style: Derive more length stuff, and shrink MaxLength / MozLength's repr(C) representation.

This patch:

 * Makes LengthPercentageOrAuto generic, and removes a bunch of code fo
   LengthPercentageOrNone, which was used only for servo and now can use the
   normal MaxLength (with a cfg() guard for the ExtremumLength variant).

 * Shrinks MaxLength / MozLength's repr(C) reperesentation by reducing enum
   nesting. The shrinking is in preparation for using them from C++ too, though
   that'd be a different bug.

 * Moves NonNegative usage to the proper places so that stuff for them can be
   derived.

I did this on top of bug 1523071 to prove both that it could be possible and
that stuff wasn't too messy. It got a bit messy, but just because of a bug I
had fixed in bindgen long time ago already, so this updates bindgen's patch
version to grab a fix instead of ugly workarounds :)

Differential Revision: https://phabricator.services.mozilla.com/D17762

17 files changed, 334 insertions, 517 deletions

diff --git a/components/style/cbindgen.toml b/components/style/cbindgen.toml
index d76a57c9541..4c0b631d31d 100644
--- a/components/style/cbindgen.toml
+++ b/components/style/cbindgen.toml
@@ -99,7 +99,7 @@ item_types = ["enums", "structs", "typedefs"]
   template<typename T> inline nscoord ResolveWith(T aPercentageGetter) const;
 """
 
-"LengthPercentageOrAuto" = """
+"GenericLengthPercentageOrAuto" = """
   inline const StyleLengthPercentage& AsLengthPercentage() const;
   inline bool HasPercent() const;
   inline bool ConvertsToLength() const;
diff --git a/components/style/gecko/conversions.rs b/components/style/gecko/conversions.rs
index 0f6ac89c9f2..ccaa16c844c 100644
--- a/components/style/gecko/conversions.rs
+++ b/components/style/gecko/conversions.rs
@@ -27,6 +27,7 @@ use crate::values::computed::{LengthPercentageOrAuto, NonNegativeLengthPercentag
 use crate::values::generics::box_::VerticalAlign;
 use crate::values::generics::grid::{TrackListValue, TrackSize};
 use crate::values::generics::image::{CompatMode, GradientItem, Image as GenericImage};
+use crate::values::generics::length::LengthPercentageOrAuto as GenericLengthPercentageOrAuto;
 use crate::values::generics::rect::Rect;
 use crate::values::generics::NonNegative;
 use app_units::Au;
@@ -62,19 +63,19 @@ impl From<nsStyleCoord_CalcValue> for LengthPercentage {
     }
 }
 
-impl LengthPercentageOrAuto {
+impl NonNegativeLengthPercentageOrAuto {
     /// Convert this value in an appropriate `nsStyleCoord::CalcValue`.
     pub fn to_calc_value(&self) -> Option<nsStyleCoord_CalcValue> {
         match *self {
-            LengthPercentageOrAuto::LengthPercentage(len) => Some(From::from(len)),
-            LengthPercentageOrAuto::Auto => None,
+            GenericLengthPercentageOrAuto::LengthPercentage(ref len) => Some(From::from(len.0)),
+            GenericLengthPercentageOrAuto::Auto => None,
         }
     }
 }
 
 impl From<nsStyleCoord_CalcValue> for LengthPercentageOrAuto {
     fn from(other: nsStyleCoord_CalcValue) -> LengthPercentageOrAuto {
-        LengthPercentageOrAuto::LengthPercentage(LengthPercentage::from(other))
+        GenericLengthPercentageOrAuto::LengthPercentage(LengthPercentage::from(other))
     }
 }
 
