style: Add a Zero trait that doesn't require Add, and use it in place of num_traits and IsZeroLength.

Use it to be consistent in InsetRect serialization and storage between Servo and
Gecko.

Differential Revision: https://phabricator.services.mozilla.com/D21493

components/style/values/generics/basic_shape.rs

@@ -11,6 +11,7 @@ use crate::values::generics::border::BorderRadius;
 use crate::values::generics::position::Position;
 use crate::values::generics::rect::Rect;
 use crate::values::specified::SVGPathData;
+use crate::Zero;
 use std::fmt::{self, Write};
 use style_traits::{CssWriter, ToCss};
 
@@ -127,7 +128,7 @@ pub enum BasicShape<H, V, LengthPercentage, NonNegativeLengthPercentage> {
 )]
 pub struct InsetRect<LengthPercentage, NonNegativeLengthPercentage> {
     pub rect: Rect<LengthPercentage>,
-    pub round: Option<BorderRadius<NonNegativeLengthPercentage>>,
+    pub round: BorderRadius<NonNegativeLengthPercentage>,
 }
 
 /// <https://drafts.csswg.org/css-shapes/#funcdef-circle>
@@ -311,7 +312,7 @@ impl<B, T, U> ToAnimatedZero for ShapeSource<B, T, U> {
 impl<Length, NonNegativeLength> ToCss for InsetRect<Length, NonNegativeLength>
 where
     Length: ToCss + PartialEq,
-    NonNegativeLength: ToCss + PartialEq,
+    NonNegativeLength: ToCss + PartialEq + Zero,
 {
     fn to_css<W>(&self, dest: &mut CssWriter<W>) -> fmt::Result
     where
@@ -319,9 +320,9 @@ where
     {
         dest.write_str("inset(")?;
         self.rect.to_css(dest)?;
-        if let Some(ref radius) = self.round {
+        if !self.round.is_zero() {
             dest.write_str(" round ")?;
-            radius.to_css(dest)?;
+            self.round.to_css(dest)?;
         }
         dest.write_str(")")
     }

components/style/values/generics/border.rs

@@ -6,6 +6,7 @@
 
 use crate::values::generics::rect::Rect;
 use crate::values::generics::size::Size2D;
+use crate::Zero;
 use std::fmt::{self, Write};
 use style_traits::{CssWriter, ToCss};
 
@@ -65,6 +66,16 @@ impl<L> BorderCornerRadius<L> {
     }
 }
 
+impl<L: Zero> Zero for BorderCornerRadius<L> {
+    fn zero() -> Self {
+        BorderCornerRadius(Size2D::zero())
+    }
+
+    fn is_zero(&self) -> bool {
+        self.0.is_zero()
+    }
+}
+
 /// A generic value for the `border-spacing` property.
 #[derive(
     Animate,
@@ -135,12 +146,7 @@ impl<L> BorderRadius<L> {
             bottom_left: bl,
         }
     }
-}
 
-impl<L> BorderRadius<L>
-where
-    L: PartialEq + ToCss,
-{
     /// Serialises two given rects following the syntax of the `border-radius``
     /// property.
     pub fn serialize_rects<W>(
@@ -149,6 +155,7 @@ where
         dest: &mut CssWriter<W>,
     ) -> fmt::Result
     where
+        L: PartialEq + ToCss,
         W: Write,
     {
         widths.to_css(dest)?;
@@ -160,6 +167,24 @@ where
     }
 }
 
+impl<L: Zero> Zero for BorderRadius<L> {
+    fn zero() -> Self {
+        Self::new(
+            BorderCornerRadius::<L>::zero(),
+            BorderCornerRadius::<L>::zero(),
+            BorderCornerRadius::<L>::zero(),
+            BorderCornerRadius::<L>::zero(),
+        )
+    }
+
+    fn is_zero(&self) -> bool {
+        self.top_left.is_zero() &&
+            self.top_right.is_zero() &&
+            self.bottom_right.is_zero() &&
+            self.bottom_left.is_zero()
+    }
+}
+
 impl<L> ToCss for BorderRadius<L>
 where
     L: PartialEq + ToCss,

components/style/values/generics/length.rs

@@ -7,8 +7,8 @@
 use crate::parser::{Parse, ParserContext};
 #[cfg(feature = "gecko")]
 use crate::values::computed::ExtremumLength;
+use crate::Zero;
 use cssparser::Parser;
-use num_traits::Zero;
 use style_traits::ParseError;
 
 /// A `<length-percentage> | auto` value.
@@ -67,6 +67,19 @@ impl<LengthPercentage> LengthPercentageOrAuto<LengthPercentage> {
     }
 }
 
