Auto merge of #14049 - Wafflespeanut:lon, r=SimonSapin

Add a generic type for sharing some CSS types

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This would be useful for types such as `T(pub Option<U>)` or any type that's a mixture of two types (like `LengthOrFoo` for example). Well, it's a bit ugly, especially because we have to address the types as `Either::First` and `Either::Second` everywhere, but I don't have a brighter idea :smile:

---
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- [x] `./mach build -d` does not report any errors
- [x] `./mach test-tidy` does not report any errors

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- [x] These changes do not require tests because it's a refactor

r? @SimonSapin (cc @Manishearth @emilio)

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11 files changed, 125 insertions, 117 deletions

diff --git a/components/layout/display_list_builder.rs b/components/layout/display_list_builder.rs
index 3e5328afc27..ec881ea9bcb 100644
--- a/components/layout/display_list_builder.rs
+++ b/components/layout/display_list_builder.rs
@@ -52,9 +52,8 @@ use style::logical_geometry::{LogicalPoint, LogicalRect, LogicalSize, WritingMod
 use style::properties::{self, ServoComputedValues};
 use style::properties::style_structs;
 use style::servo::restyle_damage::REPAINT;
-use style::values::RGBA;
-use style::values::computed;
-use style::values::computed::{Gradient, GradientKind, LengthOrNone, LengthOrPercentage, LengthOrPercentageOrAuto};
+use style::values::{self, Either, RGBA, computed};
+use style::values::computed::{Gradient, GradientKind, LengthOrPercentage, LengthOrPercentageOrAuto};
 use style::values::specified::{AngleOrCorner, HorizontalDirection, VerticalDirection};
 use style_traits::cursor::Cursor;
 use table_cell::CollapsedBordersForCell;
@@ -1563,7 +1562,7 @@ impl FragmentDisplayListBuilding for Fragment {
 
         let transform = self.transform_matrix(&border_box);
         let perspective = match self.style().get_effects().perspective {
-            LengthOrNone::Length(d) => {
+            Either::First(length) => {
                 let perspective_origin = self.style().get_effects().perspective_origin;
                 let perspective_origin =
                     Point2D::new(model::specified(perspective_origin.horizontal,
@@ -1578,11 +1577,11 @@ impl FragmentDisplayListBuilding for Fragment {
                                                                   -perspective_origin.y,
                                                                   0.0);
 
-                let perspective_matrix = create_perspective_matrix(d);
+                let perspective_matrix = create_perspective_matrix(length);
 
                 pre_transform.pre_mul(&perspective_matrix).pre_mul(&post_transform)
             }
-            LengthOrNone::None => {
+            Either::Second(values::None_) => {
                 Matrix4D::identity()
             }
         };
diff --git a/components/layout/fragment.rs b/components/layout/fragment.rs
index 265f140ab63..7ff692e913b 100644
--- a/components/layout/fragment.rs
+++ b/components/layout/fragment.rs
@@ -49,7 +49,8 @@ use style::properties::ServoComputedValues;
 use style::selector_impl::RestyleDamage;
 use style::servo::restyle_damage::RECONSTRUCT_FLOW;
 use style::str::char_is_whitespace;
-use style::values::computed::{LengthOrNone, LengthOrPercentage, LengthOrPercentageOrAuto};
+use style::values::Either;
+use style::values::computed::{LengthOrPercentage, LengthOrPercentageOrAuto};
 use style::values::computed::LengthOrPercentageOrNone;
 use text;
 use text::TextRunScanner;
@@ -2586,7 +2587,7 @@ impl Fragment {
 
         // TODO(mrobinson): Determine if this is necessary, since blocks with
         // transformations already create stacking contexts.
-        if self.style().get_effects().perspective != LengthOrNone::None {
+        if let Either::First(ref _length) = self.style().get_effects().perspective {
             return true
         }
 