@@ -82,7 +83,7 @@ impl From<nsStyleCoord_CalcValue> for LengthPercentageOrAuto {
 // disappear as we move more stuff to cbindgen.
 impl From<nsStyleCoord_CalcValue> for NonNegativeLengthPercentageOrAuto {
     fn from(other: nsStyleCoord_CalcValue) -> Self {
-        NonNegative(LengthPercentageOrAuto::LengthPercentage(
+        GenericLengthPercentageOrAuto::LengthPercentage(NonNegative(
             LengthPercentage::with_clamping_mode(
                 Au(other.mLength).into(),
                 if other.mHasPercent {
diff --git a/components/style/gecko/values.rs b/components/style/gecko/values.rs
index 42177bf0858..ac3495a7504 100644
--- a/components/style/gecko/values.rs
+++ b/components/style/gecko/values.rs
@@ -14,15 +14,15 @@ use crate::media_queries::Device;
 use crate::values::computed::basic_shape::ShapeRadius as ComputedShapeRadius;
 use crate::values::computed::FlexBasis as ComputedFlexBasis;
 use crate::values::computed::{Angle, ExtremumLength, Length, LengthPercentage};
-use crate::values::computed::{LengthPercentageOrAuto, Percentage};
-use crate::values::computed::{LengthPercentageOrNone, Number, NumberOrPercentage};
 use crate::values::computed::{MaxLength as ComputedMaxLength, MozLength as ComputedMozLength};
+use crate::values::computed::{NonNegativeLengthPercentage, Percentage};
+use crate::values::computed::{Number, NumberOrPercentage};
 use crate::values::generics::basic_shape::ShapeRadius;
 use crate::values::generics::box_::Perspective;
 use crate::values::generics::flex::FlexBasis;
 use crate::values::generics::gecko::ScrollSnapPoint;
 use crate::values::generics::grid::{TrackBreadth, TrackKeyword};
-use crate::values::generics::length::{MaxLength, MozLength};
+use crate::values::generics::length::{LengthPercentageOrAuto, MaxLength, MozLength};
 use crate::values::generics::{CounterStyleOrNone, NonNegative};
 use crate::values::{Auto, Either, None_, Normal};
 use crate::Atom;
@@ -183,7 +183,10 @@ impl GeckoStyleCoordConvertible for Length {
     }
 }
 
-impl GeckoStyleCoordConvertible for LengthPercentageOrAuto {
+impl<LengthPercentage> GeckoStyleCoordConvertible for LengthPercentageOrAuto<LengthPercentage>
+where
+    LengthPercentage: GeckoStyleCoordConvertible,
+{
     fn to_gecko_style_coord<T: CoordDataMut>(&self, coord: &mut T) {
         match *self {
             LengthPercentageOrAuto::Auto => coord.set_value(CoordDataValue::Auto),
@@ -200,23 +203,6 @@ impl GeckoStyleCoordConvertible for LengthPercentageOrAuto {
     }
 }
 
-impl GeckoStyleCoordConvertible for LengthPercentageOrNone {
-    fn to_gecko_style_coord<T: CoordDataMut>(&self, coord: &mut T) {
-        match *self {
-            LengthPercentageOrNone::None => coord.set_value(CoordDataValue::None),
-            LengthPercentageOrNone::LengthPercentage(ref lp) => lp.to_gecko_style_coord(coord),
-        }
-    }
-
-    fn from_gecko_style_coord<T: CoordData>(coord: &T) -> Option<Self> {
-        match coord.as_value() {
-            CoordDataValue::None => Some(LengthPercentageOrNone::None),
-            _ => LengthPercentage::from_gecko_style_coord(coord)
-                .map(LengthPercentageOrNone::LengthPercentage),
-        }
-    }
-}
-
 impl<L: GeckoStyleCoordConvertible> GeckoStyleCoordConvertible for TrackBreadth<L> {
     fn to_gecko_style_coord<T: CoordDataMut>(&self, coord: &mut T) {
         match *self {
@@ -367,34 +353,40 @@ impl GeckoStyleCoordConvertible for ExtremumLength {
 impl GeckoStyleCoordConvertible for ComputedMozLength {
     fn to_gecko_style_coord<T: CoordDataMut>(&self, coord: &mut T) {
         match *self {
-            MozLength::LengthPercentageOrAuto(ref lpoa) => lpoa.to_gecko_style_coord(coord),
+            MozLength::LengthPercentage(ref lpoa) => lpoa.to_gecko_style_coord(coord),
+            MozLength::Auto => coord.set_value(CoordDataValue::Auto),
             MozLength::ExtremumLength(ref e) => e.to_gecko_style_coord(coord),
         }
     }
 
