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diff --git a/servo/components/style/values/specified/angle.rs b/servo/components/style/values/specified/angle.rs
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+++ b/servo/components/style/values/specified/angle.rs
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+/* 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 https://mozilla.org/MPL/2.0/. */
+
+//! Specified angles.
+
+use crate::parser::{Parse, ParserContext};
+use crate::values::computed::angle::Angle as ComputedAngle;
+use crate::values::computed::{Context, ToComputedValue};
+use crate::values::specified::calc::CalcNode;
+use crate::values::CSSFloat;
+use crate::Zero;
+use cssparser::{Parser, Token};
+use std::f32::consts::PI;
+use std::fmt::{self, Write};
+use style_traits::{CssWriter, ParseError, SpecifiedValueInfo, ToCss};
+
+/// A specified angle dimension.
+#[cfg_attr(feature = "servo", derive(Deserialize, Serialize))]
+#[derive(Clone, Copy, Debug, MallocSizeOf, PartialEq, PartialOrd, ToCss, ToShmem)]
+pub enum AngleDimension {
+    /// An angle with degree unit.
+    #[css(dimension)]
+    Deg(CSSFloat),
+    /// An angle with gradian unit.
+    #[css(dimension)]
+    Grad(CSSFloat),
+    /// An angle with radian unit.
+    #[css(dimension)]
+    Rad(CSSFloat),
+    /// An angle with turn unit.
+    #[css(dimension)]
+    Turn(CSSFloat),
+}
+
+impl Zero for AngleDimension {
+    fn zero() -> Self {
+        AngleDimension::Deg(0.)
+    }
+
+    fn is_zero(&self) -> bool {
+        match *self {
+            AngleDimension::Deg(ref f) |
+            AngleDimension::Grad(ref f) |
+            AngleDimension::Rad(ref f) |
+            AngleDimension::Turn(ref f) => *f == 0.,
+        }
+    }
+}
+
+impl AngleDimension {
+    /// Returns the amount of degrees this angle represents.
+    #[inline]
+    fn degrees(&self) -> CSSFloat {
+        const DEG_PER_RAD: f32 = 180.0 / PI;
+        const DEG_PER_TURN: f32 = 360.0;
+        const DEG_PER_GRAD: f32 = 180.0 / 200.0;
+
+        match *self {
+            AngleDimension::Deg(d) => d,
+            AngleDimension::Rad(rad) => rad * DEG_PER_RAD,
+            AngleDimension::Turn(turns) => turns * DEG_PER_TURN,
+            AngleDimension::Grad(gradians) => gradians * DEG_PER_GRAD,
+        }
+    }
+}
+
+/// A specified Angle value, which is just the angle dimension, plus whether it
+/// was specified as `calc()` or not.
+#[cfg_attr(feature = "servo", derive(Deserialize, Serialize))]
+#[derive(Clone, Copy, Debug, MallocSizeOf, PartialEq, ToShmem)]
+pub struct Angle {
+    value: AngleDimension,
+    was_calc: bool,
+}
+
+impl Zero for Angle {
+    fn zero() -> Self {
+        Self {
+            value: Zero::zero(),
+            was_calc: false,
+        }
+    }
+
+    fn is_zero(&self) -> bool {
+        self.value.is_zero()
+    }
+}
+
+impl ToCss for Angle {
+    fn to_css<W>(&self, dest: &mut CssWriter<W>) -> fmt::Result
+    where
+        W: 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 = ComputedAngle;
+
+    #[inline]
+    fn to_computed_value(&self, _context: &Context) -> Self::ComputedValue {
+        ComputedAngle::from_degrees(self.degrees())
+    }
+
+    #[inline]
+    fn from_computed_value(computed: &Self::ComputedValue) -> Self {
+        Angle {
+            value: AngleDimension::Deg(computed.degrees()),
+            was_calc: false,
+        }
+    }
+}
+
+impl Angle {
+    /// Creates an angle with the given value in degrees.
+    #[inline]
+    pub fn from_degrees(value: CSSFloat, was_calc: bool) -> Self {
+        Angle {
+            value: AngleDimension::Deg(value),
+            was_calc,
+        }
+    }
+
+    /// Creates an angle with the given value in radians.
