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parser.rb
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# encoding: utf-8
require_relative 'token-scanner'
require_relative 'tokenizer'
module Crass
# Parses a CSS string or list of tokens.
#
# 5. http://dev.w3.org/csswg/css-syntax/#parsing
class Parser
BLOCK_END_TOKENS = {
:'{' => :'}',
:'[' => :']',
:'(' => :')'
}
# -- Class Methods ---------------------------------------------------------
# Parses CSS properties (such as the contents of an HTML element's `style`
# attribute) and returns a parse tree.
#
# See {Tokenizer#initialize} for _options_.
#
# 5.3.6. http://dev.w3.org/csswg/css-syntax/#parse-a-list-of-declarations
def self.parse_properties(input, options = {})
Parser.new(input, options).parse_properties
end
# Parses CSS rules (such as the content of a `@media` block) and returns a
# parse tree. The only difference from {parse_stylesheet} is that CDO/CDC
# nodes (`<!--` and `-->`) aren't ignored.
#
# See {Tokenizer#initialize} for _options_.
#
# 5.3.3. http://dev.w3.org/csswg/css-syntax/#parse-a-list-of-rules
def self.parse_rules(input, options = {})
parser = Parser.new(input, options)
rules = parser.consume_rules
rules.map do |rule|
if rule[:node] == :qualified_rule
parser.create_style_rule(rule)
else
rule
end
end
end
# Parses a CSS stylesheet and returns a parse tree.
#
# See {Tokenizer#initialize} for _options_.
#
# 5.3.2. http://dev.w3.org/csswg/css-syntax/#parse-a-stylesheet
def self.parse_stylesheet(input, options = {})
parser = Parser.new(input, options)
rules = parser.consume_rules(:top_level => true)
rules.map do |rule|
if rule[:node] == :qualified_rule
parser.create_style_rule(rule)
else
rule
end
end
end
# Converts a node or array of nodes into a CSS string based on their
# original tokenized input.
#
# Options:
#
# * **:exclude_comments** - When `true`, comments will be excluded.
#
def self.stringify(nodes, options = {})
nodes = [nodes] unless nodes.is_a?(Array)
string = String.new
nodes.each do |node|
next if node.nil?
case node[:node]
when :at_rule
string << '@'
string << node[:name]
string << self.stringify(node[:prelude], options)
if node[:block]
string << '{' << self.stringify(node[:block], options) << '}'
else
string << ';'
end
when :comment
string << node[:raw] unless options[:exclude_comments]
when :simple_block
string << node[:start]
string << self.stringify(node[:value], options)
string << node[:end]
when :style_rule
string << self.stringify(node[:selector][:tokens], options)
string << '{' << self.stringify(node[:children], options) << '}'
else
if node.key?(:raw)
string << node[:raw]
elsif node.key?(:tokens)
string << self.stringify(node[:tokens], options)
end
end
end
string
end
# -- Instance Methods ------------------------------------------------------
# {TokenScanner} wrapping the tokens generated from this parser's input.
attr_reader :tokens
# Initializes a parser based on the given _input_, which may be a CSS string
# or an array of tokens.
#
# See {Tokenizer#initialize} for _options_.
def initialize(input, options = {})
unless input.kind_of?(Enumerable)
input = Tokenizer.tokenize(input, options)
end
@tokens = TokenScanner.new(input)
end
# Consumes an at-rule and returns it.
#
# 5.4.2. http://dev.w3.org/csswg/css-syntax-3/#consume-at-rule
def consume_at_rule(input = @tokens)
rule = {}
rule[:tokens] = input.collect do
rule[:name] = input.consume[:value]
rule[:prelude] = []
while token = input.consume
node = token[:node]
if node == :comment # Non-standard.
