Replace CallbackError display message

This can result in allocating the same slot twice and rewriting old value.
Lua uses (registry) table length to find next free slot and having Nil in the middle of the table can impact length calculation.
With this fix we ensure that Nil values uses a special LUA_REFNIL slot.

.github/workflows/coverage.yml

@@ -10,14 +10,14 @@ jobs:
       options: --security-opt seccomp=unconfined
     steps:
       - name: Checkout repository
-        uses: actions/checkout@v2
+        uses: actions/checkout@v3
 
-      - name: Generate code coverage
+      - name: Generate coverage report
         run: |
           cargo tarpaulin --verbose --features lua54,vendored,async,send,serialize,macros --out xml --exclude-files benches --exclude-files build --exclude-files mlua_derive --exclude-files src/ffi --exclude-files tests
 
-      - name: Upload to codecov.io
-        uses: codecov/codecov-action@v1
+      - name: Upload report to codecov.io
+        uses: codecov/codecov-action@v3
         with:
           token: ${{secrets.CODECOV_TOKEN}}
           fail_ci_if_error: false

.github/workflows/main.yml

@@ -7,35 +7,34 @@ jobs:
     runs-on: ${{ matrix.os }}
     strategy:
       matrix:
-        os: [ubuntu-20.04, macos-latest, windows-latest]
+        os: [ubuntu-22.04, macos-latest, windows-latest]
         rust: [stable]
         lua: [lua54, lua53, lua52, lua51, luajit, luau]
         include:
-        - os: ubuntu-20.04
-          target: x86_64-unknown-linux-gnu
-        - os: macos-latest
-          target: x86_64-apple-darwin
-        - os: windows-latest
-          target: x86_64-pc-windows-msvc
+          - os: ubuntu-22.04
+            target: x86_64-unknown-linux-gnu
+          - os: macos-latest
+            target: x86_64-apple-darwin
+          - os: windows-latest
+            target: x86_64-pc-windows-msvc
     steps:
-    - uses: actions/checkout@v2
-    - uses: actions-rs/toolchain@v1
-      with:
-        toolchain: ${{ matrix.rust }}
-        target: ${{ matrix.target }}
-        override: true
-    - uses: Swatinem/rust-cache@v1
-    - name: Build ${{ matrix.lua }} vendored
-      run: |
-        cargo build --features "${{ matrix.lua }},vendored"
-        cargo build --features "${{ matrix.lua }},vendored,async,send,serialize,macros,parking_lot"
-      shell: bash
-    - name: Build ${{ matrix.lua }} pkg-config
-      if: ${{ matrix.os == 'ubuntu-20.04' && matrix.lua != 'lua54' }}
-      run: |
-        sudo apt-get update
-        sudo apt-get install -y --no-install-recommends liblua5.3-dev liblua5.2-dev liblua5.1-0-dev libluajit-5.1-dev
-        cargo build --features "${{ matrix.lua }}"
+      - uses: actions/checkout@v3
+      - uses: dtolnay/rust-toolchain@stable
+        with:
+          toolchain: ${{ matrix.rust }}
+          target: ${{ matrix.target }}
+      - uses: Swatinem/rust-cache@v2
+      - name: Build ${{ matrix.lua }} vendored
+        run: |
+          cargo build --features "${{ matrix.lua }},vendored"
+          cargo build --features "${{ matrix.lua }},vendored,async,send,serialize,macros,parking_lot"
+        shell: bash
+      - name: Build ${{ matrix.lua }} pkg-config
+        if: ${{ matrix.os == 'ubuntu-22.04' }}
+        run: |
+          sudo apt-get update
+          sudo apt-get install -y --no-install-recommends liblua5.4-dev liblua5.3-dev liblua5.2-dev liblua5.1-0-dev libluajit-5.1-dev
+          cargo build --features "${{ matrix.lua }}"
 
   build_aarch64_cross_macos:
     name: Cross-compile to aarch64-apple-darwin
@@ -45,60 +44,57 @@ jobs:
       matrix:
         lua: [lua54, lua53, lua52, lua51, luajit]
     steps:
-    - uses: actions/checkout@v2
-    - uses: actions-rs/toolchain@v1
-      with:
-        toolchain: stable
-        target: aarch64-apple-darwin
-        override: true
-    - name: Cross-compile
-      run: cargo build --target aarch64-apple-darwin --features "${{ matrix.lua }},vendored,async,send,serialize,macros,parking_lot"
+      - uses: actions/checkout@v3
+      - uses: dtolnay/rust-toolchain@stable
+        with:
+          toolchain: stable
+          target: aarch64-apple-darwin
+      - name: Cross-compile
+        run: cargo build --target aarch64-apple-darwin --features "${{ matrix.lua }},vendored,async,send,serialize,macros,parking_lot"
 
   build_aarch64_cross_ubuntu:
     name: Cross-compile to aarch64-unknown-linux-gnu
-    runs-on: ubuntu-20.04
+    runs-on: ubuntu-22.04
     needs: build
     strategy:
       matrix:
         lua: [lua54, lua53, lua52, lua51, luajit]
     steps:
-    - uses: actions/checkout@v2
-    - uses: actions-rs/toolchain@v1
-      with:
-        toolchain: stable
-        target: aarch64-unknown-linux-gnu
-        override: true
-    - name: Install ARM compiler toolchain
-      run: |
-        sudo apt-get update
-        sudo apt-get install -y --no-install-recommends gcc-aarch64-linux-gnu libc6-dev-arm64-cross
-      shell: bash
-    - name: Cross-compile
-      run: cargo build --target aarch64-unknown-linux-gnu --features "${{ matrix.lua }},vendored,async,send,serialize,macros,parking_lot"
-      shell: bash
+      - uses: actions/checkout@v3
+      - uses: dtolnay/rust-toolchain@stable
+        with:
+          toolchain: stable
+          target: aarch64-unknown-linux-gnu
+      - name: Install ARM compiler toolchain
+        run: |
+          sudo apt-get update
+          sudo apt-get install -y --no-install-recommends gcc-aarch64-linux-gnu libc6-dev-arm64-cross
+        shell: bash
+      - name: Cross-compile
+        run: cargo build --target aarch64-unknown-linux-gnu --features "${{ matrix.lua }},vendored,async,send,serialize,macros,parking_lot"
+        shell: bash
 
   build_armv7_cross_ubuntu:
     name: Cross-compile to armv7-unknown-linux-gnueabihf
-    runs-on: ubuntu-20.04
+    runs-on: ubuntu-22.04
     needs: build
     strategy:
       matrix:
         lua: [lua54, lua53, lua52, lua51]
     steps:
-    - uses: actions/checkout@v2
-    - uses: actions-rs/toolchain@v1
-      with:
-        toolchain: stable
-        target: armv7-unknown-linux-gnueabihf
-        override: true
-    - name: Install ARM compiler toolchain
-      run: |
-        sudo apt-get update
-        sudo apt-get install -y --no-install-recommends gcc-arm-linux-gnueabihf libc-dev-armhf-cross
-      shell: bash
-    - name: Cross-compile
-      run: cargo build --target armv7-unknown-linux-gnueabihf --features "${{ matrix.lua }},vendored,async,send,serialize,macros,parking_lot"
-      shell: bash
+      - uses: actions/checkout@v3
+      - uses: dtolnay/rust-toolchain@stable
+        with:
+          toolchain: stable
+          target: armv7-unknown-linux-gnueabihf
+      - name: Install ARM compiler toolchain
+        run: |
+          sudo apt-get update
+          sudo apt-get install -y --no-install-recommends gcc-arm-linux-gnueabihf libc-dev-armhf-cross
+        shell: bash
+      - name: Cross-compile
+        run: cargo build --target armv7-unknown-linux-gnueabihf --features "${{ matrix.lua }},vendored,async,send,serialize,macros,parking_lot"
+        shell: bash
 
   test:
     name: Test
@@ -106,35 +102,34 @@ jobs:
     needs: build
     strategy:
       matrix:
-        os: [ubuntu-20.04, macos-latest, windows-latest]
+        os: [ubuntu-22.04, macos-latest, windows-latest]
         rust: [stable, nightly]
         lua: [lua54, lua53, lua52, lua51, luajit, luajit52, luau]
         include:
-        - os: ubuntu-20.04
-          target: x86_64-unknown-linux-gnu
-        - os: macos-latest
-          target: x86_64-apple-darwin
-        - os: windows-latest
-          target: x86_64-pc-windows-msvc
+          - os: ubuntu-22.04
+            target: x86_64-unknown-linux-gnu
+          - os: macos-latest
+            target: x86_64-apple-darwin
+          - os: windows-latest
+            target: x86_64-pc-windows-msvc
     steps:
-    - uses: actions/checkout@v2
-    - uses: actions-rs/toolchain@v1
-      with:
-        toolchain: ${{ matrix.rust }}
-        target: ${{ matrix.target }}
-        override: true
-    - uses: Swatinem/rust-cache@v1
-    - name: Run ${{ matrix.lua }} tests
-      run: |
-        cargo test --features "${{ matrix.lua }},vendored"
-        cargo test --features "${{ matrix.lua }},vendored,async,send,serialize,macros,parking_lot"
-      shell: bash
-    - name: Run compile tests (macos lua54)
-      if: ${{ matrix.os == 'macos-latest' && matrix.lua == 'lua54' }}
-      run: |
-        TRYBUILD=overwrite cargo test --features "${{ matrix.lua }},vendored" -- --ignored
-        TRYBUILD=overwrite cargo test --features "${{ matrix.lua }},vendored,async,send,serialize,macros,parking_lot" -- --ignored
-      shell: bash
+      - uses: actions/checkout@v3
+      - uses: dtolnay/rust-toolchain@stable
+        with:
+          toolchain: ${{ matrix.rust }}
+          target: ${{ matrix.target }}
+      - uses: Swatinem/rust-cache@v1
+      - name: Run ${{ matrix.lua }} tests
+        run: |
+          cargo test --features "${{ matrix.lua }},vendored"
+          cargo test --features "${{ matrix.lua }},vendored,async,send,serialize,macros,parking_lot"
+        shell: bash
+      - name: Run compile tests (macos lua54)
+        if: ${{ matrix.os == 'macos-latest' && matrix.lua == 'lua54' }}
+        run: |
+          TRYBUILD=overwrite cargo test --features "${{ matrix.lua }},vendored" -- --ignored
+          TRYBUILD=overwrite cargo test --features "${{ matrix.lua }},vendored,async,send,serialize,macros,parking_lot" -- --ignored
+        shell: bash
 
   test_with_sanitizer:
     name: Test with address sanitizer
@@ -142,25 +137,24 @@ jobs:
     needs: build
     strategy:
       matrix:
-        os: [ubuntu-20.04]
+        os: [ubuntu-22.04]
         rust: [nightly]
         lua: [lua54, lua53, lua52, lua51, luajit, luau]
         include:
-        - os: ubuntu-20.04
-          target: x86_64-unknown-linux-gnu
+          - os: ubuntu-22.04
+            target: x86_64-unknown-linux-gnu
     steps:
-    - uses: actions/checkout@v2
-    - uses: actions-rs/toolchain@v1
-      with:
-        toolchain: ${{ matrix.rust }}
-        target: ${{ matrix.target }}
-        override: true
-    - uses: Swatinem/rust-cache@v1
-    - name: Run ${{ matrix.lua }} tests with address sanitizer
-      run: |
-        RUSTFLAGS="-Z sanitizer=address" \
-          cargo test --tests --features "${{ matrix.lua }},vendored,async,send,serialize,macros,parking_lot" --target x86_64-unknown-linux-gnu -- --skip test_too_many_recursions
-      shell: bash
+      - uses: actions/checkout@v3
+      - uses: dtolnay/rust-toolchain@stable
+        with:
+          toolchain: ${{ matrix.rust }}
+          target: ${{ matrix.target }}
+      - uses: Swatinem/rust-cache@v1
+      - name: Run ${{ matrix.lua }} tests with address sanitizer
+        run: |
+          RUSTFLAGS="-Z sanitizer=address" \
+            cargo test --tests --features "${{ matrix.lua }},vendored,async,send,serialize,macros,parking_lot" --target x86_64-unknown-linux-gnu -- --skip test_too_many_recursions
+        shell: bash
 
   test_modules:
     name: Test modules
@@ -168,27 +162,26 @@ jobs:
     needs: build
     strategy:
       matrix:
-        os: [ubuntu-20.04, macos-latest]
+        os: [ubuntu-22.04, macos-latest]
         rust: [stable]
         lua: [lua54, lua53, lua52, lua51, luajit]
         include:
-        - os: ubuntu-20.04
-          target: x86_64-unknown-linux-gnu
-        - os: macos-latest
-          target: x86_64-apple-darwin
+          - os: ubuntu-22.04
+            target: x86_64-unknown-linux-gnu
+          - os: macos-latest
+            target: x86_64-apple-darwin
     steps:
-    - uses: actions/checkout@v2
-    - uses: actions-rs/toolchain@v1
-      with:
-        toolchain: ${{ matrix.rust }}
-        target: ${{ matrix.target }}
-        override: true
-    - uses: Swatinem/rust-cache@v1
-    - name: Run ${{ matrix.lua }} module tests
-      run: |
-        (cd tests/module && cargo build --release --features "${{ matrix.lua }}")
-        (cd tests/module/loader && cargo test --release --features "${{ matrix.lua }},vendored")
-      shell: bash
+      - uses: actions/checkout@v3
+      - uses: dtolnay/rust-toolchain@stable
+        with:
+          toolchain: ${{ matrix.rust }}
+          target: ${{ matrix.target }}
+      - uses: Swatinem/rust-cache@v1
+      - name: Run ${{ matrix.lua }} module tests
+        run: |
+          (cd tests/module && cargo build --release --features "${{ matrix.lua }}")
+          (cd tests/module/loader && cargo test --release --features "${{ matrix.lua }},vendored")
+        shell: bash
 