     fn from_gecko_style_coord<T: CoordData>(coord: &T) -> Option<Self> {
-        LengthPercentageOrAuto::from_gecko_style_coord(coord)
-            .map(MozLength::LengthPercentageOrAuto)
-            .or_else(|| {
-                ExtremumLength::from_gecko_style_coord(coord).map(MozLength::ExtremumLength)
-            })
+        if let CoordDataValue::Auto = coord.as_value() {
+            return Some(MozLength::Auto);
+        }
+        if let Some(lp) = NonNegativeLengthPercentage::from_gecko_style_coord(coord) {
+            return Some(MozLength::LengthPercentage(lp));
+        }
+        ExtremumLength::from_gecko_style_coord(coord).map(MozLength::ExtremumLength)
     }
 }
 
 impl GeckoStyleCoordConvertible for ComputedMaxLength {
     fn to_gecko_style_coord<T: CoordDataMut>(&self, coord: &mut T) {
         match *self {
-            MaxLength::LengthPercentageOrNone(ref lpon) => lpon.to_gecko_style_coord(coord),
+            MaxLength::LengthPercentage(ref lpon) => lpon.to_gecko_style_coord(coord),
+            MaxLength::None => coord.set_value(CoordDataValue::None),
             MaxLength::ExtremumLength(ref e) => e.to_gecko_style_coord(coord),
         }
     }
 
     fn from_gecko_style_coord<T: CoordData>(coord: &T) -> Option<Self> {
-        LengthPercentageOrNone::from_gecko_style_coord(coord)
-            .map(MaxLength::LengthPercentageOrNone)
-            .or_else(|| {
-                ExtremumLength::from_gecko_style_coord(coord).map(MaxLength::ExtremumLength)
-            })
+        if let CoordDataValue::None = coord.as_value() {
+            return Some(MaxLength::None);
+        }
+        if let Some(lp) = NonNegativeLengthPercentage::from_gecko_style_coord(coord) {
+            return Some(MaxLength::LengthPercentage(lp));
+        }
+        ExtremumLength::from_gecko_style_coord(coord).map(MaxLength::ExtremumLength)
     }
 }
 
