Modernize lua read (part 2 & 3): C++ templating assurance (#7410)

* Modernize lua read (part 2 & 3): C++ templating assurance

Implement the boolean reader
Implement the string reader
Also remove unused & unimplemented script_error_handler
Add a reader with default value

src/script/common/helper.cpp

@@ -0,0 +1,73 @@
+/*
+Minetest
+Copyright (C) 2018 nerzhul, Loic Blot <loic.blot@unix-experience.fr>
+
+This program is free software; you can redistribute it and/or modify
+it under the terms of the GNU Lesser General Public License as published by
+the Free Software Foundation; either version 2.1 of the License, or
+(at your option) any later version.
+
+This program is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+GNU Lesser General Public License for more details.
+
+You should have received a copy of the GNU Lesser General Public License along
+with this program; if not, write to the Free Software Foundation, Inc.,
+51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+*/
+
+#include "helper.h"
+#include <cmath>
+#include <sstream>
+#include "c_types.h"
+
+bool LuaHelper::isNaN(lua_State *L, int idx)
+{
+	return lua_type(L, idx) == LUA_TNUMBER && std::isnan(lua_tonumber(L, idx));
+}
+
+/*
+ * Read template functions
+ */
+template <> bool LuaHelper::readParam(lua_State *L, int index)
+{
+	return lua_toboolean(L, index) != 0;
+}
+
+template <> bool LuaHelper::readParam(lua_State *L, int index, const bool &default_value)
+{
+	if (lua_isnil(L, index))
+		return default_value;
+
+	return lua_toboolean(L, index) != 0;
+}
+
+template <> float LuaHelper::readParam(lua_State *L, int index)
+{
+	if (isNaN(L, index))
+		throw LuaError("NaN value is not allowed.");
+
+	return (float)luaL_checknumber(L, index);
+}
+
+template <> std::string LuaHelper::readParam(lua_State *L, int index)
+{
+	std::string result;
+	const char *str = luaL_checkstring(L, index);
+	result.append(str);
+	return result;
+}
+
+template <>
+std::string LuaHelper::readParam(
+		lua_State *L, int index, const std::string &default_value)
+{
+	std::string result;
+	const char *str = lua_tostring(L, index);
+	if (str)
+		result.append(str);
+	else
+		result = default_value;
+	return result;
+}