servo/components/style/values/specified/mod.rs

/* This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

//! Specified values.
//!
//! TODO(emilio): Enhance docs.

use Namespace;
use context::QuirksMode;
use cssparser::{Parser, Token, serialize_identifier};
use parser::{ParserContext, Parse};
use self::grid::TrackSizeOrRepeat;
use self::url::SpecifiedUrl;
use std::ascii::AsciiExt;
use std::f32;
use std::fmt;
use style_traits::ToCss;
use style_traits::values::specified::AllowedNumericType;
use super::{Auto, CSSFloat, CSSInteger, Either, None_};
use super::computed::{self, Context};
use super::computed::{Shadow as ComputedShadow, ToComputedValue};
use super::generics::grid::{TrackBreadth as GenericTrackBreadth, TrackSize as GenericTrackSize};
use super::generics::grid::TrackList as GenericTrackList;
use values::computed::ComputedValueAsSpecified;
use values::specified::calc::CalcNode;

pub use properties::animated_properties::TransitionProperty;
#[cfg(feature = "gecko")]
pub use self::align::{AlignItems, AlignJustifyContent, AlignJustifySelf, JustifyItems};
pub use self::background::BackgroundSize;
pub use self::border::{BorderCornerRadius, BorderImageSlice, BorderImageWidth};
pub use self::border::{BorderImageSideWidth, BorderRadius, BorderSideWidth};
pub use self::color::{Color, RGBAColor};
pub use self::rect::LengthOrNumberRect;
#[cfg(feature = "gecko")]
pub use self::gecko::ScrollSnapPoint;
pub use self::image::{ColorStop, EndingShape as GradientEndingShape, Gradient};
pub use self::image::{GradientItem, GradientKind, Image, ImageRect, ImageLayer};
pub use self::length::AbsoluteLength;
pub use self::length::{FontRelativeLength, ViewportPercentageLength, CharacterWidth, Length, CalcLengthOrPercentage};
pub use self::length::{Percentage, LengthOrNone, LengthOrNumber, LengthOrPercentage, LengthOrPercentageOrAuto};
pub use self::length::{LengthOrPercentageOrNone, LengthOrPercentageOrAutoOrContent, NoCalcLength};
pub use self::length::{MaxLength, MozLength};
pub use self::position::{Position, PositionComponent};
pub use self::text::{InitialLetter, LetterSpacing, LineHeight, WordSpacing};
pub use self::transform::{TimingFunction, TransformOrigin};
pub use super::generics::grid::GridLine;

#[cfg(feature = "gecko")]
pub mod align;
pub mod background;
pub mod basic_shape;
pub mod border;
pub mod calc;
pub mod color;
#[cfg(feature = "gecko")]
pub mod gecko;
pub mod grid;
pub mod image;
pub mod length;
pub mod position;
pub mod rect;
pub mod text;
pub mod transform;

/// Common handling for the specified value CSS url() values.
pub mod url {
use cssparser::Parser;
use parser::{Parse, ParserContext};
use values::computed::ComputedValueAsSpecified;

#[cfg(feature = "servo")]
pub use ::servo::url::*;
#[cfg(feature = "gecko")]
pub use ::gecko::url::*;

impl Parse for SpecifiedUrl {
    fn parse(context: &ParserContext, input: &mut Parser) -> Result<Self, ()> {
        let url = try!(input.expect_url());
        Self::parse_from_string(url, context)
    }
}

impl Eq for SpecifiedUrl {}

// TODO(emilio): Maybe consider ComputedUrl to save a word in style structs?
impl ComputedValueAsSpecified for SpecifiedUrl {}

no_viewport_percentage!(SpecifiedUrl);
}

/// Parse an `<integer>` value, handling `calc()` correctly.
pub fn parse_integer(context: &ParserContext, input: &mut Parser) -> Result<Integer, ()> {
    match try!(input.next()) {
        Token::Number(ref value) => value.int_value.ok_or(()).map(Integer::new),
        Token::Function(ref name) if name.eq_ignore_ascii_case("calc") => {
            let result = try!(input.parse_nested_block(|i| {
                CalcNode::parse_integer(context, i)
            }));

            Ok(Integer::from_calc(result))
        }
        _ => Err(())
    }
}

/// Parse a `<number>` value, handling `calc()` correctly, and without length
/// limitations.
pub fn parse_number(context: &ParserContext, input: &mut Parser) -> Result<Number, ()> {
    parse_number_with_clamping_mode(context, input, AllowedNumericType::All)
}