diff --git a/components/style/properties/gecko.mako.rs b/components/style/properties/gecko.mako.rs
index 798e39adb27..297357446a2 100644
--- a/components/style/properties/gecko.mako.rs
+++ b/components/style/properties/gecko.mako.rs
@@ -1390,7 +1390,6 @@ impl Clone for ${style_struct.gecko_struct_name} {
         "LengthOrNormal": impl_style_coord,
         "LengthPercentage": impl_simple,
         "LengthPercentageOrAuto": impl_style_coord,
-        "LengthPercentageOrNone": impl_style_coord,
         "MaxLength": impl_style_coord,
         "MozLength": impl_style_coord,
         "MozScriptMinSize": impl_absolute_length,
@@ -3831,11 +3830,11 @@ fn static_assert() {
             BackgroundSize::Explicit { width: explicit_width, height: explicit_height } => {
                 let mut w_type = nsStyleImageLayers_Size_DimensionType::eAuto;
                 let mut h_type = nsStyleImageLayers_Size_DimensionType::eAuto;
-                if let Some(w) = explicit_width.0.to_calc_value() {
+                if let Some(w) = explicit_width.to_calc_value() {
                     width = w;
                     w_type = nsStyleImageLayers_Size_DimensionType::eLengthPercentage;
                 }
-                if let Some(h) = explicit_height.0.to_calc_value() {
+                if let Some(h) = explicit_height.to_calc_value() {
                     height = h;
                     h_type = nsStyleImageLayers_Size_DimensionType::eLengthPercentage;
                 }
diff --git a/components/style/properties/longhands/position.mako.rs b/components/style/properties/longhands/position.mako.rs
index cc5515dbac7..2a0f86d056a 100644
--- a/components/style/properties/longhands/position.mako.rs
+++ b/components/style/properties/longhands/position.mako.rs
@@ -13,7 +13,7 @@
     ${helpers.predefined_type(
         side,
         "LengthPercentageOrAuto",
-        "computed::LengthPercentageOrAuto::Auto",
+        "computed::LengthPercentageOrAuto::auto()",
         spec="https://www.w3.org/TR/CSS2/visuren.html#propdef-%s" % side,
         flags="GETCS_NEEDS_LAYOUT_FLUSH",
         animation_value_type="ComputedValue",
@@ -27,7 +27,7 @@
     ${helpers.predefined_type(
         "inset-%s" % side,
         "LengthPercentageOrAuto",
-        "computed::LengthPercentageOrAuto::Auto",
+        "computed::LengthPercentageOrAuto::auto()",
         spec="https://drafts.csswg.org/css-logical-props/#propdef-inset-%s" % side,
         flags="GETCS_NEEDS_LAYOUT_FLUSH",
         alias="offset-%s:layout.css.offset-logical-properties.enabled" % side,
@@ -270,24 +270,12 @@ ${helpers.predefined_type(
             animation_value_type="MozLength",
             servo_restyle_damage="reflow",
         )}
-        ${helpers.predefined_type(
-            "max-%s" % size,
-            "MaxLength",
-            "computed::MaxLength::none()",
-            logical=logical,
-            logical_group="max-size",
-            allow_quirks=not logical,
-            spec=spec % size,
-            animation_value_type="MaxLength",
-            servo_restyle_damage="reflow",
-        )}
     % else:
         // servo versions (no keyword support)
         ${helpers.predefined_type(
             size,
-            "LengthPercentageOrAuto",
-            "computed::LengthPercentageOrAuto::Auto",
-            "parse_non_negative",
+            "NonNegativeLengthPercentageOrAuto",
+            "computed::NonNegativeLengthPercentageOrAuto::auto()",
             spec=spec % size,
             logical_group="size",
             allow_quirks=not logical,
@@ -296,9 +284,8 @@ ${helpers.predefined_type(
         )}
         ${helpers.predefined_type(
             "min-%s" % size,
-            "LengthPercentage",
-            "computed::LengthPercentage::zero()",
-            "parse_non_negative",
+            "NonNegativeLengthPercentage",
+            "computed::NonNegativeLengthPercentage::zero()",
             spec=spec % ("min-%s" % size),
             logical_group="min-size",
             animation_value_type="ComputedValue",
@@ -306,19 +293,18 @@ ${helpers.predefined_type(
             allow_quirks=not logical,
             servo_restyle_damage="reflow",
         )}
-        ${helpers.predefined_type(
-            "max-%s" % size,
-            "LengthPercentageOrNone",
-            "computed::LengthPercentageOrNone::None",
-            "parse_non_negative",
-            spec=spec % ("max-%s" % size),
-            logical_group="max-size",
-            animation_value_type="ComputedValue",
-            logical=logical,
-            allow_quirks=not logical,
-            servo_restyle_damage="reflow",
-        )}
     % endif
+    ${helpers.predefined_type(
+        "max-%s" % size,
+        "MaxLength",
+        "computed::MaxLength::none()",
+        logical=logical,
+        logical_group="max-size",
+        allow_quirks=not logical,
+        spec=spec % size,
+        animation_value_type="MaxLength",
+        servo_restyle_damage="reflow",
+    )}
 % endfor
 
 ${helpers.single_keyword(
diff --git a/components/style/properties/properties.mako.rs b/components/style/properties/properties.mako.rs
index 0e7364d445c..62d27922ccb 100644
--- a/components/style/properties/properties.mako.rs
+++ b/components/style/properties/properties.mako.rs
@@ -3016,7 +3016,7 @@ impl ComputedValuesInner {
 
     /// Get the logical computed inline size.
     #[inline]
-    pub fn content_inline_size(&self) -> computed::LengthPercentageOrAuto {
+    pub fn content_inline_size(&self) -> computed::NonNegativeLengthPercentageOrAuto {
         let position_style = self.get_position();
         if self.writing_mode.is_vertical() {
             position_style.height
@@ -3027,35 +3027,35 @@ impl ComputedValuesInner {
 
