Improve flexibility around vendored librariesmain

compat53 is vendored since #1757 as it is required to run luarocks with lua 5.1 or 5.2.

However, this introduced some issues as the GNUmakefile install rule places these in the same place where `luarocks install compat53` would install them. This means you get conflicts if you install the actual package:
```
Warning: /.../prefix/share/lua/5.1/compat53/init.lua is not tracked by this installation of LuaRocks. Moving it to /.../prefix/share/lua/5.1/compat53/init.lua~
Warning: /.../prefix/share/lua/5.1/compat53/module.lua is not tracked by this installation of LuaRocks. Moving it to /.../prefix/share/lua/5.1/compat53/module.lua~
Warning: /.../prefix/share/lua/5.1/compat53/file_mt.lua is not tracked by this installation of LuaRocks. Moving it to /.../prefix/share/lua/5.1/compat53/file_mt.lua~
```

It is also not ideal for linux package maintainers to include a vendored package, see: https://github.com/luarocks/luarocks/pull/1757#issuecomment-3409873412.

To solve these issues, this patchset makes the following changes:
- GNUmakefile now places the compat53 files under `luarocks/vendor/compat53` (which is added internally to the luarocks script's `package.path`). This way a user's installation of compat53 does not interfere at all with luarocks one.
- Added `--with-system-compat53` option to configure script for external packaging systems.
- Fixed install.bat's logic for deciding whether to vendor compat53, as the current script includes it for every version.

install.bat already places luarocks sources outside of LUAPATH, so that part can stay as is.

I've also inverted the version check to avoid the need for future patches like: #1850.

7 files changed, 4286 insertions, 0 deletions

diff --git a/vendor/argparse.d.tl b/vendor/argparse.d.tl
new file mode 100644
index 00000000..812786c4
--- /dev/null
+++ b/vendor/argparse.d.tl
@@ -0,0 +1,111 @@
+
+local record argparse
+        type Args = {string : {string} | string | boolean}
+
+        record Parser
+                name: function(self: Parser, name: string): Parser
+                description: function(self: Parser, description: string): Parser
+                epilog: function(self: Parser, epilog: string): Parser
+
+                flag: function(self: Parser, flag: string): Option
+                flag: function(self: Parser, shortalias: string, longalias: string): Option
+
+                parse: function(self: Parser, argv: {string}): Args
+                pparse: function(self: Parser, argv: {string}): boolean, Args | string
+
+                error: function(self: Parser, error: string)
+
+                argument: function(self: Parser, name: string, description: string): Argument
+
+                get_usage: function(self: Parser): string
+                get_help: function(self: Parser): string
+
+                option: function(self: Parser, name: string, description?: string, default?: string, convert?: function | {function}, args?: {string}, count?: integer | string): Option
+                option: function(self: Parser, name: string, description?: string, default?: string, convert?: {string:string}, args?: {string}, count?: integer | string): Option
+
+                require_command: function(self: Parser, require_command: boolean): Parser
+                command_target: function(self: Parser, command_target: string): Parser
+
+                command: function(self: Parser, name: string, description: string, epilog: string): Command
+
+                add_help: function(self: Parser, boolean)
+
+                help_max_width: function(self: Parser, number): Parser
+                add_help_command: function(self: Parser, ?string | {string: any}): Parser
+                add_complete_command: function(self: Parser, ?string | {string: any}): Parser
+
+                group: function(self: Parser, ...:any): Parser
+
+                -- TODO: should be Argument | Option
+                mutex: function(self: Parser, ...: any)
+
+                record Opts
+                        name: string
+                        description: string
+                        epilog: string
+                end
+                metamethod __call: function(Parser, Opts): Parser
+                metamethod __call: function(Parser, string, string, string): Parser
+        end
+
+        type ActionCallback = function(args: Args, index: string, val: string | boolean | {string}, overwrite: boolean)
+
+        record Argument
+                choices: function(self: Argument, choices: {string}): Argument
+
+                convert: function(self: Argument, convert: function | {function}): Argument
+                convert: function(self: Argument, convert: {string:string}): Argument
+
+                args: function(self: Argument, args: string | integer): Argument
+
+                action: function(self: Argument, cb: ActionCallback)
+        end
+
+        record Option
+                name: function(self: Option, name: string): Option
+                description: function(self: Option, description: string): Option
+
+                argname: function(self: Option, argname: string | {string}): Option
+
+                count: function(self: Option, count: integer | string): Option
+
+                choices: function(self: Option, {string}): Option
+
+                default: function(self: Option, string): Option
+
+                defmode: function(self: Option, string): Option
+
+                target: function(self: Option, target: string): Option
+
+                args: function(self: Option, args: string|integer): Option
+
+                action: function(self: Option, cb: ActionCallback)
+
+                hidden_name: function(self: Option, string)
+
+                hidden: function(self: Option, boolean)
+
+                convert: function(self: Option, function)
+        end
+
+        record Command
+                summary: function(self: Command, summary: string): Command
+                description: function(self: Command, description: string): Command
+
+                argument: function(self: Command, name: string, description?: string): Argument
+
+                option: function(self: Command, name: string, description: string): Option
+
+                flag: function(self: Command, string, ?string): Option
+
+                handle_options: function(self: Command, boolean): Command
+
+                mutex: function(self: Command, ...: any) --! copied over from Parser
+
+                group: function(self: Command, ...:any): Command --! copied over from Parser
+        end
+
+        metamethod __call: function(self: argparse, name: string, description: string, epilog: string): Parser
+end
+
+return argparse
diff --git a/vendor/argparse.lua b/vendor/argparse.lua
new file mode 100644
index 00000000..2c2585dd
--- /dev/null
+++ b/vendor/argparse.lua
@@ -0,0 +1,2103 @@
+-- The MIT License (MIT)
+
+-- Copyright (c) 2013 - 2018 Peter Melnichenko
+--                      2019 Paul Ouellette
+
+-- Permission is hereby granted, free of charge, to any person obtaining a copy of
+-- this software and associated documentation files (the "Software"), to deal in
+-- the Software without restriction, including without limitation the rights to
+-- use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of
+-- the Software, and to permit persons to whom the Software is furnished to do so,
+-- subject to the following conditions:
+
+-- The above copyright notice and this permission notice shall be included in all
+-- copies or substantial portions of the Software.
+
+-- THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+-- IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
+-- FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
+-- COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER
+-- IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
+-- CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+
+local function deep_update(t1, t2)
+   for k, v in pairs(t2) do
+      if type(v) == "table" then
+         v = deep_update({}, v)
+      end
+
+      t1[k] = v
+   end
+
+   return t1
+end
+
+-- A property is a tuple {name, callback}.
+-- properties.args is number of properties that can be set as arguments
+-- when calling an object.
+local function class(prototype, properties, parent)
+   -- Class is the metatable of its instances.
+   local cl = {}
+   cl.__index = cl
+
+   if parent then
+      cl.__prototype = deep_update(deep_update({}, parent.__prototype), prototype)
+   else
+      cl.__prototype = prototype
+   end
+
+   if properties then
+      local names = {}
+
+      -- Create setter methods and fill set of property names.
+      for _, property in ipairs(properties) do
+         local name, callback = property[1], property[2]
+
+         cl[name] = function(self, value)
+            if not callback(self, value) then
+               self["_" .. name] = value
+            end
+
+            return self
+         end
+
+         names[name] = true
+      end
+
+      function cl.__call(self, ...)
+         -- When calling an object, if the first argument is a table,
+         -- interpret keys as property names, else delegate arguments
+         -- to corresponding setters in order.
+         if type((...)) == "table" then
+            for name, value in pairs((...)) do
+               if names[name] then
+                  self[name](self, value)
+               end
+            end
+         else
+            local nargs = select("#", ...)
+
+            for i, property in ipairs(properties) do
+               if i > nargs or i > properties.args then
+                  break
+               end
+
+               local arg = select(i, ...)
+
+               if arg ~= nil then
+                  self[property[1]](self, arg)
+               end
+            end
+         end
+
+         return self
+      end
+   end
+
+   -- If indexing class fails, fallback to its parent.
+   local class_metatable = {}
+   class_metatable.__index = parent
+
+   function class_metatable.__call(self, ...)
+      -- Calling a class returns its instance.
+      -- Arguments are delegated to the instance.
+      local object = deep_update({}, self.__prototype)
+      setmetatable(object, self)
+      return object(...)
+   end
+
+   return setmetatable(cl, class_metatable)
+end
+
+local function typecheck(name, types, value)
+   for _, type_ in ipairs(types) do
+      if type(value) == type_ then
+         return true
+      end
+   end
+
+   error(("bad property '%s' (%s expected, got %s)"):format(name, table.concat(types, " or "), type(value)))
+end
+
+local function typechecked(name, ...)
+   local types = {...}
+   return {name, function(_, value) typecheck(name, types, value) end}
+end
+
+local multiname = {"name", function(self, value)
+   typecheck("name", {"string"}, value)
+
+   for alias in value:gmatch("%S+") do
+      self._name = self._name or alias
+      table.insert(self._aliases, alias)
+      table.insert(self._public_aliases, alias)
+      -- If alias contains '_', accept '-' also.
+      if alias:find("_", 1, true) then
+         table.insert(self._aliases, (alias:gsub("_", "-")))
+      end
+   end
+
+   -- Do not set _name as with other properties.
+   return true
+end}
+
+local multiname_hidden = {"hidden_name", function(self, value)
+   typecheck("hidden_name", {"string"}, value)
+
+   for alias in value:gmatch("%S+") do
+      table.insert(self._aliases, alias)
+      if alias:find("_", 1, true) then
+         table.insert(self._aliases, (alias:gsub("_", "-")))
+      end
+   end
+
+   return true
+end}
+
+local function parse_boundaries(str)
+   if tonumber(str) then
+      return tonumber(str), tonumber(str)
+   end
+
+   if str == "*" then
+      return 0, math.huge
+   end
+
+   if str == "+" then
+      return 1, math.huge
+   end
+
+   if str == "?" then
+      return 0, 1
+   end
+
+   if str:match "^%d+%-%d+$" then
+      local min, max = str:match "^(%d+)%-(%d+)$"
+      return tonumber(min), tonumber(max)
+   end
+
+   if str:match "^%d+%+$" then
+      local min = str:match "^(%d+)%+$"
+      return tonumber(min), math.huge
+   end
+end
+
+local function boundaries(name)
+   return {name, function(self, value)
+      typecheck(name, {"number", "string"}, value)
+
+      local min, max = parse_boundaries(value)
+
+      if not min then
+         error(("bad property '%s'"):format(name))
+      end
+
+      self["_min" .. name], self["_max" .. name] = min, max
+   end}
+end
+
+local actions = {}
+
+local option_action = {"action", function(_, value)
+   typecheck("action", {"function", "string"}, value)
+
+   if type(value) == "string" and not actions[value] then
+      error(("unknown action '%s'"):format(value))
+   end
+end}
+
+local option_init = {"init", function(self)
+   self._has_init = true
+end}
+
+local option_default = {"default", function(self, value)
+   if type(value) ~= "string" then
+      self._init = value
+      self._has_init = true
+      return true
+   end
+end}
+
+local add_help = {"add_help", function(self, value)
+   typecheck("add_help", {"boolean", "string", "table"}, value)
+
+   if self._help_option_idx then
+      table.remove(self._options, self._help_option_idx)
+      self._help_option_idx = nil
+   end
+
+   if value then
+      local help = self:flag()
+         :description "Show this help message and exit."
+         :action(function()
+            print(self:get_help())
+            os.exit(0)
+         end)
+
+      if value ~= true then
+         help = help(value)
+      end
+
+      if not help._name then
+         help "-h" "--help"
+      end
+
+      self._help_option_idx = #self._options
+   end
+end}
+
+local Parser = class({
+   _arguments = {},
+   _options = {},
+   _commands = {},
+   _mutexes = {},
+   _groups = {},
+   _require_command = true,
+   _handle_options = true
+}, {
+   args = 3,
+   typechecked("name", "string"),
+   typechecked("description", "string"),
+   typechecked("epilog", "string"),
+   typechecked("usage", "string"),
+   typechecked("help", "string"),
+   typechecked("require_command", "boolean"),
+   typechecked("handle_options", "boolean"),
+   typechecked("action", "function"),
+   typechecked("command_target", "string"),
+   typechecked("help_vertical_space", "number"),
+   typechecked("usage_margin", "number"),
+   typechecked("usage_max_width", "number"),
+   typechecked("help_usage_margin", "number"),
+   typechecked("help_description_margin", "number"),
+   typechecked("help_max_width", "number"),
+   add_help
+})
+
+local Command = class({
+   _aliases = {},
+   _public_aliases = {}
+}, {
+   args = 3,
+   multiname,
+   typechecked("description", "string"),
+   typechecked("epilog", "string"),
+   multiname_hidden,
+   typechecked("summary", "string"),
+   typechecked("target", "string"),
+   typechecked("usage", "string"),
+   typechecked("help", "string"),
+   typechecked("require_command", "boolean"),
+   typechecked("handle_options", "boolean"),
+   typechecked("action", "function"),
+   typechecked("command_target", "string"),
+   typechecked("help_vertical_space", "number"),
+   typechecked("usage_margin", "number"),
+   typechecked("usage_max_width", "number"),
+   typechecked("help_usage_margin", "number"),
+   typechecked("help_description_margin", "number"),
+   typechecked("help_max_width", "number"),
+   typechecked("hidden", "boolean"),
+   add_help
+}, Parser)
+
+local Argument = class({
+   _minargs = 1,
+   _maxargs = 1,
+   _mincount = 1,
+   _maxcount = 1,
+   _defmode = "unused",
+   _show_default = true
+}, {
+   args = 5,
+   typechecked("name", "string"),
+   typechecked("description", "string"),
+   option_default,
+   typechecked("convert", "function", "table"),
+   boundaries("args"),
+   typechecked("target", "string"),
+   typechecked("defmode", "string"),
+   typechecked("show_default", "boolean"),
+   typechecked("argname", "string", "table"),
+   typechecked("choices", "table"),
+   typechecked("hidden", "boolean"),
+   option_action,
+   option_init
+})
+
+local Option = class({
+   _aliases = {},
+   _public_aliases = {},
+   _mincount = 0,
+   _overwrite = true
+}, {
+   args = 6,
+   multiname,
+   typechecked("description", "string"),
+   option_default,
+   typechecked("convert", "function", "table"),
+   boundaries("args"),
+   boundaries("count"),
+   multiname_hidden,
+   typechecked("target", "string"),
+   typechecked("defmode", "string"),
+   typechecked("show_default", "boolean"),
+   typechecked("overwrite", "boolean"),
+   typechecked("argname", "string", "table"),
+   typechecked("choices", "table"),
+   typechecked("hidden", "boolean"),
+   option_action,
+   option_init
+}, Argument)
+
+function Parser:_inherit_property(name, default)
+   local element = self
+
+   while true do
+      local value = element["_" .. name]
+
+      if value ~= nil then
+         return value
+      end
+
+      if not element._parent then
+         return default
+      end
+
+      element = element._parent
+   end
+end
+
+function Argument:_get_argument_list()
+   local buf = {}
+   local i = 1
+
+   while i <= math.min(self._minargs, 3) do
+      local argname = self:_get_argname(i)
+
+      if self._default and self._defmode:find "a" then
+         argname = "[" .. argname .. "]"
+      end
+
+      table.insert(buf, argname)
+      i = i+1
+   end
+
+   while i <= math.min(self._maxargs, 3) do
+      table.insert(buf, "[" .. self:_get_argname(i) .. "]")
+      i = i+1
+
+      if self._maxargs == math.huge then
+         break
+      end
+   end
+
+   if i < self._maxargs then
+      table.insert(buf, "...")
