Add comment preservation (section-accurate comments) and order preservation (both of sections and keys), meaning that if the comments are at the top of sections or at the top of the file, and the output table's metatable isn't modified, the ini file written out should exactly match the one read in, ignoring whitespace

inifile/inifile.lua

@@ -1,4 +1,4 @@
--- Copyright 2011 Bart van Strien. All rights reserved.
+-- Copyright 2011-2013 Bart van Strien. All rights reserved.
 -- 
 -- Redistribution and use in source and binary forms, with or without modification, are
 -- permitted provided that the following conditions are met:
@@ -53,34 +53,116 @@ function inifile.parse(name, backend)
 	backend = backend or defaultBackend
 	local t = {}
 	local section
+	local comments = {}
+	local sectionorder = {}
+	local cursectionorder
+
 	for line in backends[backend].lines(name) do
+
+		-- Section headers
 		local s = line:match("^%[([^%]]+)%]$")
 		if s then
 			section = s
 			t[section] = t[section] or {}
+			cursectionorder = {name = section}
+			table.insert(sectionorder, cursectionorder)
 		end
+
+		-- Comments
+		s = line:match("^;(.+)$")
+		if s then
+			local commentsection = section or comments
+			comments[commentsection] = comments[commentsection] or {}
+			table.insert(comments[commentsection], s)
+		end
+
+		-- Key-value pairs
 		local key, value = line:match("^(%w+)%s-=%s-(.+)$")
 		if tonumber(value) then value = tonumber(value) end
 		if value == "true" then value = true end
 		if value == "false" then value = false end
 		if key and value ~= nil then
 			t[section][key] = value
+			table.insert(cursectionorder, key)
 		end
 	end
-	return t
+
+	-- Store our metadata in the __inifile field in the metatable
+	return setmetatable(t, {
+		__inifile = {
+			comments = comments,
+			sectionorder = sectionorder,
+		}
+	})
 end
 
 function inifile.save(name, t, backend)
 	backend = backend or defaultBackend
-	local contents = ""
-	for section, s in pairs(t) do
-		local sec = ("[%s]\n"):format(section)
-		for key, value in pairs(s) do
-			sec = sec .. ("%s=%s\n"):format(key, tostring(value))
-		end
-		contents = contents .. sec .. "\n"
+	local contents = {}
+
+	-- Get our metadata if it exists
+	local metadata = getmetatable(t)
+	local comments, sectionorder
+
+	if metadata then metadata = metadata.__inifile end
+	if metadata then
+		comments = metadata.comments
+		sectionorder = metadata.sectionorder
 	end
-	return backends[backend].write(name, contents)
+
+	-- If there are comments before sections,
+	-- write them out now
+	if comments and comments[comments] then
+		for i, v in ipairs(comments[comments]) do
+			table.insert(contents, (";%s"):format(v))
+		end
+		table.insert(contents, "")
+	end
+
+	local function writevalue(section, key)
+		local value = section[key]
+		table.insert(contents, ("%s=%s"):format(key, tostring(value)))
+	end
+
+	local function writesection(section, order)
+		local s = t[section]
+		table.insert(contents, ("[%s]"):format(section))
+
+		-- Write our comments out again, sadly we have only achieved
+		-- section-accuracy so far
+		if comments and comments[section] then
+			for i, v in ipairs(comments[section]) do
+				table.insert(contents, (";%s"):format(v))
+			end
+		end
+
+		-- Write the key-value pairs with optional order
+		if order then
+			for _, v in ipairs(order) do
+				writevalue(s, v)
+			end
+		else
+			for i, _ in pairs(s) do
+				writevalue(s, i)
+			end
+		end
+
+		-- Newline after the section
+		table.insert(contents, "")
+	end
+
+	-- Write the sections, with optional order
+	if sectionorder then
+		for _, v in ipairs(sectionorder) do
+			writesection(v.name, v)
+		end
+	else
+		for i, _ in pairs(contents) do
+			writesection(i)
+		end
+	end
+
+	return backends[backend].write(name, table.concat(contents, "\n"))
 end
 
 return inifile