Introduce #[css(function)] for #[derive(ToCss)]

Any variant with this attribute gets serialised as a CSS function,
using the variant name as the function name.

components/style/values/generics/gecko.rs

@@ -5,15 +5,13 @@
 //! Generic types for legacy Gecko-only properties that should probably be
 //! unshipped at some point in the future.
 
-use std::fmt;
-use style_traits::ToCss;
-
 /// A generic value for scroll snap points.
-#[derive(Clone, Copy, Debug, HasViewportPercentage, PartialEq, ToComputedValue)]
+#[derive(Clone, Copy, Debug, HasViewportPercentage, PartialEq, ToComputedValue, ToCss)]
 pub enum ScrollSnapPoint<LengthOrPercentage> {
     /// `none`
     None,
     /// `repeat(<length-or-percentage>)`
+    #[css(function)]
     Repeat(LengthOrPercentage)
 }
 
@@ -33,22 +31,3 @@ impl<L> ScrollSnapPoint<L> {
         }
     }
 }
-
-impl<L> ToCss for ScrollSnapPoint<L>
-where
-    L: ToCss,
-{
-    fn to_css<W>(&self, dest: &mut W) -> fmt::Result
-    where
-        W: fmt::Write,
-    {
-        match *self {
-            ScrollSnapPoint::None => dest.write_str("none"),
-            ScrollSnapPoint::Repeat(ref length) => {
-                dest.write_str("repeat(")?;
-                length.to_css(dest)?;
-                dest.write_str(")")
-            },
-        }
-    }
-}

components/style/values/generics/mod.rs

@@ -54,13 +54,14 @@ impl SymbolsType {
 ///
 /// Since wherever <counter-style> is used, 'none' is a valid value as
 /// well, we combine them into one type to make code simpler.
-#[derive(Clone, Debug, PartialEq, Eq)]
+#[derive(Clone, Debug, Eq, PartialEq, ToCss)]
 pub enum CounterStyleOrNone {
-    /// none
-    None_,
-    /// <counter-style-name>
+    /// `none`
+    None,
+    /// `<counter-style-name>`
     Name(CustomIdent),
-    /// symbols()
+    /// `symbols()`
+    #[css(function)]
     Symbols(SymbolsType, Symbols),
 }
 
@@ -84,7 +85,7 @@ impl Parse for CounterStyleOrNone {
             return Ok(CounterStyleOrNone::Name(name));
         }
         if input.try(|i| i.expect_ident_matching("none")).is_ok() {
-            return Ok(CounterStyleOrNone::None_);
+            return Ok(CounterStyleOrNone::None);
         }
         if input.try(|i| i.expect_function_matching("symbols")).is_ok() {
             return input.parse_nested_block(|input| {
@@ -108,23 +109,6 @@ impl Parse for CounterStyleOrNone {
     }
 }
 
-impl ToCss for CounterStyleOrNone {
-    #[inline]
-    fn to_css<W>(&self, dest: &mut W) -> fmt::Result where W: fmt::Write {
-        match self {
-            &CounterStyleOrNone::None_ => dest.write_str("none"),
-            &CounterStyleOrNone::Name(ref name) => name.to_css(dest),
-            &CounterStyleOrNone::Symbols(ref symbols_type, ref symbols) => {
-                dest.write_str("symbols(")?;
-                symbols_type.to_css(dest)?;
-                dest.write_str(" ")?;
-                symbols.to_css(dest)?;
-                dest.write_str(")")
-            }
-        }
-    }
-}
-
 /// A settings tag, defined by a four-character tag and a setting value
 ///
 /// For font-feature-settings, this is a tag and an integer,