Module:parameters

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This module provides processing and checking of template arguments.

process[edit]

process(args, params, return_unknown)

Processes arguments with a given list of parameters, and returns a table containing the processed arguments. The args parameter specifies the arguments to be processed; they are the arguments you might retrieve from frame:getParent().args. The params parameter specifies a list of valid parameters, and consists of a table. If an argument is encountered that is not in the parameter table, an error is shown.

The parameters table should have the parameter names as the indexes, and a (possibly empty) table of parameter tags as the value. An empty table as the value merely states that the parameter exists, but should not receive any special treatment. Possible parameter tags are listed below.

An example parameters table (from Module:translations):

{
	[1] = {required = true, default = "und"},
	[2] = {},
	[3] = {list = true},
	["alt"] = {},
	["sc"] = {},
	["tr"] = {},
}

The return_unknown parameter, if set to true, prevents the function from triggering an error when it comes across an argument with a name that it doesn't recognise. Instead, the return value is a pair of values: the first is the processed arguments as usual, while the second contains all the unrecognised arguments that were left unprocessed. This allows you to do multi-stage processing, where the entire set of arguments that a template should accept is not known at once. For example, an inflection-table might do some generic processing on some arguments, but then defer processing of the remainder to the function that handles a specific inflectional type.

Parameter tags[edit]

required=true
The parameter is required; an error is shown if it is not present. The template's page itself is an exception; no error is shown there.
default=
Specifies a default value for the parameter, if it is absent or empty. When used on list parameters, this specifies a default value for the first item in the list only. Note that it is not possible to generate a default that depends on the value of other parameters.
If used together with required=true, the default applies only to the template's page itself. This can be used to show an example text.
alias_of=
Treat the parameter as an alias of another. When arguments are specified for this parameter, they will automatically be renamed and stored under the alias name. This allows for parameters with multiple alternative names, while still treating them as if they had only one name. It is even possible for the alias_of= to have a name that is not a parameter itself.
Aliases should not be required, as this prevents the other name or names of the parameter from being used. Parameters that are aliases and required at the same time are tracked (see Special:WhatLinksHere/Template:tracking/parameters/required alias).
allow_empty=true
If the argument is an empty string value, it is not converted to nil, but kept as-is.
type=
Specifies what value type to convert the argument into. The default is to leave it as a text string. Alternatives are:
type="boolean"
The value is treated as a boolean value, either true or false. No value, the empty string, and the strings "0", "no", "n" and "false" are treated as false, all other values are considered true.
type="number"
The value is converted into a number, unless it is nil.
list=
Treat the parameter as a list of values, each having its own parameter name, rather than a single value. The parameters will have a number at the end, except for the first. For example, list=true on a parameter named "head" will include the parameters |head=, |head2=, |head3= and so on. If the parameter name is a number, another number doesn't get appended, but the counting simply continues, e.g. for parameter 3 the sequence is |3=, |4=, |5= etc. List parameters are returned as numbered lists, so for a template that is given the parameters head=a|head2=b|head3=c, the processed value of the parameter "head" will be {"a", "b", "c"}.
The value for list= can also be a string. This tells the module that parameters other than the first should have a different name, which is useful when the first parameter in a list is a number, but the remainder is named. An example would be for genders: list="g" on a parameter named 1 would have parameters |1=, |g2=, |g3= etc.
If the number is not located at the end, it can be specified by putting an equal sign "=" at the number position. For example, parameters "f1accel", "f2accel", ... can be captured by using the parameter name "f=accel", as is done in Module:headword/templates.
allow_holes=true
This is used in conjunction with list-type parameters. By default, the values are tightly packed in the resulting list. This means that if, for example, an entry specified head=a|head3=c but not |head2=, the returned list will be {"a", "c"}, with the values stored as index 1 and 2, not 1 and 3. If it is desirable to keep the numbering intact, for example if the numbers of several list parameters correlate with each other (like those of {{compound}}), then this tag can be specified.
If allow_holes=true is given, there may be nil values in between two real values, which makes many of Lua's table processing functions no longer work, like # or ipairs(). To remedy this, the resulting table will contain an additional named value, maxindex, which tells you the highest numeric index that is present in the table. In the example above, the resulting table will now be {"a", nil, "c", maxindex=3}. That way, you can iterate over the values from 1 to maxindex, while skipping nil values in between.

local export = {}

-- A helper function to escape magic characters in a string
-- Magic characters: ^$()%.[]*+-?
local plain = require("Module:string").pattern_escape

