Derive the most trivial ToAnimatedZero impls

components/style_derive/to_animated_zero.rs

@@ -0,0 +1,79 @@
+/* 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 http://mozilla.org/MPL/2.0/. */
+
+use quote;
+use syn;
+use synstructure;
+
+pub fn derive(input: syn::DeriveInput) -> quote::Tokens {
+    let name = &input.ident;
+    let (impl_generics, ty_generics, where_clause) = input.generics.split_for_impl();
+    let mut where_clause = where_clause.clone();
+    for param in &input.generics.ty_params {
+        where_clause.predicates.push(
+            where_predicate(syn::Ty::Path(None, param.ident.clone().into())),
+        );
+    }
+
+    let to_body = match_body(&input);
+
+    quote! {
+        impl #impl_generics ::values::animated::ToAnimatedZero for #name #ty_generics #where_clause {
+            #[allow(unused_variables)]
+            #[inline]
+            fn to_animated_zero(&self) -> Result<Self, ()> {
+                match *self {
+                    #to_body
+                }
+            }
+        }
+    }
+}
+
+fn match_body(input: &syn::DeriveInput) -> quote::Tokens {
+    synstructure::each_variant(&input, &synstructure::BindStyle::Ref.into(), |fields, variant| {
+        let name = if let syn::Body::Enum(_) = input.body {
+            format!("{}::{}", input.ident, variant.ident).into()
+        } else {
+            variant.ident.clone()
+        };
+        let (zero, computed_fields) = synstructure::match_pattern(
+            &name,
+            &variant.data,
+            &synstructure::BindStyle::Move.into(),
+        );
+        let fields_pairs = fields.iter().zip(computed_fields.iter());
+        let mut computations = quote!();
+        computations.append_all(fields_pairs.map(|(field, computed_field)| {
+            quote! {
+                let #computed_field = ::values::animated::ToAnimatedZero::to_animated_zero(#field)?;
+            }
+        }));
+        Some(quote!(
+            #computations
+            Ok(#zero)
+        ))
+    })
+}
+
+fn where_predicate(ty: syn::Ty) -> syn::WherePredicate {
+    syn::WherePredicate::BoundPredicate(syn::WhereBoundPredicate {
+        bound_lifetimes: vec![],
+        bounded_ty: ty,
+        bounds: vec![syn::TyParamBound::Trait(
+            syn::PolyTraitRef {
+                bound_lifetimes: vec![],
+                trait_ref: syn::Path {
+                    global: true,
+                    segments: vec![
+                        "values".into(),
+                        "animated".into(),
+                        "ToAnimatedZero".into(),
+                    ],
+                },
+            },
+            syn::TraitBoundModifier::None,
+        )],
+    })
+}