Module:template parser

--[[
NOTE: This module works by using recursive backtracking to build a node tree, which can then be traversed as necessary.

Because it is called by a number of high-use modules, it has been optimised for speed using a profiler, since it is used to scrape data from large numbers of pages very quickly. To that end, it rolls some of its own methods in cases where this is faster than using a function from one of the standard libraries. Please DO NOT "simplify" the code by removing these, since you are almost guaranteed to slow things down, which could seriously impact performance on pages which call this module hundreds or thousands of times.

It has also been designed to emulate the native parser's behaviour as much as possible, which in some cases means replicating bugs or unintuitive behaviours in that code; these should not be "fixed", since it is important that the outputs are the same. Most of these originate from deficient regular expressions, which can't be used here, so the bugs have to be manually reintroduced as special cases (e.g. onlyinclude tags being case-sensitive and whitespace intolerant, unlike all other tags). If any of these are fixed, this module should also be updated accordingly.
]]
local export = {}

local pages_module = "Module:pages"
local parser_module = "Module:parser"
local string_utilities_module = "Module:string utilities"
local table_module = "Module:table"

local require = require

local m_parser = require(parser_module)
local mw = mw
local mw_title = mw.title
local mw_uri = mw.uri
local string = string
local table = table

local anchor_encode = mw_uri.anchorEncode
local build_template -- defined as export.buildTemplate below
local class_else_type = m_parser.class_else_type
local concat = table.concat
local encode_uri = mw_uri.encode
local find = string.find
local format = string.format
local getmetatable = getmetatable
local gsub = string.gsub
local html_create = mw.html.create
local insert = table.insert
local is_node = m_parser.is_node
local load_data = mw.loadData
local lower = string.lower
local make_title = mw_title.makeTitle -- unconditionally adds the specified namespace prefix
local match = string.match
local new_title = mw_title.new -- specified namespace prefix is only added if the input doesn't contain one
local next = next
local pairs = pairs
local parse -- defined as export.parse below
local parse_template_name -- defined below
local pcall = pcall
local rep = string.rep
local reverse = string.reverse
local select = select
local sub = string.sub
local title_equals = mw_title.equals
local tostring = m_parser.tostring
local type = type
local umatch = mw.ustring.match

local data = load_data("Module:template parser/data")
local frame = mw.getCurrentFrame()
local magic_words = load_data("Module:data/magic words")
local parser_extension_tags = load_data("Module:data/parser extension tags")
local php_htmlspecialchars_data = data.php_htmlspecialchars
local valid_attribute_name = data.valid_attribute_name

-- Functions in other modules that load locally on demand by dereferencing themselves.
local function decode_entities(...)
	decode_entities = require(string_utilities_module).decode_entities
	return decode_entities(...)
end

local function encode_entities(...)
	encode_entities = require(string_utilities_module).encode_entities
	return encode_entities(...)
end

local function is_valid_title(...)
	is_valid_title = require(pages_module).is_valid_title
	return is_valid_title(...)
end

local function pattern_escape(...)
	pattern_escape = require(string_utilities_module).pattern_escape
	return pattern_escape(...)
end

local function php_trim(...)
	php_trim = require(string_utilities_module).php_trim
	return php_trim(...)
end

local function replacement_escape(...)
	replacement_escape = require(string_utilities_module).replacement_escape
	return replacement_escape(...)
end

local function scribunto_param_key(...)
	scribunto_param_key = require(string_utilities_module).scribunto_param_key
	return scribunto_param_key(...)
end

local function sorted_pairs(...)
	sorted_pairs = require(table_module).sortedPairs
	return sorted_pairs(...)
end

local function split(...)
	split = require(string_utilities_module).split
	return split(...)
end

local function table_len(...)
	table_len = require(table_module).length
	return table_len(...)
end

local function uupper(...)
	uupper = require(string_utilities_module).upper
	return uupper(...)
end

local Parser, Node = m_parser.new()

local function php_htmlspecialchars(str, compat)
	return (gsub(str, compat and "" or "", php_htmlspecialchars_data))
end

------------------------------------------------------------------------------------
--
-- Nodes
--
------------------------------------------------------------------------------------

Node.keys_to_remove = {"handler", "head", "pattern", "route", "step"}

local function expand(obj, frame_args)
	return is_node(obj) and obj:expand(frame_args) or obj
end
export.expand = expand

function Node:expand(frame_args)
	local output = {}
	for i = 1, #self do
		output = expand(self, frame_args)
	end
	return concat(output)
end

local Wikitext = Node:new_class("wikitext")

-- force_node ensures the output will always be a node.
function Wikitext:new(this, force_node)
	if type(this) ~= "table" then
		return force_node and Node.new(self, {this}) or this
	elseif #this == 1 then
		local this1 = this
		return force_node and not is_node(this1) and Node.new(self, this) or this1
	end
	local success, str = pcall(concat, this)
	if success then
		return force_node and Node.new(self, {str}) or str
	end
	return Node.new(self, this)
end

-- First value is the parameter name.
-- Second value is the parameter's default value.
-- Any additional values are ignored: e.g. "{{{a|b|c}}}" is parameter "a" with default value "b" (*not* "b|c").
local Parameter = Node:new_class("parameter")

function Parameter:new(this)
	local this2 = this
	if class_else_type(this2) == "argument" then
		insert(this2, 2, "=")
		this2 = Wikitext:new(this2)
	end
	return Node.new(self, {this, this2})
end

function Parameter:__tostring()
	local output = {}
	for i = 1, #self do
		output = tostring(self)
	end
	return "{{{" .. concat(output, "|") .. "}}}"
end

function Parameter:next(i)
	i = i + 1
	if i <= 2 then
		return self, self, i
	end
end

function Parameter:get_name(frame_args)
	return scribunto_param_key(expand(self, frame_args))
end

function Parameter:get_default(frame_args)
	local default = self
	if default ~= nil then
		return expand(default, frame_args)
	end
	return "{{{" .. expand(self, frame_args) .. "}}}"
end

function Parameter:expand(frame_args)
	if frame_args == nil then
		return self:get_default()
	end
	local name = expand(self, frame_args)
	local val = frame_args -- Parameter in use.
	if val ~= nil then
		return val
	end
	val = self -- Default.
	if val ~= nil then
		return expand(val, frame_args)
	end
	return "{{{" .. name .. "}}}"
end

local Argument = Node:new_class("argument")

function Argument:__tostring()
	return tostring(self) .. "=" .. tostring(self)
end

function Argument:expand(frame_args)
	return expand(self, frame_args) .. "=" .. expand(self, frame_args)
end

local Template = Node:new_class("template")

function Template:__tostring()
	local output = {}
	for i = 1, #self do
		output = tostring(self)
	end
	return "{{" .. concat(output, "|") .. "}}"
end

