
            assert_stack(state, 1);
            #[cfg(any(feature = "lua54", feature = "lua53", feature = "lua52"))]
            ffi::lua_rawgeti(state, ffi::LUA_REGISTRYINDEX, ffi::LUA_RIDX_GLOBALS);
            #[cfg(any(feature = "lua51", feature = "luajit", feature = "luau"))]
            ffi::lua_pushvalue(state, ffi::LUA_GLOBALSINDEX);
            Table(lua.pop_ref())
        }
    }

    /// Returns a handle to the active `Thread`. For calls to `Lua` this will be the main Lua
    /// thread, for parameters given to a callback, this will be whatever Lua thread called the
    /// callback.
    pub fn current_thread(&self) -> Thread {
        let lua = self.lock();
        let state = lua.state();
        unsafe {
            let _sg = StackGuard::new(state);
            assert_stack(state, 1);
            ffi::lua_pushthread(state);
            Thread(lua.pop_ref(), state)
        }
    }

    /// Calls the given function with a `Scope` parameter, giving the function the ability to create
    /// userdata and callbacks from rust types that are !Send or non-'static.
    ///
    /// The lifetime of any function or userdata created through `Scope` lasts only until the
    /// completion of this method call, on completion all such created values are automatically
    /// dropped and Lua references to them are invalidated. If a script accesses a value created
    /// through `Scope` outside of this method, a Lua error will result. Since we can ensure the
    /// lifetime of values created through `Scope`, and we know that `Lua` cannot be sent to another
    /// thread while `Scope` is live, it is safe to allow !Send datatypes and whose lifetimes only
    /// outlive the scope lifetime.
    ///
    /// Inside the scope callback, all handles created through Scope will share the same unique 'lua
    /// lifetime of the parent `Lua`. This allows scoped and non-scoped values to be mixed in
    /// API calls, which is very useful (e.g. passing a scoped userdata to a non-scoped function).
    /// However, this also enables handles to scoped values to be trivially leaked from the given
    /// callback. This is not dangerous, though!  After the callback returns, all scoped values are
    /// invalidated, which means that though references may exist, the Rust types backing them have
    /// dropped. `Function` types will error when called, and `AnyUserData` will be typeless. It
    /// would be impossible to prevent handles to scoped values from escaping anyway, since you
    /// would always be able to smuggle them through Lua state.
    // pub fn scope<'lua, 'scope, R>(
    //     &'lua self,
    //     f: impl FnOnce(&Scope<'lua, 'scope>) -> Result<R>,
    // ) -> Result<R>
    // where
    //     'lua: 'scope,
    // {
    //     f(&Scope::new(self))
    // }

    /// Attempts to coerce a Lua value into a String in a manner consistent with Lua's internal
    /// behavior.
    ///
    /// To succeed, the value must be a string (in which case this is a no-op), an integer, or a
    /// number.
    pub fn coerce_string(&self, v: Value) -> Result<Option<String>> {
        Ok(match v {
            Value::String(s) => Some(s),
            v => unsafe {
                let lua = self.lock();
                let state = lua.state();
                let _sg = StackGuard::new(state);
                check_stack(state, 4)?;

                lua.push_value(&v)?;
                let res = if lua.unlikely_memory_error() {
                    ffi::lua_tolstring(state, -1, ptr::null_mut())
                } else {
                    protect_lua!(state, 1, 1, |state| {
                        ffi::lua_tolstring(state, -1, ptr::null_mut())
                    })?
                };
                if !res.is_null() {
                    Some(String(lua.pop_ref()))
                } else {
                    None
                }
            },
        })
    }

    /// Attempts to coerce a Lua value into an integer in a manner consistent with Lua's internal
    /// behavior.
    ///
    /// To succeed, the value must be an integer, a floating point number that has an exact
    /// representation as an integer, or a string that can be converted to an integer. Refer to the
    /// Lua manual for details.
    pub fn coerce_integer(&self, v: Value) -> Result<Option<Integer>> {
        Ok(match v {
            Value::Integer(i) => Some(i),
            v => unsafe {
                let lua = self.lock();
                let state = lua.state();
                let _sg = StackGuard::new(state);
                check_stack(state, 2)?;

                lua.push_value(&v)?;
                let mut isint = 0;
                let i = ffi::lua_tointegerx(state, -1, &mut isint);
                if isint == 0 {
                    None
                } else {
                    Some(i)
                }
            },
        })
    }

