Cannot build in `module` mode on `macos-15` (arm64 GH Actions runner)

[mrcjkb]

To reproduce

I have a minimal repro that builds successfully on ubuntu-24.05 and windows-2025, but fails on macos-15
[full build log].

• Use the module mode example in the readme.
• Build on the macos-15 GH Actions runner

Results in the following error:

error: linking with `cc` failed: exit status: 1
  |
  = note:  "cc" "-Wl,-exported_symbols_list" "-Wl,/var/folders/x7/ch5v91h56_zbvbd1y2f600dm0000gn/T/rustcBDSZ2h/list" "/var/folders/x7/ch5v91h56_zbvbd1y2f600dm0000gn/T/rustcBDSZ2h/symbols.o" "<2 object files omitted>" "/Users/runner/work/mlua-module-macos-repro/mlua-module-macos-repro/target/debug/deps/{libmlua-9ac4efec35a36a5e.rlib,libeither-129d90b1e1a89791.rlib,librustc_hash-fd49dc5d5ac9b28a.rlib,libparking_lot-bd683189d2ee7117.rlib,libparking_lot_core-12cd0aade44ee458.rlib,liblibc-496d21bb259f4e1f.rlib,libcfg_if-cc1472d4f2383a67.rlib,libsmallvec-38d880f420f64a9d.rlib,liblock_api-50bb8b071d94eec1.rlib,libscopeguard-112dd4a32172bb08.rlib,libmlua_sys-9b8c609292190d38.rlib,libnum_traits-dbd2d00ac47bbbf7.rlib,libbstr-5709a75b056ad338.rlib,libmemchr-95941c9c2888c479.rlib}.rlib" "<sysroot>/lib/rustlib/aarch64-apple-darwin/lib/{libstd-*,libpanic_unwind-*,libobject-*,libmemchr-*,libaddr2line-*,libgimli-*,librustc_demangle-*,libstd_detect-*,libhashbrown-*,librustc_std_workspace_alloc-*,libminiz_oxide-*,libadler2-*,libunwind-*,libcfg_if-*,liblibc-*,librustc_std_workspace_core-*,liballoc-*,libcore-*,libcompiler_builtins-*}.rlib" "-liconv" "-lSystem" "-lc" "-lm" "-arch" "arm64" "-mmacosx-version-min=11.0.0" "-o" "/Users/runner/work/mlua-module-macos-repro/mlua-module-macos-repro/target/debug/deps/libmlua_module_macos_repro.dylib" "-Wl,-dead_strip" "-dynamiclib" "-nodefaultlibs"
  = note: some arguments are omitted. use `--verbose` to show all linker arguments
  = note: Undefined symbols for architecture arm64:
            "_luaL_callmeta", referenced from:
                mlua_sys::lua51::compat::luaL_tolstring::hcbb2fcb7d872bfc2 in libmlua_sys-9b8c609292190d38.rlib[3](mlua_sys-9b8c609292190d38.mlua_sys.908a23f71ddd9b6d-cgu.0.rcgu.o)
            "_luaL_error", referenced from:
...

[khvzak]

You need to provide a config with linker instruction to resolve unknown symbols (this is required for macos):

.cargo/config.toml

[target.aarch64-apple-darwin]
rustflags = [
  "-C", "link-arg=-undefined",
  "-C", "link-arg=dynamic_lookup",
]

PS The config example is in README

[mrcjkb]

Oops, I completely missed that. My bad.

Thanks for the quick response 🙏

[mrcjkb]

In case someone else comes across this:

adding the .cargo/config.toml entry doesn't appear to be enough for github actions.

I added this step:

      - name: "Setup environment for aarch64-darwin"
        run: echo "RUSTFLAGS=${RUSTFLAGS} -C link-arg=-undefined -C link-arg=dynamic_lookup" >> "${GITHUB_ENV}"
        if: startsWith(matrix.target, 'aarch64-apple-darwin')