savefile.lua does not use os.tmpname() since it's unreliable on windows

ludobits/m/savefile.lua

@@ -10,10 +10,11 @@
 -- file.save({ foo = "bar" })
 --
 
-local M = {}
+local M = {
+	tmpname = "___lbtmp"
+}
 
-
-local function get_path(filename)
+function M.get_path(filename)
 	local path = sys.get_save_file(sys.get_config("project.title"):gsub(" ", "_"), filename)
 	return path
 end
@@ -22,7 +23,7 @@ end
 -- @param filename
 -- @return file instance
 function M.open(filename)
-	local path = get_path(filename)
+	local path = M.get_path(filename)
 	local instance = {}
 
 	--- Load the contents of the file
@@ -37,7 +38,14 @@ function M.open(filename)
 	-- @return error_message
 	function instance.save(t)
 		assert(t and type(t) == "table", "You must provide a table to save")
-		local tmpname = os.tmpname()
+		--local tmpname = ((sys.get_sys_info().system_name == "Windows") and os.getenv("TMP") or "") .. os.tmpname()
+		-- os.tmpname() is not very reliable on windows (it doesn't return a valid path to a temp file)
+		-- it's better to return the path to an application local file, and in this case we use the same filename
+		-- every time so that we do not pollute the filesystem with many temporary files in case of problems
+		-- when writing to the file
+		-- it is reasonable to assume that a filename such as "___lbtmp" isn't used by any other part of the
+		-- system, and if that is actually the case it is possible to change it
+		local tmpname = M.get_path(M.tmpname)
 		local success = sys.save(tmpname, t)
 		if not success then
 			return false, "Unable to save file"