Luon: Incorporate changes to MT serializer

luon.lua

@@ -1,15 +1,14 @@
-local assert, next, pairs, pcall, error, type, table_insert, table_concat, string_format, string_match, setmetatable, select, setfenv, math_huge, loadfile, loadstring
-	= assert, next, pairs, pcall, error, type, table.insert, table.concat, string.format, string.match, setmetatable, select, setfenv, math.huge, loadfile, loadstring
+-- Lua module to serialize values as Lua code
+
+local assert, error, rawget, pairs, pcall, type, setfenv, setmetatable, select, loadstring, loadfile
+	= assert, error, rawget, pairs, pcall, type, setfenv, setmetatable, select, loadstring, loadfile
+
+local table_concat, string_format, math_huge
+	= table.concat, string.format, math.huge
 
 local count_objects = modlib.table.count_objects
 local is_identifier = modlib.text.is_identifier
 
--- Build a table with the succeeding character from A-Z
-local succ = {}
-for char = ("A"):byte(), ("Z"):byte() - 1 do
-	succ[string.char(char)] = string.char(char + 1)
-end
-
 local function quote(string)
 	return string_format("%q", string)
 end
@@ -31,73 +30,93 @@ end
 aux_read = {}
 
 function write(self, value, write)
-	local reference = {"A"}
-	local function increment_reference(place)
-		if not reference[place] then
-			reference[place] = "B"
-		elseif reference[place] == "Z" then
-			reference[place] = "A"
-			return increment_reference(place + 1)
-		else
-			reference[place] = succ[reference[place]]
-		end
-	end
+	-- TODO evaluate custom aux. writers *before* writing for circular structs
+	local reference, refnum = "1", 1
+	-- [object] = reference
 	local references = {}
+	-- Circular tables that must be filled using `table[key] = value` statements
 	local to_fill = {}
-	-- TODO sort objects by count, give frequently referenced objects shorter references
+
+	-- TODO (?) sort objects by count, give frequently referenced objects shorter references
 	for object, count in pairs(count_objects(value)) do
 		local type_ = type(object)
-		if count >= 2 and (type_ ~= "string" or #reference + 2 < #object) then
-			local ref = table_concat(reference)
-			write(ref)
-			write"="
-			write(type_ == "table" and "{}" or quote(object))
-			write";"
-			references[object] = ref
-			if type_ == "table" then
-				to_fill[object] = ref
+		-- 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
-			increment_reference(1)
+			write"_["
+			write(reference)
+			write"]="
+			if type_ == "table" then
+				write"{}"
+			elseif type_ == "string" then
+				write(quote(object))
+			end
+			write";"
+			references[object] = reference
+			if type_ == "table" then
+				to_fill[object] = reference
+			end
+			refnum = refnum + 1
+			reference = string_format("%d", refnum)
 		end
 	end
-	local function is_short_key(key)
+	-- Used to decide whether we should do "key=..."
+	local function use_short_key(key)
 		return not references[key] and type(key) == "string" and is_identifier(key)
 	end
 	local function dump(value)
 		-- Primitive types
 		if value == nil then
 			return write"nil"
-		end
-		if value == true then
+		end if value == true then
 			return write"true"
-		end
-		if value == false then
+		end if value == false then
 			return write"false"
 		end
 		local type_ = type(value)
 		if type_ == "number" then
+			-- Explicit handling of special values for forwards compatibility
+			if value ~= value then -- nan
+				return write"0/0"
+			end if value == math_huge then
+				return write"1/0"
+			end if value == -math_huge then
+				return write"-1/0"
+			end
 			return write(string_format("%.17g", value))
 		end
 		-- Reference types: table and string
 		local ref = references[value]
 		if ref then
 			-- Referenced
-			return write(ref)
-		elseif type_ == "string" then
+			write"_["
+			write(ref)
+			return write"]"
+		end if type_ == "string" then
 			return write(quote(value))
-		elseif type_ == "table" then
-			local first = true
+		end if type_ == "table" then
 			write"{"
-			local len = #value
-			for i = 1, len do
-				if not first then write";" end
-				dump(value[i])
-				first = false
+			-- First write list keys:
+			-- Don't use the table length #value here as it may horribly fail
+			-- for tables which use large integers as keys in the hash part;
+			-- stop at the first "hole" (nil value) instead
+			local len = 0
+			local first = true -- whether this is the first entry, which may not have a leading comma
+			while true do
+				local v = rawget(value, len + 1) -- use rawget to avoid metatables like the vector metatable
+				if v == nil then break end
+				if first then first = false else write(",") end
+				dump(v)
+				len = len + 1
 			end
-			for k, v in next, value do
+			-- Now write map keys ([key] = value)
+			for k, v in pairs(value) do
+				-- We have written all non-float keys in [1, len] already
 				if type(k) ~= "number" or k % 1 ~= 0 or k < 1 or k > len then
-					if not first then write";" end
-					if is_short_key(k) then
+					if first then first = false else write(",") end
+					if use_short_key(k) then
 						write(k)
 					else
 						write"["
@@ -106,36 +125,36 @@ function write(self, value, write)
 					end
 					write"="
 					dump(v)
-					first = false
 				end
 			end
-			write"}"
-		else
-			-- TODO move aux_write to start, to allow dealing with metatables etc.?
-			(function(func, ...)
-				-- functions are the only way to deal with varargs
-				if not func then
-					return error("unsupported type: " .. type_)
-				end
-				write(func)
-				write"("
-				local n = select("#", ...)
-				local args = {...}
-				for i = 1, n - 1 do
-					dump(args[i])
-					write","
-				end
-				if n > 0 then
-					write(args[n])
-				end
-				write")"
-			end)(self:aux_write(value))
+			return write"}"
 		end
+		-- TODO move aux_write to start, to allow dealing with metatables etc.?
+		return (function(func, ...)
+			-- functions are the only way to deal with varargs
+			if not func then
+				return error("unsupported type: " .. type_)
+			end
+			write(func)
+			write"("
+			local n = select("#", ...)
+			for i = 1, n - 1 do
+				dump(select(i, ...))
+				write","
+			end
+			if n > 0 then
+				dump(select(n, ...))
+			end
+			write")"
+		end)(self:aux_write(value))
 	end
+	-- Write the statements to fill circular tables
 	for table, ref in pairs(to_fill) do
 		for k, v in pairs(table) do
+			write"_["
 			write(ref)
-			if is_short_key(k) then
+			write"]"
+			if use_short_key(k) then
 				write"."
 				write(k)
 			else
@@ -161,15 +180,14 @@ end
 function write_string(self, value)
 	local rope = {}
 	self:write(value, function(text)
-		table_insert(rope, text)
+		rope[#rope + 1] = text
 	end)
 	return table_concat(rope)
 end
 
 function read(self, ...)
 	local read = assert(...)
-	-- math.huge is serialized to inf, 0/0 is serialized to -nan
-	-- TODO verify this is actually the case, see https://en.wikipedia.org/wiki/Printf_format_string
+	-- math.huge was serialized to inf, 0/0 was serialized to -nan by `%.17g`
 	setfenv(read, setmetatable({inf = math_huge, nan = 0/0}, {__index = self.aux_read}))
 	local success, value_or_err = pcall(read)
 	if success then