Module:Arguments

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This module provides easy processing of arguments passed from #invoke. It is a meta-module, meant for use by other modules, and should not be called from #invoke directly. Its features include:

  • Easy trimming of arguments and removal of blank arguments.
  • Arguments can be passed by both the current frame and by the parent frame at the same time. (More details below.)
  • Arguments can be passed in directly from another Lua module or from the debug console.
  • Arguments are fetched as needed, which can help avoid (some) problems with <ref>…</ref> tags.
  • Most features can be customized.

Basic use

First, you need to load the module. It contains one function, named getArgs.

local getArgs = require('Module:Arguments').getArgs

In the most basic scenario, you can use getArgs inside your main function. The variable args is a table containing the arguments from #invoke. (See below for details.)

local getArgs = require('Module:Arguments').getArgs
local p = {}

function p.main(frame)
	local args = getArgs(frame)
	-- Main module code goes here.
end

return p

However, the recommended practice is to use a function just for processing arguments from #invoke. This means that if someone calls your module from another Lua module you don't have to have a frame object available, which improves performance.

local getArgs = require('Module:Arguments').getArgs
local p = {}

function p.main(frame)
	local args = getArgs(frame)
	return p._main(args)
end

function p._main(args)
	-- Main module code goes here.
end

return p

If you want multiple functions to use the arguments, and you also want them to be accessible from #invoke, you can use a wrapper function.

local getArgs = require('Module:Arguments').getArgs

local function makeInvokeFunc(funcName)
	return function (frame)
		local args = getArgs(frame)
		return p[funcName](args)
	end
end

local p = {}

p.func1 = makeInvokeFunc('_func1')

function p._func1(args)
	-- Code for the first function goes here.
end

p.func2 = makeInvokeFunc('_func2')

function p._func2(args)
	-- Code for the second function goes here.
end

return p

Options

The following options are available. They are explained in the sections below.

local args = getArgs(frame, {
	trim = false,
	removeBlanks = false,
	valueFunc = function (key, value)
		-- Code for processing one argument
	end,
	frameOnly = true,
	parentOnly = true,
	parentFirst = true,
	wrappers = {
		'Template:A wrapper template',
		'Template:Another wrapper template'
	},
	readOnly = true,
	noOverwrite = true
})

Trimming and removing blanks

Blank arguments often trip up coders new to converting MediaWiki templates to Lua. In template syntax, blank strings and strings consisting only of whitespace are considered false. However, in Lua, blank strings and strings consisting of whitespace are considered true. This means that if you don't pay attention to such arguments when you write your Lua modules, you might treat something as true that should actually be treated as false. To avoid this, by default this module removes all blank arguments.

Similarly, whitespace can cause problems when dealing with positional arguments. Although whitespace is trimmed for named arguments coming from #invoke, it is preserved for positional arguments. Most of the time this additional whitespace is not desired, so this module trims it off by default.

However, sometimes you want to use blank arguments as input, and sometimes you want to keep additional whitespace. This can be necessary to convert some templates exactly as they were written. If you want to do this, you can set the trim and removeBlanks arguments to false.

local args = getArgs(frame, {
	trim = false,
	removeBlanks = false
})

Custom formatting of arguments

Sometimes you want to remove some blank arguments but not others, or perhaps you might want to put all of the positional arguments in lower case. To do things like this you can use the valueFunc option. The input to this option must be a function that takes two parameters, key and value, and returns a single value. This value is what you will get when you access the field key in the args table.

Example 1: this function preserves whitespace for the first positional argument, but trims all other arguments and removes all other blank arguments.

local args = getArgs(frame, {
	valueFunc = function (key, value)
		if key == 1 then
			return value
		elseif value then
			value = mw.text.trim(value)
			if value ~= '' then
				return value
			end
		end
		return nil
	end
})

Example 2: this function removes blank arguments and converts all arguments to lower case, but doesn't trim whitespace from positional parameters.

local args = getArgs(frame, {
	valueFunc = function (key, value)
		if not value then
			return nil
		end
		value = mw.ustring.lower(value)
		if mw.ustring.find(value, '%S') then
			return value
		end
		return nil
	end
})

Note: the above functions will fail if passed input that is not of type string or nil. This might be the case if you use the getArgs function in the main function of your module, and that function is called by another Lua module. In this case, you will need to check the type of your input. This is not a problem if you are using a function specially for arguments from #invoke (i.e. you have p.main and p._main functions, or something similar).

