style: Teach ComputeSquaredDistance derive about #[animation(constant)].

Differential Revision: https://phabricator.services.mozilla.com/D5337

components/style/values/animated/effects.rs

@@ -11,7 +11,6 @@ use values::computed::{Angle, Number};
 use values::computed::length::Length;
 #[cfg(feature = "gecko")]
 use values::computed::url::ComputedUrl;
-use values::distance::{ComputeSquaredDistance, SquaredDistance};
 use values::generics::effects::BoxShadow as GenericBoxShadow;
 use values::generics::effects::Filter as GenericFilter;
 use values::generics::effects::SimpleShadow as GenericSimpleShadow;
@@ -29,14 +28,3 @@ pub type Filter = GenericFilter<Angle, Number, Length, Impossible, Impossible>;
 
 /// An animated value for the `drop-shadow()` filter.
 pub type SimpleShadow = GenericSimpleShadow<Color, Length, Length>;
-
-impl ComputeSquaredDistance for BoxShadow {
-    #[inline]
-    fn compute_squared_distance(&self, other: &Self) -> Result<SquaredDistance, ()> {
-        if self.inset != other.inset {
-            return Err(());
-        }
-        Ok(self.base.compute_squared_distance(&other.base)? +
-            self.spread.compute_squared_distance(&other.spread)?)
-    }
-}

components/style/values/generics/effects.rs

@@ -8,6 +8,7 @@
 #[derive(
     Animate,
     Clone,
+    ComputeSquaredDistance,
     Debug,
     MallocSizeOf,
     PartialEq,

components/style/values/generics/font.rs

@@ -13,7 +13,6 @@ use std::fmt::{self, Write};
 use std::io::Cursor;
 use style_traits::{CssWriter, KeywordsCollectFn, ParseError};
 use style_traits::{SpecifiedValueInfo, StyleParseErrorKind, ToCss};
-use values::distance::{ComputeSquaredDistance, SquaredDistance};
 
 /// https://drafts.csswg.org/css-fonts-4/#feature-tag-value
 #[derive(Clone, Debug, Eq, MallocSizeOf, PartialEq, SpecifiedValueInfo, ToComputedValue)]
@@ -47,7 +46,16 @@ where
 ///
 /// https://drafts.csswg.org/css-fonts-4/#font-variation-settings-def
 #[derive(
-    Animate, Clone, Debug, Eq, MallocSizeOf, PartialEq, SpecifiedValueInfo, ToComputedValue, ToCss,
+    Animate,
+    Clone,
+    ComputeSquaredDistance,
+    Debug,
+    Eq,
+    MallocSizeOf,
+    PartialEq,
+    SpecifiedValueInfo,
+    ToComputedValue,
+    ToCss,
 )]
 pub struct VariationValue<Number> {
     /// A four-character tag, packed into a u32 (one byte per character).
@@ -57,19 +65,6 @@ pub struct VariationValue<Number> {
     pub value: Number,
 }
 
-impl<Number> ComputeSquaredDistance for VariationValue<Number>
-where
-    Number: ComputeSquaredDistance,
-{
-    #[inline]
-    fn compute_squared_distance(&self, other: &Self) -> Result<SquaredDistance, ()> {
-        if self.tag != other.tag {
-            return Err(());
-        }
-        self.value.compute_squared_distance(&other.value)
-    }
-}
-
 /// A value both for font-variation-settings and font-feature-settings.
 #[css(comma)]
 #[derive(Clone, Debug, Eq, MallocSizeOf, PartialEq, SpecifiedValueInfo, ToComputedValue, ToCss)]

components/style/values/specified/svg_path.rs

@@ -538,13 +538,6 @@ impl ToCss for ArcFlag {
     }
 }
 
-impl ComputeSquaredDistance for ArcFlag {
-    #[inline]
-    fn compute_squared_distance(&self, other: &Self) -> Result<SquaredDistance, ()> {
-        (self.0 as i32).compute_squared_distance(&(other.0 as i32))
-    }
-}
-
 /// SVG Path parser.
 struct PathParser<'a> {
     chars: Peekable<Cloned<slice::Iter<'a, u8>>>,

components/style_derive/compute_squared_distance.rs

@@ -2,7 +2,7 @@
  * 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/. */
 
-use animate::{AnimationInputAttrs, AnimationVariantAttrs};
+use animate::{AnimationInputAttrs, AnimationVariantAttrs, AnimationFieldAttrs};
 use cg;
 use quote::Tokens;
 use syn::{DeriveInput, Path};
@@ -47,8 +47,23 @@ pub fn derive(mut input: DeriveInput) -> Tokens {
                             parse_quote!(#ty: ::values::distance::ComputeSquaredDistance),
                         );
                     }
-                    quote! {
+
-                        ::values::distance::ComputeSquaredDistance::compute_squared_distance(#this, #other)?
+                    let animation_field_attrs =
+                        cg::parse_field_attrs::<AnimationFieldAttrs>(&this.ast());
+
+                    if animation_field_attrs.constant {
+                        quote! {
+                            {
+                                if #this != #other {
+                                    return Err(());
+                                }
+                                ::values::distance::SquaredDistance::from_sqrt(0.)
+                            }
+                        }
+                    } else {
+                        quote! {
+                            ::values::distance::ComputeSquaredDistance::compute_squared_distance(#this, #other)?
+                        }
                     }
                 }), quote!(+));
                 sum