+   end
+
+   return buf
+end
+
+function Argument:_get_usage()
+   local usage = table.concat(self:_get_argument_list(), " ")
+
+   if self._default and self._defmode:find "u" then
+      if self._maxargs > 1 or (self._minargs == 1 and not self._defmode:find "a") then
+         usage = "[" .. usage .. "]"
+      end
+   end
+
+   return usage
+end
+
+function actions.store_true(result, target)
+   result[target] = true
+end
+
+function actions.store_false(result, target)
+   result[target] = false
+end
+
+function actions.store(result, target, argument)
+   result[target] = argument
+end
+
+function actions.count(result, target, _, overwrite)
+   if not overwrite then
+      result[target] = result[target] + 1
+   end
+end
+
+function actions.append(result, target, argument, overwrite)
+   result[target] = result[target] or {}
+   table.insert(result[target], argument)
+
+   if overwrite then
+      table.remove(result[target], 1)
+   end
+end
+
+function actions.concat(result, target, arguments, overwrite)
+   if overwrite then
+      error("'concat' action can't handle too many invocations")
+   end
+
+   result[target] = result[target] or {}
+
+   for _, argument in ipairs(arguments) do
+      table.insert(result[target], argument)
+   end
+end
+
+function Argument:_get_action()
+   local action, init
+
+   if self._maxcount == 1 then
+      if self._maxargs == 0 then
+         action, init = "store_true", nil
+      else
+         action, init = "store", nil
+      end
+   else
+      if self._maxargs == 0 then
+         action, init = "count", 0
+      else
+         action, init = "append", {}
+      end
+   end
+
+   if self._action then
+      action = self._action
+   end
+
+   if self._has_init then
+      init = self._init
+   end
+
+   if type(action) == "string" then
+      action = actions[action]
+   end
+
+   return action, init
+end
+
+-- Returns placeholder for `narg`-th argument.
+function Argument:_get_argname(narg)
+   local argname = self._argname or self:_get_default_argname()
+
+   if type(argname) == "table" then
+      return argname[narg]
+   else
+      return argname
+   end
+end
+
+function Argument:_get_choices_list()
+   return "{" .. table.concat(self._choices, ",") .. "}"
+end
+
+function Argument:_get_default_argname()
+   if self._choices then
+      return self:_get_choices_list()
+   else
+      return "<" .. self._name .. ">"
+   end
+end
+
+function Option:_get_default_argname()
+   if self._choices then
+      return self:_get_choices_list()
+   else
+      return "<" .. self:_get_default_target() .. ">"
+   end
+end
+
+-- Returns labels to be shown in the help message.
+function Argument:_get_label_lines()
+   if self._choices then
+      return {self:_get_choices_list()}
+   else
+      return {self._name}
+   end
+end
+
+function Option:_get_label_lines()
+   local argument_list = self:_get_argument_list()
+
+   if #argument_list == 0 then
+      -- Don't put aliases for simple flags like `-h` on different lines.
+      return {table.concat(self._public_aliases, ", ")}
+   end
+
+   local longest_alias_length = -1
+
+   for _, alias in ipairs(self._public_aliases) do
+      longest_alias_length = math.max(longest_alias_length, #alias)
+   end
+
+   local argument_list_repr = table.concat(argument_list, " ")
+   local lines = {}
+
+   for i, alias in ipairs(self._public_aliases) do
+      local line = (" "):rep(longest_alias_length - #alias) .. alias .. " " .. argument_list_repr
+
+      if i ~= #self._public_aliases then
+         line = line .. ","
+      end
+
+      table.insert(lines, line)
+   end
+
+   return lines
+end
+
+function Command:_get_label_lines()
+   return {table.concat(self._public_aliases, ", ")}
+end
+
+function Argument:_get_description()
+   if self._default and self._show_default then
+      if self._description then
+         return ("%s (default: %s)"):format(self._description, self._default)
+      else
+         return ("default: %s"):format(self._default)
+      end
+   else
+      return self._description or ""
+   end
+end
+
+function Command:_get_description()
+   return self._summary or self._description or ""
+end
+
+function Option:_get_usage()
+   local usage = self:_get_argument_list()
+   table.insert(usage, 1, self._name)
+   usage = table.concat(usage, " ")
+
+   if self._mincount == 0 or self._default then
+      usage = "[" .. usage .. "]"
+   end
+
+   return usage
+end
+
+function Argument:_get_default_target()
+   return self._name
+end
+
+function Option:_get_default_target()
+   local res
+
+   for _, alias in ipairs(self._public_aliases) do
+      if alias:sub(1, 1) == alias:sub(2, 2) then
+         res = alias:sub(3)
+         break
+      end
+   end
+
+   res = res or self._name:sub(2)
+   return (res:gsub("-", "_"))
+end
+
+function Option:_is_vararg()
+   return self._maxargs ~= self._minargs
+end
+
+function Parser:_get_fullname(exclude_root)
+   local parent = self._parent
+   if exclude_root and not parent then
+      return ""
+   end
+   local buf = {self._name}
+
+   while parent do
+      if not exclude_root or parent._parent then
+         table.insert(buf, 1, parent._name)
+      end
+      parent = parent._parent
+   end
+
+   return table.concat(buf, " ")
+end
+
+function Parser:_update_charset(charset)
+   charset = charset or {}
+
+   for _, command in ipairs(self._commands) do
+      command:_update_charset(charset)
+   end
+
+   for _, option in ipairs(self._options) do
+      for _, alias in ipairs(option._aliases) do
+         charset[alias:sub(1, 1)] = true
+      end
+   end
+
+   return charset
+end
+
+function Parser:argument(...)
+   local argument = Argument(...)
+   table.insert(self._arguments, argument)
+   return argument
+end
+
+function Parser:option(...)
+   local option = Option(...)
+   table.insert(self._options, option)
+   return option
+end
+
+function Parser:flag(...)
+   return self:option():args(0)(...)
+end
+
+function Parser:command(...)
+   local command = Command():add_help(true)(...)
+   command._parent = self
+   table.insert(self._commands, command)
+   return command
+end
+
+function Parser:mutex(...)
+   local elements = {...}
+
+   for i, element in ipairs(elements) do
+      local mt = getmetatable(element)
+      assert(mt == Option or mt == Argument, ("bad argument #%d to 'mutex' (Option or Argument expected)"):format(i))
+   end
+
+   table.insert(self._mutexes, elements)
+   return self
+end
+
+function Parser:group(name, ...)
+   assert(type(name) == "string", ("bad argument #1 to 'group' (string expected, got %s)"):format(type(name)))
+
+   local group = {name = name, ...}
+
+   for i, element in ipairs(group) do
+      local mt = getmetatable(element)
+      assert(mt == Option or mt == Argument or mt == Command,
+         ("bad argument #%d to 'group' (Option or Argument or Command expected)"):format(i + 1))
+   end
+
+   table.insert(self._groups, group)
+   return self
+end
+
+local usage_welcome = "Usage: "
+
+function Parser:get_usage()
+   if self._usage then
+      return self._usage
+   end
+
+   local usage_margin = self:_inherit_property("usage_margin", #usage_welcome)
+   local max_usage_width = self:_inherit_property("usage_max_width", 70)
+   local lines = {usage_welcome .. self:_get_fullname()}
+
+   local function add(s)
+      if #lines[#lines]+1+#s <= max_usage_width then
+         lines[#lines] = lines[#lines] .. " " .. s
+      else
+         lines[#lines+1] = (" "):rep(usage_margin) .. s
+      end
+   end
+
+   -- Normally options are before positional arguments in usage messages.
+   -- However, vararg options should be after, because they can't be reliable used
+   -- before a positional argument.
+   -- Mutexes come into play, too, and are shown as soon as possible.
+   -- Overall, output usages in the following order:
+   -- 1. Mutexes that don't have positional arguments or vararg options.
+   -- 2. Options that are not in any mutexes and are not vararg.
+   -- 3. Positional arguments - on their own or as a part of a mutex.
+   -- 4. Remaining mutexes.
+   -- 5. Remaining options.
+
+   local elements_in_mutexes = {}
+   local added_elements = {}
+   local added_mutexes = {}
+   local argument_to_mutexes = {}
+
+   local function add_mutex(mutex, main_argument)
+      if added_mutexes[mutex] then
+         return
+      end
+
+      added_mutexes[mutex] = true
+      local buf = {}
+
+      for _, element in ipairs(mutex) do
+         if not element._hidden and not added_elements[element] then
+            if getmetatable(element) == Option or element == main_argument then
+               table.insert(buf, element:_get_usage())
+               added_elements[element] = true
+            end
+         end
+      end
+
+      if #buf == 1 then
+         add(buf[1])
+      elseif #buf > 1 then
+         add("(" .. table.concat(buf, " | ") .. ")")
+      end
+   end
+
+   local function add_element(element)
+      if not element._hidden and not added_elements[element] then
+         add(element:_get_usage())
+         added_elements[element] = true
+      end
+   end
+
+   for _, mutex in ipairs(self._mutexes) do
+      local is_vararg = false
+      local has_argument = false
+
+      for _, element in ipairs(mutex) do
+         if getmetatable(element) == Option then
+            if element:_is_vararg() then
+               is_vararg = true
+            end
+         else
+            has_argument = true
+            argument_to_mutexes[element] = argument_to_mutexes[element] or {}
+            table.insert(argument_to_mutexes[element], mutex)
+         end
+
+         elements_in_mutexes[element] = true
+      end
+
+      if not is_vararg and not has_argument then
+         add_mutex(mutex)
+      end
+   end
+
+   for _, option in ipairs(self._options) do
+      if not elements_in_mutexes[option] and not option:_is_vararg() then
+         add_element(option)
+      end
+   end
+
+   -- Add usages for positional arguments, together with one mutex containing them, if they are in a mutex.
+   for _, argument in ipairs(self._arguments) do
+      -- Pick a mutex as a part of which to show this argument, take the first one that's still available.
+      local mutex
+
+      if elements_in_mutexes[argument] then
+         for _, argument_mutex in ipairs(argument_to_mutexes[argument]) do
+            if not added_mutexes[argument_mutex] then
+               mutex = argument_mutex
+            end
+         end
+      end
+
+      if mutex then
+         add_mutex(mutex, argument)
+      else
+         add_element(argument)
+      end
+   end
+
+   for _, mutex in ipairs(self._mutexes) do
+      add_mutex(mutex)
+   end
+
+   for _, option in ipairs(self._options) do
+      add_element(option)
+   end
+
+   if #self._commands > 0 then
+      if self._require_command then
+         add("<command>")
+      else
+         add("[<command>]")
+      end
+
+      add("...")
+   end
+
+   return table.concat(lines, "\n")
+end
+
+local function split_lines(s)
+   if s == "" then
+      return {}
+   end
+
+   local lines = {}
+
+   if s:sub(-1) ~= "\n" then
+      s = s .. "\n"
+   end
+
+   for line in s:gmatch("([^\n]*)\n") do
+      table.insert(lines, line)
+   end
+
+   return lines
+end
+
+local function autowrap_line(line, max_length)
+   -- Algorithm for splitting lines is simple and greedy.
+   local result_lines = {}
+
+   -- Preserve original indentation of the line, put this at the beginning of each result line.
+   -- If the first word looks like a list marker ('*', '+', or '-'), add spaces so that starts
+   -- of the second and the following lines vertically align with the start of the second word.
+   local indentation = line:match("^ *")
+
+   if line:find("^ *[%*%+%-]") then
+      indentation = indentation .. " " .. line:match("^ *[%*%+%-]( *)")
+   end
+
+   -- Parts of the last line being assembled.
+   local line_parts = {}
+
+   -- Length of the current line.
+   local line_length = 0
+
+   -- Index of the next character to consider.
+   local index = 1
+
+   while true do
+      local word_start, word_finish, word = line:find("([^ ]+)", index)
+
+      if not word_start then
+         -- Ignore trailing spaces, if any.
+         break
+      end
+
+      local preceding_spaces = line:sub(index, word_start - 1)
+      index = word_finish + 1
+
+      if (#line_parts == 0) or (line_length + #preceding_spaces + #word <= max_length) then
+         -- Either this is the very first word or it fits as an addition to the current line, add it.
+         table.insert(line_parts, preceding_spaces) -- For the very first word this adds the indentation.
+         table.insert(line_parts, word)
+         line_length = line_length + #preceding_spaces + #word
+      else
+         -- Does not fit, finish current line and put the word into a new one.
+         table.insert(result_lines, table.concat(line_parts))
+         line_parts = {indentation, word}
+         line_length = #indentation + #word
+      end
+   end
+
+   if #line_parts > 0 then
+      table.insert(result_lines, table.concat(line_parts))
+   end
+
+   if #result_lines == 0 then
+      -- Preserve empty lines.
+      result_lines[1] = ""
+   end
+
+   return result_lines
+end
+
+-- Automatically wraps lines within given array,
+-- attempting to limit line length to `max_length`.
+-- Existing line splits are preserved.
+local function autowrap(lines, max_length)
+   local result_lines = {}
+
+   for _, line in ipairs(lines) do
+      local autowrapped_lines = autowrap_line(line, max_length)
+
+      for _, autowrapped_line in ipairs(autowrapped_lines) do
+         table.insert(result_lines, autowrapped_line)
+      end
+   end
+
+   return result_lines
+end
+
+function Parser:_get_element_help(element)
+   local label_lines = element:_get_label_lines()
+   local description_lines = split_lines(element:_get_description())
+
+   local result_lines = {}
+
+   -- All label lines should have the same length (except the last one, it has no comma).
+   -- If too long, start description after all the label lines.
+   -- Otherwise, combine label and description lines.
+
+   local usage_margin_len = self:_inherit_property("help_usage_margin", 3)
+   local usage_margin = (" "):rep(usage_margin_len)
+   local description_margin_len = self:_inherit_property("help_description_margin", 25)
+   local description_margin = (" "):rep(description_margin_len)
+
+   local help_max_width = self:_inherit_property("help_max_width")
+
+   if help_max_width then
+      local description_max_width = math.max(help_max_width - description_margin_len, 10)
+      description_lines = autowrap(description_lines, description_max_width)
+   end
+
+   if #label_lines[1] >= (description_margin_len - usage_margin_len) then
+      for _, label_line in ipairs(label_lines) do
+         table.insert(result_lines, usage_margin .. label_line)
+      end
+
+      for _, description_line in ipairs(description_lines) do
+         table.insert(result_lines, description_margin .. description_line)
+      end
+   else
+      for i = 1, math.max(#label_lines, #description_lines) do
+         local label_line = label_lines[i]
+         local description_line = description_lines[i]
+
+         local line = ""
+
+         if label_line then
+            line = usage_margin .. label_line
+         end
+
+         if description_line and description_line ~= "" then
+            line = line .. (" "):rep(description_margin_len - #line) .. description_line
+         end
+
+         table.insert(result_lines, line)
+      end
+   end
+
+   return table.concat(result_lines, "\n")
+end
+
+local function get_group_types(group)
+   local types = {}
+
+   for _, element in ipairs(group) do
+      types[getmetatable(element)] = true
+   end
+
+   return types
+end
+
+function Parser:_add_group_help(blocks, added_elements, label, elements)
+   local buf = {label}
+
+   for _, element in ipairs(elements) do
+      if not element._hidden and not added_elements[element] then
+         added_elements[element] = true
+         table.insert(buf, self:_get_element_help(element))
+      end
+   end
+
+   if #buf > 1 then
+      table.insert(blocks, table.concat(buf, ("\n"):rep(self:_inherit_property("help_vertical_space", 0) + 1)))
+   end
+end
+
+function Parser:get_help()
+   if self._help then
+      return self._help
+   end
+
+   local blocks = {self:get_usage()}
+
+   local help_max_width = self:_inherit_property("help_max_width")
+
+   if self._description then
+      local description = self._description
+
+      if help_max_width then
+         description = table.concat(autowrap(split_lines(description), help_max_width), "\n")
+      end
+
+      table.insert(blocks, description)
+   end
+
+   -- 1. Put groups containing arguments first, then other arguments.
+   -- 2. Put remaining groups containing options, then other options.
+   -- 3. Put remaining groups containing commands, then other commands.
+   -- Assume that an element can't be in several groups.