/// Parse a `<number>` value, with a given clamping mode.
pub fn parse_number_with_clamping_mode(context: &ParserContext,
                                       input: &mut Parser,
                                       clamping_mode: AllowedNumericType)
                                       -> Result<Number, ()> {
    match try!(input.next()) {
        Token::Number(ref value) if clamping_mode.is_ok(value.value) => {
            Ok(Number {
                value: value.value.min(f32::MAX).max(f32::MIN),
                calc_clamping_mode: None,
            })
        },
        Token::Function(ref name) if name.eq_ignore_ascii_case("calc") => {
            let result = try!(input.parse_nested_block(|i| {
                CalcNode::parse_number(context, i)
            }));

            Ok(Number {
                value: result.min(f32::MAX).max(f32::MIN),
                calc_clamping_mode: Some(clamping_mode),
            })
        }
        _ => Err(())
    }
}

#[derive(Clone, Copy, Debug, HasViewportPercentage, PartialEq)]
#[cfg_attr(feature = "servo", derive(HeapSizeOf, Deserialize, Serialize))]
/// An angle consisting of a value and a unit.
///
/// Computed Angle is essentially same as specified angle except calc
/// value serialization. Therefore we are using computed Angle enum
/// to hold the value and unit type.
pub struct Angle {
    value: computed::Angle,
    was_calc: bool,
}

impl ToCss for Angle {
    fn to_css<W>(&self, dest: &mut W) -> fmt::Result where W: fmt::Write {
        if self.was_calc {
            dest.write_str("calc(")?;
        }
        self.value.to_css(dest)?;
        if self.was_calc {
            dest.write_str(")")?;
        }
        Ok(())
    }
}

impl ToComputedValue for Angle {
    type ComputedValue = computed::Angle;

    fn to_computed_value(&self, _context: &Context) -> Self::ComputedValue {
        self.value
    }

    fn from_computed_value(computed: &Self::ComputedValue) -> Self {
        Angle {
            value: *computed,
            was_calc: false,
        }
    }
}

impl Angle {
    /// Returns an angle with the given value in degrees.
    pub fn from_degrees(value: CSSFloat, was_calc: bool) -> Self {
        Angle { value: computed::Angle::Degree(value), was_calc: was_calc }
    }

    /// Returns an angle with the given value in gradians.
    pub fn from_gradians(value: CSSFloat, was_calc: bool) -> Self {
        Angle { value: computed::Angle::Gradian(value), was_calc: was_calc }
    }

    /// Returns an angle with the given value in turns.
    pub fn from_turns(value: CSSFloat, was_calc: bool) -> Self {
        Angle { value: computed::Angle::Turn(value), was_calc: was_calc }
    }

    /// Returns an angle with the given value in radians.
    pub fn from_radians(value: CSSFloat, was_calc: bool) -> Self {
        Angle { value: computed::Angle::Radian(value), was_calc: was_calc }
    }

    #[inline]
    #[allow(missing_docs)]
    pub fn radians(self) -> f32 {
        self.value.radians()
    }

    /// Returns an angle value that represents zero.
    pub fn zero() -> Self {
        Self::from_degrees(0.0, false)
    }

    /// Returns an `Angle` parsed from a `calc()` expression.
    pub fn from_calc(radians: CSSFloat) -> Self {
        Angle {
            value: computed::Angle::Radian(radians),
            was_calc: true,
        }
    }
}

impl Parse for Angle {
    /// Parses an angle according to CSS-VALUES § 6.1.
    fn parse(context: &ParserContext, input: &mut Parser) -> Result<Self, ()> {
        match try!(input.next()) {
            Token::Dimension(ref value, ref unit) => {
                Angle::parse_dimension(value.value,
                                       unit,
                                       /* from_calc = */ false)
            }
            Token::Function(ref name) if name.eq_ignore_ascii_case("calc") => {
                input.parse_nested_block(|i| CalcNode::parse_angle(context, i))
            }
            _ => Err(())
        }
    }
}

impl Angle {
    /// Parse an `<angle>` value given a value and an unit.
    pub fn parse_dimension(
        value: CSSFloat,
        unit: &str,
        from_calc: bool)
        -> Result<Angle, ()>
    {
        let angle = match_ignore_ascii_case! { unit,
            "deg" => Angle::from_degrees(value, from_calc),
            "grad" => Angle::from_gradians(value, from_calc),
            "turn" => Angle::from_turns(value, from_calc),
            "rad" => Angle::from_radians(value, from_calc),
             _ => return Err(())
        };
        Ok(angle)
    }
    /// Parse an angle, including unitless 0 degree.
    ///
    /// Note that numbers without any AngleUnit, including unitless 0 angle,
    /// should be invalid. However, some properties still accept unitless 0
    /// angle and stores it as '0deg'.
    ///
    /// We can remove this and get back to the unified version Angle::parse once
    /// https://github.com/w3c/csswg-drafts/issues/1162 is resolved.
    pub fn parse_with_unitless(context: &ParserContext, input: &mut Parser) -> Result<Self, ()> {
        match try!(input.next()) {
            Token::Dimension(ref value, ref unit) => {
                Angle::parse_dimension(value.value,
                                       unit,
                                       /* from_calc = */ false)
            }
            Token::Number(ref value) if value.value == 0. => Ok(Angle::zero()),
            Token::Function(ref name) if name.eq_ignore_ascii_case("calc") => {
                input.parse_nested_block(|i| CalcNode::parse_angle(context, i))
            }
            _ => Err(())
        }
    }
}