-- Normalize the template name, check it's a valid template, then memoize results (using false for invalid titles).
-- Parser functions (e.g. {{#IF:a|b|c}}) need to have the first argument extracted from the title, as it comes after the colon. Because of this, the parser function and first argument are memoized as a table.
-- FIXME: Some parser functions have special argument handling (e.g. {{#SWITCH:}}).
do
	local page_title = mw_title.getCurrentTitle()
	local namespace_has_subpages = mw.site.namespaces.hasSubpages
	local raw_pagename = page_title.fullText
	
	local templates = {}
	local parser_variables = {}
	local parser_functions = {}
	
	local function retrieve_magic_word_data(chunk)
		local mgw_data = magic_words
		if mgw_data then
			return mgw_data
		end
		local normalized = uupper(chunk)
		mgw_data = magic_words
		if mgw_data and not mgw_data.case_sensitive then
			return mgw_data
		end
	end
	
	-- Returns the name required to transclude the title object `title` using
	-- template {{ }} syntax.
	local function get_template_invocation_name(title)
		if not is_valid_title(title) then
			error("Template invocations require a valid page title, which cannot contain an interwiki prefix.")
		end
		local namespace = title.namespace
		-- If not in the template namespace, include the prefix (or ":" if
		-- mainspace).
		if namespace ~= 10 then
			return namespace == 0 and ":" .. title.text or title.prefixedText
		end
		-- If in the template namespace and it shares a name with a magic word,
		-- it needs the prefix "Template:".
		local text = title.text
		local colon = find(text, ":", 1, true)
		if not colon then
			local mgw_data = retrieve_magic_word_data(text)
			return mgw_data and mgw_data.parser_variable and title.prefixedText or text
		end
		local mgw_data = retrieve_magic_word_data(sub(text, 1, colon - 1))
		if mgw_data and (mgw_data.parser_function or mgw_data.transclusion_modifier) then
			return title.prefixedText
		end
		-- Also if "Template:" is necessary for disambiguation (e.g.
		-- "Template:Category:Foo" can't be abbreviated to "Category:Foo").
		local check = new_title(text, 10)
		return check and title_equals(title, check) and text or title.prefixedText
	end
	export.getTemplateInvocationName = get_template_invocation_name
	
	-- Resolve any redirects. If the redirect target is an interwiki link, then
	-- the template won't fail, but the redirect page itself gets transcluded
	-- (i.e. the template name shouldn't be normalized to the target).
	-- title.redirectTarget increments the expensive parser function count, but
	-- avoids extraneous transclusions polluting template lists and the
	-- performance hit caused by indiscriminately grabbing redirectTarget.
	-- However, if the expensive parser function limit has already been hit,
	-- redirectTarget is used as a fallback.
	local function resolve_redirect(title, force_transclusion)
		if not force_transclusion then
			local success, is_redirect = pcall(getmetatable(title).__index, title, "isRedirect")
			if success and not is_redirect then
				return title
			end
		end
		local redirect = title.redirectTarget
		return is_valid_title(redirect) and redirect or title
	end
	
	function parse_template_name(name, has_args, fragment, force_transclusion)
		local chunks, colon, start, n, p = {}, find(name, ":", 1, true), 1, 0, 0
		while colon do
			-- Pattern applies PHP ltrim.
			local mgw_data = retrieve_magic_word_data(match(sub(name, start, colon - 1), ".*") or "")
			if not mgw_data then
				break
			end
			local priority = mgw_data.priority
			if not (priority and priority > p) then
				local pf = mgw_data.parser_function and mgw_data.name or nil
				if pf then
					n = n + 1
					chunks = pf .. ":"
					return chunks, "parser function", sub(name, colon + 1)
				end
				break
			end
			n = n + 1
			chunks = mgw_data.name .. ":"
			start, p = colon + 1, priority
			colon = find(name, ":", start, true)
		end
		if start > 1 then
			name = sub(name, start)
		end
		name = php_trim(name)
		-- Parser variables can only take SUBST:/SAFESUBST: as modifiers.
		if not has_args and p <= 1 then
			local mgw_data = retrieve_magic_word_data(name)
			local pv = mgw_data and mgw_data.parser_variable and mgw_data.name or nil
			if pv then
				n = n + 1
				chunks = pv
				return chunks, "parser variable"
			end
		end
		-- Handle relative template names.
		if namespace_has_subpages then
			-- If the name starts with "/", it's treated as a subpage of the
			-- current page. Final slashes are trimmed, but this can't affect
			-- the intervening slash (e.g. {{///}} refers to "{{PAGENAME}}/").
			local initial = sub(name, 1, 1)
			if initial == "/" then
				name = raw_pagename .. (match(name, "^/.*") or "/")
			-- If it starts with "../", trim it and any that follow, and go up
			-- that many subpage levels. Then, treat any additional text as
			-- a subpage of that page; final slashes are trimmed.
			elseif initial == "." and sub(name, 2, 3) == "./" then
				local n = 4
				while sub(name, n, n + 2) == "../" do
					n = n + 3
				end
				-- Retain an initial "/".
				name = sub(name, n - 1)
				-- Trim the relevant number of subpages from the pagename.
				local pagename, i = reverse(raw_pagename), 0
				for _ = 1, (n - 1) / 3 do
					i = find(pagename, "/", i + 1, true)
					-- Fail if there aren't enough slashes.
					if not i then
						return nil
					end
				end
				-- Add the subpage text; since the intervening "/" is retained
				-- in `name`, it can be trimmed along with any other final
				-- slashes (e.g. {{..///}} refers to "{{BASEPAGENAME}}".)
				name = reverse(sub(pagename, i + 1)) .. (match(name, "^.*") or "")
			end
		end
		local title = new_title(name, 10)
		if not is_valid_title(title) then
			return nil
		end
		-- If `fragment` is set, save the original title's fragment, since it
		-- won't carry through to any redirect targets.
		if fragment then
			fragment = title.fragment
		end
		title = resolve_redirect(title, force_transclusion)
		local chunk = get_template_invocation_name(title)
		-- Set the fragment (if applicable).
		if fragment then
			chunk = chunk .. "#" .. fragment
		end
		chunks = chunk
		return chunks, "template"
	end
	
