style: Improve #[derive(Parse)].

I want to do this so that I can get rid of Either<>. The reasons for getting rid
of either are multiple:

 * It doesn't generate as nice C++ code using cbindgen.
 * It isn't that nice to use either from Rust.
 * cbindgen has bugs with zero-sized types.

I started using this for ColorOrAuto and a few others, for now.

Differential Revision: https://phabricator.services.mozilla.com/D19844

components/style/values/specified/font.rs

@@ -17,7 +17,7 @@ use crate::values::generics::font::{KeywordSize, VariationValue};
 use crate::values::generics::NonNegative;
 use crate::values::specified::length::{FontBaseSize, AU_PER_PT, AU_PER_PX};
 use crate::values::specified::{AllowQuirks, Angle, Integer, LengthPercentage};
-use crate::values::specified::{NoCalcLength, Number, Percentage};
+use crate::values::specified::{NoCalcLength, Number, NonNegativeNumber, Percentage};
 use crate::values::CustomIdent;
 use crate::Atom;
 use app_units::Au;
@@ -81,7 +81,7 @@ pub const MAX_FONT_WEIGHT: f32 = 1000.;
 /// A specified font-weight value.
 ///
 /// https://drafts.csswg.org/css-fonts-4/#propdef-font-weight
-#[derive(Clone, Copy, Debug, MallocSizeOf, PartialEq, SpecifiedValueInfo, ToCss)]
+#[derive(Clone, Copy, Debug, MallocSizeOf, Parse, PartialEq, SpecifiedValueInfo, ToCss)]
 pub enum FontWeight {
     /// `<font-weight-absolute>`
     Absolute(AbsoluteFontWeight),
@@ -111,22 +111,6 @@ impl FontWeight {
     }
 }
 
-impl Parse for FontWeight {
-    fn parse<'i, 't>(
-        context: &ParserContext,
-        input: &mut Parser<'i, 't>,
-    ) -> Result<FontWeight, ParseError<'i>> {
-        if let Ok(absolute) = input.try(|input| AbsoluteFontWeight::parse(context, input)) {
-            return Ok(FontWeight::Absolute(absolute));
-        }
-
-        Ok(try_match_ident_ignore_ascii_case! { input,
-            "bolder" => FontWeight::Bolder,
-            "lighter" => FontWeight::Lighter,
-        })
-    }
-}
-
 impl ToComputedValue for FontWeight {
     type ComputedValue = computed::FontWeight;
 
@@ -335,7 +319,7 @@ impl SpecifiedFontStyle {
 }
 
 /// The specified value of the `font-style` property.
-#[derive(Clone, Copy, Debug, MallocSizeOf, PartialEq, SpecifiedValueInfo, ToCss)]
+#[derive(Clone, Copy, Debug, MallocSizeOf, Parse, PartialEq, SpecifiedValueInfo, ToCss)]
 #[allow(missing_docs)]
 pub enum FontStyle {
     Specified(SpecifiedFontStyle),
@@ -368,20 +352,11 @@ impl ToComputedValue for FontStyle {
     }
 }
 
-impl Parse for FontStyle {
-    fn parse<'i, 't>(
-        context: &ParserContext,
-        input: &mut Parser<'i, 't>,
-    ) -> Result<Self, ParseError<'i>> {
-        Ok(FontStyle::Specified(SpecifiedFontStyle::parse(
-            context, input,
-        )?))
-    }
-}
-
 /// A value for the `font-stretch` property.
 ///
 /// https://drafts.csswg.org/css-fonts-4/#font-stretch-prop
+///
+/// TODO(emilio): We could derive Parse if we had NonNegativePercentage.
 #[allow(missing_docs)]
 #[derive(Clone, Copy, Debug, MallocSizeOf, PartialEq, SpecifiedValueInfo, ToCss)]
 #[repr(u8)]
@@ -628,13 +603,13 @@ impl Parse for FamilyName {
     }
 }
 
-#[derive(Clone, Copy, Debug, MallocSizeOf, PartialEq, SpecifiedValueInfo, ToCss)]
+#[derive(Clone, Copy, Debug, MallocSizeOf, Parse, PartialEq, SpecifiedValueInfo, ToCss)]
 /// Preserve the readability of text when font fallback occurs
 pub enum FontSizeAdjust {
     /// None variant
     None,
     /// Number variant
-    Number(Number),
+    Number(NonNegativeNumber),
     /// system font
     #[css(skip)]
     System(SystemFont),
@@ -657,7 +632,9 @@ impl ToComputedValue for FontSizeAdjust {
         match *self {
             FontSizeAdjust::None => computed::FontSizeAdjust::None,
             FontSizeAdjust::Number(ref n) => {
-                computed::FontSizeAdjust::Number(n.to_computed_value(context))
+                // The computed version handles clamping of animated values
+                // itself.
+                computed::FontSizeAdjust::Number(n.to_computed_value(context).0)
             },
             FontSizeAdjust::System(_) => self.compute_system(context),
         }
@@ -666,32 +643,13 @@ impl ToComputedValue for FontSizeAdjust {
     fn from_computed_value(computed: &computed::FontSizeAdjust) -> Self {
         match *computed {
             computed::FontSizeAdjust::None => FontSizeAdjust::None,
-            computed::FontSizeAdjust::Number(ref v) => {
-                FontSizeAdjust::Number(Number::from_computed_value(v))
+            computed::FontSizeAdjust::Number(v) => {
+                FontSizeAdjust::Number(NonNegativeNumber::from_computed_value(&v.into()))
             },
         }
     }
 }
 
-impl Parse for FontSizeAdjust {
-    /// none | <number>
-    fn parse<'i, 't>(
-        context: &ParserContext,
-        input: &mut Parser<'i, 't>,
-    ) -> Result<FontSizeAdjust, ParseError<'i>> {
-        if input
-            .try(|input| input.expect_ident_matching("none"))
-            .is_ok()
-        {
-            return Ok(FontSizeAdjust::None);
-        }
-
-        Ok(FontSizeAdjust::Number(Number::parse_non_negative(
-            context, input,
-        )?))
-    }
-}
-
 /// Additional information for specified keyword-derived font sizes.
 pub type KeywordInfo = generics::KeywordInfo<NonNegativeLength>;