+impl<LengthPercentage: Zero> Zero for LengthPercentageOrAuto<LengthPercentage> {
+    fn zero() -> Self {
+        LengthPercentageOrAuto::LengthPercentage(Zero::zero())
+    }
+
+    fn is_zero(&self) -> bool {
+        match *self {
+            LengthPercentageOrAuto::LengthPercentage(ref l) => l.is_zero(),
+            LengthPercentageOrAuto::Auto => false,
+        }
+    }
+}
+
 impl<LengthPercentage: Parse> Parse for LengthPercentageOrAuto<LengthPercentage> {
     fn parse<'i, 't>(
         context: &ParserContext,
@@ -186,12 +199,15 @@ pub enum GenericLengthOrNumber<L, N> {
 
 pub use self::GenericLengthOrNumber as LengthOrNumber;
 
-impl<L, N> LengthOrNumber<L, N> {
-    /// Returns `0`.
-    pub fn zero() -> Self
-    where
-        N: Zero,
-    {
-        LengthOrNumber::Number(num_traits::Zero::zero())
+impl<L, N: Zero> Zero for LengthOrNumber<L, N> {
+    fn zero() -> Self {
+        LengthOrNumber::Number(Zero::zero())
+    }
+
+    fn is_zero(&self) -> bool {
+        match *self {
+            LengthOrNumber::Number(ref n) => n.is_zero(),
+            LengthOrNumber::Length(..) => false,
+        }
     }
 }

components/style/values/generics/mod.rs

@@ -8,8 +8,8 @@
 use super::CustomIdent;
 use crate::counter_style::{parse_counter_style_name, Symbols};
 use crate::parser::{Parse, ParserContext};
+use crate::Zero;
 use cssparser::Parser;
-use num_traits::Zero;
 use std::ops::Add;
 use style_traits::{KeywordsCollectFn, ParseError};
 use style_traits::{SpecifiedValueInfo, StyleParseErrorKind};

components/style/values/generics/size.rs

@@ -5,6 +5,7 @@
 //! Generic type for CSS properties that are composed by two dimensions.
 
 use crate::parser::ParserContext;
+use crate::Zero;
 use cssparser::Parser;
 use std::fmt::{self, Write};
 use style_traits::{CssWriter, ParseError, ToCss};
@@ -84,3 +85,13 @@ where
         Ok(())
     }
 }
+
+impl<L: Zero> Zero for Size2D<L> {
+    fn zero() -> Self {
+        Self::new(L::zero(), L::zero())
+    }
+
+    fn is_zero(&self) -> bool {
+        self.width.is_zero() && self.height.is_zero()
+    }
+}

components/style/values/generics/transform.rs

@@ -10,9 +10,9 @@ use crate::values::specified::angle::Angle as SpecifiedAngle;
 use crate::values::specified::length::Length as SpecifiedLength;
 use crate::values::specified::length::LengthPercentage as SpecifiedLengthPercentage;
 use crate::values::{computed, CSSFloat};
+use crate::Zero;
 use app_units::Au;
 use euclid::{self, Rect, Transform3D};
-use num_traits::Zero;
 use std::fmt::{self, Write};
 use style_traits::{CssWriter, ToCss};
 
@@ -643,16 +643,7 @@ pub enum Translate<LengthPercentage, Length> {
     Translate3D(LengthPercentage, LengthPercentage, Length),
 }
 
-/// A trait to check if this is a zero length.
-/// An alternative way is use num_traits::Zero. However, in order to implement num_traits::Zero,
-/// we also have to implement Add, which may be complicated for LengthPercentage::Calc.
-/// We could do this if other types also need it. If so, we could drop this trait.
-pub trait IsZeroLength {
-    /// Returns true if this is a zero length.
-    fn is_zero_length(&self) -> bool;
-}
-
-impl<LoP: ToCss + IsZeroLength, L: ToCss> ToCss for Translate<LoP, L> {
+impl<LoP: ToCss + Zero, L: ToCss> ToCss for Translate<LoP, L> {
     fn to_css<W>(&self, dest: &mut CssWriter<W>) -> fmt::Result
     where
         W: fmt::Write,
@@ -670,7 +661,7 @@ impl<LoP: ToCss + IsZeroLength, L: ToCss> ToCss for Translate<LoP, L> {
             Translate::None => dest.write_str("none"),
             Translate::Translate(ref x, ref y) => {
                 x.to_css(dest)?;
-                if !y.is_zero_length() {
+                if !y.is_zero() {
                     dest.write_char(' ')?;
                     y.to_css(dest)?;
                 }