	-- Note: force_transclusion avoids incrementing the expensive parser
	-- function count by forcing transclusion instead. This should only be used
	-- when there is a real risk that the expensive parser function limit of
	-- 500 will be hit.
	local function process_name(self, frame_args, force_transclusion)
		local name = expand(self, frame_args)
		local has_args, norm = #self > 1
		if not has_args then
			norm = parser_variables
			if norm then
				return norm, "parser variable"
			end
		end
		norm = templates
		if norm then
			local pf_arg1 = parser_functions
			return norm, pf_arg1 and "parser function" or "template", pf_arg1
		elseif norm == false then
			return nil
		end
		local chunks, subclass, pf_arg1 = parse_template_name(name, has_args, nil, force_transclusion)
		-- Fail if invalid.
		if not chunks then
			templates = false
			return nil
		end
		local chunk1 = chunks
		-- Fail on SUBST:.
		if chunk1 == "SUBST:" then
			templates = false
			return nil
		-- Any modifiers are ignored.
		elseif subclass == "parser function" then
			local pf = chunks
			templates = pf
			parser_functions = pf_arg1
			return pf, "parser function", pf_arg1
		end
		-- Ignore SAFESUBST:, and treat MSGNW: as a parser function with the pagename as its first argument (ignoring any RAW: that comes after).
		if chunks == "MSGNW:" then
			pf_arg1 = chunks
			local pf = "MSGNW:"
			templates = pf
			parser_functions = pf_arg1
			return pf, "parser function", pf_arg1
		end
		-- Ignore any remaining modifiers, as they've done their job.
		local output = chunks
		if subclass == "parser variable" then
			parser_variables = output
		else
			templates = output
		end
		return output, subclass
	end
	
	function Template:get_name(frame_args, force_transclusion)
		-- Only return the first return value.
		return (process_name(self, frame_args, force_transclusion))
	end
	
	function Template:get_arguments(frame_args)
		local name, subclass, pf_arg1 = process_name(self, frame_args)
		if name == nil then
			return nil
		elseif subclass == "parser variable" then
			return {}
		end
		local template_args = {}
		if subclass == "parser function" then
			template_args = pf_arg1
			for i = 2, #self do
				template_args = expand(self, frame_args) -- Not trimmed.
			end
			return template_args
		end
		local implicit = 0
		for i = 2, #self do
			local arg = self
			if class_else_type(arg) == "argument" then
				template_args, frame_args))] = php_trim(expand(arg, frame_args))
			else
				implicit = implicit + 1
				template_args = expand(arg, frame_args) -- Not trimmed.
			end
		end
		return template_args
	end
end

-- BIG TODO: manual template expansion.
function Template:expand()
	return frame:preprocess(tostring(self))
end

local Tag = Node:new_class("tag")

function Tag:__tostring()
	local open_tag, attributes, n = {"<", self.name}, self:get_attributes(), 2
	for attr, value in next, attributes do
		n = n + 1
		open_tag = " " .. php_htmlspecialchars(attr) .. "=\"" .. php_htmlspecialchars(value, true) .. "\""
	end
	if self.self_closing then
		return concat(open_tag) .. "/>"
	end
	return concat(open_tag) .. ">" .. concat(self) .. "</" .. self.name .. ">"
end

function Tag:get_attributes()
	local raw = self.attributes
	if not raw then
		self.attributes = {}
		return self.attributes
	elseif type(raw) == "table" then
		return raw
	end
	if sub(raw, -1) == "/" then
		raw = sub(raw, 1, -2)
	end
	local attributes, head = {}, 1
	-- Semi-manual implementation of the native regex.
	while true do
		local name, loc = match(raw, "(*)()", head)
		if not name then
			break
		end
		head = loc
		local value
		loc = match(raw, "^*=*()", head)
		if loc then
			head = loc
			-- Either "", '' or the value ends on a space/at the end. Missing
			-- end quotes are repaired by closing the value at the end.
			value, loc = match(raw, "^\"(*)\"?()", head)
			if not value then
				value, loc = match(raw, "^'(*)'?()", head)
				if not value then
					value, loc = match(raw, "^(*)()", head)
				end
			end
			head = loc
		end
		-- valid_attribute_name is a pattern matching a valid attribute name.
		-- Defined in the data due to its length - see there for more info.
		if umatch(name, valid_attribute_name) then
			-- Sanitizer applies PHP strtolower (ASCII-only).
			attributes = value and decode_entities(
				php_trim((gsub(value, "+", " ")))
			) or ""
		end
	end
	self.attributes = attributes
	return attributes
end

function Tag:expand()
	return frame:preprocess(tostring(self))
end

local Heading = Node:new_class("heading")

function Heading:new(this)
	if #this > 1 then
		local success, str = pcall(concat, this)
		if success then
			return Node.new(self, {
				str,
				level = this.level,
				section = this.section,
				index = this.index
			})
		end
	end
	return Node.new(self, this)
end

function Heading:__tostring()
	local eq = rep("=", self.level)
	return eq .. Node.__tostring(self) .. eq
end

do
	local expand_node = Node.expand
	
	-- Expanded heading names can contain "\n" (e.g. inside nowiki tags), which
	-- causes any heading containing them to fail. However, in such cases, the
	-- native parser still treats it as a heading for the purpose of section
	-- numbers.
	local function validate_name(self, frame_args)
		local name = expand_node(self, frame_args)
		if find(name, "\n", 1, true) then
			return nil
		end
		return name
	end
	
	function Heading:get_name(frame_args)
		local name = validate_name(self, frame_args)
		return name ~= nil and php_trim(name) or nil
	end
	
	-- FIXME: account for anchor disambiguation.
	function Heading:get_anchor(frame_args)
		local name = validate_name(self, frame_args)
		return name ~= nil and decode_entities(anchor_encode(name)) or nil
	end
	
	function Heading:expand(frame_args)
		local eq = rep("=", self.level)
		return eq .. expand_node(self, frame_args) .. eq
	end
end

------------------------------------------------------------------------------------
--
-- Parser
--
------------------------------------------------------------------------------------

function Parser:read(i, j)
	local head, i = self.head, i or 0
	return sub(self.text, head + i, head + (j or i))
end

function Parser:advance(n)
	self.head = self.head + (n or self.step or 1)
end

function Parser:jump(head)
	self.head = head
	self.nxt = nil
end

function Parser:set_pattern(pattern)
	local layer = self
	layer.pattern = pattern
	layer.nxt = nil
end

function Parser:consume()
	local layer = self
	local this = layer.nxt
	if this then
		layer.nxt = nil
	else
		local text, head = self.text, self.head
		local loc1, loc2 = find(text, layer.pattern, head)
		if loc1 == head or not loc1 then
			this = sub(text, head, loc2)
		else
			this = sub(text, head, loc1 - 1)
			layer.nxt = sub(text, loc1, loc2)
		end
	end
	layer.step = #this
	return layer.handler(self, this)
end

-- Template or parameter.