+   local groups_by_type = {
+      [Argument] = {},
+      [Option] = {},
+      [Command] = {}
+   }
+
+   for _, group in ipairs(self._groups) do
+      local group_types = get_group_types(group)
+
+      for _, mt in ipairs({Argument, Option, Command}) do
+         if group_types[mt] then
+            table.insert(groups_by_type[mt], group)
+            break
+         end
+      end
+   end
+
+   local default_groups = {
+      {name = "Arguments", type = Argument, elements = self._arguments},
+      {name = "Options", type = Option, elements = self._options},
+      {name = "Commands", type = Command, elements = self._commands}
+   }
+
+   local added_elements = {}
+
+   for _, default_group in ipairs(default_groups) do
+      local type_groups = groups_by_type[default_group.type]
+
+      for _, group in ipairs(type_groups) do
+         self:_add_group_help(blocks, added_elements, group.name .. ":", group)
+      end
+
+      local default_label = default_group.name .. ":"
+
+      if #type_groups > 0 then
+         default_label = "Other " .. default_label:gsub("^.", string.lower)
+      end
+
+      self:_add_group_help(blocks, added_elements, default_label, default_group.elements)
+   end
+
+   if self._epilog then
+      local epilog = self._epilog
+
+      if help_max_width then
+         epilog = table.concat(autowrap(split_lines(epilog), help_max_width), "\n")
+      end
+
+      table.insert(blocks, epilog)
+   end
+
+   return table.concat(blocks, "\n\n")
+end
+
+function Parser:add_help_command(value)
+   if value then
+      assert(type(value) == "string" or type(value) == "table",
+         ("bad argument #1 to 'add_help_command' (string or table expected, got %s)"):format(type(value)))
+   end
+
+   local help = self:command()
+      :description "Show help for commands."
+   help:argument "command"
+      :description "The command to show help for."
+      :args "?"
+      :action(function(_, _, cmd)
+         if not cmd then
+            print(self:get_help())
+            os.exit(0)
+         else
+            for _, command in ipairs(self._commands) do
+               for _, alias in ipairs(command._aliases) do
+                  if alias == cmd then
+                     print(command:get_help())
+                     os.exit(0)
+                  end
+               end
+            end
+         end
+         help:error(("unknown command '%s'"):format(cmd))
+      end)
+
+   if value then
+      help = help(value)
+   end
+
+   if not help._name then
+      help "help"
+   end
+
+   help._is_help_command = true
+   return self
+end
+
+function Parser:_is_shell_safe()
+   if self._basename then
+      if self._basename:find("[^%w_%-%+%.]") then
+         return false
+      end
+   else
+      for _, alias in ipairs(self._aliases) do
+         if alias:find("[^%w_%-%+%.]") then
+            return false
+         end
+      end
+   end
+   for _, option in ipairs(self._options) do
+      for _, alias in ipairs(option._aliases) do
+         if alias:find("[^%w_%-%+%.]") then
+            return false
+         end
+      end
+      if option._choices then
+         for _, choice in ipairs(option._choices) do
+            if choice:find("[%s'\"]") then
+               return false
+            end
+         end
+      end
+   end
+   for _, argument in ipairs(self._arguments) do
+      if argument._choices then
+         for _, choice in ipairs(argument._choices) do
+            if choice:find("[%s'\"]") then
+               return false
+            end
+         end
+      end
+   end
+   for _, command in ipairs(self._commands) do
+      if not command:_is_shell_safe() then
+         return false
+      end
+   end
+   return true
+end
+
+function Parser:add_complete(value)
+   if value then
+      assert(type(value) == "string" or type(value) == "table",
+         ("bad argument #1 to 'add_complete' (string or table expected, got %s)"):format(type(value)))
+   end
+
+   local complete = self:option()
+      :description "Output a shell completion script for the specified shell."
+      :args(1)
+      :choices {"bash", "zsh", "fish"}
+      :action(function(_, _, shell)
+         io.write(self["get_" .. shell .. "_complete"](self))
+         os.exit(0)
+      end)
+
+   if value then
+      complete = complete(value)
+   end
+
+   if not complete._name then
+      complete "--completion"
+   end
+
+   return self
+end
+
+function Parser:add_complete_command(value)
+   if value then
+      assert(type(value) == "string" or type(value) == "table",
+         ("bad argument #1 to 'add_complete_command' (string or table expected, got %s)"):format(type(value)))
+   end
+
+   local complete = self:command()
+      :description "Output a shell completion script."
+   complete:argument "shell"
+      :description "The shell to output a completion script for."
+      :choices {"bash", "zsh", "fish"}
+      :action(function(_, _, shell)
+         io.write(self["get_" .. shell .. "_complete"](self))
+         os.exit(0)
+      end)
+
+   if value then
+      complete = complete(value)
+   end
+
+   if not complete._name then
+      complete "completion"
+   end
+
+   return self
+end
+
+local function base_name(pathname)
+   return pathname:gsub("[/\\]*$", ""):match(".*[/\\]([^/\\]*)") or pathname
+end
+
+local function get_short_description(element)
+   local short = element:_get_description():match("^(.-)%.%s")
+   return short or element:_get_description():match("^(.-)%.?$")
+end
+
+function Parser:_get_options()
+   local options = {}
+   for _, option in ipairs(self._options) do
+      for _, alias in ipairs(option._aliases) do
+         table.insert(options, alias)
+      end
+   end
+   return table.concat(options, " ")
+end
+
+function Parser:_get_commands()
+   local commands = {}
+   for _, command in ipairs(self._commands) do
+      for _, alias in ipairs(command._aliases) do
+         table.insert(commands, alias)
+      end
+   end
+   return table.concat(commands, " ")
+end
+
+function Parser:_bash_option_args(buf, indent)
+   local opts = {}
+   for _, option in ipairs(self._options) do
+      if option._choices or option._minargs > 0 then
+         local compreply
+         if option._choices then
+            compreply = 'COMPREPLY=($(compgen -W "' .. table.concat(option._choices, " ") .. '" -- "$cur"))'
+         else
+            compreply = 'COMPREPLY=($(compgen -f -- "$cur"))'
+         end
+         table.insert(opts, (" "):rep(indent + 4) .. table.concat(option._aliases, "|") .. ")")
+         table.insert(opts, (" "):rep(indent + 8) .. compreply)
+         table.insert(opts, (" "):rep(indent + 8) .. "return 0")
+         table.insert(opts, (" "):rep(indent + 8) .. ";;")
+      end
+   end
+
+   if #opts > 0 then
+      table.insert(buf, (" "):rep(indent) .. 'case "$prev" in')
+      table.insert(buf, table.concat(opts, "\n"))
+      table.insert(buf, (" "):rep(indent) .. "esac\n")
+   end
+end
+
+function Parser:_bash_get_cmd(buf, indent)
+   if #self._commands == 0 then
+      return
+   end
+
+   table.insert(buf, (" "):rep(indent) .. 'args=("${args[@]:1}")')
+   table.insert(buf, (" "):rep(indent) .. 'for arg in "${args[@]}"; do')
+   table.insert(buf, (" "):rep(indent + 4) .. 'case "$arg" in')
+
+   for _, command in ipairs(self._commands) do
+      table.insert(buf, (" "):rep(indent + 8) .. table.concat(command._aliases, "|") .. ")")
+      if self._parent then
+         table.insert(buf, (" "):rep(indent + 12) .. 'cmd="$cmd ' .. command._name .. '"')
+      else
+         table.insert(buf, (" "):rep(indent + 12) .. 'cmd="' .. command._name .. '"')
+      end
+      table.insert(buf, (" "):rep(indent + 12) .. 'opts="$opts ' .. command:_get_options() .. '"')
+      command:_bash_get_cmd(buf, indent + 12)
+      table.insert(buf, (" "):rep(indent + 12) .. "break")
+      table.insert(buf, (" "):rep(indent + 12) .. ";;")
+   end
+
+   table.insert(buf, (" "):rep(indent + 4) .. "esac")
+   table.insert(buf, (" "):rep(indent) .. "done")
+end
+
+function Parser:_bash_cmd_completions(buf)
+   local cmd_buf = {}
+   if self._parent then
+      self:_bash_option_args(cmd_buf, 12)
+   end
+   if #self._commands > 0 then
+      table.insert(cmd_buf, (" "):rep(12) .. 'COMPREPLY=($(compgen -W "' .. self:_get_commands() .. '" -- "$cur"))')
+   elseif self._is_help_command then
+      table.insert(cmd_buf, (" "):rep(12)
+         .. 'COMPREPLY=($(compgen -W "'
+         .. self._parent:_get_commands()
+         .. '" -- "$cur"))')
+   end
+   if #cmd_buf > 0 then
+      table.insert(buf, (" "):rep(8) .. "'" .. self:_get_fullname(true) .. "')")
+      table.insert(buf, table.concat(cmd_buf, "\n"))
+      table.insert(buf, (" "):rep(12) .. ";;")
+   end
+
+   for _, command in ipairs(self._commands) do
+      command:_bash_cmd_completions(buf)
+   end
+end
+
+function Parser:get_bash_complete()
+   self._basename = base_name(self._name)
+   assert(self:_is_shell_safe())
+   local buf = {([[
+_%s() {
+    local IFS=$' \t\n'
+    local args cur prev cmd opts arg
+    args=("${COMP_WORDS[@]}")
+    cur="${COMP_WORDS[COMP_CWORD]}"
+    prev="${COMP_WORDS[COMP_CWORD-1]}"
+    opts="%s"
+]]):format(self._basename, self:_get_options())}
+
+   self:_bash_option_args(buf, 4)
+   self:_bash_get_cmd(buf, 4)
+   if #self._commands > 0 then
+      table.insert(buf, "")
+      table.insert(buf, (" "):rep(4) .. 'case "$cmd" in')
+      self:_bash_cmd_completions(buf)
+      table.insert(buf, (" "):rep(4) .. "esac\n")
+   end
+
+   table.insert(buf, ([=[
+    if [[ "$cur" = -* ]]; then
+        COMPREPLY=($(compgen -W "$opts" -- "$cur"))
+    fi
+}
+
+complete -F _%s -o bashdefault -o default %s
+]=]):format(self._basename, self._basename))
+
+   return table.concat(buf, "\n")
+end
+
+function Parser:_zsh_arguments(buf, cmd_name, indent)
+   if self._parent then
+      table.insert(buf, (" "):rep(indent) .. "options=(")
+      table.insert(buf, (" "):rep(indent + 2) .. "$options")
+   else
+      table.insert(buf, (" "):rep(indent) .. "local -a options=(")
+   end
+
+   for _, option in ipairs(self._options) do
+      local line = {}
+      if #option._aliases > 1 then
+         if option._maxcount > 1 then
+            table.insert(line, '"*"')
+         end
+         table.insert(line, "{" .. table.concat(option._aliases, ",") .. '}"')
+      else
+         table.insert(line, '"')
+         if option._maxcount > 1 then
+            table.insert(line, "*")
+         end
+         table.insert(line, option._name)
+      end
+      if option._description then
+         local description = get_short_description(option):gsub('["%]:`$]', "\\%0")
+         table.insert(line, "[" .. description .. "]")
+      end
+      if option._maxargs == math.huge then
+         table.insert(line, ":*")
+      end
+      if option._choices then
+         table.insert(line, ": :(" .. table.concat(option._choices, " ") .. ")")
+      elseif option._maxargs > 0 then
+         table.insert(line, ": :_files")
+      end
+      table.insert(line, '"')
+      table.insert(buf, (" "):rep(indent + 2) .. table.concat(line))
+   end
+
+   table.insert(buf, (" "):rep(indent) .. ")")
+   table.insert(buf, (" "):rep(indent) .. "_arguments -s -S \\")
+   table.insert(buf, (" "):rep(indent + 2) .. "$options \\")
+
+   if self._is_help_command then
+      table.insert(buf, (" "):rep(indent + 2) .. '": :(' .. self._parent:_get_commands() .. ')" \\')
+   else
+      for _, argument in ipairs(self._arguments) do
+         local spec
+         if argument._choices then
+            spec = ": :(" .. table.concat(argument._choices, " ") .. ")"
+         else
+            spec = ": :_files"
+         end
+         if argument._maxargs == math.huge then
+            table.insert(buf, (" "):rep(indent + 2) .. '"*' .. spec .. '" \\')
+            break
+         end
+         for _ = 1, argument._maxargs do
+            table.insert(buf, (" "):rep(indent + 2) .. '"' .. spec .. '" \\')
+         end
+      end
+
+      if #self._commands > 0 then
+         table.insert(buf, (" "):rep(indent + 2) .. '": :_' .. cmd_name .. '_cmds" \\')
+         table.insert(buf, (" "):rep(indent + 2) .. '"*:: :->args" \\')
+      end
+   end
+
+   table.insert(buf, (" "):rep(indent + 2) .. "&& return 0")
+end
+
+function Parser:_zsh_cmds(buf, cmd_name)
+   table.insert(buf, "\n_" .. cmd_name .. "_cmds() {")
+   table.insert(buf, "  local -a commands=(")
+
+   for _, command in ipairs(self._commands) do
+      local line = {}
+      if #command._aliases > 1 then
+         table.insert(line, "{" .. table.concat(command._aliases, ",") .. '}"')
+      else
+         table.insert(line, '"' .. command._name)
+      end
+      if command._description then
+         table.insert(line, ":" .. get_short_description(command):gsub('["`$]', "\\%0"))
+      end
+      table.insert(buf, "    " .. table.concat(line) .. '"')
+   end
+
+   table.insert(buf, '  )\n  _describe "command" commands\n}')
+end
+
+function Parser:_zsh_complete_help(buf, cmds_buf, cmd_name, indent)
+   if #self._commands == 0 then
+      return
+   end
+
+   self:_zsh_cmds(cmds_buf, cmd_name)
+   table.insert(buf, "\n" .. (" "):rep(indent) .. "case $words[1] in")
+
+   for _, command in ipairs(self._commands) do
+      local name = cmd_name .. "_" .. command._name
+      table.insert(buf, (" "):rep(indent + 2) .. table.concat(command._aliases, "|") .. ")")
+      command:_zsh_arguments(buf, name, indent + 4)
+      command:_zsh_complete_help(buf, cmds_buf, name, indent + 4)
+      table.insert(buf, (" "):rep(indent + 4) .. ";;\n")
+   end
+
+   table.insert(buf, (" "):rep(indent) .. "esac")
+end
+
+function Parser:get_zsh_complete()
+   self._basename = base_name(self._name)
+   assert(self:_is_shell_safe())
+   local buf = {("#compdef %s\n"):format(self._basename)}
+   local cmds_buf = {}
+   table.insert(buf, "_" .. self._basename .. "() {")
+   if #self._commands > 0 then
+      table.insert(buf, "  local context state state_descr line")
+      table.insert(buf, "  typeset -A opt_args\n")
+   end
+   self:_zsh_arguments(buf, self._basename, 2)
+   self:_zsh_complete_help(buf, cmds_buf, self._basename, 2)
+   table.insert(buf, "\n  return 1")
+   table.insert(buf, "}")
+
+   local result = table.concat(buf, "\n")
+   if #cmds_buf > 0 then
+      result = result .. "\n" .. table.concat(cmds_buf, "\n")
+   end
+   return result .. "\n\n_" .. self._basename .. "\n"
+end
+
+local function fish_escape(string)
+   return string:gsub("[\\']", "\\%0")
+end
+
+function Parser:_fish_get_cmd(buf, indent)
+   if #self._commands == 0 then
+      return
+   end
+
+   table.insert(buf, (" "):rep(indent) .. "set -e cmdline[1]")
+   table.insert(buf, (" "):rep(indent) .. "for arg in $cmdline")
+   table.insert(buf, (" "):rep(indent + 4) .. "switch $arg")
+
+   for _, command in ipairs(self._commands) do
+      table.insert(buf, (" "):rep(indent + 8) .. "case " .. table.concat(command._aliases, " "))
+      table.insert(buf, (" "):rep(indent + 12) .. "set cmd $cmd " .. command._name)
+      command:_fish_get_cmd(buf, indent + 12)
+      table.insert(buf, (" "):rep(indent + 12) .. "break")
+   end
+
+   table.insert(buf, (" "):rep(indent + 4) .. "end")
+   table.insert(buf, (" "):rep(indent) .. "end")
+end
+
+function Parser:_fish_complete_help(buf, basename)
+   local prefix = "complete -c " .. basename
+   table.insert(buf, "")
+
+   for _, command in ipairs(self._commands) do
+      local aliases = table.concat(command._aliases, " ")
+      local line
+      if self._parent then
+         line = ("%s -n '__fish_%s_using_command %s' -xa '%s'")
+            :format(prefix, basename, self:_get_fullname(true), aliases)
+      else
+         line = ("%s -n '__fish_%s_using_command' -xa '%s'"):format(prefix, basename, aliases)
+      end
+      if command._description then
+         line = ("%s -d '%s'"):format(line, fish_escape(get_short_description(command)))
+      end
+      table.insert(buf, line)
+   end
+
+   if self._is_help_command then
+      local line = ("%s -n '__fish_%s_using_command %s' -xa '%s'")
+         :format(prefix, basename, self:_get_fullname(true), self._parent:_get_commands())
+      table.insert(buf, line)
+   end
+
+   for _, option in ipairs(self._options) do
+      local parts = {prefix}
+
+      if self._parent then
+         table.insert(parts, "-n '__fish_" .. basename .. "_seen_command " .. self:_get_fullname(true) .. "'")
+      end
+
+      for _, alias in ipairs(option._aliases) do
+         if alias:match("^%-.$") then
+            table.insert(parts, "-s " .. alias:sub(2))
+         elseif alias:match("^%-%-.+") then
+            table.insert(parts, "-l " .. alias:sub(3))
+         end
+      end
+
+      if option._choices then
+         table.insert(parts, "-xa '" .. table.concat(option._choices, " ") .. "'")
+      elseif option._minargs > 0 then
+         table.insert(parts, "-r")
+      end
+
+      if option._description then
+         table.insert(parts, "-d '" .. fish_escape(get_short_description(option)) .. "'")
+      end
+
+      table.insert(buf, table.concat(parts, " "))
+   end
+
+   for _, command in ipairs(self._commands) do
+      command:_fish_complete_help(buf, basename)
+   end
+end
+
+function Parser:get_fish_complete()
+   self._basename = base_name(self._name)
+   assert(self:_is_shell_safe())
+   local buf = {}
+
+   if #self._commands > 0 then
+      table.insert(buf, ([[
+function __fish_%s_print_command
+    set -l cmdline (commandline -poc)
+    set -l cmd]]):format(self._basename))
+      self:_fish_get_cmd(buf, 4)
+      table.insert(buf, ([[
+    echo "$cmd"
+end
+
+function __fish_%s_using_command
+    test (__fish_%s_print_command) = "$argv"
+    and return 0
+    or return 1
+end
+
+function __fish_%s_seen_command
+    string match -q "$argv*" (__fish_%s_print_command)
+    and return 0
+    or return 1
+end]]):format(self._basename, self._basename, self._basename, self._basename))
+   end
+
+   self:_fish_complete_help(buf, self._basename)
+   return table.concat(buf, "\n") .. "\n"
+end
+
+local function get_tip(context, wrong_name)
+   local context_pool = {}
+   local possible_name
+   local possible_names = {}
+
+   for name in pairs(context) do
+      if type(name) == "string" then
+         for i = 1, #name do
+            possible_name = name:sub(1, i - 1) .. name:sub(i + 1)
+
+            if not context_pool[possible_name] then
+               context_pool[possible_name] = {}
+            end
+
+            table.insert(context_pool[possible_name], name)
+         end
+      end
+   end
+
+   for i = 1, #wrong_name + 1 do
+      possible_name = wrong_name:sub(1, i - 1) .. wrong_name:sub(i + 1)
+
+      if context[possible_name] then
+         possible_names[possible_name] = true
+      elseif context_pool[possible_name] then
+         for _, name in ipairs(context_pool[possible_name]) do
+            possible_names[name] = true
+         end
+      end
+   end
+
+   local first = next(possible_names)
+
+   if first then
+      if next(possible_names, first) then
+         local possible_names_arr = {}
+
+         for name in pairs(possible_names) do
+            table.insert(possible_names_arr, "'" .. name .. "'")
+         end
+
+         table.sort(possible_names_arr)
+         return "\nDid you mean one of these: " .. table.concat(possible_names_arr, " ") .. "?"
