Use generics for the line-height property

components/style/values/generics/text.rs

@@ -0,0 +1,47 @@
+/* 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/. */
+
+//! Generic types for text properties.
+
+use std::fmt;
+use style_traits::ToCss;
+
+/// A generic value for the `line-height` property.
+#[cfg_attr(feature = "servo", derive(HeapSizeOf))]
+#[derive(Clone, Copy, Debug, HasViewportPercentage, PartialEq)]
+pub enum LineHeight<Number, LengthOrPercentage> {
+    /// `normal`
+    Normal,
+    /// `-moz-block-height`
+    #[cfg(feature = "gecko")]
+    MozBlockHeight,
+    /// `<number>`
+    Number(Number),
+    /// `<length-or-percentage>`
+    Length(LengthOrPercentage),
+}
+
+impl<N, L> LineHeight<N, L> {
+    /// Returns `normal`.
+    #[inline]
+    pub fn normal() -> Self {
+        LineHeight::Normal
+    }
+}
+
+impl<N, L> ToCss for LineHeight<N, L>
+    where N: ToCss, L: ToCss,
+{
+    fn to_css<W>(&self, dest: &mut W) -> fmt::Result
+        where W: fmt::Write,
+    {
+        match *self {
+            LineHeight::Normal => dest.write_str("normal"),
+            #[cfg(feature = "gecko")]
+            LineHeight::MozBlockHeight => dest.write_str("-moz-block-height"),
+            LineHeight::Number(ref number) => number.to_css(dest),
+            LineHeight::Length(ref value) => value.to_css(dest),
+        }
+    }
+}