-- Parsed by matching the opening braces innermost-to-outermost (ignoring lone closing braces). Parameters {{{ }}} take priority over templates {{ }} where possible, but a double closing brace will always result in a closure, even if there are 3+ opening braces.

-- For example, "{{{{foo}}}}" (4) is parsed as a parameter enclosed by single braces, and "{{{{{foo}}}}}" (5) is a parameter inside a template. However, "{{{{{foo }} }}}" is a template inside a parameter, due to "}}" forcing the closure of the inner node.
do
	-- Handlers.
	local handle_name
	local handle_argument
	
	local function do_template_or_parameter(self, inner_node)
		self:push_sublayer(handle_name)
		self:set_pattern("")
		-- If a node has already been parsed, nest it at the start of the new
		-- outer node (e.g. when parsing"{{{{foo}}bar}}", the template "{{foo}}"
		-- is parsed first, since it's the innermost, and becomes the first
		-- node of the outer template.
		if inner_node then
			self:emit(inner_node)
		end
	end
	
	function handle_name(self, ...)
		handle_name = self:switch(handle_name, {
			 = Parser.heading_block,
			 = Parser.tag,
			 = Parser.wikilink_block,
			 = Parser.braces,
			
			 = function(self)
				self:emit(Wikitext:new(self:pop_sublayer()))
				self:push_sublayer(handle_argument)
				self:set_pattern("")
			end,
			
			 = function(self)
				if self:read(1) == "}" then
					self:emit(Wikitext:new(self:pop_sublayer()))
					return self:pop()
				end
				self:emit("}")
			end,
			
			 = Parser.fail_route,
			 = Parser.emit
		})
		return handle_name(self, ...)
	end
	
	function handle_argument(self, ...)
		local function emit_argument(self)
			local arg = Wikitext:new(self:pop_sublayer())
			local layer = self
			local key = layer.key
			if key then
				arg = Argument:new{key, arg}
				layer.key = nil
			end
			self:emit(arg)
		end
		
		handle_argument = self:switch(handle_argument, {
			 = function(self)
				return self:heading_block("\n", self.key and "=" or "==")
			end,
			
			 = Parser.tag,
			
			 = function(self)
				local key = Wikitext:new(self:pop_sublayer())
				self.key = key
				self:push_sublayer(handle_argument)
				self:set_pattern("")
			end,
			
			 = Parser.wikilink_block,
			 = Parser.braces,
			
			 = function(self)
				emit_argument(self)
				self:push_sublayer(handle_argument)
				self:set_pattern("")
			end,
			
			 = function(self)
				if self:read(1) == "}" then
					emit_argument(self)
					return self:pop()
				end
				self:emit("}")
			end,
			
			 = Parser.fail_route,
			 = Parser.emit
		})
		return handle_argument(self, ...)
	end
	
	function Parser:template_or_parameter()
		local text, head, node_to_emit, failed = self.text, self.head
		-- Comments/tags interrupt the brace count.
		local braces = match(text, "^{+()", head) - head
		self:advance(braces)
		while true do
			local success, node = self:try(do_template_or_parameter, node_to_emit)
			-- Fail means no "}}" or "}}}" was found, so emit any remaining
			-- unmatched opening braces before any templates/parameters that
			-- were found.
			if not success then
				self:emit(rep("{", braces))
				failed = true
				break
			-- If there are 3+ opening and closing braces, it's a parameter.
			elseif braces >= 3 and self:read(2) == "}" then
				self:advance(3)
				braces = braces - 3
				node = Parameter:new(node)
			-- Otherwise, it's a template.
			else
				self:advance(2)
				braces = braces - 2
				node = Template:new(node)
			end
			local index = head + braces
			node.index = index
			node.raw = sub(text, index, self.head - 1)
			node_to_emit = node
			-- Terminate once not enough braces remain for further matches.
			if braces == 0 then
				break
			-- Emit any stray opening brace before any matched nodes.
			elseif braces == 1 then
				self:emit("{")
				break
			end
		end
		if node_to_emit then
			self:emit(node_to_emit)
		end
		return braces, failed
	end
end

-- Tag.
do
	local end_tags = data.end_tags
	
	-- Handlers.
	local handle_start
	local handle_tag
	
	local function do_tag(self)
		local layer = self
		layer.handler, layer.index = handle_start, self.head
		self:set_pattern("")
		self:advance()
	end
	
	local function is_ignored_tag(self, this)
		if self.transcluded then
			return this == "includeonly"
		end
		return this == "noinclude" or this == "onlyinclude"
	end
	
	local function ignored_tag(self, text, head)
		local loc = find(text, ">", head, true)
		if not loc then
			return self:fail_route()
		end
		self:jump(loc)
		local tag = self:pop()
		tag.ignored = true
		return tag
	end
	
	function handle_start(self, this)
		if this == "/" then
			local text, head = self.text, self.head + 1
			local this = match(text, "^+", head)
			if this and is_ignored_tag(self, lower(this)) then
				head = head + #this
				if not match(text, "^/", head) then
					return ignored_tag(self, text, head)
				end
			end
			return self:fail_route()
		elseif this == "" then
			return self:fail_route()
		end
		-- Tags are only case-insensitive with ASCII characters.
		local raw_name = this
		this = lower(this)
		local end_tag_pattern = end_tags
		if not end_tag_pattern then -- Validity check.
			return self:fail_route()
		end
		local layer = self
		local text, head = self.text, self.head + layer.step
		if match(text, "^/", head) then
			return self:fail_route()
		elseif is_ignored_tag(self, this) then
			return ignored_tag(self, text, head)
		-- If an onlyinclude tag is not ignored (and cannot be active since it
		-- would have triggered special handling earlier), it must be plaintext.
		elseif this == "onlyinclude" then
			return self:fail_route()
		elseif this == "noinclude" or this == "includeonly" then
			layer.ignored = true -- Ignored block.
			layer.raw_name = raw_name
		end
		layer.name, layer.handler, layer.end_tag_pattern = this, handle_tag, end_tag_pattern
		self:set_pattern(">")
	end
	
