Allow deriving Parse for keywords.

components/style_derive/parse.rs

@@ -0,0 +1,74 @@
+/* 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 cg;
+use quote::Tokens;
+use syn::DeriveInput;
+use synstructure;
+
+pub fn derive(input: DeriveInput) -> Tokens {
+    let name = &input.ident;
+
+    let mut match_body = quote! {};
+
+    let style = synstructure::BindStyle::Ref.into();
+    synstructure::each_variant(&input, &style, |bindings, variant| {
+        assert!(
+            bindings.is_empty(),
+            "Parse is only supported for single-variant enums for now"
+        );
+
+        let identifier = cg::to_css_identifier(variant.ident.as_ref());
+        match_body = quote! {
+            #match_body
+            #identifier => Ok(#name::#variant),
+        }
+    });
+
+    let parse_trait_impl = quote! {
+        impl ::parser::Parse for #name {
+            #[inline]
+            fn parse<'i, 't>(
+                _: &::parser::ParserContext,
+                input: &mut ::cssparser::Parser<'i, 't>,
+            ) -> Result<Self, ::style_traits::ParseError<'i>> {
+                Self::parse(input)
+            }
+        }
+    };
+
+    // TODO(emilio): It'd be nice to get rid of these, but that makes the
+    // conversion harder...
+    let methods_impl = quote! {
+        impl #name {
+            /// Parse this keyword.
+            #[inline]
+            pub fn parse<'i, 't>(
+                input: &mut ::cssparser::Parser<'i, 't>,
+            ) -> Result<Self, ::style_traits::ParseError<'i>> {
+                let location = input.current_source_location();
+                let ident = input.expect_ident()?;
+                Self::from_ident(ident.as_ref()).map_err(|()| {
+                    location.new_unexpected_token_error(
+                        ::cssparser::Token::Ident(ident.clone())
+                    )
+                })
+            }
+
+            /// Parse this keyword from a string slice.
+            #[inline]
+            pub fn from_ident(ident: &str) -> Result<Self, ()> {
+                match_ignore_ascii_case! { ident,
+                    #match_body
+                    _ => Err(()),
+                }
+            }
+        }
+    };
+
+    quote! {
+        #parse_trait_impl
+        #methods_impl
+    }
+}