+      else
+         return "\nDid you mean '" .. first .. "'?"
+      end
+   else
+      return ""
+   end
+end
+
+local ElementState = class({
+   invocations = 0
+})
+
+function ElementState:__call(state, element)
+   self.state = state
+   self.result = state.result
+   self.element = element
+   self.target = element._target or element:_get_default_target()
+   self.action, self.result[self.target] = element:_get_action()
+   return self
+end
+
+function ElementState:error(fmt, ...)
+   self.state:error(fmt, ...)
+end
+
+function ElementState:convert(argument, index)
+   local converter = self.element._convert
+
+   if converter then
+      local ok, err
+
+      if type(converter) == "function" then
+         ok, err = converter(argument)
+      elseif type(converter[index]) == "function" then
+         ok, err = converter[index](argument)
+      else
+         ok = converter[argument]
+      end
+
+      if ok == nil then
+         self:error(err and "%s" or "malformed argument '%s'", err or argument)
+      end
+
+      argument = ok
+   end
+
+   return argument
+end
+
+function ElementState:default(mode)
+   return self.element._defmode:find(mode) and self.element._default
+end
+
+local function bound(noun, min, max, is_max)
+   local res = ""
+
+   if min ~= max then
+      res = "at " .. (is_max and "most" or "least") .. " "
+   end
+
+   local number = is_max and max or min
+   return res .. tostring(number) .. " " .. noun ..  (number == 1 and "" or "s")
+end
+
+function ElementState:set_name(alias)
+   self.name = ("%s '%s'"):format(alias and "option" or "argument", alias or self.element._name)
+end
+
+function ElementState:invoke()
+   self.open = true
+   self.overwrite = false
+
+   if self.invocations >= self.element._maxcount then
+      if self.element._overwrite then
+         self.overwrite = true
+      else
+         local num_times_repr = bound("time", self.element._mincount, self.element._maxcount, true)
+         self:error("%s must be used %s", self.name, num_times_repr)
+      end
+   else
+      self.invocations = self.invocations + 1
+   end
+
+   self.args = {}
+
+   if self.element._maxargs <= 0 then
+      self:close()
+   end
+
+   return self.open
+end
+
+function ElementState:check_choices(argument)
+   if self.element._choices then
+      for _, choice in ipairs(self.element._choices) do
+         if argument == choice then
+            return
+         end
+      end
+      local choices_list = "'" .. table.concat(self.element._choices, "', '") .. "'"
+      local is_option = getmetatable(self.element) == Option
+      self:error("%s%s must be one of %s", is_option and "argument for " or "", self.name, choices_list)
+   end
+end
+
+function ElementState:pass(argument)
+   self:check_choices(argument)
+   argument = self:convert(argument, #self.args + 1)
+   table.insert(self.args, argument)
+
+   if #self.args >= self.element._maxargs then
+      self:close()
+   end
+
+   return self.open
+end
+
+function ElementState:complete_invocation()
+   while #self.args < self.element._minargs do
+      self:pass(self.element._default)
+   end
+end
+
+function ElementState:close()
+   if self.open then
+      self.open = false
+
+      if #self.args < self.element._minargs then
+         if self:default("a") then
+            self:complete_invocation()
+         else
+            if #self.args == 0 then
+               if getmetatable(self.element) == Argument then
+                  self:error("missing %s", self.name)
+               elseif self.element._maxargs == 1 then
+                  self:error("%s requires an argument", self.name)
+               end
+            end
+
+            self:error("%s requires %s", self.name, bound("argument", self.element._minargs, self.element._maxargs))
+         end
+      end
+
+      local args
+
+      if self.element._maxargs == 0 then
+         args = self.args[1]
+      elseif self.element._maxargs == 1 then
+         if self.element._minargs == 0 and self.element._mincount ~= self.element._maxcount then
+            args = self.args
+         else
+            args = self.args[1]
+         end
+      else
+         args = self.args
+      end
+
+      self.action(self.result, self.target, args, self.overwrite)
+   end
+end
+
+local ParseState = class({
+   result = {},
+   options = {},
+   arguments = {},
+   argument_i = 1,
+   element_to_mutexes = {},
+   mutex_to_element_state = {},
+   command_actions = {}
+})
+
+function ParseState:__call(parser, error_handler)
+   self.parser = parser
+   self.error_handler = error_handler
+   self.charset = parser:_update_charset()
+   self:switch(parser)
+   return self
+end
+
+function ParseState:error(fmt, ...)
+   self.error_handler(self.parser, fmt:format(...))
+end
+
+function ParseState:switch(parser)
+   self.parser = parser
+
+   if parser._action then
+      table.insert(self.command_actions, {action = parser._action, name = parser._name})
+   end
+
+   for _, option in ipairs(parser._options) do
+      option = ElementState(self, option)
+      table.insert(self.options, option)
+
+      for _, alias in ipairs(option.element._aliases) do
+         self.options[alias] = option
+      end
+   end
+
+   for _, mutex in ipairs(parser._mutexes) do
+      for _, element in ipairs(mutex) do
+         if not self.element_to_mutexes[element] then
+            self.element_to_mutexes[element] = {}
+         end
+
+         table.insert(self.element_to_mutexes[element], mutex)
+      end
+   end
+
+   for _, argument in ipairs(parser._arguments) do
+      argument = ElementState(self, argument)
+      table.insert(self.arguments, argument)
+      argument:set_name()
+      argument:invoke()
+   end
+
+   self.handle_options = parser._handle_options
+   self.argument = self.arguments[self.argument_i]
+   self.commands = parser._commands
+
+   for _, command in ipairs(self.commands) do
+      for _, alias in ipairs(command._aliases) do
+         self.commands[alias] = command
+      end
+   end
+end
+
+function ParseState:get_option(name)
+   local option = self.options[name]
+
+   if not option then
+      self:error("unknown option '%s'%s", name, get_tip(self.options, name))
+   else
+      return option
+   end
+end
+
+function ParseState:get_command(name)
+   local command = self.commands[name]
+
+   if not command then
+      if #self.commands > 0 then
+         self:error("unknown command '%s'%s", name, get_tip(self.commands, name))
+      else
+         self:error("too many arguments")
+      end
+   else
+      return command
+   end
+end
+
+function ParseState:check_mutexes(element_state)
+   if self.element_to_mutexes[element_state.element] then
+      for _, mutex in ipairs(self.element_to_mutexes[element_state.element]) do
+         local used_element_state = self.mutex_to_element_state[mutex]
+
+         if used_element_state and used_element_state ~= element_state then
+            self:error("%s can not be used together with %s", element_state.name, used_element_state.name)
+         else
+            self.mutex_to_element_state[mutex] = element_state
+         end
+      end
+   end
+end
+
+function ParseState:invoke(option, name)
+   self:close()
+   option:set_name(name)
+   self:check_mutexes(option, name)
+
+   if option:invoke() then
+      self.option = option
+   end
+end
+
+function ParseState:pass(arg)
+   if self.option then
+      if not self.option:pass(arg) then
+         self.option = nil
+      end
+   elseif self.argument then
+      self:check_mutexes(self.argument)
+
+      if not self.argument:pass(arg) then
+         self.argument_i = self.argument_i + 1
+         self.argument = self.arguments[self.argument_i]
+      end
+   else
+      local command = self:get_command(arg)
+      self.result[command._target or command._name] = true
+
+      if self.parser._command_target then
+         self.result[self.parser._command_target] = command._name
+      end
+
+      self:switch(command)
+   end
+end
+
+function ParseState:close()
+   if self.option then
+      self.option:close()
+      self.option = nil
+   end
+end
+
+function ParseState:finalize()
+   self:close()
+
+   for i = self.argument_i, #self.arguments do
+      local argument = self.arguments[i]
+      if #argument.args == 0 and argument:default("u") then
+         argument:complete_invocation()
+      else
+         argument:close()
+      end
+   end
+
+   if self.parser._require_command and #self.commands > 0 then
+      self:error("a command is required")
+   end
+
+   for _, option in ipairs(self.options) do
+      option.name = option.name or ("option '%s'"):format(option.element._name)
+
+      if option.invocations == 0 then
+         if option:default("u") then
+            option:invoke()
+            option:complete_invocation()
+            option:close()
+         end
+      end
+
+      local mincount = option.element._mincount
+
+      if option.invocations < mincount then
+         if option:default("a") then
+            while option.invocations < mincount do
+               option:invoke()
+               option:close()
+            end
+         elseif option.invocations == 0 then
+            self:error("missing %s", option.name)
+         else
+            self:error("%s must be used %s", option.name, bound("time", mincount, option.element._maxcount))
+         end
+      end
+   end
+
+   for i = #self.command_actions, 1, -1 do
+      self.command_actions[i].action(self.result, self.command_actions[i].name)
+   end
+end
+
+function ParseState:parse(args)
+   for _, arg in ipairs(args) do
+      local plain = true
+
+      if self.handle_options then
+         local first = arg:sub(1, 1)
+
+         if self.charset[first] then
+            if #arg > 1 then
+               plain = false
+
+               if arg:sub(2, 2) == first then
+                  if #arg == 2 then
+                     if self.options[arg] then
+                        local option = self:get_option(arg)
+                        self:invoke(option, arg)
+                     else
+                        self:close()
+                     end
+
+                     self.handle_options = false
+                  else
+                     local equals = arg:find "="
+                     if equals then
+                        local name = arg:sub(1, equals - 1)
+                        local option = self:get_option(name)
+
+                        if option.element._maxargs <= 0 then
+                           self:error("option '%s' does not take arguments", name)
+                        end
+
+                        self:invoke(option, name)
+                        self:pass(arg:sub(equals + 1))
+                     else
+                        local option = self:get_option(arg)
+                        self:invoke(option, arg)
+                     end
+                  end
+               else
+                  for i = 2, #arg do
+                     local name = first .. arg:sub(i, i)
+                     local option = self:get_option(name)
+                     self:invoke(option, name)
+
+                     if i ~= #arg and option.element._maxargs > 0 then
+                        self:pass(arg:sub(i + 1))
+                        break
+                     end
+                  end
+               end
+            end
+         end
+      end
+
+      if plain then
+         self:pass(arg)
+      end
+   end
+
+   self:finalize()
+   return self.result
+end
+
+function Parser:error(msg)
+   io.stderr:write(("%s\n\nError: %s\n"):format(self:get_usage(), msg))
+   os.exit(1)
+end
+
+-- Compatibility with strict.lua and other checkers:
+local default_cmdline = rawget(_G, "arg") or {}
+
+function Parser:_parse(args, error_handler)
+   return ParseState(self, error_handler):parse(args or default_cmdline)
+end
+
+function Parser:parse(args)
+   return self:_parse(args, self.error)
+end
+
+local function xpcall_error_handler(err)
+   if not debug then
+      return tostring(err)
+   end
+   return tostring(err) .. "\noriginal " .. debug.traceback("", 2):sub(2)
+end
+
+function Parser:pparse(args)
+   local parse_error
+
+   local ok, result = xpcall(function()
+      return self:_parse(args, function(_, err)
+         parse_error = err
+         error(err, 0)
+      end)
+   end, xpcall_error_handler)
+
+   if ok then
+      return true, result
+   elseif not parse_error then
+      error(result, 0)
+   else
+      return false, parse_error
+   end
+end
+
+local argparse = {}
+
+argparse.version = "0.7.0"
+
+setmetatable(argparse, {__call = function(_, ...)
+   return Parser(default_cmdline[0]):add_help(true)(...)
+end})
+
+return argparse
diff --git a/vendor/compat53/file_mt.lua b/vendor/compat53/file_mt.lua
new file mode 100644
index 00000000..6433619d
--- /dev/null
+++ b/vendor/compat53/file_mt.lua
@@ -0,0 +1,71 @@
+local lua_version = _VERSION:sub(-3)
+
+local M = {}
+
+local unpack = lua_version == "5.1" and unpack or table.unpack
+
+local function addasterisk(fmt)
+   if type(fmt) == "string" and fmt:sub(1, 1) ~= "*" then
+      return "*"..fmt
+   else
+      return fmt
+   end
+end
+
+function M.update_file_meta(file_meta, is_luajit52)
+
+   -- make '*' optional for file:read and file:lines
+
+   local file_lines = file_meta.__index.lines
+   file_meta.__index.lines = function(self, ...)
+      local n = select('#', ...)
+      for i = 1, n do
+         local a = select(i, ...)
+         local b = addasterisk(a)
+         -- as an optimization we only allocate a table for the
+         -- modified format arguments when we have a '*' somewhere
+         if a ~= b then
+            local args = { ... }
+            args[i] = b
+            for j = i+1, n do
+               args[j] = addasterisk(args[j])
+            end
+            return file_lines(self, unpack(args, 1, n))
+         end
+      end
+      return file_lines(self, ...)