diff --git a/components/style/properties/helpers.mako.rs b/components/style/properties/helpers.mako.rs
index fe7bac7efe9..9c0aa616136 100644
--- a/components/style/properties/helpers.mako.rs
+++ b/components/style/properties/helpers.mako.rs
@@ -178,7 +178,7 @@
             use parser::{ParserContext, ParserContextExtraData};
             use properties::{CSSWideKeyword, DeclaredValue, Shorthand};
         % endif
-        #[allow(unused_imports)]
+        use values::{Auto, Either, None_, Normal};
         use cascade_info::CascadeInfo;
         use error_reporting::ParseErrorReporter;
         use parser::Parse;
diff --git a/components/style/properties/helpers/animated_properties.mako.rs b/components/style/properties/helpers/animated_properties.mako.rs
index 8b8e3c0b92f..39f9abaf29b 100644
--- a/components/style/properties/helpers/animated_properties.mako.rs
+++ b/components/style/properties/helpers/animated_properties.mako.rs
@@ -22,6 +22,7 @@ use std::cmp;
 use std::fmt;
 use style_traits::ToCss;
 use super::ComputedValues;
+use values::Either;
 use values::computed::{Angle, LengthOrPercentageOrAuto, LengthOrPercentageOrNone};
 use values::computed::{BorderRadiusSize, LengthOrNone};
 use values::computed::{CalcLengthOrPercentage, LengthOrPercentage};
@@ -682,8 +683,8 @@ impl Interpolate for BoxShadow {
 impl Interpolate for LengthOrNone {
     fn interpolate(&self, other: &Self, progress: f64) -> Result<Self, ()> {
         match (*self, *other) {
-            (LengthOrNone::Length(ref len), LengthOrNone::Length(ref other)) =>
-                len.interpolate(&other, progress).map(LengthOrNone::Length),
+            (Either::First(ref length), Either::First(ref other)) =>
+                length.interpolate(&other, progress).map(Either::First),
             _ => Err(()),
         }
     }
diff --git a/components/style/properties/longhand/effects.mako.rs b/components/style/properties/longhand/effects.mako.rs
index 5949bc48704..87595133b91 100644
--- a/components/style/properties/longhand/effects.mako.rs
+++ b/components/style/properties/longhand/effects.mako.rs
@@ -1395,7 +1395,7 @@ ${helpers.single_keyword("transform-style",
 
 ${helpers.predefined_type("perspective",
                           "LengthOrNone",
-                          "computed::LengthOrNone::None",
+                          "Either::Second(None_)",
                           products="servo",
                           animatable=True)}
 
diff --git a/components/style/properties/properties.mako.rs b/components/style/properties/properties.mako.rs
index ca72c0c38aa..dfa2593e1cb 100644
--- a/components/style/properties/properties.mako.rs
+++ b/components/style/properties/properties.mako.rs
@@ -30,6 +30,7 @@ use logical_geometry::WritingMode;
 use parser::{ParserContext, ParserContextExtraData};
 use style_traits::ToCss;
 use stylesheets::Origin;
+#[cfg(feature = "servo")] use values::Either;
 use values::{HasViewportPercentage, computed};
 use cascade_info::CascadeInfo;
 use rule_tree::StrongRuleNode;
@@ -1249,7 +1250,7 @@ impl ComputedValues {
             if effects.transform.0.is_some() {
                 return transform_style::T::flat;
             }
-            if effects.perspective != computed::LengthOrNone::None {
+            if let Either::First(ref _length) = effects.perspective {
                 return transform_style::T::flat;
             }
         }
diff --git a/components/style/values/computed/length.rs b/components/style/values/computed/length.rs
index 5d3044c3ac7..b08c3806ceb 100644
--- a/components/style/values/computed/length.rs
+++ b/components/style/values/computed/length.rs
@@ -7,7 +7,7 @@ use ordered_float::NotNaN;
 use std::fmt;
 use style_traits::ToCss;
 use super::{Number, ToComputedValue, Context};
-use values::{CSSFloat, specified};
+use values::{CSSFloat, Either, None_, specified};
 
 pub use cssparser::Color as CSSColor;
 pub use super::image::{EndingShape as GradientShape, Gradient, GradientKind, Image};
@@ -452,61 +452,7 @@ impl ToCss for LengthOrPercentageOrNone {
     }
 }
 
-#[derive(PartialEq, Clone, Copy)]
-#[cfg_attr(feature = "servo", derive(HeapSizeOf))]
-pub enum LengthOrNone {
-    Length(Au),
-    None,
-}
-
-impl fmt::Debug for LengthOrNone {
-    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
-        match *self {
-            LengthOrNone::Length(length) => write!(f, "{:?}", length),
-            LengthOrNone::None => write!(f, "none"),
-        }
-    }
-}
-
-impl ToComputedValue for specified::LengthOrNone {
-    type ComputedValue = LengthOrNone;
-
-    #[inline]
-    fn to_computed_value(&self, context: &Context) -> LengthOrNone {
-        match *self {
-            specified::LengthOrNone::Length(specified::Length::Calc(calc, range)) => {
-                LengthOrNone::Length(range.clamp(calc.to_computed_value(context).length()))
-            }
-            specified::LengthOrNone::Length(value) => {
-                LengthOrNone::Length(value.to_computed_value(context))
-            }
-            specified::LengthOrNone::None => {
-                LengthOrNone::None
-            }
-        }
-    }
-
-    #[inline]
-    fn from_computed_value(computed: &LengthOrNone) -> Self {
-        match *computed {
-            LengthOrNone::Length(au) => {
-                specified::LengthOrNone::Length(ToComputedValue::from_computed_value(&au))
-            }
-            LengthOrNone::None => {
-                specified::LengthOrNone::None
-            }
-        }
-    }
-}
-
-impl ToCss for LengthOrNone {
-    fn to_css<W>(&self, dest: &mut W) -> fmt::Result where W: fmt::Write {
-        match *self {
-            LengthOrNone::Length(length) => length.to_css(dest),
-            LengthOrNone::None => dest.write_str("none"),
-        }
-    }
-}
+pub type LengthOrNone = Either<Length, None_>;
 