   test_modules_windows:
     name: Test modules on Windows
@@ -201,41 +194,39 @@ jobs:
       run:
         shell: msys2 {0}
     steps:
-    - uses: msys2/setup-msys2@v2
-    - uses: actions/checkout@v2
-    - name: Install Rust & Lua
-      run: |
-        pacman -S --noconfirm mingw-w64-x86_64-rust mingw-w64-x86_64-lua mingw-w64-x86_64-luajit mingw-w64-x86_64-pkg-config
-    - name: Run ${{ matrix.lua }} module tests
-      run: |
-        (cd tests/module && cargo build --release --features "${{ matrix.lua }}")
-        (cd tests/module/loader && cargo test --release --features "${{ matrix.lua }}")
+      - uses: msys2/setup-msys2@v2
+      - uses: actions/checkout@v3
+      - name: Install Rust & Lua
+        run: |
+          pacman -S --noconfirm mingw-w64-x86_64-rust mingw-w64-x86_64-lua mingw-w64-x86_64-luajit mingw-w64-x86_64-pkg-config
+      - name: Run ${{ matrix.lua }} module tests
+        run: |
+          (cd tests/module && cargo build --release --features "${{ matrix.lua }}")
+          (cd tests/module/loader && cargo test --release --features "${{ matrix.lua }}")
 
   rustfmt:
     name: Rustfmt
-    runs-on: ubuntu-20.04
+    runs-on: ubuntu-22.04
     steps:
-    - uses: actions/checkout@v2
-    - uses: actions-rs/toolchain@v1
-      with:
-        toolchain: stable
-        components: rustfmt
-        override: true
-    - run: cargo fmt -- --check
+      - uses: actions/checkout@v3
+      - uses: dtolnay/rust-toolchain@stable
+        with:
+          toolchain: stable
+          components: rustfmt
+      - run: cargo fmt -- --check
 
   clippy:
     name: Clippy check
-    runs-on: ubuntu-20.04
+    runs-on: ubuntu-22.04
     strategy:
       matrix:
         lua: [lua54, lua53, lua52, lua51, luajit, luau]
     steps:
-      - uses: actions/checkout@v2
-      - uses: actions-rs/toolchain@v1
+      - uses: actions/checkout@v3
+      - uses: dtolnay/rust-toolchain@stable
         with:
-            toolchain: nightly
-            components: clippy
-            override: true
+          toolchain: nightly
+          components: clippy
       - uses: actions-rs/clippy-check@v1
         with:
           token: ${{ secrets.GITHUB_TOKEN }}

CHANGELOG.md

@@ -1,3 +1,32 @@
+## v0.8.6
+
+- Fixed bug when recycled Registry slot can be set to Nil
+
+## v0.8.5
+
+- Fixed potential unsoundness when using `Layout::from_size_align_unchecked` and Rust 1.65+
+- Performance optimizations around string and table creation in standalone mode
+- Added fast track path to Table `get`/`set`/`len` methods without metatable
+- Added new methods `push`/`pop`/`raw_push`/`raw_pop` to Table
+- Fix getting caller information from `Lua::load`
+- Better checks and tests when trying to modify a Luau readonly table
+
+## v0.8.4
+
+- Minimal Luau updated to 0.548
+
+## v0.8.3
+
+- Close to-be-closed variables for Lua 5.4 when using call_async functions (#192)
+- Fixed Lua assertion when inspecting another thread stack. (#195)
+- Use more reliable way to create LuaJIT VM (which can fail if use Rust allocator on non-x86 platforms)
+
+## v0.8.2
+
+- Performance optimizations in handling UserData
+- Minimal Luau updated to 0.536
+- Fixed bug in `Function::bind` when passing empty binds and no arguments (#189)
+
 ## v0.8.1
 
 - Added `Lua::create_proxy` for accessing to UserData static fields and functions without instance

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "mlua"
-version = "0.8.1" # remember to update html_root_url and mlua_derive
+version = "0.8.6" # remember to update html_root_url and mlua_derive
 authors = ["Aleksandr Orlenko <zxteam@pm.me>", "kyren <catherine@chucklefish.org>"]
 edition = "2021"
 repository = "https://github.com/khvzak/mlua"
@@ -58,10 +58,10 @@ cc = { version = "1.0" }
 pkg-config = { version = "0.3.17" }
 lua-src = { version = ">= 544.0.0, < 550.0.0", optional = true }
 luajit-src = { version = ">= 210.4.0, < 220.0.0", optional = true }
-luau0-src = { version = "0.3.2", optional = true }
+luau0-src = { version = "0.4.0", optional = true }
 
 [dev-dependencies]
-rustyline = "9.0"
+rustyline = "10.0"
 criterion = { version = "0.3.4", features = ["html_reports", "async_tokio"] }
 trybuild = "1.0"
 futures = "0.3.5"

FAQ.md

@@ -0,0 +1,21 @@
+# mlua FAQ
+
+This file is for general questions that don't fit into the README or crate docs.
+
+## Loading a C module fails with error `undefined symbol: lua_xxx`. How to fix?
+
+Add the following rustflags to your [.cargo/config](http://doc.crates.io/config.html) in order to properly export Lua symbols:
+
+```toml
+[target.x86_64-unknown-linux-gnu]
+rustflags = ["-C", "link-args=-rdynamic"]
+
+[target.x86_64-apple-darwin]
+rustflags = ["-C", "link-args=-rdynamic"]
+```
+
+## I want to add support for a Lua VM fork to mlua. Do you accept pull requests?
+
+Adding new feature flag to support a Lua VM fork is a major step that requires huge effort to maintain it.
+Regular updates, testing, checking compatibility, etc.
+That's why I don't plan to support new Lua VM forks or other languages in mlua.

README.md

@@ -11,7 +11,11 @@
 [codecov.io]: https://codecov.io/gh/khvzak/mlua
 [MSRV]: https://img.shields.io/badge/rust-1.56+-brightgreen.svg?&logo=rust
 
-[Guided Tour](examples/guided_tour.rs)
+[Guided Tour] | [Benchmarks] | [FAQ]
+
+[Guided Tour]: examples/guided_tour.rs
+[Benchmarks]: https://github.com/khvzak/script-bench-rs
+[FAQ]: FAQ.md
 
 `mlua` is bindings to [Lua](https://www.lua.org) programming language for Rust with a goal to provide
 _safe_ (as far as it's possible), high level, easy to use, practical and flexible API.

examples/repl.rs

@@ -5,7 +5,7 @@ use rustyline::Editor;
 
 fn main() {
     let lua = Lua::new();
-    let mut editor = Editor::<()>::new();
+    let mut editor = Editor::<()>::new().expect("Failed to make rustyline editor");
 
     loop {
         let mut prompt = "> ";

src/error.rs

@@ -249,7 +249,7 @@ impl fmt::Display for Error {
                 write!(fmt, "RegistryKey used from different Lua state")
             }
             Error::CallbackError { ref cause, ref traceback } => {
-                writeln!(fmt, "callback error")?;
+                writeln!(fmt, "{}", cause)?;
                 // Trace errors down to the root
                 let (mut cause, mut full_traceback) = (cause, None);
                 while let Error::CallbackError { cause: ref cause2, traceback: ref traceback2 } = **cause {
@@ -269,7 +269,9 @@ impl fmt::Display for Error {
                 } else {
                     writeln!(fmt, "{}", traceback.trim_end())?;
                 }
-                write!(fmt, "caused by: {}", cause)
+
+                Ok(())
+                // write!(fmt, "caused by: {}", cause)
             }
             Error::PreviouslyResumedPanic => {
                 write!(fmt, "previously resumed panic returned again")

src/ffi/lua51/lua.rs

@@ -324,6 +324,12 @@ pub unsafe fn lua_tostring(L: *mut lua_State, i: c_int) -> *const c_char {
     lua_tolstring(L, i, ptr::null_mut())
 }
 
+#[inline(always)]
+pub unsafe fn lua_xpush(from: *mut lua_State, to: *mut lua_State, idx: c_int) {
+    lua_pushvalue(from, idx);
+    lua_xmove(from, to, 1);
+}
+
 //
 // Debug API
 //

src/ffi/lua52/lua.rs

@@ -410,6 +410,12 @@ pub unsafe fn lua_tostring(L: *mut lua_State, i: c_int) -> *const c_char {
     lua_tolstring(L, i, ptr::null_mut())
 }
 
+#[inline(always)]
+pub unsafe fn lua_xpush(from: *mut lua_State, to: *mut lua_State, idx: c_int) {
+    lua_pushvalue(from, idx);
+    lua_xmove(from, to, 1);
+}
+
 //
 // Debug API
 //

src/ffi/lua53/lua.rs

@@ -434,6 +434,12 @@ pub unsafe fn lua_replace(L: *mut lua_State, idx: c_int) {
     lua_pop(L, 1)
 }
 
+#[inline(always)]
+pub unsafe fn lua_xpush(from: *mut lua_State, to: *mut lua_State, idx: c_int) {
+    lua_pushvalue(from, idx);
+    lua_xmove(from, to, 1);
+}
+
 //
 // Debug API
 //

src/ffi/lua54/lua.rs

@@ -455,6 +455,12 @@ pub unsafe fn lua_replace(L: *mut lua_State, idx: c_int) {
     lua_pop(L, 1)
 }
 
+#[inline(always)]
+pub unsafe fn lua_xpush(from: *mut lua_State, to: *mut lua_State, idx: c_int) {
+    lua_pushvalue(from, idx);
+    lua_xmove(from, to, 1);
+}
+
 #[inline(always)]
 pub unsafe fn lua_newuserdata(L: *mut lua_State, sz: usize) -> *mut c_void {
     lua_newuserdatauv(L, sz, 1)

src/ffi/luau/compat.rs

@@ -341,7 +341,7 @@ pub unsafe fn luaL_loadbufferx(
         fn free(p: *mut c_void);
     }
 
-    let chunk_is_text = (*data as u8) >= b'\n';
+    let chunk_is_text = size == 0 || (*data as u8) >= b'\n';
     if !mode.is_null() {
         let modeb = CStr::from_ptr(mode).to_bytes();
         if !chunk_is_text && !modeb.contains(&b'b') {
@@ -423,7 +423,7 @@ pub unsafe fn luaL_traceback(
             level = numlevels - COMPAT53_LEVELS2; // and skip to last ones
         } else {
             lua_getinfo(L1, level, cstr!("sln"), &mut ar);
-            lua_pushfstring(L, cstr!("\n\t%s:"), ar.short_src.as_ptr());
+            lua_pushfstring(L, cstr!("\n\t%s:"), ar.short_src);
             if ar.currentline > 0 {
                 lua_pushfstring(L, cstr!("%d:"), ar.currentline);
             }

src/ffi/luau/lua.rs

@@ -257,15 +257,18 @@ extern "C" {
 extern "C" {
     pub fn lua_error(L: *mut lua_State) -> !;
     pub fn lua_next(L: *mut lua_State, idx: c_int) -> c_int;
+    pub fn lua_rawiter(L: *mut lua_State, idx: c_int, iter: c_int) -> c_int;
     pub fn lua_concat(L: *mut lua_State, n: c_int);
     // TODO: lua_encodepointer
     pub fn lua_clock() -> c_double;
+    pub fn lua_setuserdatatag(L: *mut lua_State, idx: c_int, tag: c_int);
     pub fn lua_setuserdatadtor(
         L: *mut lua_State,
         tag: c_int,
         dtor: Option<unsafe extern "C" fn(*mut lua_State, *mut c_void)>,
     );
     pub fn lua_clonefunction(L: *mut lua_State, idx: c_int);
+    pub fn lua_cleartable(L: *mut lua_State, idx: c_int);
 }
 
 //
@@ -437,7 +440,12 @@ extern "C" {
     pub fn lua_setupvalue(L: *mut lua_State, funcindex: c_int, n: c_int) -> *const c_char;
 
     pub fn lua_singlestep(L: *mut lua_State, enabled: c_int);
-    pub fn lua_breakpoint(L: *mut lua_State, funcindex: c_int, line: c_int, enabled: c_int);
+    pub fn lua_breakpoint(
+        L: *mut lua_State,
+        funcindex: c_int,
+        line: c_int,
+        enabled: c_int,
+    ) -> c_int;
 
     pub fn lua_getcoverage(
         L: *mut lua_State,
@@ -454,13 +462,14 @@ pub struct lua_Debug {
     pub name: *const c_char,
     pub what: *const c_char,
     pub source: *const c_char,
+    pub short_src: *const c_char,
     pub linedefined: c_int,
     pub currentline: c_int,
     pub nupvals: u8,
     pub nparams: u8,
     pub isvararg: c_char,
-    pub short_src: [c_char; LUA_IDSIZE],
     pub userdata: *mut c_void,
+    pub ssbuf: [c_char; LUA_IDSIZE],
 }
 
