Module not found on Windows (again)

[kkew3]

I encounter the same issue as #101 while developing a very simple lua module using rust: https://github.com/kkew3/expose-shared-library/tree/ci/examples/mixed-rust-lua-project. The build is run on github windows-2022 runner. I tried setting LUA_INC, LUA_LIB, LUA_LIB_NAME and copying lua51.dll to lua.dll as mentioned in chipsenkbeil/distant.nvim#57 by @khvzak, yet with no luck. The error is:

D:\a\expose-shared-library\expose-shared-library\.lua\bin\lua.exe: error loading module 'sum_as_string_rs' from file '.\sum_as_string_rs.dll':
	The specified module could not be found.


stack traceback:
	[C]: ?
	[C]: in function 'require'
	main.lua:1: in main chunk
	[C]: ?

I confirm exactly the same code works on macOS and ubuntu.

The excerpt of github workflow:

name: CI
runs-on: ${{ matrix.job.os }}
strategy:
  fail-fast: false
  matrix:
    lang:
      - lua
    job:
      - { os: windows-2022, target: x86_64-pc-windows-msvc }

steps:
  - name: Install lua prerequisite
    if: matrix.lang == 'lua'
    uses: ilammy/msvc-dev-cmd@v1
  - name: Setup lua
    if: matrix.lang == 'lua'
    uses: leafo/gh-actions-lua@v10
    with:
      luaVersion: '5.1.5'
  # Reference: https://github.com/chipsenkbeil/distant.nvim/issues/57#issuecomment-971992482
  - name: Copy lua lib files
    if: matrix.lang == 'lua' && matrix.job.os == 'windows-2022'
    shell: bash
    run: |
      cp .lua/lib/lua51.dll .lua/lib/lua.dll
      cp .lua/lib/lua51.lib .lua/lib/lua.lib

  - name: Install Rust toolchain
    uses: dtolnay/rust-toolchain@stable
    with:
      targets: ${{ matrix.job.target }}

  - name: Build and check (without '--target')
    shell: bash
    run: |
      case ${{ matrix.lang }} in
        lua)
          cd examples/mixed-rust-lua-project
          find lua -type f -name '*.so' -o -name '*.dll' -exec rm -f {} +
          cargo clean
          # Reference: https://github.com/chipsenkbeil/distant.nvim/issues/57#issuecomment-969256617
          export LUA_INC="$GITHUB_WORKSPACE/.lua/include"
          export LUA_LIB="$GITHUB_WORKSPACE/.lua/lib"
          export LUA_LIB_NAME=lua
          # Reference: https://github.com/rust-lang/cargo/issues/3687#issuecomment-336762567
          case ${{ matrix.job.os }} in
            windows-*)
              MSVC_PATH="$(echo "$PATH" | tr : '\n' | grep MSVC | head -n1)"
              export PATH="$MSVC_PATH:$PATH"
              cargo build --release
              ;;
          esac
          cd lua
          lua main.lua
          ;;
      esac

For your convenience, here are related files:

Cargo.toml:

[package]
name = "sum_as_string_rs"
version = "0.1.0"
edition = "2021"

[lib]
name = "sum_as_string_rs"
crate-type = ["cdylib"]

[dependencies]
mlua = { version = "0.10", features = ["lua51", "module"] }

[build-dependencies]
expose-shared-library = { path = "../..", features = ["lua"] }

There is an expose-shared-library in build-dependencies. It's used to copy the output dll file to the directory where main.lua file resides.

build.rs:

use std::path::PathBuf;

fn main() {
    add_extension_module_link_args();
    let my_package_dir: PathBuf =
        [env!("CARGO_MANIFEST_DIR"), "lua"].iter().collect();
    expose_shared_library::expose_shared_library(my_package_dir).unwrap();
}

#[cfg(target_os = "macos")]
fn add_extension_module_link_args() {
    println!("cargo::rustc-link-arg=-undefined");
    println!("cargo::rustc-link-arg=dynamic_lookup");
}

#[cfg(not(target_os = "macos"))]
fn add_extension_module_link_args() {}

src/lib.rs:

use mlua::prelude::*;

fn sum_as_string(_: &Lua, (a, b): (usize, usize)) -> LuaResult<String> {
    Ok((a + b).to_string())
}

#[mlua::lua_module]
fn sum_as_string_rs(lua: &Lua) -> LuaResult<LuaTable> {
    let exports = lua.create_table()?;
    exports.set("sum_as_string", lua.create_function(sum_as_string)?)?;
    Ok(exports)
}

main.lua:

print(require("sum_as_string_rs").sum_as_string(1, 2))

Thank you so much for your help!

[khvzak]

The modules functionality on Windows is actually tested for mlua in github CI, see the instructions:

  test_modules_windows:
    name: Test modules on Windows
    runs-on: windows-latest
    needs: build
    strategy:
      matrix:
        lua: [lua54, luajit]
    defaults:
      run:
        shell: msys2 {0}
    steps:
      - uses: msys2/setup-msys2@v2
      - uses: actions/checkout@main
      - 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 }}")

Lua modules on windows are automatically linked with lua5x.dll without requiring the physical file. You don't need lua.dll anymore.
Also could you try to not set any LUA_xxx env variables.

[kkew3]

Thanks for your detailed explanation. By looking into the source code of mlua, it seems that by "automatically linked with lua5x.dll", pkg-config is required to be installed, which is not always available on Windows. So I stick to my original method of setting LUA_LIB=$GITHUB_WORKSPACE/.lua/lib and LUA_LIB_NAME=lua51. One important step is to add $GITHUB_WORKSPACE/.lua/lib to PATH so that the lua51.dll can be found at runtime. And the error is gone.

[kkew3]

I think leafo/gh-actions-lua@v10 is the one to blame for this issue:

leafo/gh-actions-lua#38