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-rw-r--r--components/style_derive/to_css.rs70
1 files changed, 70 insertions, 0 deletions
diff --git a/components/style_derive/to_css.rs b/components/style_derive/to_css.rs
new file mode 100644
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+++ b/components/style_derive/to_css.rs
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+/* 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 style = synstructure::BindStyle::Ref.into();
+ let match_body = synstructure::each_variant(&input, &style, |bindings, _| {
+ if bindings.is_empty() {
+ panic!("unit variants are not yet supported");
+ }
+ let (first, rest) = bindings.split_first().expect("unit variants are not yet supported");
+ where_clause.predicates.push(where_predicate(first.field.ty.clone()));
+ let mut expr = quote! {
+ ::style_traits::ToCss::to_css(#first, dest)
+ };
+ for binding in rest {
+ where_clause.predicates.push(where_predicate(binding.field.ty.clone()));
+ expr = quote! {
+ #expr?;
+ dest.write_str(" ")?;
+ ::style_traits::ToCss::to_css(#binding, dest)
+ };
+ }
+ Some(expr)
+ });
+
+ quote! {
+ impl #impl_generics ::style_traits::ToCss for #name #ty_generics #where_clause {
+ #[allow(unused_variables, unused_imports)]
+ #[inline]
+ fn to_css<W>(&self, dest: &mut W) -> ::std::fmt::Result
+ where
+ W: ::std::fmt::Write
+ {
+ match *self {
+ #match_body
+ }
+ }
+ }
+ }
+}
+
+/// `#ty: ::style_traits::ToCss`
+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!["style_traits".into(), "ToCss".into()],
+ },
+ },
+ syn::TraitBoundModifier::None
+ )],
+ })
+}