Examples 1 and 2 with type checking

Example 1:

local args = getArgs(frame, {
	valueFunc = function (key, value)
		if key == 1 then
			return value
		elseif type(value) == 'string' then
			value = mw.text.trim(value)
			if value ~= '' then
				return value
			else
				return nil
			end
		else
			return value
		end
	end
})

Example 2:

local args = getArgs(frame, {
	valueFunc = function (key, value)
		if type(value) == 'string' then
			value = mw.ustring.lower(value)
			if mw.ustring.find(value, '%S') then
				return value
			else
				return nil
			end
		else
			return value
		end
	end
})

Also, please note that the valueFunc function is called more or less every time an argument is requested from the args table, so if you care about performance you should make sure you aren't doing anything inefficient with your code.

Frames and parent frames

Arguments in the args table can be passed from the current frame or from its parent frame at the same time. To understand what this means, it is easiest to give an example. Let's say that we have a module called Module:ExampleArgs. This module prints the first two positional arguments that it is passed.

Module:ExampleArgs code
local getArgs = require('Module:Arguments').getArgs
local p = {}

function p.main(frame)
	local args = getArgs(frame)
	return p._main(args)
end

function p._main(args)
	local first = args[1] or ''
	local second = args[2] or ''
	return first .. ' ' .. second
end

return p

Module:ExampleArgs is then called by Template:ExampleArgs, which contains the code {{#invoke:ExampleArgs|main|firstInvokeArg}}. This produces the result "firstInvokeArg".

Now if we were to call Template:ExampleArgs, the following would happen:

Code Result
{{ExampleArgs}} firstInvokeArg
{{ExampleArgs|firstTemplateArg}} firstInvokeArg
{{ExampleArgs|firstTemplateArg|secondTemplateArg}} firstInvokeArg secondTemplateArg

There are three options you can set to change this behaviour: frameOnly, parentOnly and parentFirst. If you set frameOnly then only arguments passed from the current frame will be accepted; if you set parentOnly then only arguments passed from the parent frame will be accepted; and if you set parentFirst then arguments will be passed from both the current and parent frames, but the parent frame will have priority over the current frame. Here are the results in terms of Template:ExampleArgs:

frameOnly
Code Result
{{ExampleArgs}} firstInvokeArg
{{ExampleArgs|firstTemplateArg}} firstInvokeArg
{{ExampleArgs|firstTemplateArg|secondTemplateArg}} firstInvokeArg
parentOnly
Code Result
{{ExampleArgs}}
{{ExampleArgs|firstTemplateArg}} firstTemplateArg
{{ExampleArgs|firstTemplateArg|secondTemplateArg}} firstTemplateArg secondTemplateArg
parentFirst
Code Result
{{ExampleArgs}} firstInvokeArg
{{ExampleArgs|firstTemplateArg}} firstTemplateArg
{{ExampleArgs|firstTemplateArg|secondTemplateArg}} firstTemplateArg secondTemplateArg

Notes:

  1. If you set both the frameOnly and parentOnly options, the module won't fetch any arguments at all from #invoke. This is probably not what you want.
  2. In some situations a parent frame may not be available, e.g. if getArgs is passed the parent frame rather than the current frame. In this case, only the frame arguments will be used (unless parentOnly is set, in which case no arguments will be used) and the parentFirst and frameOnly options will have no effect.

Wrappers

The wrappers option is used to specify a limited number of templates as wrapper templates, that is, templates whose only purpose is to call a module. If the module detects that it is being called from a wrapper template, it will only check for arguments in the parent frame; otherwise it will only check for arguments in the frame passed to getArgs. This allows modules to be called by either #invoke or through a wrapper template without the loss of performance associated with having to check both the frame and the parent frame for each argument lookup.

For example, the only content of Template:Side box (excluding content in <noinclude>…</noinclude> tags) is {{#invoke:Side box|main}}. There is no point in checking the arguments passed directly to the #invoke statement for this template, as no arguments will ever be specified there. We can avoid checking arguments passed to #invoke by using the parentOnly option, but if we do this then #invoke will not work from other pages either. If this were the case, the |text=Some text in the code {{#invoke:Side box|main|text=Some text}} would be ignored completely, no matter what page it was used from. By using the wrappers option to specify 'Template:Side box' as a wrapper, we can make {{#invoke:Side box|main|text=Some text}} work from most pages, while still not requiring that the module check for arguments on the Template:Side box page itself.