 //

src/ffi/mod.rs

@@ -79,9 +79,11 @@ pub(crate) fn keep_lua_symbols() {
     symbols.push(lua_tocfunction as _);
     symbols.push(luaL_loadstring as _);
     symbols.push(luaL_openlibs as _);
-    if cfg!(any(feature = "lua54", feature = "lua53", feature = "lua52")) {
+    #[cfg(any(feature = "lua54", feature = "lua53", feature = "lua52"))]
+    {
         symbols.push(lua_getglobal as _);
         symbols.push(lua_setglobal as _);
+        symbols.push(luaL_setfuncs as _);
     }
 }
 

src/function.rs

@@ -114,7 +114,7 @@ impl<'lua> Function<'lua> {
         R::from_lua_multi(results, lua)
     }
 
-    /// Returns a Feature that, when polled, calls `self`, passing `args` as function arguments,
+    /// Returns a future that, when polled, calls `self`, passing `args` as function arguments,
     /// and drives the execution.
     ///
     /// Internally it wraps the function to an [`AsyncThread`].
@@ -198,7 +198,9 @@ impl<'lua> Function<'lua> {
             for i in 0..nbinds {
                 ffi::lua_pushvalue(state, ffi::lua_upvalueindex(i + 2));
             }
-            ffi::lua_rotate(state, 1, nbinds);
+            if nargs > 0 {
+                ffi::lua_rotate(state, 1, nbinds);
+            }
 
             nargs + nbinds
         }
@@ -208,6 +210,10 @@ impl<'lua> Function<'lua> {
         let args = args.to_lua_multi(lua)?;
         let nargs = args.len() as c_int;
 
+        if nargs == 0 {
+            return Ok(self.clone());
+        }
+
         if nargs + 1 > ffi::LUA_MAX_UPVALUES {
             return Err(Error::BindError);
         }
@@ -267,10 +273,13 @@ impl<'lua> Function<'lua> {
                 name_what: None,
                 what: ptr_to_cstr_bytes(ar.what).map(|s| s.to_vec()),
                 source: ptr_to_cstr_bytes(ar.source).map(|s| s.to_vec()),
-                short_src: ptr_to_cstr_bytes(&ar.short_src as *const _).map(|s| s.to_vec()),
-                line_defined: ar.linedefined as i32,
                 #[cfg(not(feature = "luau"))]
-                last_line_defined: ar.lastlinedefined as i32,
+                short_src: ptr_to_cstr_bytes(ar.short_src.as_ptr()).map(|s| s.to_vec()),
+                #[cfg(feature = "luau")]
+                short_src: ptr_to_cstr_bytes(ar.short_src).map(|s| s.to_vec()),
+                line_defined: ar.linedefined,
+                #[cfg(not(feature = "luau"))]
+                last_line_defined: ar.lastlinedefined,
             }
         }
     }
@@ -306,8 +315,7 @@ impl<'lua> Function<'lua> {
 
             lua.push_ref(&self.0);
             let data_ptr = &mut data as *mut Vec<u8> as *mut c_void;
-            let strip = if strip { 1 } else { 0 };
-            ffi::lua_dump(lua.state, writer, data_ptr, strip);
+            ffi::lua_dump(lua.state, writer, data_ptr, strip as i32);
             ffi::lua_pop(lua.state, 1);
         }
 

src/hook.rs

@@ -102,10 +102,13 @@ impl<'lua> Debug<'lua> {
 
             DebugSource {
                 source: ptr_to_cstr_bytes((*self.ar.get()).source),
-                short_src: ptr_to_cstr_bytes((*self.ar.get()).short_src.as_ptr()),
-                line_defined: (*self.ar.get()).linedefined as i32,
                 #[cfg(not(feature = "luau"))]
-                last_line_defined: (*self.ar.get()).lastlinedefined as i32,
+                short_src: ptr_to_cstr_bytes((*self.ar.get()).short_src.as_ptr()),
+                #[cfg(feature = "luau")]
+                short_src: ptr_to_cstr_bytes((*self.ar.get()).short_src),
+                line_defined: (*self.ar.get()).linedefined,
+                #[cfg(not(feature = "luau"))]
+                last_line_defined: (*self.ar.get()).lastlinedefined,
                 what: ptr_to_cstr_bytes((*self.ar.get()).what),
             }
         }
@@ -125,7 +128,7 @@ impl<'lua> Debug<'lua> {
                 "lua_getinfo failed with `l`"
             );
 
-            (*self.ar.get()).currentline as i32
+            (*self.ar.get()).currentline
         }
     }
 

src/lib.rs

@@ -72,7 +72,7 @@
 //! [`serde::Deserialize`]: https://docs.serde.rs/serde/de/trait.Deserialize.html
 
 // mlua types in rustdoc of other crates get linked to here.
-#![doc(html_root_url = "https://docs.rs/mlua/0.8.1")]
+#![doc(html_root_url = "https://docs.rs/mlua/0.8.6")]
 // Deny warnings inside doc tests / examples. When this isn't present, rustdoc doesn't show *any*
 // warnings at all.
 #![doc(test(attr(deny(warnings))))]

src/lua.rs

@@ -25,7 +25,7 @@ use crate::string::String;
 use crate::table::Table;
 use crate::thread::Thread;
 use crate::types::{
-    Callback, CallbackUpvalue, DestructedUserdataMT, Integer, LightUserData, LuaRef, MaybeSend,
+    Callback, CallbackUpvalue, DestructedUserdata, Integer, LightUserData, LuaRef, MaybeSend,
     Number, RegistryKey,
 };
 use crate::userdata::{AnyUserData, UserData, UserDataCell};
@@ -88,6 +88,8 @@ pub(crate) struct ExtraData {
 
     registered_userdata: FxHashMap<TypeId, c_int>,
     registered_userdata_mt: FxHashMap<*const c_void, Option<TypeId>>,
+
+    // When Lua instance dropped, setting `None` would prevent collecting `RegistryKey`s
     registry_unref_list: Arc<Mutex<Option<Vec<c_int>>>>,
 
     #[cfg(not(feature = "send"))]
@@ -111,6 +113,9 @@ pub(crate) struct ExtraData {
     #[cfg(feature = "async")]
     recycled_thread_cache: Vec<c_int>,
 
+    // Address of `WrappedFailure` metatable
+    wrapped_failure_mt_ptr: *const c_void,
+
     // Index of `Option<Waker>` userdata on the ref thread
     #[cfg(feature = "async")]
     ref_waker_idx: c_int,
@@ -399,6 +404,11 @@ impl Lua {
                 return ptr::null_mut();
             }
 
+            // Do not allocate more than isize::MAX
+            if nsize > isize::MAX as usize {
+                return ptr::null_mut();
+            }
+
             // Are we fit to the memory limits?
             let mut mem_diff = nsize as isize;
             if !ptr.is_null() {
@@ -408,12 +418,14 @@ impl Lua {
             if mem_info.memory_limit > 0 && new_used_memory > mem_info.memory_limit {
                 return ptr::null_mut();
             }
-
-            let new_layout = Layout::from_size_align_unchecked(nsize, ffi::SYS_MIN_ALIGN);
             mem_info.used_memory += mem_diff;
 
             if ptr.is_null() {
                 // Allocate new memory
+                let new_layout = match Layout::from_size_align(nsize, ffi::SYS_MIN_ALIGN) {
+                    Ok(layout) => layout,
+                    Err(_) => return ptr::null_mut(),
+                };
                 let new_ptr = alloc::alloc(new_layout) as *mut c_void;
                 if new_ptr.is_null() {
                     alloc::handle_alloc_error(new_layout);
@@ -425,7 +437,7 @@ impl Lua {
             let old_layout = Layout::from_size_align_unchecked(osize, ffi::SYS_MIN_ALIGN);
             let new_ptr = alloc::realloc(ptr as *mut u8, old_layout, nsize) as *mut c_void;
             if new_ptr.is_null() {
-                alloc::handle_alloc_error(new_layout);
+                alloc::handle_alloc_error(old_layout);
             }
             new_ptr
         }
@@ -434,12 +446,19 @@ impl Lua {
         let use_rust_allocator = !(cfg!(feature = "luajit") && cfg!(not(feature = "vendored")));
 
         let (state, mem_info) = if use_rust_allocator {
-            let mem_info = Box::into_raw(Box::new(MemoryInfo::default()));
-            let state = ffi::lua_newstate(allocator, mem_info as *mut c_void);
+            let mut mem_info = Box::into_raw(Box::new(MemoryInfo::default()));
+            let mut state = ffi::lua_newstate(allocator, mem_info as *mut c_void);
+            // If state is null (it's possible for LuaJIT on non-x86 arch) then switch to Lua internal allocator
+            if state.is_null() {
+                drop(Box::from_raw(mem_info));
+                mem_info = ptr::null_mut();
+                state = ffi::luaL_newstate();
+            }
             (state, mem_info)
         } else {
             (ffi::luaL_newstate(), ptr::null_mut())
         };
+        assert!(!state.is_null(), "Failed to instantiate Lua VM");
 
         ffi::luaL_requiref(state, cstr!("_G"), ffi::luaopen_base, 1);
         ffi::lua_pop(state, 1);
@@ -493,6 +512,7 @@ impl Lua {
     /// by calling this function again.
     #[allow(clippy::missing_safety_doc)]
     pub unsafe fn init_from_ptr(state: *mut ffi::lua_State) -> Lua {
+        assert!(!state.is_null(), "Lua state is NULL");
         let main_state = get_main_state(state).unwrap_or(state);
         let main_state_top = ffi::lua_gettop(main_state);
 
@@ -538,6 +558,13 @@ impl Lua {
             "Error while creating ref thread",
         );
 
+        let wrapped_failure_mt_ptr = {
+            get_gc_metatable::<WrappedFailure>(state);
+            let ptr = ffi::lua_topointer(state, -1);
+            ffi::lua_pop(state, 1);
+            ptr
+        };
+
         // Create empty Waker slot on the ref thread
         #[cfg(feature = "async")]
         let ref_waker_idx = {
@@ -568,6 +595,7 @@ impl Lua {
             multivalue_cache: Vec::with_capacity(MULTIVALUE_CACHE_SIZE),
             #[cfg(feature = "async")]
             recycled_thread_cache: Vec::new(),
+            wrapped_failure_mt_ptr,
             #[cfg(feature = "async")]
             ref_waker_idx,
             #[cfg(not(feature = "luau"))]
@@ -591,13 +619,13 @@ impl Lua {
             "Error while storing extra data",
         );
 
-        // Register `DestructedUserdataMT` type
+        // Register `DestructedUserdata` type
         get_destructed_userdata_metatable(main_state);
         let destructed_mt_ptr = ffi::lua_topointer(main_state, -1);
-        let destructed_mt_typeid = Some(TypeId::of::<DestructedUserdataMT>());
+        let destructed_ud_typeid = TypeId::of::<DestructedUserdata>();
         (*extra.get())
             .registered_userdata_mt
-            .insert(destructed_mt_ptr, destructed_mt_typeid);
+            .insert(destructed_mt_ptr, Some(destructed_ud_typeid));
         ffi::lua_pop(main_state, 1);
 
         mlua_debug_assert!(
@@ -863,10 +891,8 @@ impl Lua {
                         ffi::luaL_sandboxthread(state);
                     } else {
                         // Restore original `LUA_GLOBALSINDEX`
-                        self.ref_thread_exec(|ref_thread| {
-                            ffi::lua_xpush(ref_thread, state, ffi::LUA_GLOBALSINDEX);
-                            ffi::lua_replace(state, ffi::LUA_GLOBALSINDEX);
-                        });
+                        ffi::lua_xpush(self.ref_thread(), state, ffi::LUA_GLOBALSINDEX);
+                        ffi::lua_replace(state, ffi::LUA_GLOBALSINDEX);
                         ffi::luaL_sandbox(state, 0);
                     }
                 })?;
@@ -1105,7 +1131,7 @@ impl Lua {
     #[cfg_attr(docsrs, doc(cfg(feature = "lua54")))]
     pub fn warning<S: Into<Vec<u8>>>(&self, msg: S, tocont: bool) -> Result<()> {
         let msg = CString::new(msg).map_err(|err| Error::RuntimeError(err.to_string()))?;
-        unsafe { ffi::lua_warning(self.state, msg.as_ptr(), if tocont { 1 } else { 0 }) };
+        unsafe { ffi::lua_warning(self.state, msg.as_ptr(), tocont as c_int) };
         Ok(())
     }
 
@@ -1347,9 +1373,8 @@ impl Lua {
     where
         S: AsChunk<'lua> + ?Sized,
     {
-        let name = chunk
-            .name()
-            .unwrap_or_else(|| Location::caller().to_string());
+        let caller = Location::caller();
+        let name = chunk.name().unwrap_or_else(|| caller.to_string());
 
         Chunk {
             lua: self,
@@ -1409,11 +1434,15 @@ impl Lua {
         S: AsRef<[u8]> + ?Sized,
     {
         unsafe {
+            if self.unlikely_memory_error() {
+                push_string(self.ref_thread(), s.as_ref(), false)?;
+                return Ok(String(self.pop_ref_thread()));
+            }
+
             let _sg = StackGuard::new(self.state);
             check_stack(self.state, 3)?;
 