    /// Attempts to coerce a Lua value into a Number in a manner consistent with Lua's internal
    /// behavior.
    ///
    /// To succeed, the value must be a number or a string that can be converted to a number. Refer
    /// to the Lua manual for details.
    pub fn coerce_number(&self, v: Value) -> Result<Option<Number>> {
        Ok(match v {
            Value::Number(n) => Some(n),
            v => unsafe {
                let lua = self.lock();
                let state = lua.state();
                let _sg = StackGuard::new(state);
                check_stack(state, 2)?;

                lua.push_value(&v)?;
                let mut isnum = 0;
                let n = ffi::lua_tonumberx(state, -1, &mut isnum);
                if isnum == 0 {
                    None
                } else {
                    Some(n)
                }
            },
        })
    }

    /// Converts a value that implements `IntoLua` into a `Value` instance.
    #[inline]
    pub fn pack(&self, t: impl IntoLua) -> Result<Value> {
        t.into_lua(self)
    }

    /// Converts a `Value` instance into a value that implements `FromLua`.
    #[inline]
    pub fn unpack<T: FromLua>(&self, value: Value) -> Result<T> {
        T::from_lua(value, self)
    }

    /// Converts a value that implements `IntoLuaMulti` into a `MultiValue` instance.
    #[inline]
    pub fn pack_multi(&self, t: impl IntoLuaMulti) -> Result<MultiValue> {
        t.into_lua_multi(self)
    }

    /// Converts a `MultiValue` instance into a value that implements `FromLuaMulti`.
    #[inline]
    pub fn unpack_multi<T: FromLuaMulti>(&self, value: MultiValue) -> Result<T> {
        T::from_lua_multi(value, self)
    }

    /// Set a value in the Lua registry based on a string name.
    ///
    /// This value will be available to rust from all `Lua` instances which share the same main
    /// state.
    pub fn set_named_registry_value(&self, name: &str, t: impl IntoLua) -> Result<()> {
        let lua = self.lock();
        let state = lua.state();
        unsafe {
            let _sg = StackGuard::new(state);
            check_stack(state, 5)?;

            lua.push(t)?;
            rawset_field(state, ffi::LUA_REGISTRYINDEX, name)
        }
    }

    /// Get a value from the Lua registry based on a string name.
    ///
    /// Any Lua instance which shares the underlying main state may call this method to
    /// get a value previously set by [`Lua::set_named_registry_value`].
    pub fn named_registry_value<T>(&self, name: &str) -> Result<T>
    where
        T: FromLua,
    {
        let lua = self.lock();
        let state = lua.state();
        unsafe {
            let _sg = StackGuard::new(state);
            check_stack(state, 3)?;

            let protect = !lua.unlikely_memory_error();
            push_string(state, name.as_bytes(), protect)?;
            ffi::lua_rawget(state, ffi::LUA_REGISTRYINDEX);

            T::from_stack(-1, &lua)
        }
    }

    /// Removes a named value in the Lua registry.
    ///
    /// Equivalent to calling [`Lua::set_named_registry_value`] with a value of Nil.
    pub fn unset_named_registry_value(&self, name: &str) -> Result<()> {
        self.set_named_registry_value(name, Nil)
    }

    /// Place a value in the Lua registry with an auto-generated key.
    ///
    /// This value will be available to Rust from all `Lua` instances which share the same main
    /// state.
    ///
    /// Be warned, garbage collection of values held inside the registry is not automatic, see
    /// [`RegistryKey`] for more details.
    /// However, dropped [`RegistryKey`]s automatically reused to store new values.
    pub fn create_registry_value(&self, t: impl IntoLua) -> Result<RegistryKey> {
        let lua = self.lock();
        let state = lua.state();
        unsafe {
            let _sg = StackGuard::new(state);
            check_stack(state, 4)?;

            lua.push(t)?;

            let unref_list = (*lua.extra.get()).registry_unref_list.clone();

            // Check if the value is nil (no need to store it in the registry)
            if ffi::lua_isnil(state, -1) != 0 {
                return Ok(RegistryKey::new(ffi::LUA_REFNIL, unref_list));
            }