	function handle_tag(self, this)
		if this == "" then
			return self:fail_route()
		elseif this ~= ">" then
			self.attributes = this
			return
		elseif self:read(-1) == "/" then
			self.self_closing = true
			return self:pop()
		end
		local text, head, layer = self.text, self.head + 1, self
		local loc1, loc2 = find(text, layer.end_tag_pattern, head)
		if loc1 then
			if loc1 > head then
				self:emit(sub(text, head, loc1 - 1))
			end
			self:jump(loc2)
			return self:pop()
		-- noinclude and includeonly will tolerate having no closing tag, but
		-- only if given in lowercase. This is due to a preprocessor bug, as
		-- it uses a regex with the /i (case-insensitive) flag to check for
		-- end tags, but a simple array lookup with lowercase tag names when
		-- looking up which tags should tolerate no closing tag (exact match
		-- only, so case-sensitive).
		elseif layer.ignored then
			local raw_name = layer.raw_name
			if raw_name == "noinclude" or raw_name == "includeonly" then
				self:jump(#text)
				return self:pop()
			end
		end
		return self:fail_route()
	end
	
	function Parser:tag()
		-- HTML comment.
		if self:read(1, 3) == "!--" then
			local text = self.text
			self:jump(select(2, find(text, "-->", self.head + 4, true)) or #text)
		-- onlyinclude tags (which must be lowercase with no whitespace).
		elseif self.onlyinclude and self:read(1, 13) == "/onlyinclude>" then
			local text = self.text
			self:jump(select(2, find(text, "<onlyinclude>", self.head + 14, true)) or #text)
		else
			local success, tag = self:try(do_tag)
			if not success then
				self:emit("<")
			elseif not tag.ignored then
				tag.end_tag_pattern = nil
				self:emit(Tag:new(tag))
			end
		end
	end
end

-- Heading.
-- The preparser assigns each heading a number, which is used for things like section edit links. The preparser will only do this for heading blocks which aren't nested inside templates, parameters and parser tags. In some cases (e.g. when template blocks contain untrimmed newlines), a preparsed heading may not be treated as a heading in the final output. That does not affect the preparser, however, which will always count sections based on the preparser heading count, since it can't know what a template's final output will be.
do
	-- Handlers.
	local handle_start
	local handle_body
	local handle_possible_end
	
	local function do_heading(self)
		local layer, head = self, self.head
		layer.handler, layer.index = handle_start, head
		self:set_pattern("")
		-- Comments/tags interrupt the equals count.
		local eq = match(self.text, "^=+()", head) - head
		layer.level = eq
		self:advance(eq)
	end
	
	local function do_heading_possible_end(self)
		local layer = self
		layer.handler = handle_possible_end
		self:set_pattern("")
	end
	
	function handle_start(self, ...)
		-- ===== is "=" as an L2; ======== is "==" as an L3 etc.
		local function newline(self)
			local layer = self
			local eq = layer.level
			if eq <= 2 then
				return self:fail_route()
			end
			-- Calculate which equals signs determine the heading level.
			local level_eq = eq - (2 - eq % 2)
			level_eq = level_eq > 12 and 12 or level_eq
			-- Emit the excess.
			self:emit(rep("=", eq - level_eq))
			layer.level = level_eq / 2
			return self:pop()
		end
		
		local function whitespace(self)
			local success, possible_end = self:try(do_heading_possible_end)
			if success then
				self:emit(Wikitext:new(possible_end))
				local layer = self
				layer.handler = handle_body
				self:set_pattern("")
				return self:consume()
			end
			return newline(self)
		end
		
		handle_start = self:switch(handle_start, {
			 = whitespace,
			 = newline,
			 = whitespace,
			 = newline,
			
			 = function(self)
				-- Emit any excess = signs once we know it's a conventional heading. Up till now, we couldn't know if the heading is just a string of = signs (e.g. ========), so it wasn't guaranteed that the heading text starts after the 6th.
				local layer = self
				local eq = layer.level
				if eq > 6 then
					self:emit(1, rep("=", eq - 6))
					layer.level = 6
				end
				layer.handler = handle_body
				self:set_pattern("")
				return self:consume()
			end
		})
		return handle_start(self, ...)
	end
	
	function handle_body(self, ...)
		handle_body = self:switch(handle_body, {
			 = Parser.fail_route,
			 = Parser.tag,
			
			 = function(self)
				-- Comments/tags interrupt the equals count.
				local eq = match(self.text, "^=+", self.head)
				local eq_len = #eq
				self:advance(eq_len)
				local success, possible_end = self:try(do_heading_possible_end)
				if success then
					self:emit(eq)
					self:emit(Wikitext:new(possible_end))
					return self:consume()
				end
				local layer = self
				local level = layer.level
				if eq_len > level then
					self:emit(rep("=", eq_len - level))
				elseif level > eq_len then
					layer.level = eq_len
					self:emit(1, rep("=", level - eq_len))
				end
				return self:pop()
			end,
			
			 = Parser.wikilink_block,
			
			 = function(self, this)
				return self:braces("{", true)
			end,
			
			 = Parser.fail_route,
			 = Parser.emit
		})
		return handle_body(self, ...)
	end
	
	function handle_possible_end(self, ...)
		handle_possible_end = self:switch(handle_possible_end, {
			 = Parser.fail_route,
			
			 = function(self)
				if self:read(1, 3) ~= "!--" then
					return self:pop()
				end
				local head = select(2, find(self.text, "-->", self.head + 4, true))
				if not head then
					return self:pop()
				end
				self:jump(head)
			end,
			
			 = Parser.fail_route,
			
			 = function(self, this)
				if not match(this, "^+()$") then
					return self:pop()
				end
				self:emit(this)
			end
		})
		return handle_possible_end(self, ...)
	end
	
	function Parser:heading()
		local success, heading = self:try(do_heading)
		if success then
			local section = self.section + 1
			heading.section = section
			self.section = section
			self:emit(Heading:new(heading))
			return self:consume()
		else
			self:emit("=")
		end
	end
end

------------------------------------------------------------------------------------
--
-- Block handlers
--
------------------------------------------------------------------------------------

-- Block handlers.

