Serialize: Restore forward compatibility

builtin/common/serialize.lua

@@ -70,6 +70,9 @@ local function serialize(value, write)
  local type_ = type(object)
  -- Object must appear more than once. If it is a string, the reference has to be shorter than the string.
  if count >= 2 and (type_ ~= "string" or #reference + 5 < #object) then
+ if refnum == 1 then
+ write"local _={};" -- initialize reference table
+ end
  write"_["
  write(reference)
  write("]=")
@@ -106,7 +109,15 @@ local function serialize(value, write)
  end
  local type_ = type(value)
  if type_ == "number" then
- return write(string_format("%.17g", value))
+ if value ~= value then -- nan
+ return write"0/0"
+ elseif value == math_huge then
+ return write"1/0"
+ elseif value == -math_huge then
+ return write"-1/0"
+ else
+ return write(string_format("%.17g", value))
+ end
  end
  -- Reference types: table, function and string
  local ref = references[value]
@@ -190,8 +201,6 @@ end
 
 local function dummy_func() end
 
-local nan = (0/0)^1 -- +nan
-
 function core.deserialize(str, safe)
  -- Backwards compatibility
  if str == nil then
@@ -206,8 +215,8 @@ function core.deserialize(str, safe)
  local func, err = loadstring(str)
  if not func then return nil, err end
 
- -- math.huge is serialized to inf, NaNs are serialized to nan by Lua
- local env = {inf = math_huge, nan = nan, _ = {}}
+ -- math.huge was serialized to inf and NaNs to nan by Lua in Minetest 5.6, so we have to support this here
+ local env = {inf = math_huge, nan = 0/0}
  if safe then
  env.loadstring = dummy_func
  else