It's unsafe to make almost any Lua calls when userdata destructor is running.
This can cause recursive GC run and crash.
See https://github.com/luau-lang/luau/pull/510 for some details.
The definition of lua_error in all of Lua 5.1 through 5.4 says lua_error
returns int, but the Rust definition of the same function treats it as
void (because it's known not to return). This causes link-time errors when
building for wasm targets because the wasm linker is aware of function return
types and errors out if they differ between definition and declaration.
Lua 5.4 changed lua_rawlen to return lua_Unsigned, versus size_t in earlier
versions. Change the C API signature to match, and add a wrapper function with
the same name that maintains a stable Rust API by casting to usize.
Alex Orlenko