diff options
Diffstat (limited to 'components/style_derive/to_css.rs')
-rw-r--r-- | components/style_derive/to_css.rs | 70 |
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 index 00000000000..774add083fa --- /dev/null +++ b/components/style_derive/to_css.rs @@ -0,0 +1,70 @@ +/* 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 + )], + }) +} |