// The integer values here correspond to the border conflict resolution rules in CSS 2.1 §
// 17.6.2.1. Higher values override lower values.
define_numbered_css_keyword_enum! { BorderStyle:
    "none" => none = -1,
    "solid" => solid = 6,
    "double" => double = 7,
    "dotted" => dotted = 4,
    "dashed" => dashed = 5,
    "hidden" => hidden = -2,
    "groove" => groove = 1,
    "ridge" => ridge = 3,
    "inset" => inset = 0,
    "outset" => outset = 2,
}

no_viewport_percentage!(BorderStyle);

impl BorderStyle {
    /// Whether this border style is either none or hidden.
    pub fn none_or_hidden(&self) -> bool {
        matches!(*self, BorderStyle::none | BorderStyle::hidden)
    }
}

/// A time in seconds according to CSS-VALUES § 6.2.
#[derive(Clone, Copy, Debug, HasViewportPercentage, PartialEq, PartialOrd)]
#[cfg_attr(feature = "servo", derive(HeapSizeOf))]
pub struct Time {
    seconds: CSSFloat,
    was_calc: bool,
}

impl Time {
    /// Return a `<time>` value that represents `seconds` seconds.
    pub fn from_seconds(seconds: CSSFloat) -> Self {
        Time {
            seconds: seconds,
            was_calc: false,
        }
    }

    /// Returns a time that represents a duration of zero.
    pub fn zero() -> Self {
        Self::from_seconds(0.0)
    }

    /// Returns the time in fractional seconds.
    pub fn seconds(self) -> CSSFloat {
        self.seconds
    }

    /// Parses a time according to CSS-VALUES § 6.2.
    pub fn parse_dimension(
        value: CSSFloat,
        unit: &str,
        from_calc: bool)
        -> Result<Time, ()>
    {
        let seconds = match_ignore_ascii_case! { unit,
            "s" => value,
            "ms" => value / 1000.0,
            _ => return Err(()),
        };

        Ok(Time {
            seconds: seconds,
            was_calc: from_calc,
        })
    }

    /// Returns a `Time` value from a CSS `calc()` expression.
    pub fn from_calc(seconds: CSSFloat) -> Self {
        Time {
            seconds: seconds,
            was_calc: true,
        }
    }

    fn parse_with_clamping_mode(context: &ParserContext,
                                input: &mut Parser,
                                clamping_mode: AllowedNumericType) -> Result<Self, ()> {
        match input.next() {
            Ok(Token::Dimension(ref value, ref unit)) if clamping_mode.is_ok(value.value) => {
                Time::parse_dimension(value.value, &unit, /* from_calc = */ false)
            }
            Ok(Token::Function(ref name)) if name.eq_ignore_ascii_case("calc") => {
                match input.parse_nested_block(|i| CalcNode::parse_time(context, i)) {
                    Ok(time) if clamping_mode.is_ok(time.seconds) => Ok(time),
                    _ => Err(()),
                }
            }
            _ => Err(())
        }
    }

    /// Parse <time> that values are non-negative.
    pub fn parse_non_negative(context: &ParserContext, input: &mut Parser) -> Result<Self, ()> {
        Self::parse_with_clamping_mode(context, input, AllowedNumericType::NonNegative)
    }
}

impl ToComputedValue for Time {
    type ComputedValue = computed::Time;

    fn to_computed_value(&self, _context: &Context) -> Self::ComputedValue {
        computed::Time::from_seconds(self.seconds())
    }

    fn from_computed_value(computed: &Self::ComputedValue) -> Self {
        Time {
            seconds: computed.seconds(),
            was_calc: false,
        }
    }
}

impl Parse for Time {
    fn parse(context: &ParserContext, input: &mut Parser) -> Result<Self, ()> {
        Self::parse_with_clamping_mode(context, input, AllowedNumericType::All)
    }
}

impl ToCss for Time {
    fn to_css<W>(&self, dest: &mut W) -> fmt::Result where W: fmt::Write {
        if self.was_calc {
            dest.write_str("calc(")?;
        }
        write!(dest, "{}s", self.seconds)?;
        if self.was_calc {
            dest.write_str(")")?;
        }
        Ok(())
    }
}