     /// Get the logical computed block size.
     #[inline]
-    pub fn content_block_size(&self) -> computed::LengthPercentageOrAuto {
+    pub fn content_block_size(&self) -> computed::NonNegativeLengthPercentageOrAuto {
         let position_style = self.get_position();
         if self.writing_mode.is_vertical() { position_style.width } else { position_style.height }
     }
 
     /// Get the logical computed min inline size.
     #[inline]
-    pub fn min_inline_size(&self) -> computed::LengthPercentage {
+    pub fn min_inline_size(&self) -> computed::NonNegativeLengthPercentage {
         let position_style = self.get_position();
         if self.writing_mode.is_vertical() { position_style.min_height } else { position_style.min_width }
     }
 
     /// Get the logical computed min block size.
     #[inline]
-    pub fn min_block_size(&self) -> computed::LengthPercentage {
+    pub fn min_block_size(&self) -> computed::NonNegativeLengthPercentage {
         let position_style = self.get_position();
         if self.writing_mode.is_vertical() { position_style.min_width } else { position_style.min_height }
     }
 
     /// Get the logical computed max inline size.
     #[inline]
-    pub fn max_inline_size(&self) -> computed::LengthPercentageOrNone {
+    pub fn max_inline_size(&self) -> computed::MaxLength {
         let position_style = self.get_position();
         if self.writing_mode.is_vertical() { position_style.max_height } else { position_style.max_width }
     }
 
     /// Get the logical computed max block size.
     #[inline]
-    pub fn max_block_size(&self) -> computed::LengthPercentageOrNone {
+    pub fn max_block_size(&self) -> computed::MaxLength {
         let position_style = self.get_position();
         if self.writing_mode.is_vertical() { position_style.max_width } else { position_style.max_height }
     }
diff --git a/components/style/stylesheets/viewport_rule.rs b/components/style/stylesheets/viewport_rule.rs
index 862399e065c..8325216519d 100644
--- a/components/style/stylesheets/viewport_rule.rs
+++ b/components/style/stylesheets/viewport_rule.rs
@@ -11,16 +11,17 @@ use crate::context::QuirksMode;
 use crate::error_reporting::ContextualParseError;
 use crate::font_metrics::get_metrics_provider_for_product;
 use crate::media_queries::Device;
-use crate::parser::ParserContext;
+use crate::parser::{Parse, ParserContext};
 use crate::properties::StyleBuilder;
 use crate::rule_cache::RuleCacheConditions;
 use crate::shared_lock::{SharedRwLockReadGuard, StylesheetGuards, ToCssWithGuard};
 use crate::str::CssStringWriter;
 use crate::stylesheets::{Origin, StylesheetInDocument};
 use crate::values::computed::{Context, ToComputedValue};
-use crate::values::specified::{
-    self, LengthPercentageOrAuto, NoCalcLength, ViewportPercentageLength,
-};
+use crate::values::generics::length::LengthPercentageOrAuto;
+use crate::values::generics::NonNegative;
+use crate::values::specified::{self, NoCalcLength};
+use crate::values::specified::{NonNegativeLengthPercentageOrAuto, ViewportPercentageLength};
 use app_units::Au;
 use cssparser::CowRcStr;
 use cssparser::{parse_important, AtRuleParser, DeclarationListParser, DeclarationParser, Parser};
@@ -151,7 +152,7 @@ trait FromMeta: Sized {
 #[cfg_attr(feature = "servo", derive(MallocSizeOf))]
 #[derive(Clone, Debug, PartialEq, ToCss)]
 pub enum ViewportLength {
-    Specified(LengthPercentageOrAuto),
+    Specified(NonNegativeLengthPercentageOrAuto),
     ExtendToZoom,
 }
 