 #[derive(Clone, PartialEq)]
 #[cfg_attr(feature = "servo", derive(HeapSizeOf))]
diff --git a/components/style/values/computed/mod.rs b/components/style/values/computed/mod.rs
index c73fcd73e83..14e4f49d76c 100644
--- a/components/style/values/computed/mod.rs
+++ b/components/style/values/computed/mod.rs
@@ -12,6 +12,7 @@ use super::{CSSFloat, specified};
 pub use cssparser::Color as CSSColor;
 pub use self::image::{EndingShape as GradientShape, Gradient, GradientKind, Image};
 pub use self::image::{LengthOrKeyword, LengthOrPercentageOrKeyword};
+pub use super::{Either, None_};
 pub use super::specified::{Angle, BorderStyle, Time, UrlExtraData, UrlOrNone};
 pub use self::length::{CalcLengthOrPercentage, Length, LengthOrNumber, LengthOrPercentage, LengthOrPercentageOrAuto};
 pub use self::length::{LengthOrPercentageOrAutoOrContent, LengthOrPercentageOrNone, LengthOrNone};
diff --git a/components/style/values/mod.rs b/components/style/values/mod.rs
index 46d7b304d0b..485b46c82a2 100644
--- a/components/style/values/mod.rs
+++ b/components/style/values/mod.rs
@@ -6,7 +6,11 @@
 //!
 //! [values]: https://drafts.csswg.org/css-values/
 
-pub use cssparser::RGBA;
+pub use cssparser::{RGBA, Parser};
+
+use parser::Parse;
+use std::fmt::{self, Debug};
+use style_traits::ToCss;
 
 macro_rules! define_numbered_css_keyword_enum {
     ($name: ident: $( $css: expr => $variant: ident = $value: expr ),+,) => {
@@ -59,3 +63,102 @@ impl<T> HasViewportPercentage for T where T: NoViewportPercentage {
     }
 }
 
+use self::computed::ComputedValueAsSpecified;
+
+macro_rules! define_keyword_type {
+    ($name: ident, $css: expr) => {
+        #[derive(Clone, PartialEq, Copy)]
+        #[cfg_attr(feature = "servo", derive(HeapSizeOf))]
+        pub struct $name;
+
+        impl ::style_traits::ToCss for $name {
+            fn to_css<W>(&self, dest: &mut W) -> ::std::fmt::Result where W: ::std::fmt::Write {
+                write!(dest, $css)
+            }
+        }
+
+        impl fmt::Debug for $name {
+            fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+                write!(f, $css)
+            }
+        }
+
+        impl Parse for $name {
+            fn parse(input: &mut ::cssparser::Parser) -> Result<$name, ()> {
+                input.expect_ident_matching($css).map(|_| $name)
+            }
+        }
+
+        impl ComputedValueAsSpecified for $name {}
+        impl NoViewportPercentage for $name {}
+    };
+}
+
+define_keyword_type!(None_, "none");
+define_keyword_type!(Auto, "auto");
+define_keyword_type!(Normal, "normal");
+
+#[derive(Clone, PartialEq, Copy)]
+#[cfg_attr(feature = "servo", derive(HeapSizeOf))]
+pub enum Either<A, B> {
+    First(A),
+    Second(B),
+}
+
+impl<A: Debug, B: Debug> Debug for Either<A, B> {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        match *self {
+            Either::First(ref v) => v.fmt(f),
+            Either::Second(ref v) => v.fmt(f),
+        }
+    }
+}
+
+impl<A: ToCss, B: ToCss> ToCss for Either<A, B> {
+    fn to_css<W>(&self, dest: &mut W) -> fmt::Result where W: fmt::Write {
+        match *self {
+            Either::First(ref v) => v.to_css(dest),
+            Either::Second(ref v) => v.to_css(dest),
+        }
+    }
+}
+
+impl<A: HasViewportPercentage, B: HasViewportPercentage> HasViewportPercentage for Either<A, B> {
+    fn has_viewport_percentage(&self) -> bool {
+        match *self {
+            Either::First(ref v) => v.has_viewport_percentage(),
+            Either::Second(ref v) => v.has_viewport_percentage(),
+        }
+    }
+}
+
+impl<A: Parse, B: Parse> Parse for Either<A, B> {
+    fn parse(input: &mut Parser) -> Result<Either<A, B>, ()> {
+        if let Ok(v) = input.try(|i| A::parse(i)) {
+            Ok(Either::First(v))
+        } else {
+            B::parse(input).map(Either::Second)
+        }
+    }
+}
+
+use self::computed::{Context, ToComputedValue};
+
+impl<A: ToComputedValue, B: ToComputedValue> ToComputedValue for Either<A, B> {
+    type ComputedValue = Either<A::ComputedValue, B::ComputedValue>;
+
+    fn to_computed_value(&self, context: &Context) -> Self::ComputedValue {
+        match *self {
+            Either::First(ref a) => Either::First(a.to_computed_value(context)),
+            Either::Second(ref a) => Either::Second(a.to_computed_value(context)),
+        }
+    }
+
+    #[inline]
+    fn from_computed_value(computed: &Self::ComputedValue) -> Self {
+        match *computed {
+            Either::First(ref a) => Either::First(ToComputedValue::from_computed_value(a)),
+            Either::Second(ref a) => Either::Second(ToComputedValue::from_computed_value(a)),
+        }
+    }
+}
diff --git a/components/style/values/specified/length.rs b/components/style/values/specified/length.rs
index a0ed172cab1..a8b33cb041e 100644
--- a/components/style/values/specified/length.rs
+++ b/components/style/values/specified/length.rs
@@ -13,7 +13,7 @@ use std::ops::Mul;
 use style_traits::ToCss;
 use style_traits::values::specified::AllowedNumericType;
 use super::{Angle, Number, SimplifiedValueNode, SimplifiedSumNode, Time};
-use values::{CSSFloat, FONT_MEDIUM_PX, HasViewportPercentage, computed};
+use values::{CSSFloat, Either, FONT_MEDIUM_PX, HasViewportPercentage, None_, computed};
 
