1 files changed, 65 insertions, 0 deletions
diff --git a/servo/components/style_derive/to_animated_zero.rs b/servo/components/style_derive/to_animated_zero.rs
new file mode 100644
index 0000000000..008e94cbcf
--- /dev/null
+++ b/servo/components/style_derive/to_animated_zero.rs
@@ -0,0 +1,65 @@
+/* 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/. */
+
+use crate::animate::{AnimationFieldAttrs, AnimationInputAttrs, AnimationVariantAttrs};
+use derive_common::cg;
+use proc_macro2::TokenStream;
+use quote::TokenStreamExt;
+use syn;
+use synstructure;
+
+pub fn derive(mut input: syn::DeriveInput) -> TokenStream {
+    let animation_input_attrs = cg::parse_input_attrs::<AnimationInputAttrs>(&input);
+    let no_bound = animation_input_attrs.no_bound.unwrap_or_default();
+    let mut where_clause = input.generics.where_clause.take();
+    for param in input.generics.type_params() {
+        if !no_bound.iter().any(|name| name.is_ident(&param.ident)) {
+            cg::add_predicate(
+                &mut where_clause,
+                parse_quote!(#param: crate::values::animated::ToAnimatedZero),
+            );
+        }
+    }
+
+    let to_body = synstructure::Structure::new(&input).each_variant(|variant| {
+        let attrs = cg::parse_variant_attrs_from_ast::<AnimationVariantAttrs>(&variant.ast());
+        if attrs.error {
+            return Some(quote! { Err(()) });
+        }
+        let (mapped, mapped_bindings) = cg::value(variant, "mapped");
+        let bindings_pairs = variant.bindings().iter().zip(mapped_bindings);
+        let mut computations = quote!();
+        computations.append_all(bindings_pairs.map(|(binding, mapped_binding)| {
+            let field_attrs = cg::parse_field_attrs::<AnimationFieldAttrs>(&binding.ast());
+            if field_attrs.constant {
+                quote! {
+                    let #mapped_binding = std::clone::Clone::clone(#binding);
+                }
+            } else {
+                quote! {
+                    let #mapped_binding =
+                        crate::values::animated::ToAnimatedZero::to_animated_zero(#binding)?;
+                }
+            }
+        }));
+        computations.append_all(quote! { Ok(#mapped) });
+        Some(computations)
+    });
+    input.generics.where_clause = where_clause;
+
+    let name = &input.ident;
+    let (impl_generics, ty_generics, where_clause) = input.generics.split_for_impl();
+
+    quote! {
+        impl #impl_generics crate::values::animated::ToAnimatedZero for #name #ty_generics #where_clause {
+            #[allow(unused_variables)]
+            #[inline]
+            fn to_animated_zero(&self) -> Result<Self, ()> {
+                match *self {
+                    #to_body
+                }
+            }
+        }
+    }
+}