next
elsif node == :semicolon
break
elsif node === :'{'
# Note: The spec says the block should _be_ the consumed simple
# block, but Simon Sapin's CSS parsing tests and tinycss2 expect
# only the _value_ of the consumed simple block here. I assume I'm
# interpreting the spec too literally, so I'm going with the
# tinycss2 behavior.
rule[:block] = consume_simple_block(input)[:value]
break
elsif node == :simple_block && token[:start] == '{'
# Note: The spec says the block should _be_ the simple block, but
# Simon Sapin's CSS parsing tests and tinycss2 expect only the
# _value_ of the simple block here. I assume I'm interpreting the
# spec too literally, so I'm going with the tinycss2 behavior.
rule[:block] = token[:value]
break
else
input.reconsume
rule[:prelude] << consume_component_value(input)
end
end
end
create_node(:at_rule, rule)
end
# Consumes a component value and returns it, or `nil` if there are no more
# tokens.
#
# 5.4.6. http://dev.w3.org/csswg/css-syntax-3/#consume-a-component-value
def consume_component_value(input = @tokens)
return nil unless token = input.consume
case token[:node]
when :'{', :'[', :'('
consume_simple_block(input)
when :function
if token.key?(:name)
# This is a parsed function, not a function token. This step isn't
# mentioned in the spec, but it's necessary to avoid re-parsing
# functions that have already been parsed.
token
else
consume_function(input)
end
else
token
end
end
# Consumes a declaration and returns it, or `nil` on parse error.
#
# 5.4.5. http://dev.w3.org/csswg/css-syntax-3/#consume-a-declaration
def consume_declaration(input = @tokens)
declaration = {}
value = []
declaration[:tokens] = input.collect do
declaration[:name] = input.consume[:value]
next_token = input.peek
while next_token && next_token[:node] == :whitespace
input.consume
next_token = input.peek
end
unless next_token && next_token[:node] == :colon
# Parse error.
#
# Note: The spec explicitly says to return nothing here, but Simon
# Sapin's CSS parsing tests expect an error node.
return create_node(:error, :value => 'invalid')
end
input.consume
until input.peek.nil?
value << consume_component_value(input)
end
end
# Look for !important.
important_tokens = value.reject {|token|
node = token[:node]
node == :whitespace || node == :comment || node == :semicolon
}.last(2)
if important_tokens.size == 2 &&
important_tokens[0][:node] == :delim &&
important_tokens[0][:value] == '!' &&
important_tokens[1][:node] == :ident &&
important_tokens[1][:value].downcase == 'important'
declaration[:important] = true
excl_index = value.index(important_tokens[0])
# Technically the spec doesn't require us to trim trailing tokens after
# the !important, but Simon Sapin's CSS parsing tests expect it and
# tinycss2 does it, so we'll go along with the cool kids.
value.slice!(excl_index, value.size - excl_index)
else
declaration[:important] = false
end
declaration[:value] = value
create_node(:declaration, declaration)
end
# Consumes a list of declarations and returns them.
#
# By default, the returned list may include `:comment`, `:semicolon`, and
# `:whitespace` nodes, which is non-standard.
#
# Options:
#
# * **:strict** - Set to `true` to exclude non-standard `:comment`,
# `:semicolon`, and `:whitespace` nodes.
#
# 5.4.4. http://dev.w3.org/csswg/css-syntax/#consume-a-list-of-declarations
def consume_declarations(input = @tokens, options = {})
declarations = []
while token = input.consume
case token[:node]
# Non-standard: Preserve comments, semicolons, and whitespace.
when :comment, :semicolon, :whitespace
declarations << token unless options[:strict]
when :at_keyword
# When parsing a style rule, this is a parse error. Otherwise it's
# not.
input.reconsume
declarations << consume_at_rule(input)
when :ident
decl_tokens = [token]
while next_token = input.peek
break if next_token[:node] == :semicolon
decl_tokens << consume_component_value(input)
end
if decl = consume_declaration(TokenScanner.new(decl_tokens))
declarations << decl
end
else
# Parse error (invalid property name, etc.).
#
# Note: The spec doesn't say we should append anything to the list of
# declarations here, but Simon Sapin's CSS parsing tests expect an
# error node.
declarations << create_node(:error, :value => 'invalid')
input.reconsume
while next_token = input.peek
break if next_token[:node] == :semicolon
consume_component_value(input)
end
end
end
declarations
end
# Consumes a function and returns it.
#
# 5.4.8. http://dev.w3.org/csswg/css-syntax-3/#consume-a-function
def consume_function(input = @tokens)
function = {
:name => input.current[:value],
:value => [],
:tokens => [input.current] # Non-standard, used for serialization.