@@ -159,9 +160,9 @@ impl FromMeta for ViewportLength {
     fn from_meta(value: &str) -> Option<ViewportLength> {
         macro_rules! specified {
             ($value:expr) => {
-                ViewportLength::Specified(LengthPercentageOrAuto::LengthPercentage(
+                ViewportLength::Specified(LengthPercentageOrAuto::LengthPercentage(NonNegative(
                     specified::LengthPercentage::Length($value),
-                ))
+                )))
             };
         }
 
@@ -188,7 +189,7 @@ impl ViewportLength {
     ) -> Result<Self, ParseError<'i>> {
         // we explicitly do not accept 'extend-to-zoom', since it is a UA
         // internal value for <META> viewport translation
-        LengthPercentageOrAuto::parse_non_negative(context, input).map(ViewportLength::Specified)
+        NonNegativeLengthPercentageOrAuto::parse(context, input).map(ViewportLength::Specified)
     }
 }
 
diff --git a/components/style/values/animated/length.rs b/components/style/values/animated/length.rs
index dd678f5c395..73957618cea 100644
--- a/components/style/values/animated/length.rs
+++ b/components/style/values/animated/length.rs
@@ -4,10 +4,8 @@
 
 //! Animation implementation for various length-related types.
 
-use super::{Animate, Procedure, ToAnimatedValue};
+use super::{Animate, Procedure};
 use crate::values::computed::length::LengthPercentage;
-use crate::values::computed::MaxLength as ComputedMaxLength;
-use crate::values::computed::MozLength as ComputedMozLength;
 use crate::values::computed::Percentage;
 
 /// <https://drafts.csswg.org/css-transitions/#animtype-lpcalc>
@@ -38,51 +36,3 @@ impl Animate for LengthPercentage {
         ))
     }
 }
-
-// FIXME(emilio): These should use NonNegative<> instead.
-impl ToAnimatedValue for ComputedMaxLength {
-    type AnimatedValue = Self;
-
-    #[inline]
-    fn to_animated_value(self) -> Self {
-        self
-    }
-
-    #[inline]
-    fn from_animated_value(animated: Self::AnimatedValue) -> Self {
-        use crate::values::computed::LengthPercentageOrNone;
-        use crate::values::generics::length::MaxLength as GenericMaxLength;
-        match animated {
-            GenericMaxLength::LengthPercentageOrNone(lpn) => {
-                let result = match lpn {
-                    LengthPercentageOrNone::LengthPercentage(len) => {
-                        LengthPercentageOrNone::LengthPercentage(len.clamp_to_non_negative())
-                    },
-                    LengthPercentageOrNone::None => lpn,
-                };
-                GenericMaxLength::LengthPercentageOrNone(result)
-            },
-            _ => animated,
-        }
-    }
-}
-
-impl ToAnimatedValue for ComputedMozLength {
-    type AnimatedValue = Self;
-
-    #[inline]
-    fn to_animated_value(self) -> Self {
-        self
-    }
-
-    #[inline]
-    fn from_animated_value(animated: Self::AnimatedValue) -> Self {
-        use crate::values::generics::length::MozLength as GenericMozLength;
-        match animated {
-            GenericMozLength::LengthPercentageOrAuto(lpa) => {
-                GenericMozLength::LengthPercentageOrAuto(lpa.clamp_to_non_negative())
-            },
-            _ => animated,
-        }
-    }
-}
diff --git a/components/style/values/computed/background.rs b/components/style/values/computed/background.rs
index 08f10c9c1ec..dc23915a74b 100644
--- a/components/style/values/computed/background.rs
+++ b/components/style/values/computed/background.rs
@@ -4,20 +4,21 @@
 
 //! Computed types for CSS values related to backgrounds.
 