+   end
+
+   local file_read = file_meta.__index.read
+   file_meta.__index.read = function(self, ...)
+      local n = select('#', ...)
+      for i = 1, n do
+         local a = select(i, ...)
+         local b = addasterisk(a)
+         -- as an optimization we only allocate a table for the
+         -- modified format arguments when we have a '*' somewhere
+         if a ~= b then
+            local args = { ... }
+            args[i] = b
+            for j = i+1, n do
+               args[j] = addasterisk(args[j])
+            end
+            return file_read(self, unpack(args, 1, n))
+         end
+      end
+      return file_read(self, ...)
+   end
+
+   if not is_luajit52 then
+      local file_write = file_meta.__index.write
+      file_meta.__index.write = function(self, ...)
+         local ret, err = file_write(self, ...)
+         if ret then
+            return self
+         end
+         return ret, err
+      end
+   end
+end
+
+return M
diff --git a/vendor/compat53/init.lua b/vendor/compat53/init.lua
new file mode 100644
index 00000000..b5075713
--- /dev/null
+++ b/vendor/compat53/init.lua
@@ -0,0 +1,325 @@
+local lua_version = _VERSION:sub(-3)
+
+
+if lua_version < "5.3" then
+
+   local _G, pairs, require, select, type =
+         _G, pairs, require, select, type
+   local debug, io = debug, io
+   local unpack = lua_version == "5.1" and unpack or table.unpack
+
+   local M = require("compat53.module")
+
+   -- select the most powerful getmetatable function available
+   local gmt = type(debug) == "table" and debug.getmetatable or
+               getmetatable or function() return false end
+   -- metatable for file objects from Lua's standard io library
+   local file_meta = gmt(io.stdout)
+
+
+   -- detect LuaJIT (including LUAJIT_ENABLE_LUA52COMPAT compilation flag)
+   local is_luajit = (string.dump(function() end) or ""):sub(1, 3) == "\027LJ"
+   local is_luajit52 = is_luajit and
+     #setmetatable({}, { __len = function() return 1 end }) == 1
+
+
+   if type(file_meta) == "table" and type(file_meta.__index) == "table" then
+      local file_mt = require("compat53.file_mt")
+      file_mt.update_file_meta(file_meta, is_luajit52)
+   end -- got a valid metatable for file objects
+
+
+   -- changes for Lua 5.1 only
+   if lua_version == "5.1" then
+
+      -- cache globals
+      local error, pcall, rawset, setmetatable, tostring, xpcall =
+            error, pcall, rawset, setmetatable, tostring, xpcall
+      local coroutine, package, string = coroutine, package, string
+      local coroutine_resume = coroutine.resume
+      local coroutine_running = coroutine.running
+      local coroutine_status = coroutine.status
+      local coroutine_yield = coroutine.yield
+      local io_type = io.type
+
+
+      -- make package.searchers available as an alias for package.loaders
+      local p_index = { searchers = package.loaders }
+      setmetatable(package, {
+         __index = p_index,
+         __newindex = function(p, k, v)
+            if k == "searchers" then
+               rawset(p, "loaders", v)
+               p_index.searchers = v
+            else
+               rawset(p, k, v)
+            end
+         end
+      })
+
+
+      if type(file_meta) == "table" and type(file_meta.__index) == "table" then
+         if not is_luajit then
+            local function helper(_, var_1, ...)
+               if var_1 == nil then
+                  if (...) ~= nil then
+                     error((...), 2)
+                  end
+               end
+               return var_1, ...
+            end
+
+            local function lines_iterator(st)
+               return helper(st, st.f:read(unpack(st, 1, st.n)))
+            end
+
+            local file_write = file_meta.__index.write
+            file_meta.__index.write = function(self, ...)
+               local res, msg, errno = file_write(self, ...)
+               if res then
+                  return self
+               else
+                  return nil, msg, errno
+               end
+            end
+
+            file_meta.__index.lines = function(self, ...)
+               if io_type(self) == "closed file" then
+                  error("attempt to use a closed file", 2)
+               end
+               local st = { f=self, n=select('#', ...), ... }
+               for i = 1, st.n do
+                  local t = type(st[i])
+                  if t == "string" then
+                     local fmt = st[i]:match("^*?([aln])")
+                     if not fmt then
+                        error("bad argument #"..(i+1).." to 'for iterator' (invalid format)", 2)
+                     end
+                     st[i] = "*"..fmt
+                  elseif t ~= "number" then
+                     error("bad argument #"..(i+1).." to 'for iterator' (invalid format)", 2)
+                  end
+               end
+               return lines_iterator, st
+            end
+         end -- not luajit
+      end -- file_meta valid
+
+
+      -- the (x)pcall implementations start a new coroutine internally
+      -- to allow yielding even in Lua 5.1. to allow for accurate
+      -- stack traces we keep track of the nested coroutine activations
+      -- in the weak tables below:
+      local weak_meta = { __mode = "kv" }
+      -- maps the internal pcall coroutines to the user coroutine that
+      -- *should* be running if pcall didn't use coroutines internally
+      local pcall_mainOf = setmetatable({}, weak_meta)
+      -- table that maps each running coroutine started by pcall to
+      -- the coroutine that resumed it (user coroutine *or* pcall
+      -- coroutine!)
+      local pcall_previous = setmetatable({}, weak_meta)
+      -- reverse of `pcall_mainOf`. maps a user coroutine to the
+      -- currently active pcall coroutine started within it
+      local pcall_callOf = setmetatable({}, weak_meta)
+      -- similar to `pcall_mainOf` but is used only while executing
+      -- the error handler of xpcall (thus no nesting is necessary!)
+      local xpcall_running = setmetatable({}, weak_meta)
+
+      -- handle debug functions
+      if type(debug) == "table" then
+         local debug_getinfo = debug.getinfo
+         local debug_traceback = debug.traceback
+
+         if not is_luajit then
+            local function calculate_trace_level(co, level)
+               if level ~= nil then
+                  for out = 1, 1/0 do
+                     local info = (co==nil) and debug_getinfo(out, "") or debug_getinfo(co, out, "")
+                     if info == nil then
+                        local max = out-1
+                        if level <= max then
+                           return level
+                        end
+                        return nil, level-max
+                     end
+                  end
+               end
+               return 1
+            end
+
+            local stack_pattern = "\nstack traceback:"
+            local stack_replace = ""
+            function debug.traceback(co, msg, level)
+               local lvl
+               local nilmsg
+               if type(co) ~= "thread" then
+                  co, msg, level = coroutine_running(), co, msg
+               end
+               if msg == nil then
+                  msg = ""
+                  nilmsg = true
+               elseif type(msg) ~= "string" then
+                  return msg
+               end
+               if co == nil then
+                  msg = debug_traceback(msg, level or 1)
+               else
+                  local xpco = xpcall_running[co]
+                  if xpco ~= nil then
+                     lvl, level = calculate_trace_level(xpco, level)
+                     if lvl then
+                        msg = debug_traceback(xpco, msg, lvl)
+                     else
+                        msg = msg..stack_pattern
+                     end
+                     lvl, level = calculate_trace_level(co, level)
+                     if lvl then
+                        local trace = debug_traceback(co, "", lvl)
+                        msg = msg..trace:gsub(stack_pattern, stack_replace)
+                     end
+                  else
+                     co = pcall_callOf[co] or co
+                     lvl, level = calculate_trace_level(co, level)
+                     if lvl then
+                        msg = debug_traceback(co, msg, lvl)
+                     else
+                        msg = msg..stack_pattern
+                     end
+                  end
+                  co = pcall_previous[co]
+                  while co ~= nil do
+                     lvl, level = calculate_trace_level(co, level)
+                     if lvl then
+                        local trace = debug_traceback(co, "", lvl)
+                        msg = msg..trace:gsub(stack_pattern, stack_replace)
+                     end
+                     co = pcall_previous[co]
+                  end
+               end
+               if nilmsg then
+                  msg = msg:gsub("^\n", "")
+               end
+               msg = msg:gsub("\n\t%(tail call%): %?", "\000")
+               msg = msg:gsub("\n\t%.%.%.\n", "\001\n")
+               msg = msg:gsub("\n\t%.%.%.$", "\001")
+               msg = msg:gsub("(%z+)\001(%z+)", function(some, other)
+                  return "\n\t(..."..#some+#other.."+ tail call(s)...)"
+               end)
+               msg = msg:gsub("\001(%z+)", function(zeros)
+                  return "\n\t(..."..#zeros.."+ tail call(s)...)"
+               end)
+               msg = msg:gsub("(%z+)\001", function(zeros)
+                  return "\n\t(..."..#zeros.."+ tail call(s)...)"
+               end)
+               msg = msg:gsub("%z+", function(zeros)
+                  return "\n\t(..."..#zeros.." tail call(s)...)"
+               end)
+               msg = msg:gsub("\001", function()
+                  return "\n\t..."
+               end)
+               return msg
+            end
+         end -- is not luajit
+      end -- debug table available
+
+
+      if not is_luajit52 then
+         local coroutine_running52 = M.coroutine.running
+         function M.coroutine.running()
+            local co, ismain = coroutine_running52()
+            if ismain then
+               return co, true
+            else
+               return pcall_mainOf[co] or co, false
+            end
+         end
+      end
+
+      if not is_luajit then
+         local function pcall_results(current, call, success, ...)
+            if coroutine_status(call) == "suspended" then
+               return pcall_results(current, call, coroutine_resume(call, coroutine_yield(...)))
+            end
+            if pcall_previous then
+               pcall_previous[call] = nil
+               local main = pcall_mainOf[call]
+               if main == current then current = nil end
+               pcall_callOf[main] = current
+            end
+            pcall_mainOf[call] = nil
+            return success, ...
+         end
+
+         local function pcall_exec(current, call, ...)
+            local main = pcall_mainOf[current] or current
+            pcall_mainOf[call] = main
+            if pcall_previous then
+               pcall_previous[call] = current
+               pcall_callOf[main] = call
+            end
+            return pcall_results(current, call, coroutine_resume(call, ...))
+         end
+
+         local coroutine_create52 = M.coroutine.create
+
+         local function pcall_coroutine(func)
+            if type(func) ~= "function" then
+               local callable = func
+               func = function (...) return callable(...) end
+            end
+            return coroutine_create52(func)
+         end
+
+         function M.pcall(func, ...)
+            local current = coroutine_running()
+            if not current then return pcall(func, ...) end
+            return pcall_exec(current, pcall_coroutine(func), ...)
+         end
+
+         local function xpcall_catch(current, call, msgh, success, ...)
+            if not success then
+               xpcall_running[current] = call
+               local ok, result = pcall(msgh, ...)
+               xpcall_running[current] = nil
+               if not ok then
+                  return false, "error in error handling ("..tostring(result)..")"
+               end
+               return false, result
+            end
+            return true, ...
+         end
+
+         function M.xpcall(f, msgh, ...)
+            local current = coroutine_running()
+            if not current then
+               local args, n = { ... }, select('#', ...)
+               return xpcall(function() return f(unpack(args, 1, n)) end, msgh)
+            end
+            local call = pcall_coroutine(f)
+            return xpcall_catch(current, call, msgh, pcall_exec(current, call, ...))
+         end
+      end -- not luajit
+
+   end -- lua 5.1
+
+
+   -- handle exporting to global scope
+   local function extend_table(from, to)
+      if from ~= to then
+         for k,v in pairs(from) do
+            if type(v) == "table" and
+               type(to[k]) == "table" and
+               v ~= to[k] then
+               extend_table(v, to[k])
+            else
+               to[k] = v
+            end
+         end
+      end
+   end
+
+   extend_table(M, _G)
+
+end -- lua < 5.3
+
+-- vi: set expandtab softtabstop=3 shiftwidth=3 :
diff --git a/vendor/compat53/module.lua b/vendor/compat53/module.lua
new file mode 100644
index 00000000..b580e536
--- /dev/null
+++ b/vendor/compat53/module.lua
@@ -0,0 +1,894 @@
+local _G, _VERSION = _G, _VERSION
+local lua_version = _VERSION:sub(-3)
+
+
+local M = _G
+
+if lua_version < "5.3" then
+
+   -- cache globals in upvalues
+   local error, ipairs, pairs, pcall, require, select, setmetatable, type =
+         error, ipairs, pairs, pcall, require, select, setmetatable, type
+   local debug, io, math, package, string, table =
+         debug, io, math, package, string, table
+   local io_lines = io.lines
+   local io_read = io.read
+   local io_open = io.open
+   local io_popen = io.popen
+   local io_tmpfile = io.tmpfile
+   local unpack = lua_version == "5.1" and unpack or table.unpack
+   local debug_setmetatable = type(debug) == "table" and debug.setmetatable
+
+   -- create module table
+   M = {}
+   local M_meta = {
+      __index = _G,
+      -- __newindex is set at the end
+   }
+   setmetatable(M, M_meta)
+
+   -- create subtables
+   M.io = setmetatable({}, { __index = io })
+   M.math = setmetatable({}, { __index = math })
+   M.string = setmetatable({}, { __index = string })
+   M.table = setmetatable({}, { __index = table })
+   M.utf8 = {}
+
+
+   -- select the most powerful getmetatable function available
+   local gmt = type(debug) == "table" and debug.getmetatable or
+               getmetatable or function() return false end
+
+   -- type checking functions
+   local checkinteger -- forward declararation
+
+   local function argcheck(cond, i, f, extra)
+      if not cond then
+         error("bad argument #"..i.." to '"..f.."' ("..extra..")", 0)
+      end
+   end
+
+
+   -- load utf8 library
+   local utf8_ok, utf8lib = pcall(require, "compat53.utf8")
+   if utf8_ok then
+      if lua_version == "5.1" then
+         utf8lib.charpattern = "[%z\1-\127\194-\244][\128-\191]*"
+      end
+      for k,v in pairs(utf8lib) do
+         M.utf8[k] = v
+      end
+      package.loaded["utf8"] = M.utf8
+   end
+
+
+   -- load table library
+   local table_ok, tablib = pcall(require, "compat53.table")
+   if table_ok then
+      for k,v in pairs(tablib) do
+         M.table[k] = v
+      end
+   end
+
+
+   -- load io functions
+   local io_ok, iolib = pcall(require, "compat53.io")
+   if io_ok then
+      for k,v in pairs(iolib) do
+         M.io[k] = v
+      end
+   end
+
+
+   -- load string packing functions
+   local str_ok, strlib = pcall(require, "compat53.string")
+   if str_ok then
+      for k,v in pairs(strlib) do
+         M.string[k] = v
+      end
+   end
+
+
+   -- try Roberto's struct module for string packing/unpacking if
+   -- compat53.string is unavailable
+   if not str_ok then
+      local struct_ok, struct = pcall(require, "struct")
+      if struct_ok then
+         M.string.pack = struct.pack
+         M.string.packsize = struct.size
+         M.string.unpack = struct.unpack
+      end
+   end
+
+
+   -- update math library
+   do
+      local maxint, minint = 1
+
+      while maxint+1 > maxint and 2*maxint > maxint do
+         maxint = maxint * 2
+      end
+      if 2*maxint <= maxint then
+         maxint = 2*maxint-1
+         minint = -maxint-1
+      else
+         maxint = maxint
+         minint = -maxint
+      end
+      M.math.maxinteger = maxint
+      M.math.mininteger = minint
+
+      function M.math.tointeger(n)
+         n = tonumber(n)
+         if type(n) == "number" and n <= maxint and n >= minint and n % 1 == 0 then
+            return n
+         end
+         return nil
+      end
+
+      function M.math.type(n)
+         if type(n) == "number" then
+            if n <= maxint and n >= minint and n % 1 == 0 then
+               return "integer"
+            else
+               return "float"
+            end
+         else
+            return nil
+         end
+      end
+
+      function checkinteger(x, i, f)
+         local t = type(x)
+         if t ~= "number" then
+            error("bad argument #"..i.." to '"..f..
+                  "' (number expected, got "..t..")", 0)
+         elseif x > maxint or x < minint or x % 1 ~= 0 then
+            error("bad argument #"..i.." to '"..f..