}
function[:tokens].concat(input.collect {
while token = input.consume
case token[:node]
when :')'
break
# Non-standard.
when :comment
next
else
input.reconsume
function[:value] << consume_component_value(input)
end
end
})
create_node(:function, function)
end
# Consumes a qualified rule and returns it, or `nil` if a parse error
# occurs.
#
# 5.4.3. http://dev.w3.org/csswg/css-syntax-3/#consume-a-qualified-rule
def consume_qualified_rule(input = @tokens)
rule = {:prelude => []}
rule[:tokens] = input.collect do
while true
unless token = input.consume
# Parse error.
#
# Note: The spec explicitly says to return nothing here, but Simon
# Sapin's CSS parsing tests expect an error node.
return create_node(:error, :value => 'invalid')
end
if token[:node] == :'{'
# Note: The spec says the block should _be_ the consumed simple
# block, but Simon Sapin's CSS parsing tests and tinycss2 expect
# only the _value_ of the consumed simple block here. I assume I'm
# interpreting the spec too literally, so I'm going with the
# tinycss2 behavior.
rule[:block] = consume_simple_block(input)[:value]
break
elsif token[:node] == :simple_block && token[:start] == '{'
# Note: The spec says the block should _be_ the simple block, but
# Simon Sapin's CSS parsing tests and tinycss2 expect only the
# _value_ of the simple block here. I assume I'm interpreting the
# spec too literally, so I'm going with the tinycss2 behavior.
rule[:block] = token[:value]
break
else
input.reconsume
rule[:prelude] << consume_component_value(input)
end
end
end
create_node(:qualified_rule, rule)
end
# Consumes a list of rules and returns them.
#
# 5.4.1. http://dev.w3.org/csswg/css-syntax/#consume-a-list-of-rules
def consume_rules(flags = {})
rules = []
while token = @tokens.consume
case token[:node]
# Non-standard. Spec says to discard comments and whitespace, but we
# keep them so we can serialize faithfully.
when :comment, :whitespace
rules << token
when :cdc, :cdo
unless flags[:top_level]
@tokens.reconsume
rule = consume_qualified_rule
rules << rule if rule
end
when :at_keyword
@tokens.reconsume
rule = consume_at_rule
rules << rule if rule
else
@tokens.reconsume
rule = consume_qualified_rule
rules << rule if rule
end
end
rules
end
# Consumes and returns a simple block associated with the current input
# token.
#
# 5.4.7. http://dev.w3.org/csswg/css-syntax/#consume-a-simple-block
def consume_simple_block(input = @tokens)
start_token = input.current[:node]
end_token = BLOCK_END_TOKENS[start_token]
block = {
:start => start_token.to_s,
:end => end_token.to_s,
:value => [],
:tokens => [input.current] # Non-standard. Used for serialization.
}
block[:tokens].concat(input.collect do
while token = input.consume
break if token[:node] == end_token
input.reconsume
block[:value] << consume_component_value(input)
end
end)
create_node(:simple_block, block)
end
# Creates and returns a new parse node with the given _properties_.
def create_node(type, properties = {})
{:node => type}.merge!(properties)
end
# Parses the given _input_ tokens into a selector node and returns it.
#
# Doesn't bother splitting the selector list into individual selectors or
# validating them. Feel free to do that yourself! It'll be fun!
def create_selector(input)
create_node(:selector,
:value => parse_value(input),
:tokens => input)
end
# Creates a `:style_rule` node from the given qualified _rule_, and returns
# it.
def create_style_rule(rule)
create_node(:style_rule,
:selector => create_selector(rule[:prelude]),
:children => parse_properties(rule[:block]))
end
# Parses a single component value and returns it.
#
# 5.3.7. http://dev.w3.org/csswg/css-syntax-3/#parse-a-component-value
def parse_component_value(input = @tokens)
input = TokenScanner.new(input) unless input.is_a?(TokenScanner)
while input.peek && input.peek[:node] == :whitespace
input.consume
end
if input.peek.nil?