#[derive(Clone, Copy, Debug, PartialEq, PartialOrd)]
#[cfg_attr(feature = "servo", derive(HeapSizeOf))]
#[allow(missing_docs)]
pub struct Number {
    /// The numeric value itself.
    value: CSSFloat,
    /// If this number came from a calc() expression, this tells how clamping
    /// should be done on the value.
    calc_clamping_mode: Option<AllowedNumericType>,
}

no_viewport_percentage!(Number);

impl Parse for Number {
    fn parse(context: &ParserContext, input: &mut Parser) -> Result<Self, ()> {
        parse_number(context, input)
    }
}

impl Number {
    /// Returns a new number with the value `val`.
    pub fn new(val: CSSFloat) -> Self {
        Number {
            value: val,
            calc_clamping_mode: None,
        }
    }

    /// Returns the numeric value, clamped if needed.
    pub fn get(&self) -> f32 {
        self.calc_clamping_mode.map_or(self.value, |mode| mode.clamp(self.value))
    }

    #[allow(missing_docs)]
    pub fn parse_non_negative(context: &ParserContext, input: &mut Parser) -> Result<Number, ()> {
        if context.parsing_mode.allows_all_numeric_values() {
            parse_number(context, input)
        } else {
            parse_number_with_clamping_mode(context, input, AllowedNumericType::NonNegative)
        }
    }

    #[allow(missing_docs)]
    pub fn parse_at_least_one(context: &ParserContext, input: &mut Parser) -> Result<Number, ()> {
        if context.parsing_mode.allows_all_numeric_values() {
            parse_number(context, input)
        } else {
            parse_number_with_clamping_mode(context, input, AllowedNumericType::AtLeastOne)
        }
    }
}

impl ToComputedValue for Number {
    type ComputedValue = CSSFloat;

    #[inline]
    fn to_computed_value(&self, _: &Context) -> CSSFloat { self.get() }

    #[inline]
    fn from_computed_value(computed: &CSSFloat) -> Self {
        Number {
            value: *computed,
            calc_clamping_mode: None,
        }
    }
}

impl ToCss for Number {
    fn to_css<W>(&self, dest: &mut W) -> fmt::Result
        where W: fmt::Write,
    {
        if self.calc_clamping_mode.is_some() {
            dest.write_str("calc(")?;
        }
        self.value.to_css(dest)?;
        if self.calc_clamping_mode.is_some() {
            dest.write_str(")")?;
        }
        Ok(())
    }
}

/// <number-percentage>
/// Accepts only non-negative numbers.
#[allow(missing_docs)]
#[cfg_attr(feature = "servo", derive(HeapSizeOf))]
#[derive(Clone, Copy, Debug, PartialEq, ToCss)]
pub enum NumberOrPercentage {
    Percentage(Percentage),
    Number(Number),
}

no_viewport_percentage!(NumberOrPercentage);

impl NumberOrPercentage {
    fn parse_with_clamping_mode(context: &ParserContext,
                                input: &mut Parser,
                                type_: AllowedNumericType)
                                -> Result<Self, ()> {
        if let Ok(per) = input.try(|i| Percentage::parse_with_clamping_mode(i, type_)) {
            return Ok(NumberOrPercentage::Percentage(per));
        }

        parse_number_with_clamping_mode(context, input, type_).map(NumberOrPercentage::Number)
    }

    /// Parse a non-negative number or percentage.
    pub fn parse_non_negative(context: &ParserContext, input: &mut Parser) -> Result<Self, ()> {
        Self::parse_with_clamping_mode(context, input, AllowedNumericType::NonNegative)
    }
}

impl Parse for NumberOrPercentage {
    fn parse(context: &ParserContext, input: &mut Parser) -> Result<Self, ()> {
        Self::parse_with_clamping_mode(context, input, AllowedNumericType::All)
    }
}

#[allow(missing_docs)]
#[cfg_attr(feature = "servo", derive(HeapSizeOf))]
#[derive(Clone, Copy, Debug, PartialEq, PartialOrd, ToCss)]
pub struct Opacity(Number);

no_viewport_percentage!(Opacity);

impl Parse for Opacity {
    fn parse(context: &ParserContext, input: &mut Parser) -> Result<Self, ()> {
        parse_number(context, input).map(Opacity)
    }
}

impl ToComputedValue for Opacity {
    type ComputedValue = CSSFloat;