+                  "' (number has no integer representation)", 0)
+         else
+            return x
+         end
+      end
+
+      function M.math.ult(m, n)
+         m = checkinteger(m, "1", "math.ult")
+         n = checkinteger(n, "2", "math.ult")
+         if m >= 0 and n < 0 then
+            return true
+         elseif m < 0 and n >= 0 then
+            return false
+         else
+            return m < n
+         end
+      end
+   end
+
+
+   -- assert should allow non-string error objects
+   function M.assert(cond, ...)
+      if cond then
+         return cond, ...
+      elseif select('#', ...) > 0 then
+         error((...), 2)
+      else
+         error("assertion failed!", 2)
+      end
+   end
+
+
+   -- ipairs should respect __index metamethod
+   do
+      local function ipairs_iterator(st, var)
+         var = var + 1
+         local val = st[var]
+         if val ~= nil then
+            return var, st[var]
+         end
+      end
+      function M.ipairs(t)
+         if gmt(t) ~= nil then -- t has metatable
+            return ipairs_iterator, t, 0
+         else
+            return ipairs(t)
+         end
+      end
+   end
+
+
+   -- make '*' optional for io.read and io.lines
+   do
+      local function addasterisk(fmt)
+         if type(fmt) == "string" and fmt:sub(1, 1) ~= "*" then
+            return "*"..fmt
+         else
+            return fmt
+         end
+      end
+
+      function M.io.read(...)
+         local n = select('#', ...)
+         for i = 1, n do
+            local a = select(i, ...)
+            local b = addasterisk(a)
+            -- as an optimization we only allocate a table for the
+            -- modified format arguments when we have a '*' somewhere.
+            if a ~= b then
+               local args = { ... }
+               args[i] = b
+               for j = i+1, n do
+                  args[j] = addasterisk(args[j])
+               end
+               return io_read(unpack(args, 1, n))
+            end
+         end
+         return io_read(...)
+      end
+
+      -- PUC-Rio Lua 5.1 uses a different implementation for io.lines!
+      function M.io.lines(...)
+         local n = select('#', ...)
+         for i = 2, n do
+            local a = select(i, ...)
+            local b = addasterisk(a)
+            -- as an optimization we only allocate a table for the
+            -- modified format arguments when we have a '*' somewhere.
+            if a ~= b then
+               local args = { ... }
+               args[i] = b
+               for j = i+1, n do
+                  args[j] = addasterisk(args[j])
+               end
+               return io_lines(unpack(args, 1, n))
+            end
+         end
+         return io_lines(...)
+      end
+   end
+
+
+   -- update table library (if C module not available)
+   if not table_ok then
+      local table_concat = table.concat
+      local table_insert = table.insert
+      local table_remove = table.remove
+      local table_sort = table.sort
+
+      function M.table.concat(list, sep, i, j)
+         local mt = gmt(list)
+         if type(mt) == "table" and type(mt.__len) == "function" then
+            local src = list
+            list, i, j  = {}, i or 1, j or mt.__len(src)
+            for k = i, j do
+               list[k] = src[k]
+            end
+         end
+         return table_concat(list, sep, i, j)
+      end
+
+      function M.table.insert(list, ...)
+         local mt = gmt(list)
+         local has_mt = type(mt) == "table"
+         local has_len = has_mt and type(mt.__len) == "function"
+         if has_mt and (has_len or mt.__index or mt.__newindex) then
+            local e = (has_len and mt.__len(list) or #list)+1
+            local nargs, pos, value = select('#', ...), ...
+            if nargs == 1 then
+               pos, value = e, pos
+            elseif nargs == 2 then
+               pos = checkinteger(pos, "2", "table.insert")
+               argcheck(1 <= pos and pos <= e, "2", "table.insert",
+                        "position out of bounds" )
+            else
+               error("wrong number of arguments to 'insert'", 0)
+            end
+            for i = e-1, pos, -1 do
+               list[i+1] = list[i]
+            end
+            list[pos] = value
+         else
+            return table_insert(list, ...)
+         end
+      end
+
+      function M.table.move(a1, f, e, t, a2)
+         a2 = a2 or a1
+         f = checkinteger(f, "2", "table.move")
+         argcheck(f > 0, "2", "table.move",
+                  "initial position must be positive")
+         e = checkinteger(e, "3", "table.move")
+         t = checkinteger(t, "4", "table.move")
+         if e >= f then
+            local m, n, d = 0, e-f, 1
+            if t > f then m, n, d = n, m, -1 end
+            for i = m, n, d do
+               a2[t+i] = a1[f+i]
+            end
+         end
+         return a2
+      end
+
+      function M.table.remove(list, pos)
+         local mt = gmt(list)
+         local has_mt = type(mt) == "table"
+         local has_len = has_mt and type(mt.__len) == "function"
+         if has_mt and (has_len or mt.__index or mt.__newindex) then
+            local e = (has_len and mt.__len(list) or #list)
+            pos = pos ~= nil and checkinteger(pos, "2", "table.remove") or e
+            if pos ~= e then
+               argcheck(1 <= pos and pos <= e+1, "2", "table.remove",
+                        "position out of bounds" )
+            end
+            local result = list[pos]
+            while pos < e do
+               list[pos] = list[pos+1]
+               pos = pos + 1
+            end
+            list[pos] = nil
+            return result
+         else
+            return table_remove(list, pos)
+         end
+      end
+
+      do
+         local function pivot(list, cmp, a, b)
+            local m = b - a
+            if m > 2 then
+               local c = a + (m-m%2)/2
+               local x, y, z = list[a], list[b], list[c]
+               if not cmp(x, y) then
+                  x, y, a, b = y, x, b, a
+               end
+               if not cmp(y, z) then
+                  y, b = z, c
+               end
+               if not cmp(x, y) then
+                  y, b = x, a
+               end
+               return b, y
+            else
+               return b, list[b]
+            end
+         end
+
+         local function lt_cmp(a, b)
+            return a < b
+         end
+
+         local function qsort(list, cmp, b, e)
+            if b < e then
+               local i, j, k, val = b, e, pivot(list, cmp, b, e)
+               while i < j do
+                  while i < j and cmp(list[i], val) do
+                     i = i + 1
+                  end
+                  while i < j and not cmp(list[j], val) do
+                     j = j - 1
+                  end
+                  if i < j then
+                     list[i], list[j] = list[j], list[i]
+                     if i == k then k = j end -- update pivot position
+                     i, j = i+1, j-1
+                  end
+               end
+               if i ~= k and not cmp(list[i], val) then
+                  list[i], list[k] = val, list[i]
+                  k = i -- update pivot position
+               end
+               qsort(list, cmp, b, i == k and i-1 or i)
+               return qsort(list, cmp, i+1, e)
+            end
+         end
+
+         function M.table.sort(list, cmp)
+            local mt = gmt(list)
+            local has_mt = type(mt) == "table"
+            local has_len = has_mt and type(mt.__len) == "function"
+            if has_len then
+               cmp = cmp or lt_cmp
+               local len = mt.__len(list)
+               return qsort(list, cmp, 1, len)
+            else
+               return table_sort(list, cmp)
+            end
+         end
+      end
+
+      local function unpack_helper(list, i, j, ...)
+         if j < i then
+            return ...
+         else
+            return unpack_helper(list, i, j-1, list[j], ...)
+         end
+      end
+      function M.table.unpack(list, i, j)
+         local mt = gmt(list)
+         local has_mt = type(mt) == "table"
+         local has_len = has_mt and type(mt.__len) == "function"
+         if has_mt and (has_len or mt.__index) then
+            i, j = i or 1, j or (has_len and mt.__len(list)) or #list
+            return unpack_helper(list, i, j)
+         else
+            return unpack(list, i, j)
+         end
+      end
+   end -- update table library
+
+
+   -- bring Lua 5.1 (and LuaJIT) up to speed with Lua 5.2
+   if lua_version == "5.1" then
+      -- detect LuaJIT (including LUAJIT_ENABLE_LUA52COMPAT compilation flag)
+      local is_luajit = (string.dump(function() end) or ""):sub(1, 3) == "\027LJ"
+      local is_luajit52 = is_luajit and
+        #setmetatable({}, { __len = function() return 1 end }) == 1
+
+      -- cache globals in upvalues
+      local load, loadfile, loadstring, setfenv, xpcall =
+            load, loadfile, loadstring, setfenv, xpcall
+      local coroutine, os = coroutine, os
+      local coroutine_create = coroutine.create
+      local coroutine_resume = coroutine.resume
+      local coroutine_running = coroutine.running
+      local coroutine_status = coroutine.status
+      local coroutine_yield = coroutine.yield
+      local io_input = io.input
+      local io_open = io.open
+      local io_output = io.output
+      local io_write = io.write
+      local math_log = math.log
+      local os_execute = os.execute
+      local string_find = string.find
+      local string_format = string.format
+      local string_gmatch = string.gmatch
+      local string_gsub = string.gsub
+      local string_match = string.match
+      local string_rep = string.rep
+      local table_concat = table.concat
+
+      -- create subtables
+      M.coroutine = setmetatable({}, { __index = coroutine })
+      M.os = setmetatable({}, { __index = os })
+      M.package = setmetatable({}, { __index = package })
+
+      -- handle debug functions
+      if type(debug) == "table" then
+         local debug_setfenv = debug.setfenv
+         local debug_getfenv = debug.getfenv
+
+         M.debug = setmetatable({}, { __index = debug })
+
+         if not is_luajit52 then
+            function M.debug.setuservalue(obj, value)
+               if type(obj) ~= "userdata" then
+                  error("bad argument #1 to 'setuservalue' (userdata expected, got "..
+                        type(obj)..")", 2)
+               end
+               if value == nil then value = _G end
+               if type(value) ~= "table" then
+                  error("bad argument #2 to 'setuservalue' (table expected, got "..
+                        type(value)..")", 2)
+               end
+               return debug_setfenv(obj, value)
+            end
+
+            function M.debug.getuservalue(obj)
+               if type(obj) ~= "userdata" then
+                  return nil
+               else
+                  local v = debug_getfenv(obj)
+                  if v == _G or v == package then
+                     return nil
+                  end
+                  return v
+               end
+            end
+
+            function M.debug.setmetatable(value, tab)
+               debug_setmetatable(value, tab)
+               return value
+            end
+         end -- not luajit with compat52 enabled
+      end -- debug table available
+
+
+      if not is_luajit52 then
+         function M.pairs(t)
+            local mt = gmt(t)
+            if type(mt) == "table" and type(mt.__pairs) == "function" then
+               return mt.__pairs(t)
+            else
+               return pairs(t)
+            end
+         end
+      end
+
+
+      if not is_luajit then
+         local function check_mode(mode, prefix)
+            local has = { text = false, binary = false }
+            for i = 1,#mode do
+               local c = mode:sub(i, i)
+               if c == "t" then has.text = true end
+               if c == "b" then has.binary = true end
+            end
+            local t = prefix:sub(1, 1) == "\27" and "binary" or "text"
+            if not has[t] then
+               return "attempt to load a "..t.." chunk (mode is '"..mode.."')"
+            end
+         end
+
+         function M.load(ld, source, mode, env)
+            mode = mode or "bt"
+            local chunk, msg
+            if type( ld ) == "string" then
+               if mode ~= "bt" then
+                  local merr = check_mode(mode, ld)
+                  if merr then return nil, merr end
+               end
+               chunk, msg = loadstring(ld, source)
+            else
+               local ld_type = type(ld)
+               if ld_type ~= "function" then
+                  error("bad argument #1 to 'load' (function expected, got "..
+                        ld_type..")", 2)
+               end
+               if mode ~= "bt" then
+                  local checked, merr = false, nil
+                  local function checked_ld()
+                     if checked then
+                        return ld()
+                     else
+                        checked = true
+                        local v = ld()
+                        merr = check_mode(mode, v or "")
+                        if merr then return nil end
+                        return v
+                     end
+                  end
+                  chunk, msg = load(checked_ld, source)
+                  if merr then return nil, merr end
+               else
+                  chunk, msg = load(ld, source)
+               end
+            end
+            if not chunk then
+               return chunk, msg
+            end
+            if env ~= nil then
+               setfenv(chunk, env)
+            end
+            return chunk
+         end
+
+         M.loadstring = M.load
+
+         function M.loadfile(file, mode, env)
+            mode = mode or "bt"
+            if mode ~= "bt" then
+               local f = io_open(file, "rb")
+               if f then
+                  local prefix = f:read(1)
+                  f:close()
+                  if prefix then
+                     local merr = check_mode(mode, prefix)
+                     if merr then return nil, merr end
+                  end
+               end
+            end
+            local chunk, msg = loadfile(file)
+            if not chunk then
+               return chunk, msg
+            end
+            if env ~= nil then
+               setfenv(chunk, env)
+            end
+            return chunk
+         end
+      end -- not luajit
+
+
+      if not is_luajit52 then
+         function M.rawlen(v)
+            local t = type(v)
+            if t ~= "string" and t ~= "table" then
+               error("bad argument #1 to 'rawlen' (table or string expected)", 2)
+            end
+            return #v
+         end
+      end
+
+
+      if not is_luajit then
+         function M.xpcall(f, msgh, ...)
+            local args, n = { ... }, select('#', ...)
+            return xpcall(function() return f(unpack(args, 1, n)) end, msgh)
+         end
+      end
+
+
+      if not is_luajit52 then
+         function M.os.execute(cmd)
+            local code = os_execute(cmd)
+            -- Lua 5.1 does not report exit by signal.
+            if code == 0 then
+               return true, "exit", code
+            else
+               if package.config:sub(1, 1) == '/' then
+                  code = code/256 -- only correct on Linux!
+               end
+               return nil, "exit", code
+            end
+         end
+      end
+
+
+      if not table_ok and not is_luajit52 then
+         M.table.pack = function(...)
+            return { n = select('#', ...), ... }
+         end
+      end
+
+
+      local main_coroutine = coroutine_create(function() end)
+
+      function M.coroutine.create(func)
+         local success, result = pcall(coroutine_create, func)
+         if not success then
+            if type(func) ~= "function" then
+               error("bad argument #1 (function expected)", 0)
+             end
+            result = coroutine_create(function(...) return func(...) end)
+         end
+         return result
+      end
+
+      if not is_luajit52 then
+         function M.coroutine.running()
+            local co = coroutine_running()
+            if co then
+               return co, false
+            else
+               return main_coroutine, true
+            end
+         end
+      end
+
+      function M.coroutine.yield(...)
+         local co, flag = coroutine_running()
+         if co and not flag then
+            return coroutine_yield(...)
+         else
+            error("attempt to yield from outside a coroutine", 0)
+         end
+      end
+
+      if not is_luajit then
+         function M.coroutine.resume(co, ...)
+            if co == main_coroutine then
+               return false, "cannot resume non-suspended coroutine"
+            else
+               return coroutine_resume(co, ...)
+            end
+         end
+
+         function M.coroutine.status(co)
+            local notmain = coroutine_running()
+            if co == main_coroutine then
+               return notmain and "normal" or "running"
+            else
+               return coroutine_status(co)
+            end
+         end
+      end -- not luajit
+
+
+      if not is_luajit then
+         M.math.log = function(x, base)
+            if base ~= nil then
+               return math_log(x)/math_log(base)
+            else
+               return math_log(x)
+            end
+         end
+      end
+
+
+      if not is_luajit then
+         function M.package.searchpath(name, path, sep, rep)
+            sep = (sep or "."):gsub("(%p)", "%%%1")
+            rep = (rep or package.config:sub(1, 1)):gsub("(%%)", "%%%1")
+            local pname = name:gsub(sep, rep):gsub("(%%)", "%%%1")
+            local msg = {}
+            for subpath in path:gmatch("[^;]+") do
+               local fpath = subpath:gsub("%?", pname)
+               local f = io_open(fpath, "r")
+               if f then
+                  f:close()
+                  return fpath
+               end
+               msg[#msg+1] = "\n\tno file '" .. fpath .. "'"
+            end
+            return nil, table_concat(msg)
+         end
+      end
+
+
+      local function fix_pattern(pattern)
+         return (string_gsub(pattern, "%z", "%%z"))
+      end
+
+      function M.string.find(s, pattern, ...)
+         return string_find(s, fix_pattern(pattern), ...)