return create_node(:error, :value => 'empty')
end
value = consume_component_value(input)
while input.peek && input.peek[:node] == :whitespace
input.consume
end
if input.peek.nil?
value
else
create_node(:error, :value => 'extra-input')
end
end
# Parses a list of component values and returns an array of parsed tokens.
#
# 5.3.8. http://dev.w3.org/csswg/css-syntax/#parse-a-list-of-component-values
def parse_component_values(input = @tokens)
input = TokenScanner.new(input) unless input.is_a?(TokenScanner)
tokens = []
while token = consume_component_value(input)
tokens << token
end
tokens
end
# Parses a single declaration and returns it.
#
# 5.3.5. http://dev.w3.org/csswg/css-syntax/#parse-a-declaration
def parse_declaration(input = @tokens)
input = TokenScanner.new(input) unless input.is_a?(TokenScanner)
while input.peek && input.peek[:node] == :whitespace
input.consume
end
if input.peek.nil?
# Syntax error.
return create_node(:error, :value => 'empty')
elsif input.peek[:node] != :ident
# Syntax error.
return create_node(:error, :value => 'invalid')
end
if decl = consume_declaration(input)
return decl
end
# Syntax error.
create_node(:error, :value => 'invalid')
end
# Parses a list of declarations and returns them.
#
# See {#consume_declarations} for _options_.
#
# 5.3.6. http://dev.w3.org/csswg/css-syntax/#parse-a-list-of-declarations
def parse_declarations(input = @tokens, options = {})
input = TokenScanner.new(input) unless input.is_a?(TokenScanner)
consume_declarations(input, options)
end
# Parses a list of declarations and returns an array of `:property` nodes
# (and any non-declaration nodes that were in the input). This is useful for
# parsing the contents of an HTML element's `style` attribute.
def parse_properties(input = @tokens)
properties = []
parse_declarations(input).each do |decl|
unless decl[:node] == :declaration
properties << decl
next
end
children = decl[:value].dup
children.pop if children.last && children.last[:node] == :semicolon
properties << create_node(:property,
:name => decl[:name],
:value => parse_value(decl[:value]),
:children => children,
:important => decl[:important],
:tokens => decl[:tokens])
end
properties
end
# Parses a single rule and returns it.
#
# 5.3.4. http://dev.w3.org/csswg/css-syntax-3/#parse-a-rule
def parse_rule(input = @tokens)
input = TokenScanner.new(input) unless input.is_a?(TokenScanner)
while input.peek && input.peek[:node] == :whitespace
input.consume
end
if input.peek.nil?
# Syntax error.
return create_node(:error, :value => 'empty')
elsif input.peek[:node] == :at_keyword
rule = consume_at_rule(input)
else
rule = consume_qualified_rule(input)
end
while input.peek && input.peek[:node] == :whitespace
input.consume
end
if input.peek.nil?
rule
else
# Syntax error.
create_node(:error, :value => 'extra-input')
end
end
# Returns the unescaped value of a selector name or property declaration.
def parse_value(nodes)
nodes = [nodes] unless nodes.is_a?(Array)
string = String.new
nodes.each do |node|
case node[:node]
when :comment, :semicolon
next
when :at_keyword, :ident
string << node[:value]
when :function
if node[:value].is_a?(String)
string << node[:value]
string << '('
else
string << parse_value(node[:tokens])
end
else
if node.key?(:raw)
string << node[:raw]
elsif node.key?(:tokens)
string << parse_value(node[:tokens])
end
end
end
string.strip
end
end
end