            // Try to reuse previously allocated slot
            let free_registry_id = unref_list.lock().as_mut().and_then(|x| x.pop());
            if let Some(registry_id) = free_registry_id {
                // It must be safe to replace the value without triggering memory error
                ffi::lua_rawseti(state, ffi::LUA_REGISTRYINDEX, registry_id as Integer);
                return Ok(RegistryKey::new(registry_id, unref_list));
            }

            // Allocate a new RegistryKey slot
            let registry_id = if lua.unlikely_memory_error() {
                ffi::luaL_ref(state, ffi::LUA_REGISTRYINDEX)
            } else {
                protect_lua!(state, 1, 0, |state| {
                    ffi::luaL_ref(state, ffi::LUA_REGISTRYINDEX)
                })?
            };
            Ok(RegistryKey::new(registry_id, unref_list))
        }
    }

    /// Get a value from the Lua registry by its `RegistryKey`
    ///
    /// Any Lua instance which shares the underlying main state may call this method to get a value
    /// previously placed by [`Lua::create_registry_value`].
    pub fn registry_value<T: FromLua>(&self, key: &RegistryKey) -> Result<T> {
        let lua = self.lock();
        if !lua.owns_registry_value(key) {
            return Err(Error::MismatchedRegistryKey);
        }

        let state = lua.state();
        match key.id() {
            ffi::LUA_REFNIL => T::from_lua(Value::Nil, self),
            registry_id => unsafe {
                let _sg = StackGuard::new(state);
                check_stack(state, 1)?;

                ffi::lua_rawgeti(state, ffi::LUA_REGISTRYINDEX, registry_id as Integer);
                T::from_stack(-1, &lua)
            },
        }
    }

    /// Removes a value from the Lua registry.
    ///
    /// You may call this function to manually remove a value placed in the registry with
    /// [`Lua::create_registry_value`]. In addition to manual [`RegistryKey`] removal, you can also
    /// call [`Lua::expire_registry_values`] to automatically remove values from the registry
    /// whose [`RegistryKey`]s have been dropped.
    pub fn remove_registry_value(&self, key: RegistryKey) -> Result<()> {
        let lua = self.lock();
        if !lua.owns_registry_value(&key) {
            return Err(Error::MismatchedRegistryKey);
        }

        unsafe {
            ffi::luaL_unref(lua.state(), ffi::LUA_REGISTRYINDEX, key.take());
        }
        Ok(())
    }

    /// Replaces a value in the Lua registry by its [`RegistryKey`].
    ///
    /// An identifier used in [`RegistryKey`] may possibly be changed to a new value.
    ///
    /// See [`Lua::create_registry_value`] for more details.
    pub fn replace_registry_value(&self, key: &mut RegistryKey, t: impl IntoLua) -> Result<()> {
        let lua = self.lock();
        if !lua.owns_registry_value(key) {
            return Err(Error::MismatchedRegistryKey);
        }

        let t = t.into_lua(self)?;

        let state = lua.state();
        unsafe {
            let _sg = StackGuard::new(state);
            check_stack(state, 2)?;

            match (t, key.id()) {
                (Value::Nil, ffi::LUA_REFNIL) => {
                    // Do nothing, no need to replace nil with nil
                }
                (Value::Nil, registry_id) => {
                    // Remove the value
                    ffi::luaL_unref(state, ffi::LUA_REGISTRYINDEX, registry_id);
                    key.set_id(ffi::LUA_REFNIL);
                }
                (value, ffi::LUA_REFNIL) => {
                    // Allocate a new `RegistryKey`
                    let new_key = self.create_registry_value(value)?;
                    key.set_id(new_key.take());
                }
                (value, registry_id) => {
                    // It must be safe to replace the value without triggering memory error
                    lua.push_value(&value)?;
                    ffi::lua_rawseti(state, ffi::LUA_REGISTRYINDEX, registry_id as Integer);
                }
            }
        }
        Ok(())
    }

    /// Returns true if the given [`RegistryKey`] was created by a [`Lua`] which shares the
    /// underlying main state with this [`Lua`] instance.
    ///
    /// Other than this, methods that accept a [`RegistryKey`] will return
    /// [`Error::MismatchedRegistryKey`] if passed a [`RegistryKey`] that was not created with a
    /// matching [`Lua`] state.
    #[inline]
    pub fn owns_registry_value(&self, key: &RegistryKey) -> bool {
        self.lock().owns_registry_value(key)
    }