-- A helper function that removes empty numeric indexes in a table,
-- so that the values are tightly packed like in a normal Lua table.
local remove_holes = require("Module:table").compressSparseArray

function export.process(args, params, return_unknown)
	local args_new = {}
	
	-- Process parameters for specific properties
	local required = {}
	local patterns = {}
	local list_from_index = nil
	
	for name, param in pairs(params) do
		if param.required then
			if param.alias_of then
				require("Module:debug").track("parameters/required alias")
			end
			required[name] = true
		end
		
		if param.list then
			local key = name
			if type(name) == "string" then
				key = mw.ustring.gsub(name, "=", "")
			end
			if param.default ~= nil then
				args_new[key] = {param.default, maxindex = 1}
			else
				args_new[key] = {maxindex = 0}
			end
			
			if type(param.list) == "string" then
				-- If the list property is a string, then it represents the name
				-- to be used as the prefix for list items. This is for use with lists
				-- where the first item is a numbered parameter and the
				-- subsequent ones are named, such as 1, pl2, pl3.
				if mw.ustring.find(param.list, "=") then
					patterns["^" .. mw.ustring.gsub(plain(param.list), "=", "(%%d+)") .. "$"] = name
				else
					patterns["^" .. plain(param.list) .. "(%d+)$"] = name
				end
			elseif type(name) == "number" then
				-- If the name is a number, then all indexed parameters from
				-- this number onwards go in the list.
				list_from_index = name
			else
				if mw.ustring.find(name, "=") then
					patterns["^" .. mw.ustring.gsub(plain(name), "=", "(%%d+)") .. "$"] = mw.ustring.gsub(name, "=", "")
				else
					patterns["^" .. plain(name) .. "(%d+)$"] = name
				end
			end
			
			if mw.ustring.find(name, "=") then
				require("Module:debug").track("parameters/name with equals")
				params[mw.ustring.gsub(name, "=", "")] = params[name]
				params[name] = nil
			end
		elseif param.default ~= nil then
			args_new[name] = param.default
		end
	end
	
	-- Process the arguments
	local args_unknown = {}
	
	for name, val in pairs(args) do
		local index = nil
		
		if type(name) == "number" then
			if list_from_index ~= nil and name >= list_from_index then
				index = name - list_from_index + 1
				name = list_from_index
			end
		else
			-- Does this argument name match a pattern?
			for pattern, pname in pairs(patterns) do
				index = mw.ustring.match(name, pattern)
				
				-- It matches, so store the parameter name and the
				-- numeric index extracted from the argument name.
				if index then
					index = tonumber(index)
					name = pname
					break
				end
			end
		end
		
		-- If no index was found, use 1 as the default index.
		-- This makes list parameters like g, g2, g3 put g at index 1.
		index = index or 1
		
		local param = params[name]
		
		-- If the argument is not in the list of parameters, trigger an error.
		-- return_unknown suppresses the error, and stores it in a separate list instead.
		if not param then
			if return_unknown then
				args_unknown[name] = val
			else
				error("The parameter \"" .. name .. "\" is not used by this template.")
			end
		else
			-- Remove leading and trailing whitespace
			val = mw.text.trim(val)
			
			-- Empty string is equivalent to nil unless allow_empty is true.
			if val == "" and not param.allow_empty then
				val = nil
			end
			
			-- Convert to proper type if necessary.
			if param.type == "boolean" then
				val = not (not val or val == "" or val == "0" or val == "no" or val == "n" or val == "false")
			elseif param.type == "number" and val ~= nil then
				val = tonumber(val)
			end
			
			-- Can't use "if val" alone, because val may be a boolean false.
			if val ~= nil then
				-- Mark it as no longer required, as it is present.
				required[param.alias_of or name] = nil
				
				-- Store the argument value.
				if param.list then
					-- If the parameter is an alias of another, store it as the original,
					-- but avoid overwriting it; the original takes precedence.
					if not param.alias_of then
						args_new[name][index] = val
						
						-- Store the highest index we find.
						args_new[name].maxindex = math.max(index, args_new[name].maxindex)
					elseif args[param.alias_of] == nil then
						if params[param.alias_of] and params[param.alias_of].list then
							args_new[param.alias_of][index] = val
							
							-- Store the highest index we find.
							args_new[param.alias_of].maxindex = math.max(1, args_new[param.alias_of].maxindex)
						else
							args_new[param.alias_of] = val
						end
					end
				else
					-- If the parameter is an alias of another, store it as the original,
					-- but avoid overwriting it; the original takes precedence.
					if not param.alias_of then
						args_new[name] = val
					elseif args[param.alias_of] == nil then
						if params[param.alias_of] and params[param.alias_of].list then
							args_new[param.alias_of][1] = val
							
							-- Store the highest index we find.
							args_new[param.alias_of].maxindex = math.max(1, args_new[param.alias_of].maxindex)
						else
							args_new[param.alias_of] = val
						end
					end
				end
			end
		end
	end
	
	-- The required table should now be empty.
	-- If any entry remains, trigger an error, unless we're in the template namespace.
	if mw.title.getCurrentTitle().nsText ~= "Template" then
		local list = {}
		for name, param in pairs(required) do
			table.insert(list, name)
		end
		
		local count = #list
		if count == 1 then
			error('The parameter "' .. list[1] .. '" is required.', 2)
		elseif count == 2 then
			error('The parameters "' .. table.concat(list, '" and "') .. '" are required.', 2)
		elseif count > 2 then
			error('The parameters "' .. mw.text.listToText(list, '", "', '", and "') .. '" are required.', 2)
		end
	end
	
	-- Remove holes in any list parameters if needed.
	for name, val in pairs(args_new) do
		if type(val) == "table" and not params[name].allow_holes then
			args_new[name] = remove_holes(val)
		end
	end
	
	if return_unknown then
		return args_new, args_unknown
	else
		return args_new
	end
end

return export