-use crate::values::computed::length::NonNegativeLengthPercentageOrAuto;
+use crate::values::computed::length::NonNegativeLengthPercentage;
 use crate::values::generics::background::BackgroundSize as GenericBackgroundSize;
+use crate::values::generics::length::LengthPercentageOrAuto;
 
 pub use crate::values::specified::background::BackgroundRepeat;
 
 /// A computed value for the `background-size` property.
-pub type BackgroundSize = GenericBackgroundSize<NonNegativeLengthPercentageOrAuto>;
+pub type BackgroundSize = GenericBackgroundSize<NonNegativeLengthPercentage>;
 
 impl BackgroundSize {
     /// Returns `auto auto`.
     pub fn auto() -> Self {
         GenericBackgroundSize::Explicit {
-            width: NonNegativeLengthPercentageOrAuto::auto(),
-            height: NonNegativeLengthPercentageOrAuto::auto(),
+            width: LengthPercentageOrAuto::auto(),
+            height: LengthPercentageOrAuto::auto(),
         }
     }
 }
diff --git a/components/style/values/computed/length.rs b/components/style/values/computed/length.rs
index c779594202b..313b4151d2b 100644
--- a/components/style/values/computed/length.rs
+++ b/components/style/values/computed/length.rs
@@ -7,13 +7,15 @@
 use super::{Context, Number, Percentage, ToComputedValue};
 use crate::values::animated::ToAnimatedValue;
 use crate::values::distance::{ComputeSquaredDistance, SquaredDistance};
-use crate::values::generics::length::MaxLength as GenericMaxLength;
-use crate::values::generics::length::MozLength as GenericMozLength;
+use crate::values::generics::length as generics;
+use crate::values::generics::length::{
+    MaxLength as GenericMaxLength, MozLength as GenericMozLength,
+};
 use crate::values::generics::transform::IsZeroLength;
 use crate::values::generics::NonNegative;
 use crate::values::specified::length::ViewportPercentageLength;
 use crate::values::specified::length::{AbsoluteLength, FontBaseSize, FontRelativeLength};
-use crate::values::{specified, Auto, CSSFloat, Either, IsAuto, Normal};
+use crate::values::{specified, Auto, CSSFloat, Either, Normal};
 use app_units::Au;
 use ordered_float::NotNan;
 use std::fmt::{self, Write};
@@ -452,151 +454,61 @@ impl IsZeroLength for LengthPercentage {
     }
 }
 
-#[allow(missing_docs)]
-#[css(derive_debug)]
-#[derive(
-    Animate, Clone, ComputeSquaredDistance, Copy, MallocSizeOf, PartialEq, ToAnimatedZero, ToCss,
-)]
-#[repr(C, u8)]
-pub enum LengthPercentageOrAuto {
-    LengthPercentage(LengthPercentage),
-    Auto,
-}
-
-impl LengthPercentageOrAuto {
-    /// Returns the `0` value.
-    #[inline]
-    pub fn zero() -> Self {
-        LengthPercentageOrAuto::LengthPercentage(LengthPercentage::zero())
-    }
-}
-
-/// A wrapper of LengthPercentageOrAuto, whose value must be >= 0.
-pub type NonNegativeLengthPercentageOrAuto = NonNegative<LengthPercentageOrAuto>;
+/// Some boilerplate to share between negative and non-negative
+/// length-percentage or auto.
+macro_rules! computed_length_percentage_or_auto {
+    ($inner:ty) => {
+        /// Returns the `0` value.
+        #[inline]
+        pub fn zero() -> Self {
+            generics::LengthPercentageOrAuto::LengthPercentage(<$inner>::zero())
+        }
 
-impl IsAuto for NonNegativeLengthPercentageOrAuto {
-    #[inline]
-    fn is_auto(&self) -> bool {
-        *self == Self::auto()
-    }
-}
+        /// Returns the used value.
+        #[inline]
+        pub fn to_used_value(&self, percentage_basis: Au) -> Option<Au> {
+            match *self {
+                generics::GenericLengthPercentageOrAuto::Auto => None,
+                generics::GenericLengthPercentageOrAuto::LengthPercentage(ref lp) => {
+                    Some(lp.to_used_value(percentage_basis))
+                }
+            }
+        }
 
-impl NonNegativeLengthPercentageOrAuto {
-    /// `auto`
-    #[inline]
-    pub fn auto() -> Self {
-        NonNegative(LengthPercentageOrAuto::Auto)
+        /// Returns true if the computed value is absolute 0 or 0%.
+        #[inline]
+        pub fn is_definitely_zero(&self) -> bool {
+            use values::generics::length::LengthPercentageOrAuto::*;
+            match *self {
+                LengthPercentage(ref l) => l.is_definitely_zero(),
+                Auto => false,
+            }
+        }
     }
 }
 