-            let protect = !self.unlikely_memory_error();
-            push_string(self.state, s, protect)?;
+            push_string(self.state, s.as_ref(), true)?;
             Ok(String(self.pop_ref()))
         }
     }
@@ -1429,11 +1458,15 @@ impl Lua {
     /// Lua may use these hints to preallocate memory for the new table.
     pub fn create_table_with_capacity(&self, narr: c_int, nrec: c_int) -> Result<Table> {
         unsafe {
+            if self.unlikely_memory_error() {
+                push_table(self.ref_thread(), narr, nrec, false)?;
+                return Ok(Table(self.pop_ref_thread()));
+            }
+
             let _sg = StackGuard::new(self.state);
             check_stack(self.state, 3)?;
 
-            let protect = !self.unlikely_memory_error();
-            push_table(self.state, narr, nrec, protect)?;
+            push_table(self.state, narr, nrec, true)?;
             Ok(Table(self.pop_ref()))
         }
     }
@@ -1701,15 +1734,16 @@ impl Lua {
         all(feature = "luajit", feature = "vendored"),
         feature = "luau",
     ))]
-    pub(crate) unsafe fn recycle_thread(&self, thread: &mut Thread) {
+    pub(crate) unsafe fn recycle_thread(&self, thread: &mut Thread) -> bool {
         let extra = &mut *self.extra.get();
-        let thread_state = ffi::lua_tothread(extra.ref_thread, thread.0.index);
         if extra.recycled_thread_cache.len() < extra.recycled_thread_cache.capacity() {
+            let thread_state = ffi::lua_tothread(extra.ref_thread, thread.0.index);
             #[cfg(feature = "lua54")]
             let status = ffi::lua_resetthread(thread_state);
             #[cfg(feature = "lua54")]
             if status != ffi::LUA_OK {
-                return;
+                // Error object is on top, drop it
+                ffi::lua_settop(thread_state, 0);
             }
             #[cfg(all(feature = "luajit", feature = "vendored"))]
             ffi::lua_resetthread(self.state, thread_state);
@@ -1717,7 +1751,9 @@ impl Lua {
             ffi::lua_resetthread(thread_state);
             extra.recycled_thread_cache.push(thread.0.index);
             thread.0.index = 0;
+            return true;
         }
+        false
     }
 
     /// Create a Lua userdata object from a custom userdata type.
@@ -1994,7 +2030,7 @@ impl Lua {
             check_stack(self.state, 3)?;
 
             let protect = !self.unlikely_memory_error();
-            push_string(self.state, name, protect)?;
+            push_string(self.state, name.as_ref(), protect)?;
             ffi::lua_rawget(self.state, ffi::LUA_REGISTRYINDEX);
 
             self.pop_value()
@@ -2026,6 +2062,12 @@ impl Lua {
     /// [`RegistryKey`]: crate::RegistryKey
     pub fn create_registry_value<'lua, T: ToLua<'lua>>(&'lua self, t: T) -> Result<RegistryKey> {
         let t = t.to_lua(self)?;
+        if t == Value::Nil {
+            // Special case to skip calling `luaL_ref` and use `LUA_REFNIL` instead
+            let unref_list = unsafe { (*self.extra.get()).registry_unref_list.clone() };
+            return Ok(RegistryKey::new(ffi::LUA_REFNIL, unref_list));
+        }
+
         unsafe {
             let _sg = StackGuard::new(self.state);
             check_stack(self.state, 4)?;
@@ -2033,27 +2075,20 @@ impl Lua {
             let unref_list = (*self.extra.get()).registry_unref_list.clone();
             self.push_value(t)?;
 
-            // Try to reuse previously allocated RegistryKey
+            // Try to reuse previously allocated slot
             let unref_list2 = unref_list.clone();
             let mut unref_list2 = mlua_expect!(unref_list2.lock(), "unref list poisoned");
             if let Some(registry_id) = unref_list2.as_mut().and_then(|x| x.pop()) {
                 // It must be safe to replace the value without triggering memory error
                 ffi::lua_rawseti(self.state, ffi::LUA_REGISTRYINDEX, registry_id as Integer);
-                return Ok(RegistryKey {
-                    registry_id,
-                    unref_list,
-                });
+                return Ok(RegistryKey::new(registry_id, unref_list));
             }
 
             // Allocate a new RegistryKey
             let registry_id = protect_lua!(self.state, 1, 0, |state| {
                 ffi::luaL_ref(state, ffi::LUA_REGISTRYINDEX)
             })?;
-
-            Ok(RegistryKey {
-                registry_id,
-                unref_list,
-            })
+            Ok(RegistryKey::new(registry_id, unref_list))
         }
     }
 
@@ -2068,16 +2103,16 @@ impl Lua {
             return Err(Error::MismatchedRegistryKey);
         }
 
-        let value = unsafe {
-            let _sg = StackGuard::new(self.state);
-            check_stack(self.state, 1)?;
+        let value = match key.is_nil() {
+            true => Value::Nil,
+            false => unsafe {
+                let _sg = StackGuard::new(self.state);
+                check_stack(self.state, 1)?;
 
-            ffi::lua_rawgeti(
-                self.state,
-                ffi::LUA_REGISTRYINDEX,
-                key.registry_id as Integer,
-            );
-            self.pop_value()
+                let id = key.registry_id as Integer;
+                ffi::lua_rawgeti(self.state, ffi::LUA_REGISTRYINDEX, id);
+                self.pop_value()
+            },
         };
         T::from_lua(value, self)
     }
@@ -2116,20 +2151,31 @@ impl Lua {
         }
 
         let t = t.to_lua(self)?;
+        if t == Value::Nil && key.is_nil() {
+            // Nothing to replace
+            return Ok(());
+        } else if t != Value::Nil && key.registry_id == ffi::LUA_REFNIL {
+            // We cannot update `LUA_REFNIL` slot
+            let err = "cannot replace nil value with non-nil".to_string();
+            return Err(Error::RuntimeError(err));
+        }
+
         unsafe {
             let _sg = StackGuard::new(self.state);
             check_stack(self.state, 2)?;
 
-            self.push_value(t)?;
+            let id = key.registry_id as Integer;
+            if t == Value::Nil {
+                self.push_value(Value::Integer(id))?;
+                key.set_nil(true);
+            } else {
+                self.push_value(t)?;
+                key.set_nil(false);
+            }
             // It must be safe to replace the value without triggering memory error
-            ffi::lua_rawseti(
-                self.state,
-                ffi::LUA_REGISTRYINDEX,
-                key.registry_id as Integer,
-            );
-
-            Ok(())
+            ffi::lua_rawseti(self.state, ffi::LUA_REGISTRYINDEX, id);
         }
+        Ok(())
     }
 
     /// Returns true if the given `RegistryKey` was created by a `Lua` which shares the underlying
@@ -2241,7 +2287,7 @@ impl Lua {
             }
 
             Value::Boolean(b) => {
-                ffi::lua_pushboolean(self.state, if b { 1 } else { 0 });
+                ffi::lua_pushboolean(self.state, b as c_int);
             }
 
             Value::LightUserData(ud) => {
@@ -2293,6 +2339,8 @@ impl Lua {
     // Uses 2 stack spaces, does not call checkstack
     pub(crate) unsafe fn pop_value(&self) -> Value {
         let state = self.state;
+        let extra = &mut *self.extra.get();
+
         match ffi::lua_type(state, -1) {
             ffi::LUA_TNIL => {
                 ffi::lua_pop(state, 1);
@@ -2353,9 +2401,11 @@ impl Lua {
             ffi::LUA_TFUNCTION => Value::Function(Function(self.pop_ref())),
 
             ffi::LUA_TUSERDATA => {
+                let wrapped_failure_mt_ptr = extra.wrapped_failure_mt_ptr;
                 // We must prevent interaction with userdata types other than UserData OR a WrappedError.
                 // WrappedPanics are automatically resumed.
-                match get_gc_userdata::<WrappedFailure>(state, -1).as_mut() {
+                match get_gc_userdata::<WrappedFailure>(state, -1, wrapped_failure_mt_ptr).as_mut()
+                {
                     Some(WrappedFailure::Error(err)) => {
                         let err = err.clone();
                         ffi::lua_pop(state, 1);
@@ -2394,12 +2444,6 @@ impl Lua {
             "Lua instance passed Value created from a different main Lua state"
         );
         let extra = &*self.extra.get();
-        #[cfg(not(feature = "luau"))]
-        {
-            ffi::lua_pushvalue(extra.ref_thread, lref.index);
-            ffi::lua_xmove(extra.ref_thread, self.state, 1);
-        }
-        #[cfg(feature = "luau")]
         ffi::lua_xpush(extra.ref_thread, self.state, lref.index);
     }
 
@@ -2419,6 +2463,13 @@ impl Lua {
         LuaRef { lua: self, index }
     }
 
+    // Same as `pop_ref` but assumes the value is already on the reference thread
+    pub(crate) unsafe fn pop_ref_thread(&self) -> LuaRef {
+        let extra = &mut *self.extra.get();
+        let index = ref_stack_pop(extra);
+        LuaRef { lua: self, index }
+    }
+
     pub(crate) fn clone_ref<'lua>(&'lua self, lref: &LuaRef<'lua>) -> LuaRef<'lua> {
         unsafe {
             let extra = &mut *self.extra.get();
@@ -2437,16 +2488,6 @@ impl Lua {
         }
     }
 
-    /// Executes the function provided on the ref thread
-    #[inline]
-    pub(crate) unsafe fn ref_thread_exec<F, R>(&self, f: F) -> R
-    where
-        F: FnOnce(*mut ffi::lua_State) -> R,
-    {
-        let ref_thread = (*self.extra.get()).ref_thread;
-        f(ref_thread)
-    }
-
     unsafe fn push_userdata_metatable<T: 'static + UserData>(&self) -> Result<()> {
         let extra = &mut *self.extra.get();
 
@@ -2571,6 +2612,7 @@ impl Lua {
     pub(crate) unsafe fn push_userdata_ref(&self, lref: &LuaRef) -> Result<Option<TypeId>> {
         self.push_ref(lref);
         if ffi::lua_getmetatable(self.state, -1) == 0 {
+            ffi::lua_pop(self.state, 1);
             return Err(Error::UserDataTypeMismatch);
         }
         let mt_ptr = ffi::lua_topointer(self.state, -1);
@@ -2578,7 +2620,7 @@ impl Lua {
 
         let extra = &*self.extra.get();
         match extra.registered_userdata_mt.get(&mt_ptr) {
-            Some(&type_id) if type_id == Some(TypeId::of::<DestructedUserdataMT>()) => {
+            Some(&type_id) if type_id == Some(TypeId::of::<DestructedUserdata>()) => {
                 Err(Error::UserDataDestructed)
             }
             Some(&type_id) => Ok(type_id),
@@ -2948,18 +2990,25 @@ impl Lua {
     }
 }
 
+impl LuaInner {
+    #[inline(always)]
+    pub(crate) fn ref_thread(&self) -> *mut ffi::lua_State {
+        unsafe { (*self.extra.get()).ref_thread }
+    }
+}
+
 struct StateGuard<'a>(&'a mut LuaInner, *mut ffi::lua_State);
 
 impl<'a> StateGuard<'a> {
     fn new(inner: &'a mut LuaInner, mut state: *mut ffi::lua_State) -> Self {
-        mem::swap(&mut (*inner).state, &mut state);
+        mem::swap(&mut inner.state, &mut state);
         Self(inner, state)
     }
 }
 
 impl<'a> Drop for StateGuard<'a> {
     fn drop(&mut self) {
-        mem::swap(&mut (*self.0).state, &mut self.1);
+        mem::swap(&mut self.0.state, &mut self.1);
     }
 }
 

src/serde/de.rs

@@ -71,7 +71,7 @@ impl Options {
     ///
     /// [`deny_recursive_tables`]: #structfield.deny_recursive_tables
     #[must_use]
-    pub fn deny_recursive_tables(mut self, enabled: bool) -> Self {
+    pub const fn deny_recursive_tables(mut self, enabled: bool) -> Self {
         self.deny_recursive_tables = enabled;
         self
     }

src/serde/mod.rs

@@ -10,7 +10,7 @@ use crate::ffi;
 use crate::lua::Lua;
 use crate::table::Table;
 use crate::types::LightUserData;
-use crate::util::{assert_stack, check_stack, StackGuard};
+use crate::util::check_stack;
 use crate::value::Value;
 
 /// Trait for serializing/deserializing Lua values using Serde.
@@ -205,12 +205,8 @@ impl<'lua> LuaSerdeExt<'lua> for Lua {
 
     fn array_metatable(&'lua self) -> Table<'lua> {
         unsafe {
-            let _sg = StackGuard::new(self.state);
-            assert_stack(self.state, 1);
-
-            push_array_metatable(self.state);
-
-            Table(self.pop_ref())
+            push_array_metatable(self.ref_thread());
+            Table(self.pop_ref_thread())
         }
     }
 

src/string.rs

@@ -13,7 +13,6 @@ use {
 use crate::error::{Error, Result};
 use crate::ffi;
 use crate::types::LuaRef;
-use crate::util::{assert_stack, StackGuard};
 
 /// Handle to an internal Lua string.
 ///
@@ -40,6 +39,7 @@ impl<'lua> String<'lua> {
     /// # Ok(())
     /// # }
     /// ```
+    #[inline]
     pub fn to_str(&self) -> Result<&str> {
         str::from_utf8(self.as_bytes()).map_err(|e| Error::FromLuaConversionError {
             from: "string",
@@ -66,6 +66,7 @@ impl<'lua> String<'lua> {
     /// # Ok(())
     /// # }
     /// ```
+    #[inline]
     pub fn to_string_lossy(&self) -> Cow<'_, str> {
         StdString::from_utf8_lossy(self.as_bytes())
     }
@@ -87,6 +88,7 @@ impl<'lua> String<'lua> {
     /// # Ok(())
     /// # }
     /// ```
+    #[inline]
     pub fn as_bytes(&self) -> &[u8] {
         let nulled = self.as_bytes_with_nul();
         &nulled[..nulled.len() - 1]
@@ -94,21 +96,17 @@ impl<'lua> String<'lua> {
 