    /// Remove any registry values whose [`RegistryKey`]s have all been dropped.
    ///
    /// Unlike normal handle values, [`RegistryKey`]s do not automatically remove themselves on
    /// Drop, but you can call this method to remove any unreachable registry values not
    /// manually removed by [`Lua::remove_registry_value`].
    pub fn expire_registry_values(&self) {
        let lua = self.lock();
        let state = lua.state();
        unsafe {
            let mut unref_list = (*lua.extra.get()).registry_unref_list.lock();
            let unref_list = mem::replace(&mut *unref_list, Some(Vec::new()));
            for id in mlua_expect!(unref_list, "unref list not set") {
                ffi::luaL_unref(state, ffi::LUA_REGISTRYINDEX, id);
            }
        }
    }

    /// Sets or replaces an application data object of type `T`.
    ///
    /// Application data could be accessed at any time by using [`Lua::app_data_ref`] or
    /// [`Lua::app_data_mut`] methods where `T` is the data type.
    ///
    /// # Panics
    ///
    /// Panics if the app data container is currently borrowed.
    ///
    /// # Examples
    ///
    /// ```
    /// use mlua::{Lua, Result};
    ///
    /// fn hello(lua: &Lua, _: ()) -> Result<()> {
    ///     let mut s = lua.app_data_mut::<&str>().unwrap();
    ///     assert_eq!(*s, "hello");
    ///     *s = "world";
    ///     Ok(())
    /// }
    ///
    /// fn main() -> Result<()> {
    ///     let lua = Lua::new();
    ///     lua.set_app_data("hello");
    ///     lua.create_function(hello)?.call(())?;
    ///     let s = lua.app_data_ref::<&str>().unwrap();
    ///     assert_eq!(*s, "world");
    ///     Ok(())
    /// }
    /// ```
    #[track_caller]
    pub fn set_app_data<T: MaybeSend + 'static>(&self, data: T) -> Option<T> {
        let lua = self.lock();
        let extra = unsafe { &*lua.extra.get() };
        extra.app_data.insert(data)
    }

    /// Tries to set or replace an application data object of type `T`.
    ///
    /// Returns:
    /// - `Ok(Some(old_data))` if the data object of type `T` was successfully replaced.
    /// - `Ok(None)` if the data object of type `T` was successfully inserted.
    /// - `Err(data)` if the data object of type `T` was not inserted because the container is
    ///   currently borrowed.
    ///
    /// See [`Lua::set_app_data()`] for examples.
    pub fn try_set_app_data<T: MaybeSend + 'static>(&self, data: T) -> StdResult<Option<T>, T> {
        let lua = self.lock();
        let extra = unsafe { &*lua.extra.get() };
        extra.app_data.try_insert(data)
    }

    /// Gets a reference to an application data object stored by [`Lua::set_app_data()`] of type
    /// `T`.
    ///
    /// # Panics
    ///
    /// Panics if the data object of type `T` is currently mutably borrowed. Multiple immutable
    /// reads can be taken out at the same time.
    #[track_caller]
    pub fn app_data_ref<T: 'static>(&self) -> Option<AppDataRef<T>> {
        let guard = self.lock_arc();
        let extra = unsafe { &*guard.extra.get() };
        extra.app_data.borrow(Some(guard))
    }

    /// Gets a mutable reference to an application data object stored by [`Lua::set_app_data()`] of
    /// type `T`.
    ///
    /// # Panics
    ///
    /// Panics if the data object of type `T` is currently borrowed.
    #[track_caller]
    pub fn app_data_mut<T: 'static>(&self) -> Option<AppDataRefMut<T>> {
        let guard = self.lock_arc();
        let extra = unsafe { &*guard.extra.get() };
        extra.app_data.borrow_mut(Some(guard))
    }

    /// Removes an application data of type `T`.
    ///
    /// # Panics
    ///
    /// Panics if the app data container is currently borrowed.
    #[track_caller]
    pub fn remove_app_data<T: 'static>(&self) -> Option<T> {
        let lua = self.lock();
        let extra = unsafe { &*lua.extra.get() };
        extra.app_data.remove()
    }