    #[inline]
    fn to_computed_value(&self, context: &Context) -> CSSFloat {
        self.0.to_computed_value(context).min(1.0).max(0.0)
    }

    #[inline]
    fn from_computed_value(computed: &CSSFloat) -> Self {
        Opacity(Number::from_computed_value(computed))
    }
}

#[derive(Clone, Copy, Debug, PartialEq, PartialOrd)]
#[cfg_attr(feature = "servo", derive(HeapSizeOf))]
#[allow(missing_docs)]
pub struct Integer {
    value: CSSInteger,
    was_calc: bool,
}

impl Integer {
    /// Trivially constructs a new `Integer` value.
    pub fn new(val: CSSInteger) -> Self {
        Integer {
            value: val,
            was_calc: false,
        }
    }

    /// Returns the integer value associated with this value.
    pub fn value(&self) -> CSSInteger {
        self.value
    }

    /// Trivially constructs a new integer value from a `calc()` expression.
    fn from_calc(val: CSSInteger) -> Self {
        Integer {
            value: val,
            was_calc: true,
        }
    }
}

no_viewport_percentage!(Integer);

impl Parse for Integer {
    fn parse(context: &ParserContext, input: &mut Parser) -> Result<Self, ()> {
        parse_integer(context, input)
    }
}

impl Integer {
    #[allow(missing_docs)]
    pub fn parse_with_minimum(context: &ParserContext, input: &mut Parser, min: i32) -> Result<Integer, ()> {
        match parse_integer(context, input) {
            Ok(value) if value.value() >= min => Ok(value),
            _ => Err(()),
        }
    }

    #[allow(missing_docs)]
    pub fn parse_non_negative(context: &ParserContext, input: &mut Parser) -> Result<Integer, ()> {
        Integer::parse_with_minimum(context, input, 0)
    }

    #[allow(missing_docs)]
    pub fn parse_positive(context: &ParserContext, input: &mut Parser) -> Result<Integer, ()> {
        Integer::parse_with_minimum(context, input, 1)
    }
}

impl ToComputedValue for Integer {
    type ComputedValue = i32;

    #[inline]
    fn to_computed_value(&self, _: &Context) -> i32 { self.value }

    #[inline]
    fn from_computed_value(computed: &i32) -> Self {
        Integer::new(*computed)
    }
}

impl ToCss for Integer {
    fn to_css<W>(&self, dest: &mut W) -> fmt::Result
        where W: fmt::Write,
    {
        if self.was_calc {
            dest.write_str("calc(")?;
        }
        write!(dest, "{}", self.value)?;
        if self.was_calc {
            dest.write_str(")")?;
        }
        Ok(())
    }
}

/// <integer> | auto
pub type IntegerOrAuto = Either<Integer, Auto>;

impl IntegerOrAuto {
    #[allow(missing_docs)]
    pub fn parse_positive(context: &ParserContext,
                          input: &mut Parser)
                          -> Result<IntegerOrAuto, ()> {
        match IntegerOrAuto::parse(context, input) {
            Ok(Either::First(integer)) if integer.value() <= 0 => Err(()),
            result => result,
        }
    }
}

#[allow(missing_docs)]
pub type UrlOrNone = Either<SpecifiedUrl, None_>;

/// The specified value of a grid `<track-breadth>`
pub type TrackBreadth = GenericTrackBreadth<LengthOrPercentage>;

/// The specified value of a grid `<track-size>`
pub type TrackSize = GenericTrackSize<LengthOrPercentage>;

/// The specified value of a grid `<track-list>`
/// (could also be `<auto-track-list>` or `<explicit-track-list>`)
pub type TrackList = GenericTrackList<TrackSizeOrRepeat>;

/// `<track-list> | none`
pub type TrackListOrNone = Either<TrackList, None_>;

#[derive(Clone, Debug, HasViewportPercentage, PartialEq)]
#[cfg_attr(feature = "servo", derive(HeapSizeOf))]
#[allow(missing_docs)]
pub struct Shadow {
    pub offset_x: Length,
    pub offset_y: Length,
    pub blur_radius: Length,
    pub spread_radius: Length,
    pub color: Option<Color>,
    pub inset: bool,
}

impl ToComputedValue for Shadow {
    type ComputedValue = ComputedShadow;

    #[inline]
    fn to_computed_value(&self, context: &Context) -> Self::ComputedValue {
        ComputedShadow {
            offset_x: self.offset_x.to_computed_value(context),
            offset_y: self.offset_y.to_computed_value(context),
            blur_radius: self.blur_radius.to_computed_value(context),
            spread_radius: self.spread_radius.to_computed_value(context),
            color: self.color.as_ref().unwrap_or(&Color::CurrentColor)
                             .to_computed_value(context),
            inset: self.inset,
        }
    }