     /// Get the bytes that make up this string, including the trailing nul byte.
     pub fn as_bytes_with_nul(&self) -> &[u8] {
-        let lua = self.0.lua;
+        let ref_thread = self.0.lua.ref_thread();
         unsafe {
-            let _sg = StackGuard::new(lua.state);
-            assert_stack(lua.state, 1);
-
-            lua.push_ref(&self.0);
             mlua_debug_assert!(
-                ffi::lua_type(lua.state, -1) == ffi::LUA_TSTRING,
+                ffi::lua_type(ref_thread, self.0.index) == ffi::LUA_TSTRING,
                 "string ref is not string type"
             );
 
             let mut size = 0;
             // This will not trigger a 'm' error, because the reference is guaranteed to be of
             // string type
-            let data = ffi::lua_tolstring(lua.state, -1, &mut size);
+            let data = ffi::lua_tolstring(ref_thread, self.0.index, &mut size);
 
             slice::from_raw_parts(data as *const u8, size + 1)
         }
@@ -121,8 +119,8 @@ impl<'lua> String<'lua> {
     /// Typically this function is used only for hashing and debug information.
     #[inline]
     pub fn to_pointer(&self) -> *const c_void {
-        let lua = self.0.lua;
-        unsafe { lua.ref_thread_exec(|refthr| ffi::lua_topointer(refthr, self.0.index)) }
+        let ref_thread = self.0.lua.ref_thread();
+        unsafe { ffi::lua_topointer(ref_thread, self.0.index) }
     }
 }
 

src/table.rs

@@ -58,6 +58,11 @@ impl<'lua> Table<'lua> {
     ///
     /// [`raw_set`]: #method.raw_set
     pub fn set<K: ToLua<'lua>, V: ToLua<'lua>>(&self, key: K, value: V) -> Result<()> {
+        // Fast track
+        if !self.has_metatable() {
+            return self.raw_set(key, value);
+        }
+
         let lua = self.0.lua;
         let key = key.to_lua(lua)?;
         let value = value.to_lua(lua)?;
@@ -98,6 +103,11 @@ impl<'lua> Table<'lua> {
     ///
     /// [`raw_get`]: #method.raw_get
     pub fn get<K: ToLua<'lua>, V: FromLua<'lua>>(&self, key: K) -> Result<V> {
+        // Fast track
+        if !self.has_metatable() {
+            return self.raw_get(key);
+        }
+
         let lua = self.0.lua;
         let key = key.to_lua(lua)?;
 
@@ -116,18 +126,54 @@ impl<'lua> Table<'lua> {
 
     /// Checks whether the table contains a non-nil value for `key`.
     pub fn contains_key<K: ToLua<'lua>>(&self, key: K) -> Result<bool> {
-        let lua = self.0.lua;
-        let key = key.to_lua(lua)?;
+        Ok(self.get::<_, Value>(key)? != Value::Nil)
+    }
 
+    /// Appends a value to the back of the table.
+    pub fn push<V: ToLua<'lua>>(&self, value: V) -> Result<()> {
+        // Fast track
+        if !self.has_metatable() {
+            return self.raw_push(value);
+        }
+
+        let lua = self.0.lua;
+        let value = value.to_lua(lua)?;
         unsafe {
             let _sg = StackGuard::new(lua.state);
             check_stack(lua.state, 4)?;
 
             lua.push_ref(&self.0);
-            lua.push_value(key)?;
-            protect_lua!(lua.state, 2, 1, fn(state) ffi::lua_gettable(state, -2))?;
-            Ok(ffi::lua_isnil(lua.state, -1) == 0)
+            lua.push_value(value)?;
+            protect_lua!(lua.state, 2, 0, fn(state) {
+                let len = ffi::luaL_len(state, -2) as Integer;
+                ffi::lua_seti(state, -2, len + 1);
+            })?
         }
+        Ok(())
+    }
+
+    /// Removes the last element from the table and returns it.
+    pub fn pop<V: FromLua<'lua>>(&self) -> Result<V> {
+        // Fast track
+        if !self.has_metatable() {
+            return self.raw_pop();
+        }
+
+        let lua = self.0.lua;
+        let value = unsafe {
+            let _sg = StackGuard::new(lua.state);
+            check_stack(lua.state, 4)?;
+
+            lua.push_ref(&self.0);
+            protect_lua!(lua.state, 1, 1, fn(state) {
+                let len = ffi::luaL_len(state, -1) as Integer;
+                ffi::lua_geti(state, -1, len);
+                ffi::lua_pushnil(state);
+                ffi::lua_seti(state, -3, len);
+            })?;
+            lua.pop_value()
+        };
+        V::from_lua(value, lua)
     }
 
     /// Compares two tables for equality.
@@ -188,6 +234,9 @@ impl<'lua> Table<'lua> {
 
     /// Sets a key-value pair without invoking metamethods.
     pub fn raw_set<K: ToLua<'lua>, V: ToLua<'lua>>(&self, key: K, value: V) -> Result<()> {
+        #[cfg(feature = "luau")]
+        self.check_readonly_write()?;
+
         let lua = self.0.lua;
         let key = key.to_lua(lua)?;
         let value = value.to_lua(lua)?;
@@ -199,6 +248,7 @@ impl<'lua> Table<'lua> {
             lua.push_ref(&self.0);
             lua.push_value(key)?;
             lua.push_value(value)?;
+
             if lua.unlikely_memory_error() {
                 ffi::lua_rawset(lua.state, -3);
                 ffi::lua_pop(lua.state, 1);
@@ -254,6 +304,56 @@ impl<'lua> Table<'lua> {
         }
     }
 
+    /// Appends a value to the back of the table without invoking metamethods.
+    pub fn raw_push<V: ToLua<'lua>>(&self, value: V) -> Result<()> {
+        #[cfg(feature = "luau")]
+        self.check_readonly_write()?;
+
+        let lua = self.0.lua;
+        let value = value.to_lua(lua)?;
+
+        unsafe {
+            let _sg = StackGuard::new(lua.state);
+            check_stack(lua.state, 4)?;
+
+            lua.push_ref(&self.0);
+            lua.push_value(value)?;
+
+            unsafe fn callback(state: *mut ffi::lua_State) {
+                let len = ffi::lua_rawlen(state, -2) as Integer;
+                ffi::lua_rawseti(state, -2, len + 1);
+            }
+
+            if lua.unlikely_memory_error() {
+                callback(lua.state);
+            } else {
+                protect_lua!(lua.state, 2, 0, fn(state) callback(state))?;
+            }
+        }
+        Ok(())
+    }
+
+    /// Removes the last element from the table and returns it, without invoking metamethods.
+    pub fn raw_pop<V: FromLua<'lua>>(&self) -> Result<V> {
+        #[cfg(feature = "luau")]
+        self.check_readonly_write()?;
+
+        let lua = self.0.lua;
+        let value = unsafe {
+            let _sg = StackGuard::new(lua.state);
+            check_stack(lua.state, 3)?;
+
+            lua.push_ref(&self.0);
+            let len = ffi::lua_rawlen(lua.state, -1) as Integer;
+            ffi::lua_rawgeti(lua.state, -1, len);
+            // Set slot to nil (it must be safe to do)
+            ffi::lua_pushnil(lua.state);
+            ffi::lua_rawseti(lua.state, -3, len);
+            lua.pop_value()
+        };
+        V::from_lua(value, lua)
+    }
+
     /// Removes a key from the table.
     ///
     /// If `key` is an integer, mlua shifts down the elements from `table[key+1]`,
@@ -295,6 +395,11 @@ impl<'lua> Table<'lua> {
     ///
     /// [`raw_len`]: #method.raw_len
     pub fn len(&self) -> Result<Integer> {
+        // Fast track
+        if !self.has_metatable() {
+            return Ok(self.raw_len());
+        }
+
         let lua = self.0.lua;
         unsafe {
             let _sg = StackGuard::new(lua.state);
@@ -307,14 +412,8 @@ impl<'lua> Table<'lua> {
 
     /// Returns the result of the Lua `#` operator, without invoking the `__len` metamethod.
     pub fn raw_len(&self) -> Integer {
-        let lua = self.0.lua;
-        unsafe {
-            let _sg = StackGuard::new(lua.state);
-            assert_stack(lua.state, 1);
-
-            lua.push_ref(&self.0);
-            ffi::lua_rawlen(lua.state, -1) as Integer
-        }
+        let ref_thread = self.0.lua.ref_thread();
+        unsafe { ffi::lua_rawlen(ref_thread, self.0.index) as Integer }
     }
 
     /// Returns a reference to the metatable of this table, or `None` if no metatable is set.
@@ -340,6 +439,12 @@ impl<'lua> Table<'lua> {
     /// If `metatable` is `None`, the metatable is removed (if no metatable is set, this does
     /// nothing).
     pub fn set_metatable(&self, metatable: Option<Table<'lua>>) {
+        // Workaround to throw readonly error without returning Result
+        #[cfg(feature = "luau")]
+        if self.is_readonly() {
+            panic!("attempt to modify a readonly table");
+        }
+
         let lua = self.0.lua;
         unsafe {
             let _sg = StackGuard::new(lua.state);
@@ -355,21 +460,33 @@ impl<'lua> Table<'lua> {
         }
     }
 
+    /// Returns true if the table has metatable attached.
+    #[doc(hidden)]
+    #[inline]
+    pub fn has_metatable(&self) -> bool {
+        let ref_thread = self.0.lua.ref_thread();
+        unsafe {
+            if ffi::lua_getmetatable(ref_thread, self.0.index) != 0 {
+                ffi::lua_pop(ref_thread, 1);
+                return true;
+            }
+        }
+        false
+    }
+
     /// Sets `readonly` attribute on the table.
     ///
     /// Requires `feature = "luau"`
     #[cfg(any(feature = "luau", doc))]
     #[cfg_attr(docsrs, doc(cfg(feature = "luau")))]
     pub fn set_readonly(&self, enabled: bool) {
-        let lua = self.0.lua;
+        let ref_thread = self.0.lua.ref_thread();
         unsafe {
-            lua.ref_thread_exec(|refthr| {
-                ffi::lua_setreadonly(refthr, self.0.index, enabled as _);
-                if !enabled {
-                    // Reset "safeenv" flag
-                    ffi::lua_setsafeenv(refthr, self.0.index, 0);
-                }
-            });
+            ffi::lua_setreadonly(ref_thread, self.0.index, enabled as _);
+            if !enabled {
+                // Reset "safeenv" flag
+                ffi::lua_setsafeenv(ref_thread, self.0.index, 0);
+            }
         }
     }
 
@@ -379,8 +496,8 @@ impl<'lua> Table<'lua> {
     #[cfg(any(feature = "luau", doc))]
     #[cfg_attr(docsrs, doc(cfg(feature = "luau")))]
     pub fn is_readonly(&self) -> bool {
-        let lua = self.0.lua;
-        unsafe { lua.ref_thread_exec(|refthr| ffi::lua_getreadonly(refthr, self.0.index) != 0) }
+        let ref_thread = self.0.lua.ref_thread();
+        unsafe { ffi::lua_getreadonly(ref_thread, self.0.index) != 0 }
     }
 
     /// Converts the table to a generic C pointer.
@@ -391,8 +508,8 @@ impl<'lua> Table<'lua> {
     /// Typically this function is used only for hashing and debug information.
     #[inline]
     pub fn to_pointer(&self) -> *const c_void {
-        let lua = self.0.lua;
-        unsafe { lua.ref_thread_exec(|refthr| ffi::lua_topointer(refthr, self.0.index)) }
+        let ref_thread = self.0.lua.ref_thread();
+        unsafe { ffi::lua_topointer(ref_thread, self.0.index) }
     }
 
     /// Consume this table and return an iterator over the pairs of the table.
@@ -532,6 +649,16 @@ impl<'lua> Table<'lua> {
             ffi::lua_rawequal(lua.state, -1, -2) != 0
         }
     }
+
+    #[cfg(feature = "luau")]
+    #[inline(always)]
+    pub(crate) fn check_readonly_write(&self) -> Result<()> {
+        if self.is_readonly() {
+            let err = "attempt to modify a readonly table".to_string();
+            return Err(Error::RuntimeError(err));
+        }
+        Ok(())
+    }
 }
 
 impl<'lua> PartialEq for Table<'lua> {

src/thread.rs

@@ -4,7 +4,7 @@ use std::os::raw::c_int;
 use crate::error::{Error, Result};
 use crate::ffi;
 use crate::types::LuaRef;
-use crate::util::{check_stack, error_traceback, pop_error, StackGuard};
+use crate::util::{check_stack, error_traceback_thread, pop_error, StackGuard};
 use crate::value::{FromLuaMulti, ToLuaMulti};
 
 #[cfg(any(
@@ -118,8 +118,7 @@ impl<'lua> Thread<'lua> {
             let _sg = StackGuard::new(lua.state);
             check_stack(lua.state, cmp::max(nargs + 1, 3))?;
 
