Wrap the lua core methods so you don't overwrite them

core.lua

do

  local lua = {}
  local core = setmetatable({}, { __index = lua, })

  _G = setmetatable(_G, { __index = core })

  for k,v in pairs(_G) do
    if k ~= "_G" then
      lua[k] = v
      if type(v) == "table" then
        core[k] = setmetatable({}, { __index = lua[k] })
      end
      _G[k] = nil
    end
  end

  _G.core = core
  _G.lua = lua
  
  
  setmetatable(lua, {
      __newindex = function(self, k,v)
        return error("Cannot set new items on table 'lua'")
      end,
    })
  
  getmetatable(_G).__newindex = function(self, k,v)
    print("Warning: adding new member to _G: " .. tostring(k))
    rawset(_G,k,v)
  end
end

table.ext = true

function print(...)
  return lua.print("~ ", ...)
end

foo = 2

print(table.ext, core.table.ext, lua.table.ext)