Use darling in style_derive

This allows use to handle #[css] in a way simpler fashion.

Cargo.lock

@@ -615,6 +615,36 @@ dependencies = [
  "syn 0.11.11 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
+[[package]]
+name = "darling"
+version = "0.2.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+dependencies = [
+ "darling_core 0.2.0 (registry+https://github.com/rust-lang/crates.io-index)",
+ "darling_macro 0.2.0 (registry+https://github.com/rust-lang/crates.io-index)",
+]
+
+[[package]]
+name = "darling_core"
+version = "0.2.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+dependencies = [
+ "ident_case 1.0.0 (registry+https://github.com/rust-lang/crates.io-index)",
+ "lazy_static 0.2.8 (registry+https://github.com/rust-lang/crates.io-index)",
+ "quote 0.3.15 (registry+https://github.com/rust-lang/crates.io-index)",
+ "syn 0.11.11 (registry+https://github.com/rust-lang/crates.io-index)",
+]
+
+[[package]]
+name = "darling_macro"
+version = "0.2.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+dependencies = [
+ "darling_core 0.2.0 (registry+https://github.com/rust-lang/crates.io-index)",
+ "quote 0.3.15 (registry+https://github.com/rust-lang/crates.io-index)",
+ "syn 0.11.11 (registry+https://github.com/rust-lang/crates.io-index)",
+]
+
 [[package]]
 name = "dbghelp-sys"
 version = "0.2.0"
@@ -1306,6 +1336,11 @@ dependencies = [
  "time 0.1.37 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
+[[package]]
+name = "ident_case"
+version = "1.0.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+
 [[package]]
 name = "idna"
 version = "0.1.2"
@@ -3073,6 +3108,7 @@ dependencies = [
 name = "style_derive"
 version = "0.0.1"
 dependencies = [
+ "darling 0.2.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "quote 0.3.15 (registry+https://github.com/rust-lang/crates.io-index)",
  "syn 0.11.11 (registry+https://github.com/rust-lang/crates.io-index)",
  "synstructure 0.5.2 (registry+https://github.com/rust-lang/crates.io-index)",
@@ -3711,6 +3747,9 @@ dependencies = [
 "checksum core-text 6.1.0 (registry+https://github.com/rust-lang/crates.io-index)" = "16ce16d9ed00181016c11ff48e561314bec92bfbce9fe48f319366618d4e5de6"
 "checksum cssparser 0.19.2 (registry+https://github.com/rust-lang/crates.io-index)" = "1f9442c00898020a56c9485d64c9c8f14ae30ba45be89d15846046593383467f"
 "checksum cssparser-macros 0.3.0 (registry+https://github.com/rust-lang/crates.io-index)" = "079adec4af52bb5275eadd004292028c79eb3c5f5b4ee8086a36d4197032f6df"
+"checksum darling 0.2.0 (registry+https://github.com/rust-lang/crates.io-index)" = "9861a8495606435477df581bc858ccf15a3469747edf175b94a4704fd9aaedac"
+"checksum darling_core 0.2.0 (registry+https://github.com/rust-lang/crates.io-index)" = "1486a8b00b45062c997f767738178b43219133dd0c8c826cb811e60563810821"
+"checksum darling_macro 0.2.0 (registry+https://github.com/rust-lang/crates.io-index)" = "8a86ec160aa0c3dd492dd4a14ec8104ad8f1a9400a820624db857998cc1f80f9"
 "checksum dbghelp-sys 0.2.0 (registry+https://github.com/rust-lang/crates.io-index)" = "97590ba53bcb8ac28279161ca943a924d1fd4a8fb3fa63302591647c4fc5b850"
 "checksum dbus 0.5.3 (registry+https://github.com/rust-lang/crates.io-index)" = "4aee01fb76ada3e5e7ca642ea6664ebf7308a810739ca2aca44909a1191ac254"
 "checksum debug_unreachable 0.1.1 (registry+https://github.com/rust-lang/crates.io-index)" = "9a032eac705ca39214d169f83e3d3da290af06d8d1d344d1baad2fd002dca4b3"
@@ -3769,6 +3808,7 @@ dependencies = [
 "checksum hyper 0.10.10 (registry+https://github.com/rust-lang/crates.io-index)" = "36e108e0b1fa2d17491cbaac4bc460dc0956029d10ccf83c913dd0e5db3e7f07"
 "checksum hyper-openssl 0.2.6 (registry+https://github.com/rust-lang/crates.io-index)" = "85a372eb692590b3fe014c196c30f9f52d4c42f58cd49dd94caeee1593c9cc37"
 "checksum hyper_serde 0.7.0 (registry+https://github.com/rust-lang/crates.io-index)" = "cbe43f514f80494e9329c9fc47d61b85b167d245685424637a0f4a409177e444"
+"checksum ident_case 1.0.0 (registry+https://github.com/rust-lang/crates.io-index)" = "3c9826188e666f2ed92071d2dadef6edc430b11b158b5b2b3f4babbcc891eaaa"
 "checksum idna 0.1.2 (registry+https://github.com/rust-lang/crates.io-index)" = "2233d4940b1f19f0418c158509cd7396b8d70a5db5705ce410914dc8fa603b37"
 "checksum image 0.12.4 (registry+https://github.com/rust-lang/crates.io-index)" = "d95816db758249fe16f23a4e23f1a3a817fe11892dbfd1c5836f625324702158"
 "checksum immeta 0.3.5 (registry+https://github.com/rust-lang/crates.io-index)" = "0b9260463a221bfe3f02100c56e2d14c050d5ffe7e44a43d0a1b2b1f2b523502"