-            let thread_state =
-                lua.ref_thread_exec(|ref_thread| ffi::lua_tothread(ref_thread, self.0.index));
+            let thread_state = ffi::lua_tothread(lua.ref_thread(), self.0.index);
 
             let status = ffi::lua_status(thread_state);
             if status != ffi::LUA_YIELD && ffi::lua_gettop(thread_state) == 0 {
@@ -136,8 +135,12 @@ impl<'lua> Thread<'lua> {
 
             let ret = ffi::lua_resume(thread_state, lua.state, nargs, &mut nresults as *mut c_int);
             if ret != ffi::LUA_OK && ret != ffi::LUA_YIELD {
-                protect_lua!(lua.state, 0, 0, |_| error_traceback(thread_state))?;
-                return Err(pop_error(thread_state, ret));
+                check_stack(lua.state, 3)?;
+                protect_lua!(lua.state, 0, 1, |state| error_traceback_thread(
+                    state,
+                    thread_state
+                ))?;
+                return Err(pop_error(lua.state, ret));
             }
 
             let mut results = args; // Reuse MultiValue container
@@ -156,8 +159,7 @@ impl<'lua> Thread<'lua> {
     pub fn status(&self) -> ThreadStatus {
         let lua = self.0.lua;
         unsafe {
-            let thread_state =
-                lua.ref_thread_exec(|ref_thread| ffi::lua_tothread(ref_thread, self.0.index));
+            let thread_state = ffi::lua_tothread(lua.ref_thread(), self.0.index);
 
             let status = ffi::lua_status(thread_state);
             if status != ffi::LUA_OK && status != ffi::LUA_YIELD {
@@ -322,7 +324,7 @@ impl<'lua> Thread<'lua> {
     pub fn sandbox(&self) -> Result<()> {
         let lua = self.0.lua;
         unsafe {
-            let thread = lua.ref_thread_exec(|t| ffi::lua_tothread(t, self.0.index));
+            let thread = ffi::lua_tothread(lua.ref_thread(), self.0.index);
             check_stack(thread, 1)?;
             check_stack(lua.state, 3)?;
             // Inherit `LUA_GLOBALSINDEX` from the caller
@@ -357,7 +359,15 @@ impl<'lua, R> Drop for AsyncThread<'lua, R> {
     fn drop(&mut self) {
         if self.recycle {
             unsafe {
-                self.thread.0.lua.recycle_thread(&mut self.thread);
+                let lua = self.thread.0.lua;
+                // For Lua 5.4 this also closes all pending to-be-closed variables
+                if !lua.recycle_thread(&mut self.thread) {
+                    #[cfg(feature = "lua54")]
+                    if self.thread.status() == ThreadStatus::Error {
+                        let thread_state = ffi::lua_tothread(lua.ref_thread(), self.thread.0.index);
+                        ffi::lua_resetthread(thread_state);
+                    }
+                }
             }
         }
     }

src/types.rs

@@ -1,6 +1,7 @@
 use std::cell::UnsafeCell;
 use std::hash::{Hash, Hasher};
 use std::os::raw::{c_int, c_void};
+use std::sync::atomic::{AtomicBool, Ordering};
 use std::sync::{Arc, Mutex};
 use std::{fmt, mem, ptr};
 
@@ -83,7 +84,7 @@ pub trait MaybeSend {}
 #[cfg(not(feature = "send"))]
 impl<T> MaybeSend for T {}
 
-pub(crate) struct DestructedUserdataMT;
+pub(crate) struct DestructedUserdata;
 
 /// An auto generated key into the Lua registry.
 ///
@@ -104,6 +105,7 @@ pub(crate) struct DestructedUserdataMT;
 /// [`AnyUserData::get_user_value`]: crate::AnyUserData::get_user_value
 pub struct RegistryKey {
     pub(crate) registry_id: c_int,
+    pub(crate) is_nil: AtomicBool,
     pub(crate) unref_list: Arc<Mutex<Option<Vec<c_int>>>>,
 }
 
@@ -129,15 +131,27 @@ impl Eq for RegistryKey {}
 
 impl Drop for RegistryKey {
     fn drop(&mut self) {
-        let mut unref_list = mlua_expect!(self.unref_list.lock(), "unref list poisoned");
-        if let Some(list) = unref_list.as_mut() {
-            list.push(self.registry_id);
+        // We don't need to collect nil slot
+        if self.registry_id > ffi::LUA_REFNIL {
+            let mut unref_list = mlua_expect!(self.unref_list.lock(), "unref list poisoned");
+            if let Some(list) = unref_list.as_mut() {
+                list.push(self.registry_id);
+            }
         }
     }
 }
 
 impl RegistryKey {
-    // Destroys the RegistryKey without adding to the drop list
+    // Creates a new instance of `RegistryKey`
+    pub(crate) const fn new(id: c_int, unref_list: Arc<Mutex<Option<Vec<c_int>>>>) -> Self {
+        RegistryKey {
+            registry_id: id,
+            is_nil: AtomicBool::new(id == ffi::LUA_REFNIL),
+            unref_list,
+        }
+    }
+
+    // Destroys the `RegistryKey` without adding to the unref list
     pub(crate) fn take(self) -> c_int {
         let registry_id = self.registry_id;
         unsafe {
@@ -146,6 +160,21 @@ impl RegistryKey {
         }
         registry_id
     }
+
+    // Returns true if this `RegistryKey` holds a nil value
+    #[inline(always)]
+    pub(crate) fn is_nil(&self) -> bool {
+        self.is_nil.load(Ordering::Relaxed)
+    }
+
+    // Marks value of this `RegistryKey` as `Nil`
+    #[inline(always)]
+    pub(crate) fn set_nil(&self, enabled: bool) {
+        // We cannot replace previous value with nil in as this will break
+        // Lua mechanism to find free keys.
+        // Instead, we set a special flag to mark value as nil.
+        self.is_nil.store(enabled, Ordering::Relaxed);
+    }
 }
 
 pub(crate) struct LuaRef<'lua> {

src/util.rs

@@ -1,6 +1,7 @@
 use std::any::{Any, TypeId};
 use std::ffi::CStr;
 use std::fmt::Write;
+use std::mem::MaybeUninit;
 use std::os::raw::{c_char, c_int, c_void};
 use std::panic::{catch_unwind, resume_unwind, AssertUnwindSafe};
 use std::sync::Arc;
@@ -136,26 +137,21 @@ where
     F: Fn(*mut ffi::lua_State) -> R,
     R: Copy,
 {
-    union URes<R: Copy> {
-        uninit: (),
-        init: R,
-    }
-
     struct Params<F, R: Copy> {
         function: F,
-        result: URes<R>,
+        result: MaybeUninit<R>,
         nresults: c_int,
     }
 
     unsafe extern "C" fn do_call<F, R>(state: *mut ffi::lua_State) -> c_int
     where
-        R: Copy,
         F: Fn(*mut ffi::lua_State) -> R,
+        R: Copy,
     {
         let params = ffi::lua_touserdata(state, -1) as *mut Params<F, R>;
         ffi::lua_pop(state, 1);
 
-        (*params).result.init = ((*params).function)(state);
+        (*params).result.write(((*params).function)(state));
 
         if (*params).nresults == ffi::LUA_MULTRET {
             ffi::lua_gettop(state)
@@ -174,7 +170,7 @@ where
 
     let mut params = Params {
         function: f,
-        result: URes { uninit: () },
+        result: MaybeUninit::uninit(),
         nresults,
     };
 
@@ -185,7 +181,7 @@ where
     if ret == ffi::LUA_OK {
         // `LUA_OK` is only returned when the `do_call` function has completed successfully, so
         // `params.result` is definitely initialized.
-        Ok(params.result.init)
+        Ok(params.result.assume_init())
     } else {
         Err(pop_error(state, ret))
     }
@@ -203,7 +199,7 @@ pub unsafe fn pop_error(state: *mut ffi::lua_State, err_code: c_int) -> Error {
         "pop_error called with non-error return code"
     );
 
-    match get_gc_userdata::<WrappedFailure>(state, -1).as_mut() {
+    match get_gc_userdata::<WrappedFailure>(state, -1, ptr::null()).as_mut() {
         Some(WrappedFailure::Error(err)) => {
             ffi::lua_pop(state, 1);
             err.clone()
@@ -246,14 +242,9 @@ pub unsafe fn pop_error(state: *mut ffi::lua_State, err_code: c_int) -> Error {
     }
 }
 
-// Uses 3 stack spaces, does not call checkstack.
-#[inline]
-pub unsafe fn push_string<S: AsRef<[u8]> + ?Sized>(
-    state: *mut ffi::lua_State,
-    s: &S,
-    protect: bool,
-) -> Result<()> {
-    let s = s.as_ref();
+// Uses 3 (or 1 if unprotected) stack spaces, does not call checkstack.
+#[inline(always)]
+pub unsafe fn push_string(state: *mut ffi::lua_State, s: &[u8], protect: bool) -> Result<()> {
     if protect {
         protect_lua!(state, 0, 1, |state| {
             ffi::lua_pushlstring(state, s.as_ptr() as *const c_char, s.len());
@@ -314,13 +305,10 @@ pub unsafe fn push_userdata<T>(state: *mut ffi::lua_State, t: T, protect: bool)
 #[inline]
 pub unsafe fn push_userdata<T>(state: *mut ffi::lua_State, t: T, protect: bool) -> Result<()> {
     unsafe extern "C" fn destructor<T>(ud: *mut c_void) {
-        let ud = ud as *mut T;
-        if *(ud.offset(1) as *mut u8) == 0 {
-            ptr::drop_in_place(ud);
-        }
+        ptr::drop_in_place(ud as *mut T);
     }
 
-    let size = mem::size_of::<T>() + 1;
+    let size = mem::size_of::<T>();
     let ud = if protect {
         protect_lua!(state, 0, 1, |state| {
             ffi::lua_newuserdatadtor(state, size, destructor::<T>) as *mut T
@@ -329,7 +317,6 @@ pub unsafe fn push_userdata<T>(state: *mut ffi::lua_State, t: T, protect: bool)
         ffi::lua_newuserdatadtor(state, size, destructor::<T>) as *mut T
     };
     ptr::write(ud, t);
-    *(ud.offset(1) as *mut u8) = 0; // Mark as not destructed
 
     Ok(())
 }
@@ -373,10 +360,12 @@ pub unsafe fn take_userdata<T>(state: *mut ffi::lua_State) -> T {
     get_destructed_userdata_metatable(state);
     ffi::lua_setmetatable(state, -2);
     let ud = get_userdata::<T>(state, -1);
+
+    // Update userdata tag to disable destructor and mark as destructed
+    #[cfg(feature = "luau")]
+    ffi::lua_setuserdatatag(state, -1, 1);
+
     ffi::lua_pop(state, 1);
-    if cfg!(feature = "luau") {
-        *(ud.offset(1) as *mut u8) = 1; // Mark as destructed
-    }
     ptr::read(ud)
 }
 
@@ -394,16 +383,28 @@ pub unsafe fn push_gc_userdata<T: Any>(
 }
 
 // Uses 2 stack spaces, does not call checkstack
-pub unsafe fn get_gc_userdata<T: Any>(state: *mut ffi::lua_State, index: c_int) -> *mut T {
+pub unsafe fn get_gc_userdata<T: Any>(
+    state: *mut ffi::lua_State,
+    index: c_int,
+    mt_ptr: *const c_void,
+) -> *mut T {
     let ud = ffi::lua_touserdata(state, index) as *mut T;
     if ud.is_null() || ffi::lua_getmetatable(state, index) == 0 {
         return ptr::null_mut();
     }
-    get_gc_metatable::<T>(state);
-    let res = ffi::lua_rawequal(state, -1, -2);
-    ffi::lua_pop(state, 2);
-    if res == 0 {
-        return ptr::null_mut();
+    if !mt_ptr.is_null() {
+        let ud_mt_ptr = ffi::lua_topointer(state, -1);
+        ffi::lua_pop(state, 1);
+        if !ptr::eq(ud_mt_ptr, mt_ptr) {
+            return ptr::null_mut();
+        }
+    } else {
+        get_gc_metatable::<T>(state);
+        let res = ffi::lua_rawequal(state, -1, -2);
+        ffi::lua_pop(state, 2);
+        if res == 0 {
+            return ptr::null_mut();
+        }
     }
     ud
 }
@@ -542,7 +543,7 @@ pub unsafe fn init_userdata_metatable<T>(
         // Push `__index` generator function
         init_userdata_metatable_index(state)?;
 
-        push_string(state, "__index", true)?;
+        push_string(state, b"__index", true)?;
         let index_type = ffi::lua_rawget(state, -3);
         match index_type {
             ffi::LUA_TNIL | ffi::LUA_TTABLE | ffi::LUA_TFUNCTION => {
@@ -567,7 +568,7 @@ pub unsafe fn init_userdata_metatable<T>(
         // Push `__newindex` generator function
         init_userdata_metatable_newindex(state)?;
 
-        push_string(state, "__newindex", true)?;
+        push_string(state, b"__newindex", true)?;
         let newindex_type = ffi::lua_rawget(state, -3);
         match newindex_type {
             ffi::LUA_TNIL | ffi::LUA_TTABLE | ffi::LUA_TFUNCTION => {
@@ -679,7 +680,7 @@ pub unsafe extern "C" fn error_traceback(state: *mut ffi::lua_State) -> c_int {
         return 1;
     }
 