-- These are blocks which can affect template/parameter parsing, since they're also parsed by Parsoid at the same time (even though they aren't processed until later).

-- All blocks (including templates/parameters) can nest inside each other, but an inner block must be closed before the outer block which contains it. This is why, for example, the wikitext "{{template| ] }}" will process correctly, since the wikilink block is closed before the template closure. It makes no difference whether the block will be treated as valid or not when it's processed later on, so "{{template| ] }}" would also work, even though "]" is not a valid wikilink.

-- Note that nesting also affects pipes and equals signs, in addition to block closures.

-- These blocks can be nested to any degree, so "{{template| ] }}" will not work, since only one of the three wikilink blocks has been closed. On the other hand, "{{template| ] ]] ]] }}" will work.

-- All blocks are implicitly closed by the end of the text, since their validity is irrelevant at this stage.

-- Language conversion block.
-- Opens with "-{" and closes with "}-". However, templates/parameters take priority, so "-{{" is parsed as "-" followed by the opening of a template/parameter block (depending on what comes after).
-- Note: Language conversion blocks aren't actually enabled on the English Wiktionary, but Parsoid still parses them at this stage, so they can affect the closure of outer blocks: e.g. "]" is not a valid wikilink block, since the "]]" falls inside the new language conversion block.
do
	--Handler.
	local handle_language_conversion_block
	
	local function do_language_conversion_block(self)
		local layer = self
		layer.handler = handle_language_conversion_block
		self:set_pattern("")
	end
	
	function handle_language_conversion_block(self, ...)
		handle_language_conversion_block = self:switch(handle_language_conversion_block, {
			 = Parser.heading_block,
			 = Parser.tag,
			 = Parser.wikilink_block,
			 = Parser.braces,
			
			 = function(self)
				if self:read(1) == "-" then
					self:emit("}-")
					self:advance()
					return self:pop()
				end
				self:emit("}")
			end,
			
			 = Parser.pop,
			 = Parser.emit
		})
		return handle_language_conversion_block(self, ...)
	end
	
	function Parser:braces(this, fail_on_unclosed_braces)
		local language_conversion_block = self:read(-1) == "-"
		if self:read(1) == "{" then
			local braces, failed = self:template_or_parameter()
			-- Headings will fail if they contain an unclosed brace block.
			if failed and fail_on_unclosed_braces then
				return self:fail_route()
			-- Language conversion blocks cannot begin "-{{", but can begin
			-- "-{{{" iff parsed as "-{" + "{{".
			elseif not (language_conversion_block and braces == 1) then
				return self:consume()
			end
		else
			self:emit(this)
			if not language_conversion_block then
				return
			end
			self:advance()
		end
		self:emit(Wikitext:new(self:get(do_language_conversion_block)))
	end
end

--[==[
Headings

Opens with "\n=" (or "=" at the start of the text), and closes with "\n" or the end of the text. Note that it doesn't matter whether the heading will fail to process due to a premature newline (e.g. if there are no closing signs), so at this stage the only thing that matters for closure is the newline or end of text.

Note: Heading blocks are only parsed like this if they occur inside a template, since they do not iterate the preparser's heading count (i.e. they aren't proper headings).

Note 2: if directly inside a template argument with no previous equals signs, a newline followed by a single equals sign is parsed as an argument equals sign, not the opening of a new L1 heading block. This does not apply to any other heading levels. As such, {{template|key\n=}}, {{template|key\n=value}} or even {{template|\n=}} will successfully close, but {{template|key\n==}}, {{template|key=value\n=more value}}, {{template\n=}} etc. will not, since in the latter cases the "}}" would fall inside the new heading block.
]==]
do
	--Handler.
	local handle_heading_block
	
	local function do_heading_block(self)
		local layer = self
		layer.handler = handle_heading_block
		self:set_pattern("")
	end
	
	function handle_heading_block(self, ...)
		handle_heading_block = self:switch(handle_heading_block, {
			 = function(self)
				self:newline()
				return self:pop()
			end,
			
			 = Parser.tag,
			 = Parser.wikilink_block,
			 = Parser.braces,
			 = Parser.pop,
			 = Parser.emit
		})
		return handle_heading_block(self, ...)
	end
	
	function Parser:heading_block(this, nxt)
		self:newline()
		this = this .. (nxt or "=")
		local loc = #this - 1
		while self:read(0, loc) == this do
			self:advance()
			self:emit(Wikitext:new(self:get(do_heading_block)))
		end
	end
end

-- Wikilink block.
-- Opens with "]".
do
	-- Handler.
	local handle_wikilink_block
	
	local function do_wikilink_block(self)
		local layer = self
		layer.handler = handle_wikilink_block
		self:set_pattern("{]")
	end
	
	function handle_wikilink_block(self, ...)
		handle_wikilink_block = self:switch(handle_wikilink_block, {
			 = Parser.heading_block,
			 = Parser.tag,
			 = Parser.wikilink_block,
			
			"] = function(self)
				if self:read(1) == "]" then
					self:emit("]]")
					self:advance()
					return self:pop()
				end
				self:emit("]")
			end,
			
			 = Parser.braces,
			 = Parser.pop,
			 = Parser.emit
		})
		return handle_wikilink_block(self, ...)
	end
	
	function Parser:wikilink_block()
		if self:read(1) == "[" then
			self:emit("[[")
			self:advance(2)
			self:emit(Wikitext:new(self:get(do_wikilink_block)))
		else
			self:emit("[")
		end
	end
end

