Derive HasViewportPercentage 🍷

components/style_derive/Cargo.toml

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+[package]
+name = "style_derive"
+version = "0.0.1"
+authors = ["The Servo Project Developers"]
+license = "MPL-2.0"
+publish = false
+
+[lib]
+path = "lib.rs"
+proc-macro = true
+
+[dependencies]
+quote = "0.3"
+syn = "0.11"
+synstructure = "0.5.2"

components/style_derive/has_viewport_percentage.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, _| {
+        let (first, rest) = match bindings.split_first() {
+            None => return Some(quote!(false)),
+            Some(pair) => pair,
+        };
+        let mut expr = quote!(::style_traits::HasViewportPercentage::has_viewport_percentage(#first));
+        for binding in rest {
+            where_clause.predicates.push(where_predicate(binding.field.ty.clone()));
+            expr = quote!(#expr || ::style_traits::HasViewportPercentage::has_viewport_percentage(#binding));
+        }
+        Some(expr)
+    });
+
+    quote! {
+        impl #impl_generics ::style_traits::HasViewportPercentage for #name #ty_generics #where_clause {
+            #[allow(unused_variables, unused_imports)]
+            #[inline]
+            fn has_viewport_percentage(&self) -> bool {
+                match *self {
+                    #match_body
+                }
+            }
+        }
+    }
+}
+
+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::parse_path("::style_traits::HasViewportPercentage").unwrap(),
+            },
+            syn::TraitBoundModifier::None
+        )],
+    })
+}

components/style_derive/lib.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/. */
+
+extern crate proc_macro;
+#[macro_use] extern crate quote;
+extern crate syn;
+extern crate synstructure;
+
+use proc_macro::TokenStream;
+
+mod has_viewport_percentage;
+
+#[proc_macro_derive(HasViewportPercentage)]
+pub fn derive_has_viewport_percentage(stream: TokenStream) -> TokenStream {
+    let input = syn::parse_derive_input(&stream.to_string()).unwrap();
+    has_viewport_percentage::derive(input).to_string().parse().unwrap()
+}