Module:Redirect

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This documentation is transcluded from Module:Redirect/doc.

Note: This module is used on a lot of pages. In order not to put too much load on the servers, edits should be kept to a bare minimum. Please discuss proposed changes on the talk page first.

• Editing a module causes all pages that use the module to be re-rendered. If the module is used often, this can put a lot of load on the servers since it fills up the job queue.
• Keep in mind that displays produced by modules used on file description pages also show up on other wikis.

This module implements templates that detect and resolve redirects and soft category redirects.

Soft redirects are hard to detect and costly as they require loading and parsing the wiki page content of 'Category:' pages.

Soft redirects are category pages containing the template

• {{Category redirect|target|optional reason}}

or one of its known aliases on Commons (there are too many!!!): Template:Columns For the full list of aliases (simple redirections) of {{Category redirect}}, see

https://commons.wikimedia.org/w/index.php?title=Special:WhatLinksHere/Template:Category_redirect&hidetrans=1&hidelinks=1

For the full list of derived templates (specifying an embedded reason parameter passed to the main template), see

https://commons.wikimedia.org/w/index.php?title=Special:WhatLinksHere/Template:Category_redirect&namespace=10&hidelinks=1&hideredirs=1

The 'target' parameter value for these templates may be prefixed by 'Category:' or ':Category:' or not (it is implied).

There should exist only one soft-redirect or redirection per page. If you need several redirections (because the original name was ambiguous and could refer to several distinct topics), this means that this redirection page has to be converted into a disambiguation page, providing a list of links to the different possible targets (each linked target page may be possibly followed by a short descriptive comment without any link, in order to help users making the right choice).

-- This module provides functions for getting the target of a redirect page.

local p = {}

-- Gets a mw.title object, using pcall to avoid generating script errors if we
-- are over the expensive function count limit (among other possible causes).
local function getTitle(...)
	local success, titleObj = pcall(mw.title.new, ...)
	if success then
		return titleObj
	else
		return nil
	end
end

local function fmtTitle(page, fulltext, ck)
	if page then
		local t = getTitle(page)
		if t and (not ck or ck and t.exists) then
			return fulltext and t.fullText or t.prefixedText
		end
	end
end

function p.getTargetFromCatRedirect(text)
	local r = text:match("{{%s*[Cc]at%a*%s?redirect%s*|[%s:]*([^}|]-)[}|]") or
			  text:match(        "{{%s*[Ss]ee%s?cat%s*|[%s:]*([^}|]-)[}|]")
	return r and (r:match("^.ategory:") and r or "Category:"..r)
end

function p.getTargetFromText(text)
	return text:match("#[Rr][Ee][Dd]...[Cc][Tt][%s:]*%[%[([^]|]+)")
end

-- Get page name that a redirect leads to, or nil if it isn't a redirect.
function p.getTargetFrom(obj)
	local text = obj:getContent() or ""
	local r = p.getTargetFromText(text)

	if not r then
		if obj:inNamespace("Category") then
			r = p.getTargetFromCatRedirect(text)
		end
		if not r and obj.isRedirect then
			-- The page is a redirect, but matching failed, which may be a bug
			-- in redirect matching pattern, so throw an error.
			error(string.format(
				'could not parse redirect on page "%s"',
				fulltext and obj.fullText or obj.prefixedText
			))
		end
	end
	
	return r
end

-- Gets the target of a redirect. If the page specified is not a redirect,
-- returns nil.
function p.getTarget(page, fulltext, ck)
	-- Get the title object. Both page names and title objects are allowed
	-- as input.
	local titleObj
	if type(page) == 'string' or type(page) == 'number' then
		titleObj = getTitle(page)
	elseif type(page) == 'table' and type(page.getContent) == 'function' then
		titleObj = page
	else
		error(string.format(
			"bad argument #1 to 'getTarget'"
				.. " (string, number, or title object expected, got %s)",
			type(page)
		), 2)
	end
	
	if titleObj and titleObj.exists and
		(titleObj.isRedirect or titleObj:inNamespace("Category"))
	then
		-- Find the target by using string matching on the page content.
		return fmtTitle(p.getTargetFrom(titleObj), fulltext, ck)
	end
end

--[[
-- Given a single page name determines what page it redirects to and returns the
-- target page name, or the passed page name when not a redirect. The passed
-- page name can be given as plain text or as a page link.
-- 
-- Returns page name as plain text, or when the bracket parameter is given, as a
-- page link. Returns an error message when page does not exist or the redirect
-- target cannot be determined for some reason.
--]]
function p.luaMain(rname, bracket, fulltext, ensureTitleExists)
	if type(rname) ~= "string" or not rname:find("%S") then
		return nil
	end
	bracket = bracket and "[[%s]]" or "%s"
	rname = rname:match("%[%[(.*)%]%]") or rname
	local ret = p.getTarget(rname, fulltext, ensureTitleExists) or
				fmtTitle(rname, fulltext, ensureTitleExists)
	
	return ret and bracket:format(ret)
end

local function _main(frame, ck, alt)
	local args = require('Module:Arguments').getArgs(frame, {frameOnly = true})
	--ck = ck or args.noredlinks
	--alt = alt or args[2]
	return p.luaMain(args[1], args.bracket, args.fulltext, ck) or alt or ''
end

-- Provides access to the luaMain function from wikitext, may return redlinks,
-- albeit page titles that do not exist in the wiki. ck and alt are optional
function p.main(frame)
	return _main(frame)
end

-- main variant, returns empty string if a redlink would be returned otherwise
function p.mainE(frame)
	return _main(frame, true)
end

-- main variant, returns args[2] if a redlink would be returned otherwise
function p.mainA(frame)
	return _main(frame, true, args[2])
end

-- Returns true if the specified page is a redirect, and false otherwise.
function p.luaIsRedirect(page)
	local titleObj = getTitle(page)
	if not titleObj then
		return false
	end
	if titleObj.isRedirect then
		return true
	else
		return false
	end
end

-- Provides access to the luaIsRedirect function from wikitext, returning 'yes'
-- if the specified page is a redirect, and the blank string otherwise.
function p.isRedirect(frame)
	local args = require('Module:Arguments').getArgs(frame, {frameOnly = true})
	if p.luaIsRedirect(args[1]) then
		return 'yes'
	else
		return ''
	end
end

return p