    #[inline]
    fn from_computed_value(computed: &ComputedShadow) -> Self {
        Shadow {
            offset_x: ToComputedValue::from_computed_value(&computed.offset_x),
            offset_y: ToComputedValue::from_computed_value(&computed.offset_y),
            blur_radius: ToComputedValue::from_computed_value(&computed.blur_radius),
            spread_radius: ToComputedValue::from_computed_value(&computed.spread_radius),
            color: Some(ToComputedValue::from_computed_value(&computed.color)),
            inset: computed.inset,
        }
    }
}

impl ToCss for Shadow {
    fn to_css<W>(&self, dest: &mut W) -> fmt::Result where W: fmt::Write {
        if self.inset {
            dest.write_str("inset ")?;
        }
        self.offset_x.to_css(dest)?;
        dest.write_str(" ")?;
        self.offset_y.to_css(dest)?;
        dest.write_str(" ")?;
        self.blur_radius.to_css(dest)?;
        if self.spread_radius != Length::zero() {
            dest.write_str(" ")?;
            self.spread_radius.to_css(dest)?;
        }
        if let Some(ref color) = self.color {
            dest.write_str(" ")?;
            color.to_css(dest)?;
        }
        Ok(())
    }
}

impl Shadow {
    // disable_spread_and_inset is for filter: drop-shadow(...)
    #[allow(missing_docs)]
    pub fn parse(context: &ParserContext, input: &mut Parser, disable_spread_and_inset: bool) -> Result<Shadow, ()> {
        let mut lengths = [Length::zero(), Length::zero(), Length::zero(), Length::zero()];
        let mut lengths_parsed = false;
        let mut color = None;
        let mut inset = false;

        loop {
            if !inset && !disable_spread_and_inset {
                if input.try(|input| input.expect_ident_matching("inset")).is_ok() {
                    inset = true;
                    continue
                }
            }
            if !lengths_parsed {
                if let Ok(value) = input.try(|i| Length::parse(context, i)) {
                    lengths[0] = value;
                    lengths[1] = try!(Length::parse(context, input));
                    if let Ok(value) = input.try(|i| Length::parse_non_negative(context, i)) {
                        lengths[2] = value;
                        if !disable_spread_and_inset {
                            if let Ok(value) = input.try(|i| Length::parse(context, i)) {
                                lengths[3] = value;
                            }
                        }
                    }
                    lengths_parsed = true;
                    continue
                }
            }
            if color.is_none() {
                if let Ok(value) = input.try(|i| Color::parse(context, i)) {
                    color = Some(value);
                    continue
                }
            }
            break
        }

        // Lengths must be specified.
        if !lengths_parsed {
            return Err(())
        }

        debug_assert!(!disable_spread_and_inset || lengths[3] == Length::zero());
        Ok(Shadow {
            offset_x: lengths[0].take(),
            offset_y: lengths[1].take(),
            blur_radius: lengths[2].take(),
            spread_radius: lengths[3].take(),
            color: color,
            inset: inset,
        })
    }
}

no_viewport_percentage!(SVGPaint);

/// Specified SVG Paint value
pub type SVGPaint = ::values::generics::SVGPaint<RGBAColor>;

/// Specified SVG Paint Kind value
pub type SVGPaintKind = ::values::generics::SVGPaintKind<RGBAColor>;

impl ToComputedValue for SVGPaint {
    type ComputedValue = super::computed::SVGPaint;

    #[inline]
    fn to_computed_value(&self, context: &Context) -> Self::ComputedValue {
        super::computed::SVGPaint {
            kind: self.kind.to_computed_value(context),
            fallback: self.fallback.as_ref().map(|f| f.to_computed_value(context))
        }
    }

    #[inline]
    fn from_computed_value(computed: &Self::ComputedValue) -> Self {
        SVGPaint {
            kind: ToComputedValue::from_computed_value(&computed.kind),
            fallback: computed.fallback.as_ref().map(ToComputedValue::from_computed_value)
        }
    }
}

impl ToComputedValue for SVGPaintKind {
    type ComputedValue = super::computed::SVGPaintKind;

    #[inline]
    fn to_computed_value(&self, context: &Context) -> Self::ComputedValue {
        self.convert(|color| color.to_computed_value(context))
    }

    #[inline]
    fn from_computed_value(computed: &Self::ComputedValue) -> Self {
        computed.convert(ToComputedValue::from_computed_value)
    }
}

