Run this is a folder full of 'fdef' files to turn it into a folder of sublime-snippet files. See sample.fdef, sample.sublime-snippet, and sample-all.sublime-snippet.

fdef_to_stsnippet.lua

--[[
]]
local lfs = require("lfs")
local CWD = "./"

function readfile(path)
	local handle = io.open(path, "r")
	if (handle) then
		local data = handle:read("*a")
		handle:close()
		return data
	end
end

function writefile(path, data)
	local handle = io.open(path, "w")
	if (handle) then
		handle:write(data)
		handle:close()
		return true
	end
end

function parse_fdef(source)
	local parsed = {}

	local desc = source:match("^(.-)\n")
	parsed.desc = (#desc > 0) and desc or "no description available"

	local name, arguments = source:match("([%w%d%.%-_]+)%(([^%)]+)%)")
	parsed.name = name
	parsed.arguments = {}

	for argument in arguments:gmatch("[^%s,]+") do
		table.insert(parsed.arguments, argument)
	end

	local defaults = {}
	for name, value in source:gmatch("%w+ ([%w%d%-_]+) %(([^%)]+)%)") do
		if (tonumber(value)) then --number!
			defaults[name] = tonumber(value)
		elseif (value:match("^\".-\"$")) then --string!
			defaults[name] = value
		elseif (defaults[value]) then --backreference!
			defaults[name] = defaults[value]
		else --not sure WHAT this is
		end
	end
	parsed.defaults = defaults

	return parsed
end

function build_snippet(parsed, all)
	local name, arguments, defaults, desc = parsed.name, parsed.arguments, parsed.defaults, parsed.desc

	local buf = {
		"<!--Automatically generated by LPGhatguy's LOVE FDEF Parser-->\n<snippet>"
	}

	local arg_buf = {}
	local replace_index = 1
	for key, argument in ipairs(arguments) do
		if (defaults[argument]) then
			if (all) then
				table.insert(arg_buf, "${" .. replace_index .. ":" .. argument .. "=}${" .. replace_index + 1 .. ":" .. defaults[argument] .. "}")
				replace_index = replace_index + 2
			end
		else
			table.insert(arg_buf, "${" .. replace_index .. ":" .. argument .. "}")
			replace_index = replace_index + 1
		end
	end
	table.insert(buf, "\t<content><![CDATA[" .. name .. "(" .. table.concat(arg_buf, ", ") .. ")]]></content>")

	table.insert(buf, "\t<tabTrigger>" .. name .. "</tabTrigger>")
	table.insert(buf, "\t<scope>source.lua</scope>")
	table.insert(buf, ("\t<description><![CDATA[  %s%s]]></description>"):format(desc, all and " (all arguments)" or ""))

	table.insert(buf, "</snippet>")

	return table.concat(buf, "\n")
end

lfs.mkdir(CWD .. "output/")

for filename in lfs.dir(CWD) do
	if (filename:match("fdef$")) then
		local target = CWD .. "output/" .. filename:gsub("fdef$", "sublime-snippet")
		local targetall = CWD .. "output/" .. filename:gsub("%.fdef$", "-all.sublime-snippet")
		local parsed = parse_fdef(readfile(CWD .. filename))

		writefile(target, build_snippet(parsed))

		if (next(parsed.defaults)) then
			writefile(targetall, build_snippet(parsed, true))
		end
	end
end

sample-all.sublime-snippet

<!--Automatically generated by LPGhatguy's LOVE FDEF Parser-->
<snippet>
	<content><![CDATA[love.graphics.printf(${1:text}, ${2:x}, ${3:y}, ${4:limit}, ${5:align=}${6:"left"}, ${7:r=}${8:0}, ${9:sx=}${10:1}, ${11:sy=}${12:1}, ${13:ox=}${14:0}, ${15:oy=}${16:0}, ${17:kx=}${18:0}, ${19:ky=}${20:0})]]></content>
	<tabTrigger>love.graphics.printf</tabTrigger>
	<scope>source.lua</scope>
	<description><![CDATA[  Draws formatted text, with word wrap and alignment. (all arguments)]]></description>
</snippet>

sample.fdef

Draws formatted text, with word wrap and alignment.

love.graphics.printf( text, x, y, limit, align, r, sx, sy, ox, oy, kx, ky )
Arguments

string text
A text string.
number x
The position on the x-axis.
number y
The position on the y-axis.
number limit
Wrap the line after this many horizontal pixels.
AlignMode align ("left")
The alignment.
number r (0)
Orientation (radians).
number sx (1)
Scale factor (x-axis).
number sy (sx)
Scale factor (y-axis).
number ox (0)
Origin offset (x-axis).
number oy (0)
Origin offset (y-axis).
number kx (0)
Shearing factor (x-axis).
number ky (0)
Shearing factor (y-axis).

sample.sublime-snippet

<!--Automatically generated by LPGhatguy's LOVE FDEF Parser-->
<snippet>
	<content><![CDATA[love.graphics.printf(${1:text}, ${2:x}, ${3:y}, ${4:limit})]]></content>
	<tabTrigger>love.graphics.printf</tabTrigger>
	<scope>source.lua</scope>
	<description><![CDATA[  Draws formatted text, with word wrap and alignment.]]></description>
</snippet>