Wrappers can be specified either as a string, or as an array of strings.

local args = getArgs(frame, {
	wrappers = 'Template:Wrapper template'
})


local args = getArgs(frame, {
	wrappers = {
		'Template:Wrapper 1',
		'Template:Wrapper 2',
		-- Any number of wrapper templates can be added here.
	}
})

Notes:

  1. The module will automatically detect if it is being called from a wrapper template's /sandbox subpage, so there is no need to specify sandbox pages explicitly.
  2. The wrappers option effectively changes the default of the frameOnly and parentOnly options. If, for example, parentOnly were explicitly set to false with wrappers set, calls via wrapper templates would result in both frame and parent arguments being loaded, though calls not via wrapper templates would result in only frame arguments being loaded.
  3. If the wrappers option is set and no parent frame is available, the module will always get the arguments from the frame passed to getArgs.

Writing to the args table

Sometimes it can be useful to write new values to the args table. This is possible with the default settings of this module. (However, bear in mind that it is usually better coding style to create a new table with your new values and copy arguments from the args table as needed.)

args.foo = 'some value'

It is possible to alter this behaviour with the readOnly and noOverwrite options. If readOnly is set then it is not possible to write any values to the args table at all. If noOverwrite is set, then it is possible to add new values to the table, but it is not possible to add a value if it would overwrite any arguments that are passed from #invoke.

Ref tags

This module uses metatables to fetch arguments from #invoke. This allows access to both the frame arguments and the parent frame arguments without using the pairs() function. This can help if your module might be passed <ref>…</ref> tags as input.

As soon as <ref>…</ref> tags are accessed from Lua, they are processed by the MediaWiki software and the reference will appear in the reference list at the bottom of the article. If your module proceeds to omit the reference tag from the output, you will end up with a phantom reference - a reference that appears in the reference list, but no number that links to it. This has been a problem with modules that use pairs() to detect whether to use the arguments from the frame or the parent frame, as those modules automatically process every available argument.

This module solves this problem by allowing access to both frame and parent frame arguments, while still only fetching those arguments when it is necessary. The problem will still occur if you use pairs(args) elsewhere in your module, however.

Known limitations

The use of metatables also has its downsides. Most of the normal Lua table tools won't work properly on the args table, including the # operator, the next() function, and the functions in the table library. If using these is important for your module, you should use your own argument processing function instead of this module.