+      end
+
+      function M.string.gmatch(s, pattern)
+         return string_gmatch(s, fix_pattern(pattern))
+      end
+
+      function M.string.gsub(s, pattern, ...)
+         return string_gsub(s, fix_pattern(pattern), ...)
+      end
+
+      function M.string.match(s, pattern, ...)
+         return string_match(s, fix_pattern(pattern), ...)
+      end
+
+      if not is_luajit then
+         function M.string.rep(s, n, sep)
+            if sep ~= nil and sep ~= "" and n >= 2 then
+               return s .. string_rep(sep..s, n-1)
+            else
+               return string_rep(s, n)
+            end
+         end
+      end
+
+      if not is_luajit then
+         do
+            local addqt = {
+               ["\n"] = "\\\n",
+               ["\\"] = "\\\\",
+               ["\""] = "\\\""
+            }
+
+            local function addquoted(c, d)
+               return (addqt[c] or string_format(d~="" and "\\%03d" or "\\%d", c:byte()))..d
+            end
+
+            function M.string.format(fmt, ...)
+               local args, n = { ... }, select('#', ...)
+               local i = 0
+               local function adjust_fmt(lead, mods, kind)
+                  if #lead % 2 == 0 then
+                     i = i + 1
+                     if kind == "s" then
+                        args[i] = _G.tostring(args[i])
+                     elseif kind == "q" then
+                        args[i] = '"'..string_gsub(args[i], "([%z%c\\\"\n])(%d?)", addquoted)..'"'
+                        return lead.."%"..mods.."s"
+                     end
+                  end
+               end
+               fmt = string_gsub(fmt, "(%%*)%%([%d%.%-%+%# ]*)(%a)", adjust_fmt)
+               return string_format(fmt, unpack(args, 1, n))
+            end
+         end
+      end
+
+
+      function M.io.write(...)
+         local res, msg, errno = io_write(...)
+         if res then
+            return io_output()
+         else
+            return nil, msg, errno
+         end
+      end
+
+      if not is_luajit then
+         local function helper(st, var_1, ...)
+            if var_1 == nil then
+               if st.doclose then st.f:close() end
+               if (...) ~= nil then
+                  error((...), 2)
+               end
+            end
+            return var_1, ...
+         end
+
+         local function lines_iterator(st)
+            return helper(st, st.f:read(unpack(st, 1, st.n)))
+         end
+
+         function M.io.lines(fname, ...)
+            local doclose, file, msg
+            if fname ~= nil then
+               doclose, file, msg = true, io_open(fname, "r")
+               if not file then error(msg, 2) end
+            else
+               doclose, file = false, io_input()
+            end
+            local st = { f=file, doclose=doclose, n=select('#', ...), ... }
+            for i = 1, st.n do
+               local t = type(st[i])
+               if t == "string" then
+                  local fmt = st[i]:match("^%*?([aln])")
+                  if not fmt then
+                     error("bad argument #"..(i+1).." to 'for iterator' (invalid format)", 2)
+                  end
+                  st[i] = "*"..fmt
+               elseif t ~= "number" then
+                  error("bad argument #"..(i+1).." to 'for iterator' (invalid format)", 2)
+               end
+            end
+            return lines_iterator, st
+         end
+      end -- not luajit
+
+      if is_luajit then
+         local compat_file_meta = {}
+         local compat_file_meta_loaded = 0
+
+         local function load_compat_file_meta(file_meta)
+            -- fill compat_file_meta with original entries
+            for k, v in pairs(file_meta) do
+               compat_file_meta[k] = v
+            end
+            compat_file_meta.__index = {}
+            for k, v in pairs(file_meta.__index) do
+               compat_file_meta.__index[k] = v
+            end
+
+            compat_file_meta_loaded = 1
+
+            -- update it with compatibility functions
+            local file_mt_ok, file_mt = pcall(require, "compat53.file_mt")
+            if file_mt_ok then
+               file_mt.update_file_meta(compat_file_meta, is_luajit52)
+
+               compat_file_meta_loaded = 2
+            end
+         end
+
+         local function return_fd(fd, err, code)
+            if not fd then
+               return fd, err, code
+            end
+            if fd and debug_setmetatable then
+               if compat_file_meta_loaded == 0 then
+                  local file_meta = gmt(fd)
+                  load_compat_file_meta(file_meta)
+               end
+               if compat_file_meta_loaded == 2 then
+                  debug_setmetatable(fd, compat_file_meta)
+               end
+            end
+            return fd
+         end
+
+         function M.io.open(...)
+            return return_fd(io_open(...))
+         end
+
+         function M.io.popen(...)
+            return return_fd(io_popen(...))
+         end
+
+         function M.io.tmpfile(...)
+            return return_fd(io_tmpfile(...))
+         end
+      end
+
+   end -- lua 5.1
+
+   -- further write should be forwarded to _G
+   M_meta.__newindex = _G
+
+end -- lua < 5.3
+
+
+-- return module table
+return M
+
+-- vi: set expandtab softtabstop=3 shiftwidth=3 :
diff --git a/vendor/dkjson.d.tl b/vendor/dkjson.d.tl
new file mode 100644
index 00000000..4245e8aa
--- /dev/null
+++ b/vendor/dkjson.d.tl
@@ -0,0 +1,33 @@
+
+--[[
+- local type json = {string:json}
+]]
+
+local record dkjson
+   record JsonState
+      indent: boolean
+      keyorder: {string}
+      level: number
+      buffer: {string}
+      bufferlen: number
+      tables: {table:boolean}
+      exception: function(string, string, string, string): boolean|string, string
+   end
+   encode: function({string:any}, ?JsonState): string
+
+   decode: function(string, ?number, ?any, ?table): {string:any}, integer, string
+
+   null: table
+
+   version: string
+
+   quotestring: function(string): string
+
+   addnewline: function(JsonState)
+
+   encodeexception: function(string, any, JsonState, string): string
+
+   use_lpeg: function(): dkjson
+end
+
+return dkjson
diff --git a/vendor/dkjson.lua b/vendor/dkjson.lua
new file mode 100644
index 00000000..7a867241
--- /dev/null
+++ b/vendor/dkjson.lua
@@ -0,0 +1,749 @@
+-- Module options:
+local always_use_lpeg = false
+local register_global_module_table = false
+local global_module_name = 'json'
+
+--[==[
+
+David Kolf's JSON module for Lua 5.1 - 5.4
+
+Version 2.7
+
+
+For the documentation see the corresponding readme.txt or visit
+<http://dkolf.de/src/dkjson-lua.fsl/>.
+
+You can contact the author by sending an e-mail to 'david' at the
+domain 'dkolf.de'.
+
+
+Copyright (C) 2010-2024 David Heiko Kolf
+
+Permission is hereby granted, free of charge, to any person obtaining
+a copy of this software and associated documentation files (the
+"Software"), to deal in the Software without restriction, including
+without limitation the rights to use, copy, modify, merge, publish,
+distribute, sublicense, and/or sell copies of the Software, and to
+permit persons to whom the Software is furnished to do so, subject to
+the following conditions:
+
+The above copyright notice and this permission notice shall be
+included in all copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
+BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
+ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
+CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.
+
+--]==]
+
+-- global dependencies:
+local pairs, type, tostring, tonumber, getmetatable, setmetatable, rawset =
+      pairs, type, tostring, tonumber, getmetatable, setmetatable, rawset
+local error, require, pcall, select = error, require, pcall, select
+local floor, huge = math.floor, math.huge
+local strrep, gsub, strsub, strbyte, strchar, strfind, strlen, strformat =
+      string.rep, string.gsub, string.sub, string.byte, string.char,
+      string.find, string.len, string.format
+local strmatch = string.match
+local concat = table.concat
+
+local json = { version = "dkjson 2.7" }
+
+local jsonlpeg = {}
+
+if register_global_module_table then
+  if always_use_lpeg then
+    _G[global_module_name] = jsonlpeg
+  else
+    _G[global_module_name] = json
+  end
+end
+
+local _ENV = nil -- blocking globals in Lua 5.2 and later
+
+pcall (function()
+  -- Enable access to blocked metatables.
+  -- Don't worry, this module doesn't change anything in them.
+  local debmeta = require "debug".getmetatable
+  if debmeta then getmetatable = debmeta end
+end)
+
+json.null = setmetatable ({}, {
+  __tojson = function () return "null" end
+})
+
+local function isarray (tbl)
+  local max, n, arraylen = 0, 0, 0
+  for k,v in pairs (tbl) do
+    if k == 'n' and type(v) == 'number' then
+      arraylen = v
+      if v > max then
+        max = v
+      end
+    else
+      if type(k) ~= 'number' or k < 1 or floor(k) ~= k then
+        return false
+      end
+      if k > max then
+        max = k
+      end
+      n = n + 1
+    end
+  end
+  if max > 10 and max > arraylen and max > n * 2 then
+    return false -- don't create an array with too many holes
+  end
+  return true, max
+end
+
+local escapecodes = {
+  ["\""] = "\\\"", ["\\"] = "\\\\", ["\b"] = "\\b", ["\f"] = "\\f",
+  ["\n"] = "\\n",  ["\r"] = "\\r",  ["\t"] = "\\t"
+}
+
+local function escapeutf8 (uchar)
+  local value = escapecodes[uchar]
+  if value then
+    return value
+  end
+  local a, b, c, d = strbyte (uchar, 1, 4)
+  a, b, c, d = a or 0, b or 0, c or 0, d or 0
+  if a <= 0x7f then
+    value = a
+  elseif 0xc0 <= a and a <= 0xdf and b >= 0x80 then
+    value = (a - 0xc0) * 0x40 + b - 0x80
+  elseif 0xe0 <= a and a <= 0xef and b >= 0x80 and c >= 0x80 then
+    value = ((a - 0xe0) * 0x40 + b - 0x80) * 0x40 + c - 0x80
+  elseif 0xf0 <= a and a <= 0xf7 and b >= 0x80 and c >= 0x80 and d >= 0x80 then
+    value = (((a - 0xf0) * 0x40 + b - 0x80) * 0x40 + c - 0x80) * 0x40 + d - 0x80
+  else
+    return ""
+  end
+  if value <= 0xffff then
+    return strformat ("\\u%.4x", value)
+  elseif value <= 0x10ffff then
+    -- encode as UTF-16 surrogate pair
+    value = value - 0x10000
+    local highsur, lowsur = 0xD800 + floor (value/0x400), 0xDC00 + (value % 0x400)
+    return strformat ("\\u%.4x\\u%.4x", highsur, lowsur)
+  else
+    return ""
+  end
+end
+
+local function fsub (str, pattern, repl)
+  -- gsub always builds a new string in a buffer, even when no match
+  -- exists. First using find should be more efficient when most strings
+  -- don't contain the pattern.
+  if strfind (str, pattern) then
+    return gsub (str, pattern, repl)
+  else
+    return str
+  end
+end
+
+local function quotestring (value)
+  -- based on the regexp "escapable" in https://github.com/douglascrockford/JSON-js
+  value = fsub (value, "[%z\1-\31\"\\\127]", escapeutf8)
+  if strfind (value, "[\194\216\220\225\226\239]") then
+    value = fsub (value, "\194[\128-\159\173]", escapeutf8)
+    value = fsub (value, "\216[\128-\132]", escapeutf8)
+    value = fsub (value, "\220\143", escapeutf8)
+    value = fsub (value, "\225\158[\180\181]", escapeutf8)
+    value = fsub (value, "\226\128[\140-\143\168-\175]", escapeutf8)
+    value = fsub (value, "\226\129[\160-\175]", escapeutf8)
+    value = fsub (value, "\239\187\191", escapeutf8)
+    value = fsub (value, "\239\191[\176-\191]", escapeutf8)
+  end
+  return "\"" .. value .. "\""
+end
+json.quotestring = quotestring
+
+local function replace(str, o, n)
+  local i, j = strfind (str, o, 1, true)
+  if i then
+    return strsub(str, 1, i-1) .. n .. strsub(str, j+1, -1)
+  else
+    return str
+  end
+end
+
+-- locale independent num2str and str2num functions
+local decpoint, numfilter
+
+local function updatedecpoint ()
+  decpoint = strmatch(tostring(0.5), "([^05+])")
+  -- build a filter that can be used to remove group separators
+  numfilter = "[^0-9%-%+eE" .. gsub(decpoint, "[%^%$%(%)%%%.%[%]%*%+%-%?]", "%%%0") .. "]+"
+end
+
+updatedecpoint()
+
+local function num2str (num)
+  return replace(fsub(tostring(num), numfilter, ""), decpoint, ".")
+end
+
+local function str2num (str)
+  local num = tonumber(replace(str, ".", decpoint))
+  if not num then
+    updatedecpoint()
+    num = tonumber(replace(str, ".", decpoint))
+  end
+  return num
+end
+
+local function addnewline2 (level, buffer, buflen)
+  buffer[buflen+1] = "\n"
+  buffer[buflen+2] = strrep ("  ", level)
+  buflen = buflen + 2
+  return buflen
+end
+
+function json.addnewline (state)
+  if state.indent then
+    state.bufferlen = addnewline2 (state.level or 0,
+                           state.buffer, state.bufferlen or #(state.buffer))
+  end
+end
+
+local encode2 -- forward declaration
+
+local function addpair (key, value, prev, indent, level, buffer, buflen, tables, globalorder, state)
+  local kt = type (key)
+  if kt ~= 'string' and kt ~= 'number' then
+    return nil, "type '" .. kt .. "' is not supported as a key by JSON."
+  end
+  if prev then
+    buflen = buflen + 1
+    buffer[buflen] = ","
+  end
+  if indent then
+    buflen = addnewline2 (level, buffer, buflen)
+  end
+  buffer[buflen+1] = quotestring (key)
+  buffer[buflen+2] = ":"
+  return encode2 (value, indent, level, buffer, buflen + 2, tables, globalorder, state)
+end
+
+local function appendcustom(res, buffer, state)
+  local buflen = state.bufferlen
+  if type (res) == 'string' then
+    buflen = buflen + 1
+    buffer[buflen] = res
+  end
+  return buflen
+end
+
+local function exception(reason, value, state, buffer, buflen, defaultmessage)
+  defaultmessage = defaultmessage or reason
+  local handler = state.exception
+  if not handler then
+    return nil, defaultmessage
+  else
+    state.bufferlen = buflen
+    local ret, msg = handler (reason, value, state, defaultmessage)
+    if not ret then return nil, msg or defaultmessage end
+    return appendcustom(ret, buffer, state)
+  end
+end
+
+function json.encodeexception(reason, value, state, defaultmessage)
+  return quotestring("<" .. defaultmessage .. ">")
+end
+
+encode2 = function (value, indent, level, buffer, buflen, tables, globalorder, state)
+  local valtype = type (value)
+  local valmeta = getmetatable (value)
+  valmeta = type (valmeta) == 'table' and valmeta -- only tables
+  local valtojson = valmeta and valmeta.__tojson
+  if valtojson then
+    if tables[value] then
+      return exception('reference cycle', value, state, buffer, buflen)
+    end
+    tables[value] = true
+    state.bufferlen = buflen
+    local ret, msg = valtojson (value, state)
+    if not ret then return exception('custom encoder failed', value, state, buffer, buflen, msg) end
+    tables[value] = nil
+    buflen = appendcustom(ret, buffer, state)
+  elseif value == nil then
+    buflen = buflen + 1
+    buffer[buflen] = "null"
+  elseif valtype == 'number' then
+    local s
+    if value ~= value or value >= huge or -value >= huge then
+      -- This is the behaviour of the original JSON implementation.