-- Lines which only contain comments, " " and "\t" are eaten, so long as
-- they're bookended by "\n" (i.e. not the first or last line).
function Parser:newline()
	local text, head = self.text, self.head
	while true do
		repeat
			local loc = match(text, "^*<!%-%-()", head + 1)
			if not loc then
				break
			end
			loc = select(2, find(text, "-->", loc, true))
			head = loc or head
		until not loc
		-- Fail if no comments found.
		if head == self.head then
			break
		end
		head = match(text, "^*()\n", head + 1)
		if not head then
			break
		end
		self:jump(head)
	end
	self:emit("\n")
end

do
	-- Handlers.
	local handle_start
	local main_handler
	
	-- If `transcluded` is true, then the text is checked for a pair of
	-- onlyinclude tags. If these are found (even if they're in the wrong
	-- order), then the start of the page is treated as though it is preceded
	-- by a closing onlyinclude tag.
	-- Note 1: unlike other parser extension tags, onlyinclude tags are case-
	-- sensitive and cannot contain whitespace.
	-- Note 2: onlyinclude tags *can* be implicitly closed by the end of the
	-- text, but the hard requirement above means this can only happen if
	-- either the tags are in the wrong order or there are multiple onlyinclude
	-- blocks.
	local function do_parse(self, transcluded)
		local layer = self
		layer.handler = handle_start
		self:set_pattern(".")
		self.section = 0
		if not transcluded then
			return
		end
		self.transcluded = true
		local text = self.text
		if find(text, "</onlyinclude>", 1, true) then
			local head = find(text, "<onlyinclude>", 1, true)
			if head then
				self.onlyinclude = true
				self:jump(head + 13)
			end
		end
	end
	
	-- If the first character is "=", try parsing it as a heading.
	function handle_start(self, this)
		local layer = self
		layer.handler = main_handler
		self:set_pattern("")
		if this == "=" then
			return self:heading()
		end
		return self:consume()
	end
	
	function main_handler(self, ...)
		main_handler = self:switch(main_handler, {
			 = function(self)
				self:newline()
				if self:read(1) == "=" then
					self:advance()
					return self:heading()
				end
			end,
			
			 = Parser.tag,
			
			 = function(self)
				if self:read(1) == "{" then
					self:template_or_parameter()
					return self:consume()
				end
				self:emit("{")
			end,
			
			 = Parser.pop,
			 = Parser.emit
		})
		return main_handler(self, ...)
	end
	
	function export.parse(text, transcluded)
		local text_type = type(text)
		return (select(2, Parser:parse{
			text = text_type == "string" and text or
				text_type == "number" and tostring(text) or
				error("bad argument #1 (string expected, got " .. text_type .. ")"),
			node = {Wikitext, true},
			route = {do_parse, transcluded}
		}))
	end
	parse = export.parse
end

do
	local function next_template(iter)
		while true do
			local node = iter()
			if node == nil or class_else_type(node) == "template" then
				return node
			end
		end
	end
	
	function export.find_templates(text, not_transcluded)
		return next_template, parse(text, not not_transcluded):__pairs("next_node")
	end
end

do
	local link_parameter_1 = data.template_link_param_1
	local link_parameter_2 = data.template_link_param_2
	
	-- Generate a link. If the target title doesn't have a fragment, use "#top"
	-- (which is an implicit anchor at the top of every page), as this ensures
	-- self-links still display as links, since bold display is distracting and
	-- unintuitive for template links.
	local function link_page(title, display)
		local fragment = title.fragment
		if fragment == "" then
			fragment = "top"
		end
		return format(
			"]",
			encode_uri(title.prefixedText .. "#" .. fragment, "WIKI"),
			display
		)
	end
	
	-- pf_arg1 or pf_arg2 may need to be linked if a given parser function
	-- treats them as a pagename. If a key exists in `namespace`, the value is
	-- the namespace for the page: if not 0, then the namespace prefix will
	-- always be added to the input (e.g. {{#invoke:}} can only target the
	-- Module: namespace, so inputting "Template:foo" gives
	-- "Module:Template:foo", and "Module:foo" gives "Module:Module:foo").
	-- However, this isn't possible with mainspace (namespace 0), so prefixes
	-- are respected. make_title handles all of this automatically.
	local function finalize_arg(pagename, namespace)
		if namespace == nil then
			return pagename
		end
		local title = make_title(namespace, pagename)
		if not (title and is_valid_title(title)) then
			return pagename
		end
		return link_page(title, pagename)
	end
	
	local function render_title(name, args)
		-- parse_template_name returns a table of transclusion modifiers plus
		-- the normalized template/magic word name, which will be used as link
		-- targets. The third return value pf_arg1 is the first argument of a
		-- a parser function, which comes after the colon (e.g. "foo" in
		-- "{{#IF:foo|bar|baz}}"). This means args (i.e. the first argument
		-- that comes after a pipe is actually argument 2, and so on. Note: the
		-- second parameter of parse_template_name checks if there are any
		-- arguments, since parser variables cannot take arguments (e.g.
		-- {{CURRENTYEAR}} is a parser variable, but {{CURRENTYEAR|foo}}
		-- transcludes "Template:CURRENTYEAR"). In such cases, the returned
		-- table explicitly includes the "Template:" prefix in the template
		-- name. The third parameter instructs it to retain any fragment in the
		-- template name in the returned table, if present.
		local chunks, subclass, pf_arg1 = parse_template_name(
			name,
			args and pairs(args)(args) ~= nil,
			true
		)
		if chunks == nil then
			return name
		end
		local chunks_len = #chunks
		-- Additionally, generate the corresponding table `rawchunks`, which
		-- is a list of colon-separated chunks in the raw input. This is used
		-- to retrieve the display forms for each chunk.
		local rawchunks = split(name, ":")
		for i = 1, chunks_len - 1 do
			chunks = format(
				"]",
				encode_uri(magic_words, 1, -2)].transclusion_modifier, "WIKI"),
				rawchunks
			)
		end
		local chunk = chunks
		-- If it's a template, return a link to it with link_page, concatenating
		-- the remaining chunks in `rawchunks` to form the display text.
		-- Use new_title with the default namespace 10 (Template:) to generate
		-- a target title, which is the same setting used for retrieving
		-- templates (including those in other namespaces, as prefixes override
		-- the default).
		if subclass == "template" then
			chunks = link_page(
				new_title(chunk, 10),
				concat(rawchunks, "&#58;", chunks_len) -- :
			)
			return concat(chunks, "&#58;") -- :
		elseif subclass == "parser variable" then
			chunks = format(
				"]",
				encode_uri(magic_words.parser_variable, "WIKI"),
				rawchunks
			)
			return concat(chunks, "&#58;") -- :
		end
		-- Otherwise, it must be a parser function.
		local mgw_data = magic_words
		local link = mgw_data.parser_function or mgw_data.transclusion_modifier
		local pf_arg2 = args and args or nil
		-- Some magic words have different links,  depending on whether argument
		-- 2 is specified (e.g. "baz" in {{foo:bar|baz}}).
		if type(link) == "table" then
			link = pf_arg2 and link or link
		end
		chunks = format(
			"]",
			encode_uri(link, "WIKI"),
			rawchunks
		)
		-- #TAG: has special handling, because documentation links for parser
		-- extension tags come from ].
		if chunk == "#TAG:" then
			-- Tags are only case-insensitive with ASCII characters.
			local tag = parser_extension_tags
			if tag then
				pf_arg1 = format(
					"]",
					encode_uri(tag, "WIKI"),
					pf_arg1
				)
			end
		-- Otherwise, finalize pf_arg1 and add it to `chunks`.
		else
			pf_arg1 = finalize_arg(pf_arg1, link_parameter_1)
		end
		chunks = pf_arg1
		-- Finalize pf_arg2 (if applicable), then return.
		if pf_arg2 then
			args = finalize_arg(pf_arg2, link_parameter_2)
		end
		return concat(chunks, "&#58;") -- :
	end
	