components/style_derive/Cargo.toml

@@ -10,6 +10,7 @@ path = "lib.rs"
 proc-macro = true
 
 [dependencies]
+darling = "0.2"
 quote = "0.3.15"
 syn = { version = "0.11", features = ["visit"] }
 synstructure = "0.5.2"

components/style_derive/cg.rs

@@ -2,6 +2,7 @@
  * 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 darling::FromVariant;
 use quote::Tokens;
 use std::borrow::Cow;
 use std::iter;
@@ -136,6 +137,16 @@ where
     }
 }
 
+pub fn parse_variant_attrs<A>(variant: &Variant) -> A
+where
+    A: FromVariant,
+{
+    match A::from_variant(variant) {
+        Ok(attrs) => attrs,
+        Err(e) => panic!("failed to parse attributes: {}", e),
+    }
+}
+
 pub fn ref_pattern<'a>(
     name: &Ident,
     variant: &'a Variant,

components/style_derive/lib.rs

@@ -2,6 +2,7 @@
  * 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/. */
 
+#[macro_use] extern crate darling;
 extern crate proc_macro;
 #[macro_use] extern crate quote;
 extern crate syn;

components/style_derive/to_css.rs

@@ -16,47 +16,8 @@ pub fn derive(input: syn::DeriveInput) -> quote::Tokens {
     let style = synstructure::BindStyle::Ref.into();
     let match_body = synstructure::each_variant(&input, &style, |bindings, variant| {
         let mut identifier = to_css_identifier(variant.ident.as_ref());
-        let mut css_attrs = variant.attrs.iter().filter(|attr| attr.name() == "css");
+        let css_attrs = cg::parse_variant_attrs::<CssAttrs>(variant);
-        let (is_function, use_comma) = css_attrs.next().map_or((false, false), |attr| {
+        let separator = if css_attrs.comma { ", " } else { " " };
-            match attr.value {
-                syn::MetaItem::List(ref ident, ref items) if ident.as_ref() == "css" => {
-                    let mut nested = items.iter();
-                    let mut is_function = false;
-                    let mut use_comma = false;
-                    for attr in nested.by_ref() {
-                        match *attr {
-                            syn::NestedMetaItem::MetaItem(syn::MetaItem::Word(ref ident)) => {
-                                match ident.as_ref() {
-                                    "function" => {
-                                        if is_function {
-                                            panic!("repeated `#[css(function)]` attribute");
-                                        }
-                                        is_function = true;
-                                    },
-                                    "comma" => {
-                                        if use_comma {
-                                            panic!("repeated `#[css(comma)]` attribute");
-                                        }
-                                        use_comma = true;
-                                    },
-                                    _ => panic!("only `#[css(function | comma)]` is supported for now"),
-                                }
-                            },
-                            _ => panic!("only `#[css(<ident...>)]` is supported for now"),
-                        }
-                    }
-                    if nested.next().is_some() {
-                        panic!("only `#[css()]` or `#[css(<ident>)]` is supported for now")
-                    }
-                    (is_function, use_comma)
-                },
-                _ => panic!("only `#[css(...)]` is supported for now"),
-            }
-        });
-        if css_attrs.next().is_some() {
-            panic!("only a single `#[css(...)]` attribute is supported for now");
-        }
-        let separator = if use_comma { ", " } else { " " };
         let mut expr = if !bindings.is_empty() {
             let mut expr = quote! {};
             for binding in bindings {
@@ -80,7 +41,7 @@ pub fn derive(input: syn::DeriveInput) -> quote::Tokens {
                 ::std::fmt::Write::write_str(dest, #identifier)
             }
         };
-        if is_function {
+        if css_attrs.function {
             identifier.push_str("(");
             expr = quote! {
                 ::std::fmt::Write::write_str(dest, #identifier)?;
@@ -107,6 +68,13 @@ pub fn derive(input: syn::DeriveInput) -> quote::Tokens {
     }
 }
 
+#[derive(Default, FromVariant)]
+#[darling(attributes(css), default)]
+struct CssAttrs {
+    function: bool,
+    comma: bool,
+}
+
 /// Transforms "FooBar" to "foo-bar".
 ///
 /// If the first Camel segment is "Moz" or "Webkit", the result string