+      s = "null"
+    else
+      s = num2str (value)
+    end
+    buflen = buflen + 1
+    buffer[buflen] = s
+  elseif valtype == 'boolean' then
+    buflen = buflen + 1
+    buffer[buflen] = value and "true" or "false"
+  elseif valtype == 'string' then
+    buflen = buflen + 1
+    buffer[buflen] = quotestring (value)
+  elseif valtype == 'table' then
+    if tables[value] then
+      return exception('reference cycle', value, state, buffer, buflen)
+    end
+    tables[value] = true
+    level = level + 1
+    local isa, n = isarray (value)
+    if n == 0 and valmeta and valmeta.__jsontype == 'object' then
+      isa = false
+    end
+    local msg
+    if isa then -- JSON array
+      buflen = buflen + 1
+      buffer[buflen] = "["
+      for i = 1, n do
+        buflen, msg = encode2 (value[i], indent, level, buffer, buflen, tables, globalorder, state)
+        if not buflen then return nil, msg end
+        if i < n then
+          buflen = buflen + 1
+          buffer[buflen] = ","
+        end
+      end
+      buflen = buflen + 1
+      buffer[buflen] = "]"
+    else -- JSON object
+      local prev = false
+      buflen = buflen + 1
+      buffer[buflen] = "{"
+      local order = valmeta and valmeta.__jsonorder or globalorder
+      if order then
+        local used = {}
+        n = #order
+        for i = 1, n do
+          local k = order[i]
+          local v = value[k]
+          if v ~= nil then
+            used[k] = true
+            buflen, msg = addpair (k, v, prev, indent, level, buffer, buflen, tables, globalorder, state)
+            if not buflen then return nil, msg end
+            prev = true -- add a seperator before the next element
+          end
+        end
+        for k,v in pairs (value) do
+          if not used[k] then
+            buflen, msg = addpair (k, v, prev, indent, level, buffer, buflen, tables, globalorder, state)
+            if not buflen then return nil, msg end
+            prev = true -- add a seperator before the next element
+          end
+        end
+      else -- unordered
+        for k,v in pairs (value) do
+          buflen, msg = addpair (k, v, prev, indent, level, buffer, buflen, tables, globalorder, state)
+          if not buflen then return nil, msg end
+          prev = true -- add a seperator before the next element
+        end
+      end
+      if indent then
+        buflen = addnewline2 (level - 1, buffer, buflen)
+      end
+      buflen = buflen + 1
+      buffer[buflen] = "}"
+    end
+    tables[value] = nil
+  else
+    return exception ('unsupported type', value, state, buffer, buflen,
+      "type '" .. valtype .. "' is not supported by JSON.")
+  end
+  return buflen
+end
+
+function json.encode (value, state)
+  state = state or {}
+  local oldbuffer = state.buffer
+  local buffer = oldbuffer or {}
+  state.buffer = buffer
+  updatedecpoint()
+  local ret, msg = encode2 (value, state.indent, state.level or 0,
+                   buffer, state.bufferlen or 0, state.tables or {}, state.keyorder, state)
+  if not ret then
+    error (msg, 2)
+  elseif oldbuffer == buffer then
+    state.bufferlen = ret
+    return true
+  else
+    state.bufferlen = nil
+    state.buffer = nil
+    return concat (buffer)
+  end
+end
+
+local function loc (str, where)
+  local line, pos, linepos = 1, 1, 0
+  while true do
+    pos = strfind (str, "\n", pos, true)
+    if pos and pos < where then
+      line = line + 1
+      linepos = pos
+      pos = pos + 1
+    else
+      break
+    end
+  end
+  return "line " .. line .. ", column " .. (where - linepos)
+end
+
+local function unterminated (str, what, where)
+  return nil, strlen (str) + 1, "unterminated " .. what .. " at " .. loc (str, where)
+end
+
+local function scanwhite (str, pos)
+  while true do
+    pos = strfind (str, "%S", pos)
+    if not pos then return nil end
+    local sub2 = strsub (str, pos, pos + 1)
+    if sub2 == "\239\187" and strsub (str, pos + 2, pos + 2) == "\191" then
+      -- UTF-8 Byte Order Mark
+      pos = pos + 3
+    elseif sub2 == "//" then
+      pos = strfind (str, "[\n\r]", pos + 2)
+      if not pos then return nil end
+    elseif sub2 == "/*" then
+      pos = strfind (str, "*/", pos + 2)
+      if not pos then return nil end
+      pos = pos + 2
+    else
+      return pos
+    end
+  end
+end
+
+local escapechars = {
+  ["\""] = "\"", ["\\"] = "\\", ["/"] = "/", ["b"] = "\b", ["f"] = "\f",
+  ["n"] = "\n", ["r"] = "\r", ["t"] = "\t"
+}
+
+local function unichar (value)
+  if value < 0 then
+    return nil
+  elseif value <= 0x007f then
+    return strchar (value)
+  elseif value <= 0x07ff then
+    return strchar (0xc0 + floor(value/0x40),
+                    0x80 + (floor(value) % 0x40))
+  elseif value <= 0xffff then
+    return strchar (0xe0 + floor(value/0x1000),
+                    0x80 + (floor(value/0x40) % 0x40),
+                    0x80 + (floor(value) % 0x40))
+  elseif value <= 0x10ffff then
+    return strchar (0xf0 + floor(value/0x40000),
+                    0x80 + (floor(value/0x1000) % 0x40),
+                    0x80 + (floor(value/0x40) % 0x40),
+                    0x80 + (floor(value) % 0x40))
+  else
+    return nil
+  end
+end
+
+local function scanstring (str, pos)
+  local lastpos = pos + 1
+  local buffer, n = {}, 0
+  while true do
+    local nextpos = strfind (str, "[\"\\]", lastpos)
+    if not nextpos then
+      return unterminated (str, "string", pos)
+    end
+    if nextpos > lastpos then
+      n = n + 1
+      buffer[n] = strsub (str, lastpos, nextpos - 1)
+    end
+    if strsub (str, nextpos, nextpos) == "\"" then
+      lastpos = nextpos + 1
+      break
+    else
+      local escchar = strsub (str, nextpos + 1, nextpos + 1)
+      local value
+      if escchar == "u" then
+        value = tonumber (strsub (str, nextpos + 2, nextpos + 5), 16)
+        if value then
+          local value2
+          if 0xD800 <= value and value <= 0xDBff then
+            -- we have the high surrogate of UTF-16. Check if there is a
+            -- low surrogate escaped nearby to combine them.
+            if strsub (str, nextpos + 6, nextpos + 7) == "\\u" then
+              value2 = tonumber (strsub (str, nextpos + 8, nextpos + 11), 16)
+              if value2 and 0xDC00 <= value2 and value2 <= 0xDFFF then
+                value = (value - 0xD800)  * 0x400 + (value2 - 0xDC00) + 0x10000
+              else
+                value2 = nil -- in case it was out of range for a low surrogate
+              end
+            end
+          end
+          value = value and unichar (value)
+          if value then
+            if value2 then
+              lastpos = nextpos + 12
+            else
+              lastpos = nextpos + 6
+            end
+          end
+        end
+      end
+      if not value then
+        value = escapechars[escchar] or escchar
+        lastpos = nextpos + 2
+      end
+      n = n + 1
+      buffer[n] = value
+    end
+  end
+  if n == 1 then
+    return buffer[1], lastpos
+  elseif n > 1 then
+    return concat (buffer), lastpos
+  else
+    return "", lastpos
+  end
+end
+
+local scanvalue -- forward declaration
+
+local function scantable (what, closechar, str, startpos, nullval, objectmeta, arraymeta)
+  local len = strlen (str)
+  local tbl, n = {}, 0
+  local pos = startpos + 1
+  if what == 'object' then
+    setmetatable (tbl, objectmeta)
+  else
+    setmetatable (tbl, arraymeta)
+  end
+  while true do
+    pos = scanwhite (str, pos)
+    if not pos then return unterminated (str, what, startpos) end
+    local char = strsub (str, pos, pos)
+    if char == closechar then
+      return tbl, pos + 1
+    end
+    local val1, err
+    val1, pos, err = scanvalue (str, pos, nullval, objectmeta, arraymeta)
+    if err then return nil, pos, err end
+    pos = scanwhite (str, pos)
+    if not pos then return unterminated (str, what, startpos) end
+    char = strsub (str, pos, pos)
+    if char == ":" then
+      if val1 == nil then
+        return nil, pos, "cannot use nil as table index (at " .. loc (str, pos) .. ")"
+      end
+      pos = scanwhite (str, pos + 1)
+      if not pos then return unterminated (str, what, startpos) end
+      local val2
+      val2, pos, err = scanvalue (str, pos, nullval, objectmeta, arraymeta)
+      if err then return nil, pos, err end
+      tbl[val1] = val2
+      pos = scanwhite (str, pos)
+      if not pos then return unterminated (str, what, startpos) end
+      char = strsub (str, pos, pos)
+    else
+      n = n + 1
+      tbl[n] = val1
+    end
+    if char == "," then
+      pos = pos + 1
+    end
+  end
+end
+
+scanvalue = function (str, pos, nullval, objectmeta, arraymeta)
+  pos = pos or 1
+  pos = scanwhite (str, pos)
+  if not pos then
+    return nil, strlen (str) + 1, "no valid JSON value (reached the end)"
+  end
+  local char = strsub (str, pos, pos)
+  if char == "{" then
+    return scantable ('object', "}", str, pos, nullval, objectmeta, arraymeta)
+  elseif char == "[" then
+    return scantable ('array', "]", str, pos, nullval, objectmeta, arraymeta)
+  elseif char == "\"" then
+    return scanstring (str, pos)
+  else
+    local pstart, pend = strfind (str, "^%-?[%d%.]+[eE]?[%+%-]?%d*", pos)
+    if pstart then
+      local number = str2num (strsub (str, pstart, pend))
+      if number then
+        return number, pend + 1
+      end
+    end
+    pstart, pend = strfind (str, "^%a%w*", pos)
+    if pstart then
+      local name = strsub (str, pstart, pend)
+      if name == "true" then
+        return true, pend + 1
+      elseif name == "false" then
+        return false, pend + 1
+      elseif name == "null" then
+        return nullval, pend + 1
+      end
+    end
+    return nil, pos, "no valid JSON value at " .. loc (str, pos)
+  end
+end
+
+local function optionalmetatables(...)
+  if select("#", ...) > 0 then
+    return ...
+  else
+    return {__jsontype = 'object'}, {__jsontype = 'array'}
+  end
+end
+
+function json.decode (str, pos, nullval, ...)
+  local objectmeta, arraymeta = optionalmetatables(...)
+  return scanvalue (str, pos, nullval, objectmeta, arraymeta)
+end
+
+function json.use_lpeg ()
+  local g = require ("lpeg")
+
+  if type(g.version) == 'function' and g.version() == "0.11" then
+    error "due to a bug in LPeg 0.11, it cannot be used for JSON matching"
+  end
+
+  local pegmatch = g.match
+  local P, S, R = g.P, g.S, g.R
+
+  local function ErrorCall (str, pos, msg, state)
+    if not state.msg then
+      state.msg = msg .. " at " .. loc (str, pos)
+      state.pos = pos
+    end
+    return false
+  end
+
+  local function Err (msg)
+    return g.Cmt (g.Cc (msg) * g.Carg (2), ErrorCall)
+  end
+
+  local function ErrorUnterminatedCall (str, pos, what, state)
+    return ErrorCall (str, pos - 1, "unterminated " .. what, state)
+  end
+
+  local SingleLineComment = P"//" * (1 - S"\n\r")^0
+  local MultiLineComment = P"/*" * (1 - P"*/")^0 * P"*/"
+  local Space = (S" \n\r\t" + P"\239\187\191" + SingleLineComment + MultiLineComment)^0
+
+  local function ErrUnterminated (what)
+    return g.Cmt (g.Cc (what) * g.Carg (2), ErrorUnterminatedCall)
+  end
+
+  local PlainChar = 1 - S"\"\\\n\r"
+  local EscapeSequence = (P"\\" * g.C (S"\"\\/bfnrt" + Err "unsupported escape sequence")) / escapechars
+  local HexDigit = R("09", "af", "AF")
+  local function UTF16Surrogate (match, pos, high, low)
+    high, low = tonumber (high, 16), tonumber (low, 16)
+    if 0xD800 <= high and high <= 0xDBff and 0xDC00 <= low and low <= 0xDFFF then
+      return true, unichar ((high - 0xD800)  * 0x400 + (low - 0xDC00) + 0x10000)
+    else
+      return false
+    end
+  end
+  local function UTF16BMP (hex)
+    return unichar (tonumber (hex, 16))
+  end
+  local U16Sequence = (P"\\u" * g.C (HexDigit * HexDigit * HexDigit * HexDigit))
+  local UnicodeEscape = g.Cmt (U16Sequence * U16Sequence, UTF16Surrogate) + U16Sequence/UTF16BMP
+  local Char = UnicodeEscape + EscapeSequence + PlainChar
+  local String = P"\"" * (g.Cs (Char ^ 0) * P"\"" + ErrUnterminated "string")
+  local Integer = P"-"^(-1) * (P"0" + (R"19" * R"09"^0))
+  local Fractal = P"." * R"09"^0
+  local Exponent = (S"eE") * (S"+-")^(-1) * R"09"^1
+  local Number = (Integer * Fractal^(-1) * Exponent^(-1))/str2num
+  local Constant = P"true" * g.Cc (true) + P"false" * g.Cc (false) + P"null" * g.Carg (1)
+  local SimpleValue = Number + String + Constant
+  local ArrayContent, ObjectContent
+
+  -- The functions parsearray and parseobject parse only a single value/pair
+  -- at a time and store them directly to avoid hitting the LPeg limits.
+  local function parsearray (str, pos, nullval, state)
+    local obj, cont
+    local start = pos
+    local npos
+    local t, nt = {}, 0
+    repeat
+      obj, cont, npos = pegmatch (ArrayContent, str, pos, nullval, state)
+      if cont == 'end' then
+        return ErrorUnterminatedCall (str, start, "array", state)
+      end
+      pos = npos
+      if cont == 'cont' or cont == 'last' then
+        nt = nt + 1
+        t[nt] = obj
+      end
+    until cont ~= 'cont'
+    return pos, setmetatable (t, state.arraymeta)
+  end
+
+  local function parseobject (str, pos, nullval, state)
+    local obj, key, cont
+    local start = pos
+    local npos
+    local t = {}
+    repeat
+      key, obj, cont, npos = pegmatch (ObjectContent, str, pos, nullval, state)
+      if cont == 'end' then
+        return ErrorUnterminatedCall (str, start, "object", state)
+      end
+      pos = npos
+      if cont == 'cont' or cont == 'last' then
+        t[key] = obj
+      end
+    until cont ~= 'cont'
+    return pos, setmetatable (t, state.objectmeta)
+  end
+
+  local Array = P"[" * g.Cmt (g.Carg(1) * g.Carg(2), parsearray)
+  local Object = P"{" * g.Cmt (g.Carg(1) * g.Carg(2), parseobject)
+  local Value = Space * (Array + Object + SimpleValue)
+  local ExpectedValue = Value + Space * Err "value expected"
+  local ExpectedKey = String + Err "key expected"
+  local End = P(-1) * g.Cc'end'
+  local ErrInvalid = Err "invalid JSON"
+  ArrayContent = (Value * Space * (P"," * g.Cc'cont' + P"]" * g.Cc'last'+ End + ErrInvalid)  + g.Cc(nil) * (P"]" * g.Cc'empty' + End  + ErrInvalid)) * g.Cp()
+  local Pair = g.Cg (Space * ExpectedKey * Space * (P":" + Err "colon expected") * ExpectedValue)
+  ObjectContent = (g.Cc(nil) * g.Cc(nil) * P"}" * g.Cc'empty' + End + (Pair * Space * (P"," * g.Cc'cont' + P"}" * g.Cc'last' + End + ErrInvalid) + ErrInvalid)) * g.Cp()
+  local DecodeValue = ExpectedValue * g.Cp ()
+
+  jsonlpeg.version = json.version
+  jsonlpeg.encode = json.encode
+  jsonlpeg.null = json.null
+  jsonlpeg.quotestring = json.quotestring
+  jsonlpeg.addnewline = json.addnewline
+  jsonlpeg.encodeexception = json.encodeexception
+  jsonlpeg.using_lpeg = true
+
+  function jsonlpeg.decode (str, pos, nullval, ...)
+    local state = {}
+    state.objectmeta, state.arraymeta = optionalmetatables(...)
+    local obj, retpos = pegmatch (DecodeValue, str, pos, nullval, state)
+    if state.msg then
+      return nil, state.pos, state.msg
+    else
+      return obj, retpos
+    end
+  end
+
+  -- cache result of this function:
+  json.use_lpeg = function () return jsonlpeg end
+  jsonlpeg.use_lpeg = json.use_lpeg
+
+  return jsonlpeg
+end
+
+if always_use_lpeg then
+  return json.use_lpeg()
+end
+
+return json
+