    /// Pushes a value that implements `IntoLua` onto the Lua stack.
    ///
    /// Uses 2 stack spaces, does not call checkstack.
    #[doc(hidden)]
    #[inline(always)]
    pub unsafe fn push(&self, value: impl IntoLua) -> Result<()> {
        self.lock().push(value)
    }

    /// Returns an internal `Poll::Pending` constant used for executing async callbacks.
    #[cfg(feature = "async")]
    #[doc(hidden)]
    #[inline(always)]
    pub fn poll_pending() -> LightUserData {
        static ASYNC_POLL_PENDING: u8 = 0;
        LightUserData(&ASYNC_POLL_PENDING as *const u8 as *mut c_void)
    }

    // Luau version located in `luau/mod.rs`
    #[cfg(not(feature = "luau"))]
    fn disable_c_modules(&self) -> Result<()> {
        let package: Table = self.globals().get("package")?;

        package.set(
            "loadlib",
            self.create_function(|_, ()| -> Result<()> {
                Err(Error::SafetyError(
                    "package.loadlib is disabled in safe mode".to_string(),
                ))
            })?,
        )?;

        #[cfg(any(feature = "lua54", feature = "lua53", feature = "lua52"))]
        let searchers: Table = package.get("searchers")?;
        #[cfg(any(feature = "lua51", feature = "luajit"))]
        let searchers: Table = package.get("loaders")?;

        let loader = self.create_function(|_, ()| Ok("\n\tcan't load C modules in safe mode"))?;

        // The third and fourth searchers looks for a loader as a C library
        searchers.raw_set(3, loader)?;
        searchers.raw_remove(4)?;

        Ok(())
    }

    #[inline(always)]
    pub(crate) fn lock(&self) -> ReentrantMutexGuard<RawLua> {
        self.raw.lock()
    }

    #[inline(always)]
    pub(crate) fn lock_arc(&self) -> LuaGuard {
        LuaGuard(self.raw.lock_arc())
    }

    #[inline(always)]
    pub(crate) fn weak(&self) -> WeakLua {
        WeakLua(XRc::downgrade(&self.raw))
    }

    /// Returns a handle to the unprotected Lua state without any synchronization.
    ///
    /// This is useful where we know that the lock is already held by the caller.
    #[inline(always)]
    pub(crate) unsafe fn raw_lua(&self) -> &RawLua {
        &*self.raw.data_ptr()
    }
}

impl WeakLua {
    #[track_caller]
    #[inline(always)]
    pub(crate) fn lock(&self) -> LuaGuard {
        LuaGuard::new(self.0.upgrade().expect("Lua instance is destroyed"))
    }

    #[inline(always)]
    pub(crate) fn try_lock(&self) -> Option<LuaGuard> {
        Some(LuaGuard::new(self.0.upgrade()?))
    }

    #[track_caller]
    #[inline(always)]
    pub(crate) fn upgrade(&self) -> Lua {
        Lua {
            raw: self.0.upgrade().expect("Lua instance is destroyed"),
            collect_garbage: false,
        }
    }
}

impl PartialEq for WeakLua {
    fn eq(&self, other: &Self) -> bool {
        XWeak::ptr_eq(&self.0, &other.0)
    }
}

impl Eq for WeakLua {}

impl LuaGuard {
    #[cfg(feature = "send")]
    pub(crate) fn new(handle: XRc<ReentrantMutex<RawLua>>) -> Self {
        LuaGuard(handle.lock_arc())
    }

    #[cfg(not(feature = "send"))]
    pub(crate) fn new(handle: XRc<ReentrantMutex<RawLua>>) -> Self {
        LuaGuard(handle.into_lock_arc())
    }
}

impl Deref for LuaGuard {
    type Target = RawLua;

    fn deref(&self) -> &Self::Target {
        &self.0
    }
}

pub(crate) mod extra;
mod raw;
pub(crate) mod util;

#[cfg(test)]
mod assertions {
    use super::*;

    // Lua has lots of interior mutability, should not be RefUnwindSafe
    static_assertions::assert_not_impl_any!(Lua: std::panic::RefUnwindSafe);

    #[cfg(not(feature = "send"))]
    static_assertions::assert_not_impl_any!(Lua: Send);
    #[cfg(feature = "send")]
    static_assertions::assert_impl_all!(Lua: Send, Sync);
}