-    if get_gc_userdata::<WrappedFailure>(state, -1).is_null() {
+    if get_gc_userdata::<WrappedFailure>(state, -1, ptr::null()).is_null() {
         let s = ffi::luaL_tolstring(state, -1, ptr::null_mut());
         if ffi::lua_checkstack(state, ffi::LUA_TRACEBACK_STACK) != 0 {
             ffi::luaL_traceback(state, state, s, 0);
@@ -690,6 +691,20 @@ pub unsafe extern "C" fn error_traceback(state: *mut ffi::lua_State) -> c_int {
     1
 }
 
+// A variant of `error_traceback` that can safely inspect another (yielded) thread stack
+pub unsafe fn error_traceback_thread(state: *mut ffi::lua_State, thread: *mut ffi::lua_State) {
+    // Move error object to the main thread to safely call `__tostring` metamethod if present
+    ffi::lua_xmove(thread, state, 1);
+
+    if get_gc_userdata::<WrappedFailure>(state, -1, ptr::null()).is_null() {
+        let s = ffi::luaL_tolstring(state, -1, ptr::null_mut());
+        if ffi::lua_checkstack(state, ffi::LUA_TRACEBACK_STACK) != 0 {
+            ffi::luaL_traceback(state, thread, s, 0);
+            ffi::lua_remove(state, -2);
+        }
+    }
+}
+
 // A variant of `pcall` that does not allow Lua to catch Rust panics from `callback_error`.
 pub unsafe extern "C" fn safe_pcall(state: *mut ffi::lua_State) -> c_int {
     ffi::luaL_checkstack(state, 2, ptr::null());
@@ -706,7 +721,7 @@ pub unsafe extern "C" fn safe_pcall(state: *mut ffi::lua_State) -> c_int {
         ffi::lua_gettop(state)
     } else {
         if let Some(WrappedFailure::Panic(_)) =
-            get_gc_userdata::<WrappedFailure>(state, -1).as_ref()
+            get_gc_userdata::<WrappedFailure>(state, -1, ptr::null()).as_ref()
         {
             ffi::lua_error(state);
         }
@@ -722,7 +737,7 @@ pub unsafe extern "C" fn safe_xpcall(state: *mut ffi::lua_State) -> c_int {
         ffi::luaL_checkstack(state, 2, ptr::null());
 
         if let Some(WrappedFailure::Panic(_)) =
-            get_gc_userdata::<WrappedFailure>(state, -1).as_ref()
+            get_gc_userdata::<WrappedFailure>(state, -1, ptr::null()).as_ref()
         {
             1
         } else {
@@ -752,7 +767,7 @@ pub unsafe extern "C" fn safe_xpcall(state: *mut ffi::lua_State) -> c_int {
         ffi::lua_gettop(state) - 1
     } else {
         if let Some(WrappedFailure::Panic(_)) =
-            get_gc_userdata::<WrappedFailure>(state, -1).as_ref()
+            get_gc_userdata::<WrappedFailure>(state, -1, ptr::null()).as_ref()
         {
             ffi::lua_error(state);
         }
@@ -836,7 +851,7 @@ pub unsafe fn init_error_registry(state: *mut ffi::lua_State) -> Result<()> {
         callback_error(state, |_| {
             check_stack(state, 3)?;
 
-            let err_buf = match get_gc_userdata::<WrappedFailure>(state, -1).as_ref() {
+            let err_buf = match get_gc_userdata::<WrappedFailure>(state, -1, ptr::null()).as_ref() {
                 Some(WrappedFailure::Error(error)) => {
                     let err_buf_key = &ERROR_PRINT_BUFFER_KEY as *const u8 as *const c_void;
                     ffi::lua_rawgetp(state, ffi::LUA_REGISTRYINDEX, err_buf_key);
@@ -873,7 +888,7 @@ pub unsafe fn init_error_registry(state: *mut ffi::lua_State) -> Result<()> {
                 }
             }?;
 
-            push_string(state, &*err_buf, true)?;
+            push_string(state, (*err_buf).as_bytes(), true)?;
             (*err_buf).clear();
 
             Ok(1)
@@ -936,6 +951,8 @@ pub unsafe fn init_error_registry(state: *mut ffi::lua_State) -> Result<()> {
         "__pairs",
         #[cfg(any(feature = "lua53", feature = "lua52", feature = "luajit52"))]
         "__ipairs",
+        #[cfg(feature = "luau")]
+        "__iter",
         #[cfg(feature = "lua54")]
         "__close",
     ] {

src/value.rs

@@ -111,11 +111,11 @@ impl<'lua> Value<'lua> {
                 Value::LightUserData(ud) => ud.0,
                 Value::Table(t) => t.to_pointer(),
                 Value::String(s) => s.to_pointer(),
-                Value::Function(Function(v))
-                | Value::Thread(Thread(v))
-                | Value::UserData(AnyUserData(v)) => v
-                    .lua
-                    .ref_thread_exec(|refthr| ffi::lua_topointer(refthr, v.index)),
+                Value::Function(Function(r))
+                | Value::Thread(Thread(r))
+                | Value::UserData(AnyUserData(r)) => {
+                    ffi::lua_topointer(r.lua.ref_thread(), r.index)
+                }
                 _ => ptr::null(),
             }
         }
@@ -239,7 +239,7 @@ impl<'a, 'lua> IntoIterator for &'a MultiValue<'lua> {
 
     #[inline]
     fn into_iter(self) -> Self::IntoIter {
-        (&self.0).iter().rev()
+        self.0.iter().rev()
     }
 }
 
@@ -248,7 +248,15 @@ impl<'lua> Index<usize> for MultiValue<'lua> {
 
     #[inline]
     fn index(&self, index: usize) -> &Self::Output {
-        &self.0[self.0.len() - index - 1]
+        if let Some(result) = self.get(index) {
+            result
+        } else {
+            panic!(
+                "index out of bounds: the len is {} but the index is {}",
+                self.len(),
+                index
+            )
+        }
     }
 }
 
@@ -266,6 +274,11 @@ impl<'lua> MultiValue<'lua> {
         v
     }
 
+    #[inline]
+    pub fn get(&self, index: usize) -> Option<&Value<'lua>> {
+        self.0.get(self.0.len() - index - 1)
+    }
+
     #[inline]
     pub(crate) fn reserve(&mut self, size: usize) {
         self.0.reserve(size);

tests/async.rs

@@ -174,6 +174,38 @@ async fn test_async_return_async_closure() -> Result<()> {
     Ok(())
 }
 
+#[cfg(feature = "lua54")]
+#[tokio::test]
+async fn test_async_lua54_to_be_closed() -> Result<()> {
+    let lua = Lua::new();
+
+    let globals = lua.globals();
+    globals.set("close_count", 0)?;
+
+    let code = r#"
+        local t <close> = setmetatable({}, {
+            __close = function()
+                close_count = close_count + 1
+            end
+        })
+        error "test"
+    "#;
+    let f = lua.load(code).into_function()?;
+
+    // Test close using call_async
+    let _ = f.call_async::<_, ()>(()).await;
+    assert_eq!(globals.get::<_, usize>("close_count")?, 1);
+
+    // Don't close by default when awaiting async threads
+    let co = lua.create_thread(f.clone())?;
+    let _ = co.clone().into_async::<_, ()>(()).await;
+    assert_eq!(globals.get::<_, usize>("close_count")?, 1);
+    let _ = co.reset(f);
+    assert_eq!(globals.get::<_, usize>("close_count")?, 2);
+
+    Ok(())
+}
+
 #[tokio::test]
 async fn test_async_thread_stream() -> Result<()> {
     let lua = Lua::new();
@@ -278,6 +310,28 @@ async fn test_async_table() -> Result<()> {
     Ok(())
 }
 
+#[tokio::test]
+async fn test_async_thread_cache() -> Result<()> {
+    let options = LuaOptions::new().thread_cache_size(4);
+    let lua = Lua::new_with(StdLib::ALL_SAFE, options)?;
+
+    let error_f = lua.create_async_function(|_, ()| async move {
+        Delay::new(Duration::from_millis(10)).await;
+        Err::<(), _>(Error::RuntimeError("test".to_string()))
+    })?;
+
+    let sleep = lua.create_async_function(|_, n| async move {
+        Delay::new(Duration::from_millis(n)).await;
+        Ok(format!("elapsed:{}ms", n))
+    })?;
+
+    assert!(error_f.call_async::<_, ()>(()).await.is_err());
+    // Next call should use cached thread
+    assert_eq!(sleep.call_async::<_, String>(3).await?, "elapsed:3ms");
+
+    Ok(())
+}
+
 #[tokio::test]
 async fn test_async_userdata() -> Result<()> {
     #[derive(Clone)]
@@ -372,6 +426,30 @@ async fn test_async_userdata() -> Result<()> {
     Ok(())
 }
 
+#[tokio::test]
+async fn test_async_thread_error() -> Result<()> {
+    struct MyUserData;
+
+    impl UserData for MyUserData {
+        fn add_methods<'lua, M: UserDataMethods<'lua, Self>>(methods: &mut M) {
+            methods.add_meta_method("__tostring", |_, _this, ()| Ok("myuserdata error"))
+        }
+    }
+
+    let lua = Lua::new();
+    let result = lua
+        .load("function x(...) error(...) end x(...)")
+        .set_name("chunk")?
+        .call_async::<_, ()>(MyUserData)
+        .await;
+    assert!(
+        matches!(result, Err(Error::RuntimeError(cause)) if cause.contains("myuserdata error")),
+        "improper error traceback from dead thread"
+    );
+
+    Ok(())
+}
+
 #[tokio::test]
 async fn test_async_scope() -> Result<()> {
     let ref lua = Lua::new();

tests/compile/async_nonstatic_userdata.rs

@@ -1,8 +1,6 @@
-use mlua::{Lua, UserData, UserDataMethods};
+use mlua::{UserData, UserDataMethods};
 
 fn main() {
-    let ref lua = Lua::new();
-
     #[derive(Clone)]
     struct MyUserData<'a>(&'a i64);
 

tests/compile/async_nonstatic_userdata.stderr

@@ -1,41 +1,14 @@
-error[E0495]: cannot infer an appropriate lifetime due to conflicting requirements
-   --> tests/compile/async_nonstatic_userdata.rs:11:72
-    |
-11  |               methods.add_async_method("print", |_, data, ()| async move {
-    |  ________________________________________________________________________^
-12  | |                 println!("{}", data.0);
-13  | |                 Ok(())
-14  | |             });
-    | |_____________^
-    |
-note: first, the lifetime cannot outlive the lifetime `'a` as defined here...
-   --> tests/compile/async_nonstatic_userdata.rs:9:10
-    |
-9   |     impl<'a> UserData for MyUserData<'a> {
-    |          ^^
-note: ...so that the types are compatible
-   --> tests/compile/async_nonstatic_userdata.rs:11:72
-    |
-11  |               methods.add_async_method("print", |_, data, ()| async move {
-    |  ________________________________________________________________________^
-12  | |                 println!("{}", data.0);
-13  | |                 Ok(())
-14  | |             });
-    | |_____________^
-    = note: expected `(MyUserData<'_>,)`
-               found `(MyUserData<'a>,)`
-note: but, the lifetime must be valid for the lifetime `'lua` as defined here...
-   --> tests/compile/async_nonstatic_userdata.rs:10:24
-    |
-10  |         fn add_methods<'lua, M: UserDataMethods<'lua, Self>>(methods: &mut M) {
-    |                        ^^^^
-note: ...so that the type `impl Future<Output = [async output]>` will meet its required lifetime bounds...
-   --> tests/compile/async_nonstatic_userdata.rs:11:21
-    |
-11  |             methods.add_async_method("print", |_, data, ()| async move {
-    |                     ^^^^^^^^^^^^^^^^
-note: ...that is required by this bound
-   --> src/userdata.rs
-    |
-    |         MR: 'lua + Future<Output = Result<R>>;
-    |             ^^^^
+error: lifetime may not live long enough
+  --> tests/compile/async_nonstatic_userdata.rs:9:13
+   |
+7  |       impl<'a> UserData for MyUserData<'a> {
+   |            -- lifetime `'a` defined here
+8  |           fn add_methods<'lua, M: UserDataMethods<'lua, Self>>(methods: &mut M) {
+   |                          ---- lifetime `'lua` defined here
+9  | /             methods.add_async_method("print", |_, data, ()| async move {
+10 | |                 println!("{}", data.0);
+11 | |                 Ok(())
+12 | |             });
+   | |______________^ argument requires that `'a` must outlive `'lua`
+   |
+   = help: consider adding the following bound: `'a: 'lua`

tests/compile/function_borrow.stderr

@@ -1,10 +1,10 @@
-error[E0373]: closure may outlive the current function, but it borrows `test`, which is owned by the current function
+error[E0373]: closure may outlive the current function, but it borrows `test.0`, which is owned by the current function
   --> tests/compile/function_borrow.rs:9:33
    |
 9  |     let _ = lua.create_function(|_, ()| -> Result<i32> {
-   |                                 ^^^^^^^^^^^^^^^^^^^^^^ may outlive borrowed value `test`
+   |                                 ^^^^^^^^^^^^^^^^^^^^^^ may outlive borrowed value `test.0`
 10 |         Ok(test.0)
-   |            ------ `test` is borrowed here
+   |            ------ `test.0` is borrowed here
    |
 note: function requires argument type to outlive `'static`
   --> tests/compile/function_borrow.rs:9:13
@@ -14,7 +14,7 @@ note: function requires argument type to outlive `'static`
 10 | |         Ok(test.0)
 11 | |     });
    | |______^
-help: to force the closure to take ownership of `test` (and any other referenced variables), use the `move` keyword
+help: to force the closure to take ownership of `test.0` (and any other referenced variables), use the `move` keyword
    |
 9  |     let _ = lua.create_function(move |_, ()| -> Result<i32> {
    |                                 ++++