/// <length> | <percentage> | <number>
pub type LengthOrPercentageOrNumber = Either<Number, LengthOrPercentage>;

impl LengthOrPercentageOrNumber {
    /// parse a <length-percentage> | <number> enforcing that the contents aren't negative
    pub fn parse_non_negative(context: &ParserContext, input: &mut Parser) -> Result<Self, ()> {
        // NB: Parse numbers before Lengths so we are consistent about how to
        // recognize and serialize "0".
        if let Ok(num) = input.try(|i| Number::parse_non_negative(context, i)) {
            return Ok(Either::First(num))
        }

        LengthOrPercentage::parse_non_negative(context, input).map(Either::Second)
    }
}

#[derive(Clone, Debug, HasViewportPercentage, PartialEq)]
#[cfg_attr(feature = "servo", derive(HeapSizeOf))]
/// rect(<top>, <left>, <bottom>, <right>) used by clip and image-region
pub struct ClipRect {
    /// <top> (<length> | <auto>)
    pub top: Option<Length>,
    /// <right> (<length> | <auto>)
    pub right: Option<Length>,
    /// <bottom> (<length> | <auto>)
    pub bottom: Option<Length>,
    /// <left> (<length> | <auto>)
    pub left: Option<Length>,
}


impl ToCss for ClipRect {
    fn to_css<W>(&self, dest: &mut W) -> fmt::Result where W: fmt::Write {
        try!(dest.write_str("rect("));

        if let Some(ref top) = self.top {
            try!(top.to_css(dest));
            try!(dest.write_str(", "));
        } else {
            try!(dest.write_str("auto, "));
        }

        if let Some(ref right) = self.right {
            try!(right.to_css(dest));
            try!(dest.write_str(", "));
        } else {
            try!(dest.write_str("auto, "));
        }

        if let Some(ref bottom) = self.bottom {
            try!(bottom.to_css(dest));
            try!(dest.write_str(", "));
        } else {
            try!(dest.write_str("auto, "));
        }

        if let Some(ref left) = self.left {
            try!(left.to_css(dest));
        } else {
            try!(dest.write_str("auto"));
        }

        try!(dest.write_str(")"));
        Ok(())
    }
}

impl ToComputedValue for ClipRect {
    type ComputedValue = super::computed::ClipRect;

    #[inline]
    fn to_computed_value(&self, context: &Context) -> super::computed::ClipRect {
        super::computed::ClipRect {
            top: self.top.as_ref().map(|top| top.to_computed_value(context)),
            right: self.right.as_ref().map(|right| right.to_computed_value(context)),
            bottom: self.bottom.as_ref().map(|bottom| bottom.to_computed_value(context)),
            left: self.left.as_ref().map(|left| left.to_computed_value(context)),
        }
    }

    #[inline]
    fn from_computed_value(computed: &super::computed::ClipRect) -> Self {
        ClipRect {
            top: computed.top.map(|top| ToComputedValue::from_computed_value(&top)),
            right: computed.right.map(|right| ToComputedValue::from_computed_value(&right)),
            bottom: computed.bottom.map(|bottom| ToComputedValue::from_computed_value(&bottom)),
            left: computed.left.map(|left| ToComputedValue::from_computed_value(&left)),
        }
    }
}

impl Parse for ClipRect {
    fn parse(context: &ParserContext, input: &mut Parser) -> Result<Self, ()> {
        Self::parse_quirky(context, input, AllowQuirks::No)
    }
}

impl ClipRect {
    /// Parses a rect(<top>, <left>, <bottom>, <right>), allowing quirks.
    pub fn parse_quirky(context: &ParserContext, input: &mut Parser,
                    allow_quirks: AllowQuirks) -> Result<Self, ()> {
        use values::specified::Length;

        fn parse_argument(context: &ParserContext, input: &mut Parser,
                          allow_quirks: AllowQuirks) -> Result<Option<Length>, ()> {
            if input.try(|input| input.expect_ident_matching("auto")).is_ok() {
                Ok(None)
            } else {
                Length::parse_quirky(context, input, allow_quirks).map(Some)
            }
        }

        if !try!(input.expect_function()).eq_ignore_ascii_case("rect") {
            return Err(())
        }

        input.parse_nested_block(|input| {
            let top = try!(parse_argument(context, input, allow_quirks));
            let right;
            let bottom;
            let left;

            if input.try(|input| input.expect_comma()).is_ok() {
                right = try!(parse_argument(context, input, allow_quirks));
                try!(input.expect_comma());
                bottom = try!(parse_argument(context, input, allow_quirks));
                try!(input.expect_comma());
                left = try!(parse_argument(context, input, allow_quirks));
            } else {
                right = try!(parse_argument(context, input, allow_quirks));
                bottom = try!(parse_argument(context, input, allow_quirks));
                left = try!(parse_argument(context, input, allow_quirks));
            }
            Ok(ClipRect {
                top: top,
                right: right,
                bottom: bottom,
                left: left,
            })
        })
    }
}