	function export.buildTemplate(title, args)
		local output = {title}
		-- Iterate over all numbered parameters in order, followed by any
		-- remaining parameters in codepoint order. Implicit parameters are
		-- used wherever possible, even if explicit numbers are interpolated
		-- between them (e.g. 0 would go before any implicit parameters, and
		-- 2.5 between 2 and 3).
		-- TODO: handle "=" and "|" in params/values.
		if args then
			local iter, implicit = sorted_pairs(args), table_len(args)
			local k, v = iter()
			while k ~= nil do
				if type(k) == "number" and k >= 1 and k <= implicit and k % 1 == 0 then
					insert(output, v)
				else
					insert(output, k .. "=" .. v)
				end
				k, v = iter()
			end
		end
		return output
	end
	build_template = export.buildTemplate
	
	function export.templateLink(title, args, no_link)
		local output = build_template(no_link and title or render_title(title, args), args)
		for i = 1, #output do
			output = encode_entities(output, "={}", true, true)
		end
		return tostring(html_create("code")
			:css("white-space", "pre-wrap")
			:wikitext("&#123;&#123;" .. concat(output, "&#124;") .. "&#125;&#125;") -- {{ | }}
		)
	end
end

do
	local function next_parameter(iter)
		while true do
			local node = iter()
			if node == nil or class_else_type(node) == "parameter" then
				return node
			end
		end
	end
	
	function export.find_parameters(text, not_transcluded)
		return next_parameter, parse(text, not not_transcluded):__pairs("next_node")
	end
	
	function export.displayParameter(name, default)
		return tostring(html_create("code")
			:css("white-space", "pre-wrap")
			:wikitext("&#123;&#123;&#123;" .. concat({name, default}, "&#124;") .. "&#125;&#125;&#125;") -- {{{ | }}}
		)
	end
end

do
	local function check_level(level)
		if type(level) ~= "number" then
			error("Heading levels must be numbers.")
		elseif level < 1 or level > 6 or level % 1 ~= 0 then
			error("Heading levels must be integers between 1 and 6.")
		end
		return level
	end
	
	local function next_heading(iter)
		while true do
			local node = iter()
			if node == nil then
				return nil
			elseif class_else_type(node) == "heading" then
				local level = node.level
				if level >= iter.i and level <= iter.j then
					return node
				end
			end
		end
	end
	
	-- FIXME: should headings which contain "\n" be returned? This may depend
	-- on variable factors, like template expansion. They iterate the heading
	-- count number, but fail on rendering. However, in some cases a different
	-- heading might still be rendered due to intermediate equals signs; it
	-- may even be of a different heading level: e.g., this is parsed as an
	-- L2 heading with a newline (due to the wikilink block), but renders as the
	-- L1 heading "=foo[[". Section edit links are sometimes (but not always)
	-- present in such cases.
	
	-- ==[[=
	-- ]]==
	
	-- TODO: section numbers for edit links seem to also include headings
	-- nested inside templates and parameters (but apparently not those in
	-- parser extension tags - need to test this more). If we ever want to add
	-- section edit links manually, this will need to be accounted for.
	function export.find_headings(text, i, j)
		local iter = parse(text):__pairs("next_node")
		iter.i, iter.j = i and check_level(i) or 1, j and check_level(j) or 6
		return next_heading, iter
	end
end

do
	local function make_tag(tag)
		return tostring(html_create("code")
			:css("white-space", "pre-wrap")
			:wikitext("&lt;" .. tag .. "&gt;")
		)
	end

	-- Note: invalid tags are returned without links.
	function export.wikitagLink(tag)
		-- ">" can't appear in tags (including attributes) since the parser
		-- unconditionally treats ">" as the end of a tag.
		if find(tag, ">", 1, true) then
			return make_tag(tag)
		end
		-- Tags must start "<tagname..." or "</tagname...", with no whitespace
		-- after "<" or "</".
		local slash, tagname, remainder = match(tag, "^(/?)(+)(.*)$")
		if not tagname then
			return make_tag(tag)
		end
		-- Tags are only case-insensitive with ASCII characters.
		local link = lower(tagname)
		if (
			-- onlyinclude tags must be lowercase and are whitespace intolerant.
			link == "onlyinclude" and (link ~= tagname or remainder ~= "") or
			-- Closing wikitags (except onlyinclude) can only have whitespace
			-- after the tag name.
			slash == "/" and not match(remainder, "^%s*()$") or
			-- Tagnames cannot be followed immediately by "/", unless it comes
			-- at the end (e.g. "<nowiki/>", but not "<nowiki/ >").
			remainder ~= "/" and sub(remainder, 1, 1) == "/"
		) then
			-- Output with no link.
			return make_tag(tag)
		end
		-- Partial transclusion tags aren't in the table of parser extension
		-- tags.
		if link == "noinclude" or link == "includeonly" or link == "onlyinclude" then
			link = "mw:Transclusion#Partial transclusion"
		else
			link = parser_extension_tags
		end
		if link then
			tag = gsub(tag, pattern_escape(tagname), "]", 1)
		end
		return make_tag(tag)
	end
end

-- For convenience.
export.class_else_type = class_else_type

return export