Introduce #[animation]

For now, only #[animation(error)] is supported on variants and it makes
both #[derive(Animate)] and #[derive(ComputeSquaredDistance)] ignore
this particular variant.

components/style/properties/helpers/animated_properties.mako.rs

@@ -787,40 +787,6 @@ impl ToAnimatedZero for Visibility {
     }
 }
 
-/// https://drafts.csswg.org/css-transitions/#animtype-length
-impl Animate for VerticalAlign {
-    #[inline]
-    fn animate(&self, other: &Self, procedure: Procedure) -> Result<Self, ()> {
-        match (self, other) {
-            (
-                &VerticalAlign::LengthOrPercentage(ref this),
-                &VerticalAlign::LengthOrPercentage(ref other),
-            ) => {
-                Ok(VerticalAlign::LengthOrPercentage(
-                    this.animate(other, procedure)?
-                ))
-            },
-            _ => Err(()),
-        }
-    }
-}
-
-impl ComputeSquaredDistance for VerticalAlign {
-    #[inline]
-    fn compute_squared_distance(&self, other: &Self) -> Result<SquaredDistance, ()> {
-        match (self, other) {
-            (&VerticalAlign::LengthOrPercentage(ref this), &VerticalAlign::LengthOrPercentage(ref other)) => {
-                this.compute_squared_distance(other)
-            },
-            _ => {
-                // FIXME(nox): Should this return `Ok(SquaredDistance::Value(0.))`
-                // if `self` and `other` are the same keyword value?
-                Err(())
-            },
-        }
-    }
-}
-
 impl ToAnimatedZero for VerticalAlign {
     #[inline]
     fn to_animated_zero(&self) -> Result<Self, ()> { Err(()) }

components/style/properties/longhand/box.mako.rs

@@ -370,11 +370,12 @@ ${helpers.single_keyword("position", "static absolute relative fixed",
         /// The keywords are the same, and the `LengthOrPercentage` is computed
         /// here.
         #[allow(non_camel_case_types)]
-        #[derive(Clone, Copy, Debug, PartialEq)]
         #[cfg_attr(feature = "servo", derive(HeapSizeOf))]
+        #[derive(Animate, Clone, ComputeSquaredDistance, Copy, Debug, PartialEq)]
         pub enum T {
             % for keyword in vertical_align_keywords:
-                ${to_rust_ident(keyword)},
+            #[animation(error)] // only animatable as a length
+            ${to_rust_ident(keyword)},
             % endfor
             LengthOrPercentage(computed::LengthOrPercentage),
         }

components/style_derive/animate.rs

@@ -14,7 +14,13 @@ pub fn derive(input: syn::DeriveInput) -> quote::Tokens {
 
     let variants = cg::variants(&input);
     let mut match_body = quote!();
-    match_body.append_all(variants.iter().map(|variant| {
+    let mut append_error_clause = variants.len() > 1;
+    match_body.append_all(variants.iter().flat_map(|variant| {
+        let attrs = cg::parse_variant_attrs::<AnimateAttrs>(variant);
+        if attrs.error {
+            append_error_clause = true;
+            return None;
+        }
         let name = cg::variant_ctor(&input, variant);
         let (this_pattern, this_info) = cg::ref_pattern(&name, variant, "this");
         let (other_pattern, other_info) = cg::ref_pattern(&name, variant, "other");
@@ -29,15 +35,15 @@ pub fn derive(input: syn::DeriveInput) -> quote::Tokens {
                 let #result = ::values::animated::Animate::animate(#this, #other, procedure)?;
             }
         }));
-        quote! {
+        Some(quote! {
             (&#this_pattern, &#other_pattern) => {
                 #computations
                 Ok(#result_value)
             }
-        }
+        })
     }));
 
-    if variants.len() > 1 {
+    if append_error_clause {
         match_body = quote! { #match_body, _ => Err(()), };
     }
 
@@ -57,3 +63,9 @@ pub fn derive(input: syn::DeriveInput) -> quote::Tokens {
         }
     }
 }
+
+#[derive(Default, FromVariant)]
+#[darling(attributes(animate), default)]
+pub struct AnimateAttrs {
+    pub error: bool,
+}

components/style_derive/compute_squared_distance.rs

@@ -2,6 +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::AnimateAttrs;
 use cg;
 use quote;
 use syn;
@@ -14,7 +15,13 @@ pub fn derive(input: syn::DeriveInput) -> quote::Tokens {
 
     let variants = cg::variants(&input);
     let mut match_body = quote!();
+    let mut append_error_clause = variants.len() > 1;
     match_body.append_all(variants.iter().map(|variant| {
+        let attrs = cg::parse_variant_attrs::<AnimateAttrs>(variant);
+        if attrs.error {
+            append_error_clause = true;
+            return None;
+        }
         let name = cg::variant_ctor(&input, variant);
         let (this_pattern, this_info) = cg::ref_pattern(&name, &variant, "this");
         let (other_pattern, other_info) = cg::ref_pattern(&name, &variant, "other");
@@ -32,14 +39,14 @@ pub fn derive(input: syn::DeriveInput) -> quote::Tokens {
             }), "+");
             sum
         };
-        quote! {
+        Some(quote! {
             (&#this_pattern, &#other_pattern) => {
                 Ok(#sum)
             }
-        }
+        })
     }));
 
-    if variants.len() > 1 {
+    if append_error_clause {
         match_body = quote! { #match_body, _ => Err(()), };
     }
 

components/style_derive/lib.rs

@@ -19,13 +19,13 @@ mod to_animated_zero;
 mod to_computed_value;
 mod to_css;
 
-#[proc_macro_derive(Animate)]
+#[proc_macro_derive(Animate, attributes(animation))]
 pub fn derive_animate(stream: TokenStream) -> TokenStream {
     let input = syn::parse_derive_input(&stream.to_string()).unwrap();
     animate::derive(input).to_string().parse().unwrap()
 }
 
-#[proc_macro_derive(ComputeSquaredDistance)]
+#[proc_macro_derive(ComputeSquaredDistance, attributes(animation))]
 pub fn derive_compute_squared_distance(stream: TokenStream) -> TokenStream {
     let input = syn::parse_derive_input(&stream.to_string()).unwrap();
     compute_squared_distance::derive(input).to_string().parse().unwrap()