/// rect(...) | auto
pub type ClipRectOrAuto = Either<ClipRect, Auto>;

impl ClipRectOrAuto {
    /// Parses a ClipRect or Auto, allowing quirks.
    pub fn parse_quirky(context: &ParserContext, input: &mut Parser,
                        allow_quirks: AllowQuirks) -> Result<Self, ()> {
        if let Ok(v) = input.try(|i| ClipRect::parse_quirky(context, i, allow_quirks)) {
            Ok(Either::First(v))
        } else {
            Auto::parse(context, input).map(Either::Second)
        }
    }
}

/// <color> | auto
pub type ColorOrAuto = Either<Color, Auto>;

/// Whether quirks are allowed in this context.
#[derive(Clone, Copy, PartialEq)]
pub enum AllowQuirks {
    /// Quirks are allowed.
    Yes,
    /// Quirks are not allowed.
    No,
}

impl AllowQuirks {
    /// Returns `true` if quirks are allowed in this context.
    pub fn allowed(self, quirks_mode: QuirksMode) -> bool {
        self == AllowQuirks::Yes && quirks_mode == QuirksMode::Quirks
    }
}

#[cfg(feature = "gecko")]
/// A namespace ID
pub type NamespaceId = i32;


#[cfg(feature = "servo")]
/// A namespace ID (used by gecko only)
pub type NamespaceId = ();

/// An attr(...) rule
///
/// `[namespace? `|`]? ident`
#[derive(Clone, PartialEq, Eq, Debug)]
#[cfg_attr(feature = "servo", derive(HeapSizeOf))]
pub struct Attr {
    /// Optional namespace
    pub namespace: Option<(Namespace, NamespaceId)>,
    /// Attribute name
    pub attribute: String,
}

impl Parse for Attr {
    fn parse(context: &ParserContext, input: &mut Parser) -> Result<Attr, ()> {
        input.expect_function_matching("attr")?;
        input.parse_nested_block(|i| Attr::parse_function(context, i))
    }
}

#[cfg(feature = "gecko")]
/// Get the namespace id from the namespace map
fn get_id_for_namespace(namespace: &Namespace, context: &ParserContext) -> Result<NamespaceId, ()> {
    let namespaces_map = match context.namespaces {
        Some(map) => map,
        None => {
            // If we don't have a namespace map (e.g. in inline styles)
            // we can't parse namespaces
            return Err(());
        }
    };

    match namespaces_map.prefixes.get(&namespace.0) {
        Some(entry) => Ok(entry.1),
        None => Err(()),
    }
}

#[cfg(feature = "servo")]
/// Get the namespace id from the namespace map
fn get_id_for_namespace(_: &Namespace, _: &ParserContext) -> Result<NamespaceId, ()> {
    Ok(())
}

impl Attr {
    /// Parse contents of attr() assuming we have already parsed `attr` and are
    /// within a parse_nested_block()
    pub fn parse_function(context: &ParserContext, input: &mut Parser) -> Result<Attr, ()> {
        // Syntax is `[namespace? `|`]? ident`
        // no spaces allowed
        let first = input.try(|i| i.expect_ident()).ok();
        if let Ok(token) = input.try(|i| i.next_including_whitespace()) {
            match token {
                Token::Delim('|') => {}
                _ => return Err(()),
            }
            // must be followed by an ident
            let second_token = match input.next_including_whitespace()? {
                Token::Ident(second) => second,
                _ => return Err(()),
            };

            let ns_with_id = if let Some(ns) = first {
                let ns: Namespace = ns.into();
                let id = get_id_for_namespace(&ns, context)?;
                Some((ns, id))
            } else {
                None
            };
            return Ok(Attr {
                namespace: ns_with_id,
                attribute: second_token.into_owned(),
            })
        }

        if let Some(first) = first {
            Ok(Attr {
                namespace: None,
                attribute: first.into_owned(),
            })
        } else {
            Err(())
        }
    }
}

impl ToCss for Attr {
    fn to_css<W>(&self, dest: &mut W) -> fmt::Result where W: fmt::Write {
        dest.write_str("attr(")?;
        if let Some(ref ns) = self.namespace {
            serialize_identifier(&ns.0.to_string(), dest)?;
            dest.write_str("|")?;
        }
        serialize_identifier(&self.attribute, dest)?;
        dest.write_str(")")
    }
}

impl ComputedValueAsSpecified for Attr {}