  1 -- This module provides easy processing of arguments passed to Scribunto from
  2 -- #invoke. It is intended for use by other Lua modules, and should not be
  3 -- called from #invoke directly.
  4 
  5 local libraryUtil = require('libraryUtil')
  6 local checkType = libraryUtil.checkType
  7 
  8 local arguments = {}
  9 
 10 -- Generate four different tidyVal functions, so that we don't have to check the
 11 -- options every time we call it.
 12 
 13 local function tidyValDefault(key, val)
 14 	if type(val) == 'string' then
 15 		val = val:match('^%s*(.-)%s*$')
 16 		if val == '' then
 17 			return nil
 18 		else
 19 			return val
 20 		end
 21 	else
 22 		return val
 23 	end
 24 end
 25 
 26 local function tidyValTrimOnly(key, val)
 27 	if type(val) == 'string' then
 28 		return val:match('^%s*(.-)%s*$')
 29 	else
 30 		return val
 31 	end
 32 end
 33 
 34 local function tidyValRemoveBlanksOnly(key, val)
 35 	if type(val) == 'string' then
 36 		if val:find('%S') then
 37 			return val
 38 		else
 39 			return nil
 40 		end
 41 	else
 42 		return val
 43 	end
 44 end
 45 
 46 local function tidyValNoChange(key, val)
 47 	return val
 48 end
 49 
 50 function arguments.getArgs(frame, options)
 51 	checkType('getArgs', 1, frame, 'table', true)
 52 	checkType('getArgs', 2, options, 'table', true)
 53 	frame = frame or {}
 54 	options = options or {}
 55 
 56 	--[[
 57 	-- Get the argument tables. If we were passed a valid frame object, get the
 58 	-- frame arguments (fargs) and the parent frame arguments (pargs), depending
 59 	-- on the options set and on the parent frame's availability. If we weren't
 60 	-- passed a valid frame object, we are being called from another Lua module
 61 	-- or from the debug console, so assume that we were passed a table of args
 62 	-- directly, and assign it to a new variable (luaArgs).
 63 	--]]
 64 	local fargs, pargs, luaArgs
 65 	if type(frame.args) == 'table' and type(frame.getParent) == 'function' then
 66 		if options.wrappers then
 67 			--[[
 68 			-- The wrappers option makes Module:Arguments look up arguments in
 69 			-- either the frame argument table or the parent argument table, but
 70 			-- not both. This means that users can use either the #invoke syntax
 71 			-- or a wrapper template without the loss of performance associated
 72 			-- with looking arguments up in both the frame and the parent frame.
 73 			-- Module:Arguments will look up arguments in the parent frame
 74 			-- if it finds the parent frame's title in options.wrapper;
 75 			-- otherwise it will look up arguments in the frame object passed
 76 			-- to getArgs.
 77 			--]]
 78 			local parent = frame:getParent()
 79 			if not parent then
 80 				fargs = frame.args
 81 			else
 82 				local title = parent:getTitle():gsub('/sandbox$', '')
 83 				local found = false
 84 				if type(options.wrappers) == 'table' then
 85 					for _,v in pairs(options.wrappers) do
 86 						if v == title then
 87 							found = true
 88 							break
 89 						end
 90 					end
 91 				elseif options.wrappers == title then
 92 					found = true
 93 				end
 94 				
 95 				-- We test for false specifically here so that nil (the default) acts like true.
 96 				if found or options.frameOnly == false then
 97 					pargs = parent.args
 98 				end
 99 				if not found or options.parentOnly == false then
100 					fargs = frame.args
101 				end
102 			end
103 		else
104 			-- options.wrapper isn't set, so check the other options.
105 			if not options.parentOnly then
106 				fargs = frame.args
107 			end
108 			if not options.frameOnly then
109 				local parent = frame:getParent()
110 				pargs = parent and parent.args or nil
111 			end
112 		end
113 		if options.parentFirst then
114 			fargs, pargs = pargs, fargs
115 		end
116 	else
117 		luaArgs = frame
118 	end
119 	
120 	-- Set the order of precedence of the argument tables. If the variables are
121 	-- nil, nothing will be added to the table, which is how we avoid clashes
122 	-- between the frame/parent args and the Lua args.	
123 	local argTables = {fargs}
124 	argTables[#argTables + 1] = pargs
125 	argTables[#argTables + 1] = luaArgs
126 
127 	--[[
128 	-- Generate the tidyVal function. If it has been specified by the user, we
129 	-- use that; if not, we choose one of four functions depending on the
130 	-- options chosen. This is so that we don't have to call the options table
131 	-- every time the function is called.
132 	--]]
133 	local tidyVal = options.valueFunc
134 	if tidyVal then
135 		if type(tidyVal) ~= 'function' then
136 			error(
137 				"bad value assigned to option 'valueFunc'"
138 					.. '(function expected, got '
139 					.. type(tidyVal)
140 					.. ')',
141 				2
142 			)
143 		end
144 	elseif options.trim ~= false then
145 		if options.removeBlanks ~= false then
146 			tidyVal = tidyValDefault
147 		else
148 			tidyVal = tidyValTrimOnly
