Function luaL_loadbufferenv 

pub unsafe fn luaL_loadbufferenv(
    L: *mut lua_State,
    data: *const i8,
    size: usize,
    name: *const i8,
    mode: *const i8,
    env: i32,
) -> i32

Available on crate feature mlua and (crate features lua51 or luajit) only.