feat: Add _G global table

lib/lua/vm/stdlib.ex

@@ -37,6 +37,27 @@ defmodule Lua.VM.Stdlib do
     |> Lua.VM.Stdlib.String.install()
     |> Lua.VM.Stdlib.Math.install()
     |> Lua.VM.Stdlib.Table.install()
+    |> install_global_g()
+  end
+
+  # Install _G global table - a table that references the global environment
+  defp install_global_g(state) do
+    # Create a table containing all current globals
+    # Copy all globals into the _G table
+    g_data = state.globals
+
+    {{:tref, _id} = g_ref, state} = State.alloc_table(state, g_data)
+
+    # Set _G to point to this table
+    state = State.set_global(state, "_G", g_ref)
+
+    # Also add _G to itself so _G._G == _G
+    state =
+      State.update_table(state, g_ref, fn table ->
+        %{table | data: Map.put(table.data, "_G", g_ref)}
+      end)
+
+    state
   end
 
   # type(v) — returns the type of v as a string

test/lua_test.exs

@@ -1397,6 +1397,52 @@ defmodule LuaTest do
     end
   end
 
+  describe "_G global table" do
+    setup do
+      %{lua: Lua.new(sandboxed: [])}
+    end
+
+    test "_G references the global environment", %{lua: lua} do
+      # _G should be a table that contains itself
+      assert {[true], _} = Lua.eval!(lua, "return _G ~= nil")
+      assert {[true], _} = Lua.eval!(lua, "return type(_G) == 'table'")
+    end
+
+    test "_G contains global functions", %{lua: lua} do
+      # Standard functions should be accessible via _G
+      assert {[true], _} = Lua.eval!(lua, "return _G.print == print")
+      assert {[true], _} = Lua.eval!(lua, "return _G.type == type")
+      assert {[true], _} = Lua.eval!(lua, "return _G.tostring == tostring")
+    end
+
+    test "_G contains itself", %{lua: lua} do
+      # _G._G should reference _G
+      assert {[true], _} = Lua.eval!(lua, "return _G._G == _G")
+    end
+
+    @tag :skip
+    test "can set globals via _G", %{lua: lua} do
+      # Requires _G to be a live reference with __index/__newindex metamethods
+      code = """
+      _G.myvar = 42
+      return myvar
+      """
+
+      assert {[42], _} = Lua.eval!(lua, code)
+    end
+
+    @tag :skip
+    test "can read globals via _G", %{lua: lua} do
+      # Requires _G to be a live reference with __index metamethods
+      code = """
+      myvar = 123
+      return _G.myvar
+      """
+
+      assert {[123], _} = Lua.eval!(lua, code)
+    end
+  end
+
   defp test_file(name) do
     Path.join(["test", "fixtures", name])
   end