Auto merge of #19578 - emilio:parse-keyword, r=Manishearth,canaltinova

Allow deriving Parse on keywords.

This makes patches like #19576 much easier.

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components/style/parser.rs

@@ -149,8 +149,10 @@ pub trait Parse : Sized {
     /// Parse a value of this type.
     ///
     /// Returns an error on failure.
-    fn parse<'i, 't>(context: &ParserContext, input: &mut Parser<'i, 't>)
-                     -> Result<Self, ParseError<'i>>;
+    fn parse<'i, 't>(
+        context: &ParserContext,
+        input: &mut Parser<'i, 't>,
+    ) -> Result<Self, ParseError<'i>>;
 }
 
 impl<T> Parse for Vec<T>

components/style/values/specified/background.rs

@@ -46,11 +46,13 @@ impl BackgroundSize {
 }
 
 /// One of the keywords for `background-repeat`.
-define_css_keyword_enum! { RepeatKeyword:
-    "repeat" => Repeat,
-    "space" => Space,
-    "round" => Round,
-    "no-repeat" => NoRepeat
+#[derive(Clone, Copy, Debug, Eq, MallocSizeOf, Parse, PartialEq, ToComputedValue, ToCss)]
+#[allow(missing_docs)]
+pub enum RepeatKeyword {
+    Repeat,
+    Space,
+    Round,
+    NoRepeat,
 }
 
 /// The specified value for the `background-repeat` property.

components/style/values/specified/position.rs

@@ -42,17 +42,21 @@ pub enum PositionComponent<S> {
     Side(S, Option<LengthOrPercentage>),
 }
 
-define_css_keyword_enum! { X:
-    "left" => Left,
-    "right" => Right,
+/// A keyword for the X direction.
+#[derive(Clone, Copy, Debug, Eq, Hash, MallocSizeOf, Parse, PartialEq, ToComputedValue, ToCss)]
+#[allow(missing_docs)]
+pub enum X {
+    Left,
+    Right,
 }
-add_impls_for_keyword_enum!(X);
 
-define_css_keyword_enum! { Y:
-    "top" => Top,
-    "bottom" => Bottom,
+/// A keyword for the Y direction.
+#[derive(Clone, Copy, Debug, Eq, Hash, MallocSizeOf, Parse, PartialEq, ToComputedValue, ToCss)]
+#[allow(missing_docs)]
+pub enum Y {
+    Top,
+    Bottom,
 }
-add_impls_for_keyword_enum!(Y);
 
 impl Parse for Position {
     fn parse<'i, 't>(context: &ParserContext, input: &mut Parser<'i, 't>) -> Result<Self, ParseError<'i>> {