149 		end
150 	else
151 		if options.removeBlanks ~= false then
152 			tidyVal = tidyValRemoveBlanksOnly
153 		else
154 			tidyVal = tidyValNoChange
155 		end
156 	end
157 
158 	--[[
159 	-- Set up the args, metaArgs and nilArgs tables. args will be the one
160 	-- accessed from functions, and metaArgs will hold the actual arguments. Nil
161 	-- arguments are memoized in nilArgs, and the metatable connects all of them
162 	-- together.
163 	--]]
164 	local args, metaArgs, nilArgs, metatable = {}, {}, {}, {}
165 	setmetatable(args, metatable)
166 
167 	local function mergeArgs(iterator, tables)
168 		--[[
169 		-- Accepts multiple tables as input and merges their keys and values
170 		-- into one table using the specified iterator. If a value is already
171 		-- present it is not overwritten; tables listed earlier have precedence.
172 		-- We are also memoizing nil values, which can be overwritten if they
173 		-- are 's' (soft).
174 		--]]
175 		for _, t in ipairs(tables) do
176 			for key, val in iterator(t) do
177 				if metaArgs[key] == nil and nilArgs[key] ~= 'h' then
178 					local tidiedVal = tidyVal(key, val)
179 					if tidiedVal == nil then
180 						nilArgs[key] = 's'
181 					else
182 						metaArgs[key] = tidiedVal
183 					end
184 				end
185 			end
186 		end
187 	end
188 
189 	--[[
190 	-- Define metatable behaviour. Arguments are memoized in the metaArgs table,
191 	-- and are only fetched from the argument tables once. Fetching arguments
192 	-- from the argument tables is the most resource-intensive step in this
193 	-- module, so we try and avoid it where possible. For this reason, nil
194 	-- arguments are also memoized, in the nilArgs table. Also, we keep a record
195 	-- in the metatable of when pairs and ipairs have been called, so we do not
196 	-- run pairs and ipairs on the argument tables more than once. We also do
197 	-- not run ipairs on fargs and pargs if pairs has already been run, as all
198 	-- the arguments will already have been copied over.
199 	--]]
200 
201 	metatable.__index = function (t, key)
202 		--[[
203 		-- Fetches an argument when the args table is indexed. First we check
204 		-- to see if the value is memoized, and if not we try and fetch it from
205 		-- the argument tables. When we check memoization, we need to check
206 		-- metaArgs before nilArgs, as both can be non-nil at the same time.
207 		-- If the argument is not present in metaArgs, we also check whether
208 		-- pairs has been run yet. If pairs has already been run, we return nil.
209 		-- This is because all the arguments will have already been copied into
210 		-- metaArgs by the mergeArgs function, meaning that any other arguments
211 		-- must be nil.
212 		--]]
213 		local val = metaArgs[key]
214 		if val ~= nil then
215 			return val
216 		elseif metatable.donePairs or nilArgs[key] then
217 			return nil
218 		end
219 		for _, argTable in ipairs(argTables) do
220 			local argTableVal = tidyVal(key, argTable[key])
221 			if argTableVal ~= nil then
222 				metaArgs[key] = argTableVal
223 				return argTableVal
224 			end
225 		end
226 		nilArgs[key] = 'h'
227 		return nil
228 	end
229 
230 	metatable.__newindex = function (t, key, val)
231 		-- This function is called when a module tries to add a new value to the
232 		-- args table, or tries to change an existing value.
233 		if options.readOnly then
234 			error(
235 				'could not write to argument table key "'
236 					.. tostring(key)
237 					.. '"; the table is read-only',
238 				2
239 			)
240 		elseif options.noOverwrite and args[key] ~= nil then
241 			error(
242 				'could not write to argument table key "'
243 					.. tostring(key)
244 					.. '"; overwriting existing arguments is not permitted',
245 				2
246 			)
247 		elseif val == nil then
248 			--[[
249 			-- If the argument is to be overwritten with nil, we need to erase
250 			-- the value in metaArgs, so that __index, __pairs and __ipairs do
251 			-- not use a previous existing value, if present; and we also need
252 			-- to memoize the nil in nilArgs, so that the value isn't looked
253 			-- up in the argument tables if it is accessed again.
254 			--]]
255 			metaArgs[key] = nil
256 			nilArgs[key] = 'h'
257 		else
258 			metaArgs[key] = val
259 		end
260 	end
261 
262 	metatable.__pairs = function ()
263 		-- Called when pairs is run on the args table.
264 		if not metatable.donePairs then
265 			mergeArgs(pairs, argTables)
266 			metatable.donePairs = true
267 			metatable.doneIpairs = true
268 		end
269 		return pairs(metaArgs)
270 	end
271 
272 	metatable.__ipairs = function ()
273 		-- Called when ipairs is run on the args table.
274 		if not metatable.doneIpairs then
275 			mergeArgs(ipairs, argTables)
276 			metatable.doneIpairs = true
277 		end
278 		return ipairs(metaArgs)
279 	end
280 
281 	return args
282 end
283 
284 return arguments