tests/compile/lua_norefunwindsafe.stderr

@@ -10,7 +10,11 @@ error[E0277]: the type `UnsafeCell<mlua::lua::LuaInner>` may contain interior mu
     = note: required because it appears within the type `Arc<UnsafeCell<mlua::lua::LuaInner>>`
     = note: required because it appears within the type `Lua`
     = note: required because of the requirements on the impl of `UnwindSafe` for `&Lua`
-    = note: required because it appears within the type `[closure@$DIR/tests/compile/lua_norefunwindsafe.rs:7:18: 7:48]`
+note: required because it's used within this closure
+   --> tests/compile/lua_norefunwindsafe.rs:7:18
+    |
+7   |     catch_unwind(|| lua.create_table().unwrap());
+    |                  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 note: required by a bound in `catch_unwind`
    --> $RUST/std/src/panic.rs
     |

tests/compile/non_send.stderr

@@ -10,7 +10,14 @@ error[E0277]: `Rc<Cell<i32>>` cannot be sent between threads safely
      | |_____- within this `[closure@$DIR/tests/compile/non_send.rs:11:25: 13:6]`
      |
      = help: within `[closure@$DIR/tests/compile/non_send.rs:11:25: 13:6]`, the trait `Send` is not implemented for `Rc<Cell<i32>>`
-     = note: required because it appears within the type `[closure@$DIR/tests/compile/non_send.rs:11:25: 13:6]`
+note: required because it's used within this closure
+    --> tests/compile/non_send.rs:11:25
+     |
+11   |       lua.create_function(move |_, ()| {
+     |  _________________________^
+12   | |         Ok(data.get())
+13   | |     })?
+     | |_____^
      = note: required because of the requirements on the impl of `mlua::types::MaybeSend` for `[closure@$DIR/tests/compile/non_send.rs:11:25: 13:6]`
 note: required by a bound in `Lua::create_function`
     --> src/lua.rs

tests/compile/ref_nounwindsafe.stderr

@@ -12,7 +12,11 @@ error[E0277]: the type `UnsafeCell<mlua::lua::LuaInner>` may contain interior mu
     = note: required because of the requirements on the impl of `UnwindSafe` for `&Lua`
     = note: required because it appears within the type `mlua::types::LuaRef<'_>`
     = note: required because it appears within the type `LuaTable<'_>`
-    = note: required because it appears within the type `[closure@$DIR/tests/compile/ref_nounwindsafe.rs:8:18: 8:54]`
+note: required because it's used within this closure
+   --> tests/compile/ref_nounwindsafe.rs:8:18
+    |
+8   |     catch_unwind(move || table.set("a", "b").unwrap());
+    |                  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 note: required by a bound in `catch_unwind`
    --> $RUST/std/src/panic.rs
     |

tests/compile/scope_invariance.stderr

@@ -1,13 +1,13 @@
-error[E0373]: closure may outlive the current function, but it borrows `test`, which is owned by the current function
+error[E0373]: closure may outlive the current function, but it borrows `test.field`, which is owned by the current function
   --> tests/compile/scope_invariance.rs:14:38
    |
 9  |     lua.scope(|scope| {
    |                ----- has type `&mlua::Scope<'_, '1>`
 ...
 14 |                 .create_function_mut(|_, ()| {
-   |                                      ^^^^^^^ may outlive borrowed value `test`
+   |                                      ^^^^^^^ may outlive borrowed value `test.field`
 15 |                     test.field = 42;
-   |                     ---------- `test` is borrowed here
+   |                     ---------- `test.field` is borrowed here
    |
 note: function requires argument type to outlive `'1`
   --> tests/compile/scope_invariance.rs:13:13
@@ -19,7 +19,7 @@ note: function requires argument type to outlive `'1`
 17 | |                     Ok(())
 18 | |                 })?
    | |__________________^
-help: to force the closure to take ownership of `test` (and any other referenced variables), use the `move` keyword
+help: to force the closure to take ownership of `test.field` (and any other referenced variables), use the `move` keyword
    |
 14 |                 .create_function_mut(move |_, ()| {
    |                                      ++++

tests/compile/static_callback_args.stderr

@@ -1,33 +1,31 @@
 error[E0597]: `lua` does not live long enough
   --> tests/compile/static_callback_args.rs:12:5
    |
-12 | /     lua.create_function(|_, table: Table| {
-13 | |         BAD_TIME.with(|bt| {
-14 | |             *bt.borrow_mut() = Some(table);
-15 | |         });
-16 | |         Ok(())
-17 | |     })?
-   | |      ^
-   | |      |
-   | |______borrowed value does not live long enough
-   |        argument requires that `lua` is borrowed for `'static`
+12 |  /     lua.create_function(|_, table: Table| {
+13 |  |         BAD_TIME.with(|bt| {
+   |  |_________-
+14 | ||             *bt.borrow_mut() = Some(table);
+15 | ||         });
+   | ||__________- argument requires that `lua` is borrowed for `'static`
+16 |  |         Ok(())
+17 |  |     })?
+   |  |______^ borrowed value does not live long enough
 ...
-32 |   }
-   |   - `lua` dropped here while still borrowed
+32 |    }
+   |    - `lua` dropped here while still borrowed
 
 error[E0505]: cannot move out of `lua` because it is borrowed
   --> tests/compile/static_callback_args.rs:22:10
    |
-12 | /     lua.create_function(|_, table: Table| {
-13 | |         BAD_TIME.with(|bt| {
-14 | |             *bt.borrow_mut() = Some(table);
-15 | |         });
-16 | |         Ok(())
-17 | |     })?
-   | |      -
-   | |      |
-   | |______borrow of `lua` occurs here
-   |        argument requires that `lua` is borrowed for `'static`
+12 |  /     lua.create_function(|_, table: Table| {
+13 |  |         BAD_TIME.with(|bt| {
+   |  |_________-
+14 | ||             *bt.borrow_mut() = Some(table);
+15 | ||         });
+   | ||__________- argument requires that `lua` is borrowed for `'static`
+16 |  |         Ok(())
+17 |  |     })?
+   |  |______- borrow of `lua` occurs here
 ...
-22 |       drop(lua);
-   |            ^^^ move out of `lua` occurs here
+22 |        drop(lua);
+   |             ^^^ move out of `lua` occurs here

tests/function.rs

@@ -42,11 +42,17 @@ fn test_bind() -> Result<()> {
     concat = concat.bind("foo")?;
     concat = concat.bind("bar")?;
     concat = concat.bind(("baz", "baf"))?;
+    assert_eq!(concat.call::<_, String>(())?, "foobarbazbaf");
     assert_eq!(
         concat.call::<_, String>(("hi", "wut"))?,
         "foobarbazbafhiwut"
     );
 
+    let mut concat2 = globals.get::<_, Function>("concat")?;
+    concat2 = concat2.bind(())?;
+    assert_eq!(concat2.call::<_, String>(())?, "");
+    assert_eq!(concat2.call::<_, String>(("ab", "cd"))?, "abcd");
+
     Ok(())
 }
 

tests/luau.rs

@@ -1,7 +1,9 @@
 #![cfg(feature = "luau")]
 
 use std::env;
+use std::fmt::Debug;
 use std::fs;
+use std::panic::{catch_unwind, AssertUnwindSafe};
 use std::sync::atomic::{AtomicU64, Ordering};
 use std::sync::Arc;
 
@@ -75,18 +77,33 @@ fn test_vectors() -> Result<()> {
 fn test_readonly_table() -> Result<()> {
     let lua = Lua::new();
 
-    let t = lua.create_table()?;
+    let t = lua.create_sequence_from([1])?;
     assert!(!t.is_readonly());
     t.set_readonly(true);
     assert!(t.is_readonly());
 
-    match t.set("key", "value") {
-        Err(Error::RuntimeError(err)) if err.contains("Attempt to modify a readonly table") => {}
-        r => panic!(
-            "expected RuntimeError(...) with a specific message, got {:?}",
-            r
-        ),
-    };
+    #[track_caller]
+    fn check_readonly_error<T: Debug>(res: Result<T>) {
+        match res {
+            Err(Error::RuntimeError(e)) if e.contains("attempt to modify a readonly table") => {}
+            r => panic!("expected RuntimeError(...) with a specific message, got {r:?}"),
+        }
+    }
+
+    check_readonly_error(t.set("key", "value"));
+    check_readonly_error(t.raw_set("key", "value"));
+    check_readonly_error(t.raw_insert(1, "value"));
+    check_readonly_error(t.raw_remove(1));
+    check_readonly_error(t.push("value"));
+    check_readonly_error(t.pop::<Value>());
+    check_readonly_error(t.raw_push("value"));
+    check_readonly_error(t.raw_pop::<Value>());
+
+    // Special case
+    match catch_unwind(AssertUnwindSafe(|| t.set_metatable(None))) {
+        Ok(_) => panic!("expected panic, got nothing"),
+        Err(_) => {}
+    }
 
     Ok(())
 }
@@ -220,7 +237,7 @@ fn test_interrupts() -> Result<()> {
 }
 
 #[test]
-fn test_coverate() -> Result<()> {
+fn test_coverage() -> Result<()> {
     let lua = Lua::new();
 
     lua.set_compiler(Compiler::default().set_coverage_level(1));

tests/table.rs

@@ -109,6 +109,49 @@ fn test_table() -> Result<()> {
     Ok(())
 }
 
+#[test]
+fn test_table_push_pop() -> Result<()> {
+    let lua = Lua::new();
+
+    // Test raw access
+    let table1 = lua.create_sequence_from(vec![123])?;
+    table1.raw_push(321)?;
+    assert_eq!(
+        table1
+            .clone()
+            .raw_sequence_values::<i64>()
+            .collect::<Result<Vec<_>>>()?,
+        vec![123, 321]
+    );
+    assert_eq!(table1.raw_pop::<i64>()?, 321);
+    assert_eq!(table1.raw_pop::<i64>()?, 123);
+    assert_eq!(table1.raw_pop::<Value>()?, Value::Nil); // An extra pop should do nothing
+    assert_eq!(table1.raw_len(), 0);
+
+    // Test access through metamethods
+    let table2 = lua
+        .load(
+            r#"
+        local proxy_table = {234}
+        table2 = setmetatable({}, {
+            __len = function() return #proxy_table end,
+            __index = proxy_table,
+            __newindex = proxy_table,
+        })
+        return table2
+    "#,
+        )
+        .eval::<Table>()?;
+    table2.push(345)?;
+    assert_eq!(table2.len()?, 2);
+    assert_eq!(table2.pop::<i64>()?, 345);
+    assert_eq!(table2.pop::<i64>()?, 234);
+    assert_eq!(table2.pop::<Value>()?, Value::Nil);
+    assert_eq!(table2.len()?, 0);
+
+    Ok(())
+}
+
 #[test]
 fn test_table_sequence_from() -> Result<()> {
     let lua = Lua::new();

tests/tests.rs

@@ -73,6 +73,7 @@ fn test_load() -> Result<()> {
     let result: i32 = func.call(())?;
     assert_eq!(result, 3);
 
+    assert!(lua.load("").exec().is_ok());
     assert!(lua.load("§$%§&$%&").exec().is_err());
 
     Ok(())
@@ -792,6 +793,17 @@ fn test_replace_registry_value() -> Result<()> {
     let key = lua.create_registry_value::<i32>(42)?;
     lua.replace_registry_value(&key, "new value")?;
     assert_eq!(lua.registry_value::<String>(&key)?, "new value");
+    lua.replace_registry_value(&key, Value::Nil)?;
+    assert_eq!(lua.registry_value::<Value>(&key)?, Value::Nil);
+    lua.replace_registry_value(&key, 123)?;
+    assert_eq!(lua.registry_value::<i32>(&key)?, 123);
+
+    // It should be impossible to replace (initial) nil value with non-nil
+    let key2 = lua.create_registry_value(Value::Nil)?;
+    match lua.replace_registry_value(&key2, "abc") {
+        Err(Error::RuntimeError(_)) => {}
+        r => panic!("expected RuntimeError, got {r:?}"),
+    }
 
     Ok(())
 }
@@ -843,6 +855,28 @@ fn test_mismatched_registry_key() -> Result<()> {
     Ok(())
 }
 
+#[test]
+fn test_registry_value_reuse() -> Result<()> {
+    let lua = Lua::new();
+
+    let r1 = lua.create_registry_value("value1")?;
+    let r1_slot = format!("{r1:?}");
+    drop(r1);
+
+    // Previous slot must not be reused by nil value
+    let r2 = lua.create_registry_value(Value::Nil)?;
+    let r2_slot = format!("{r2:?}");
+    assert_ne!(r1_slot, r2_slot);
+    drop(r2);
+
+    // But should be reused by non-nil value
+    let r3 = lua.create_registry_value("value3")?;
+    let r3_slot = format!("{r3:?}");
+    assert_eq!(r1_slot, r3_slot);
+
+    Ok(())
+}
+
 #[test]
 fn test_application_data() -> Result<()> {
     let lua = Lua::new();