+    #[inline]
+    pub fn from_radians(value: CSSFloat) -> Self {
+        Angle {
+            value: AngleDimension::Rad(value),
+            was_calc: false,
+        }
+    }
+
+    /// Return `0deg`.
+    pub fn zero() -> Self {
+        Self::from_degrees(0.0, false)
+    }
+
+    /// Returns the value of the angle in degrees, mostly for `calc()`.
+    #[inline]
+    pub fn degrees(&self) -> CSSFloat {
+        self.value.degrees()
+    }
+
+    /// Returns the value of the angle in radians.
+    #[inline]
+    pub fn radians(&self) -> CSSFloat {
+        const RAD_PER_DEG: f32 = PI / 180.0;
+        self.value.degrees() * RAD_PER_DEG
+    }
+
+    /// Whether this specified angle came from a `calc()` expression.
+    #[inline]
+    pub fn was_calc(&self) -> bool {
+        self.was_calc
+    }
+
+    /// Returns an `Angle` parsed from a `calc()` expression.
+    pub fn from_calc(degrees: CSSFloat) -> Self {
+        Angle {
+            value: AngleDimension::Deg(degrees),
+            was_calc: true,
+        }
+    }
+}
+
+/// Whether to allow parsing an unitless zero as a valid angle.
+///
+/// This should always be `No`, except for exceptions like:
+///
+///   https://github.com/w3c/fxtf-drafts/issues/228
+///
+/// See also: https://github.com/w3c/csswg-drafts/issues/1162.
+#[allow(missing_docs)]
+pub enum AllowUnitlessZeroAngle {
+    Yes,
+    No,
+}
+
+impl Parse for Angle {
+    /// Parses an angle according to CSS-VALUES § 6.1.
+    fn parse<'i, 't>(
+        context: &ParserContext,
+        input: &mut Parser<'i, 't>,
+    ) -> Result<Self, ParseError<'i>> {
+        Self::parse_internal(context, input, AllowUnitlessZeroAngle::No)
+    }
+}
+
+impl Angle {
+    /// Parse an `<angle>` value given a value and an unit.
+    pub fn parse_dimension(value: CSSFloat, unit: &str, was_calc: bool) -> Result<Angle, ()> {
+        let value = match_ignore_ascii_case! { unit,
+            "deg" => AngleDimension::Deg(value),
+            "grad" => AngleDimension::Grad(value),
+            "turn" => AngleDimension::Turn(value),
+            "rad" => AngleDimension::Rad(value),
+             _ => return Err(())
+        };
+
+        Ok(Self { value, was_calc })
+    }
+
+    /// Parse an `<angle>` allowing unitless zero to represent a zero angle.
+    ///
+    /// See the comment in `AllowUnitlessZeroAngle` for why.
+    #[inline]
+    pub fn parse_with_unitless<'i, 't>(
+        context: &ParserContext,
+        input: &mut Parser<'i, 't>,
+    ) -> Result<Self, ParseError<'i>> {
+        Self::parse_internal(context, input, AllowUnitlessZeroAngle::Yes)
+    }
+
+    pub(super) fn parse_internal<'i, 't>(
+        context: &ParserContext,
+        input: &mut Parser<'i, 't>,
+        allow_unitless_zero: AllowUnitlessZeroAngle,
+    ) -> Result<Self, ParseError<'i>> {
+        let location = input.current_source_location();
+        let t = input.next()?;
+        let allow_unitless_zero = matches!(allow_unitless_zero, AllowUnitlessZeroAngle::Yes);
+        match *t {
+            Token::Dimension {
+                value, ref unit, ..
+            } => {
+                match Angle::parse_dimension(value, unit, /* from_calc = */ false) {
+                    Ok(angle) => Ok(angle),
+                    Err(()) => {
+                        let t = t.clone();
+                        Err(input.new_unexpected_token_error(t))
+                    },
+                }
+            },
+            Token::Function(ref name) => {
+                let function = CalcNode::math_function(name, location)?;
+                CalcNode::parse_angle(context, input, function)
+            },
+            Token::Number { value, .. } if value == 0. && allow_unitless_zero => Ok(Angle::zero()),
+            ref t => {
+                let t = t.clone();
+                Err(input.new_unexpected_token_error(t))
+            },
+        }
+    }
+}
+
+impl SpecifiedValueInfo for Angle {}