 pub use super::image::{AngleOrCorner, ColorStop, EndingShape as GradientEndingShape, Gradient};
 pub use super::image::{GradientKind, HorizontalDirection, Image, LengthOrKeyword, LengthOrPercentageOrKeyword};
@@ -908,55 +908,12 @@ impl LengthOrPercentageOrNone {
     }
 }
 
-#[derive(Clone, PartialEq, Copy, Debug)]
-#[cfg_attr(feature = "servo", derive(HeapSizeOf))]
-pub enum LengthOrNone {
-    Length(Length),
-    None,
-}
-
-impl HasViewportPercentage for LengthOrNone {
-    fn has_viewport_percentage(&self) -> bool {
-        match *self {
-            LengthOrNone::Length(ref length) => length.has_viewport_percentage(),
-            _ => false
-        }
-    }
-}
+pub type LengthOrNone = Either<Length, None_>;
 
-impl ToCss for LengthOrNone {
-    fn to_css<W>(&self, dest: &mut W) -> fmt::Result where W: fmt::Write {
-        match *self {
-            LengthOrNone::Length(length) => length.to_css(dest),
-            LengthOrNone::None => dest.write_str("none"),
-        }
-    }
-}
 impl LengthOrNone {
-    fn parse_internal(input: &mut Parser, context: AllowedNumericType)
-                      -> Result<LengthOrNone, ()>
-    {
-        match try!(input.next()) {
-            Token::Dimension(ref value, ref unit) if context.is_ok(value.value) =>
-                Length::parse_dimension(value.value, unit).map(LengthOrNone::Length),
-            Token::Number(ref value) if value.value == 0. =>
-                Ok(LengthOrNone::Length(Length::Absolute(Au(0)))),
-            Token::Function(ref name) if name.eq_ignore_ascii_case("calc") =>
-                input.parse_nested_block(|input| {
-                    CalcLengthOrPercentage::parse_length(input, context)
-                }).map(LengthOrNone::Length),
-            Token::Ident(ref value) if value.eq_ignore_ascii_case("none") =>
-                Ok(LengthOrNone::None),
-            _ => Err(())
-        }
-    }
-    #[inline]
-    pub fn parse(input: &mut Parser) -> Result<LengthOrNone, ()> {
-        LengthOrNone::parse_internal(input, AllowedNumericType::All)
-    }
     #[inline]
     pub fn parse_non_negative(input: &mut Parser) -> Result<LengthOrNone, ()> {
-        LengthOrNone::parse_internal(input, AllowedNumericType::NonNegative)
+        Length::parse_internal(input, AllowedNumericType::NonNegative).map(Either::First)
     }
 }
 
diff --git a/components/style/values/specified/mod.rs b/components/style/values/specified/mod.rs
index 92a8532f52d..339c565a240 100644
--- a/components/style/values/specified/mod.rs
+++ b/components/style/values/specified/mod.rs
@@ -83,7 +83,6 @@ impl ToCss for CSSRGBA {
     }
 }
 
-
 #[derive(Clone, Debug)]
 pub struct SimplifiedSumNode {
     values: Vec<SimplifiedValueNode>,