-impl ToAnimatedValue for NonNegativeLengthPercentageOrAuto {
-    type AnimatedValue = LengthPercentageOrAuto;
-
-    #[inline]
-    fn to_animated_value(self) -> Self::AnimatedValue {
-        self.0
-    }
-
-    #[inline]
-    fn from_animated_value(animated: Self::AnimatedValue) -> Self {
-        NonNegative(animated.clamp_to_non_negative())
-    }
-}
+/// A computed type for `<length-percentage> | auto`.
+pub type LengthPercentageOrAuto = generics::GenericLengthPercentageOrAuto<LengthPercentage>;
 
 impl LengthPercentageOrAuto {
-    /// Returns true if the computed value is absolute 0 or 0%.
-    #[inline]
-    pub fn is_definitely_zero(&self) -> bool {
-        use self::LengthPercentageOrAuto::*;
-        match *self {
-            LengthPercentage(ref l) => l.is_definitely_zero(),
-            Auto => false,
-        }
-    }
-
     /// Clamps the value to a non-negative value.
     pub fn clamp_to_non_negative(self) -> Self {
-        use self::LengthPercentageOrAuto::*;
+        use values::generics::length::LengthPercentageOrAuto::*;
         match self {
             LengthPercentage(l) => LengthPercentage(l.clamp_to_non_negative()),
             Auto => Auto,
         }
     }
-}
-
-impl ToComputedValue for specified::LengthPercentageOrAuto {
-    type ComputedValue = LengthPercentageOrAuto;
-
-    #[inline]
-    fn to_computed_value(&self, context: &Context) -> LengthPercentageOrAuto {
-        match *self {
-            specified::LengthPercentageOrAuto::LengthPercentage(ref value) => {
-                LengthPercentageOrAuto::LengthPercentage(value.to_computed_value(context))
-            },
-            specified::LengthPercentageOrAuto::Auto => LengthPercentageOrAuto::Auto,
-        }
-    }
-
-    #[inline]
-    fn from_computed_value(computed: &LengthPercentageOrAuto) -> Self {
-        match *computed {
-            LengthPercentageOrAuto::Auto => specified::LengthPercentageOrAuto::Auto,
-            LengthPercentageOrAuto::LengthPercentage(ref value) => {
-                specified::LengthPercentageOrAuto::LengthPercentage(
-                    ToComputedValue::from_computed_value(value),
-                )
-            },
-        }
-    }
-}
 
-#[allow(missing_docs)]
-#[css(derive_debug)]
-#[derive(
-    Animate, Clone, ComputeSquaredDistance, Copy, MallocSizeOf, PartialEq, ToAnimatedZero, ToCss,
-)]
-pub enum LengthPercentageOrNone {
-    LengthPercentage(LengthPercentage),
-    None,
-}
-
-impl LengthPercentageOrNone {
-    /// Returns the used value.
-    pub fn to_used_value(&self, containing_length: Au) -> Option<Au> {
-        match *self {
-            LengthPercentageOrNone::None => None,
-            LengthPercentageOrNone::LengthPercentage(ref lp) => {
-                Some(lp.to_used_value(containing_length))
-            },
-        }
-    }
+    computed_length_percentage_or_auto!(LengthPercentage);
 }
 
-// FIXME(emilio): Derive this.
-impl ToComputedValue for specified::LengthPercentageOrNone {
-    type ComputedValue = LengthPercentageOrNone;
-
-    #[inline]
-    fn to_computed_value(&self, context: &Context) -> LengthPercentageOrNone {
-        match *self {
-            specified::LengthPercentageOrNone::LengthPercentage(ref value) => {
-                LengthPercentageOrNone::LengthPercentage(value.to_computed_value(context))
-            },
-            specified::LengthPercentageOrNone::None => LengthPercentageOrNone::None,
-        }
-    }
+/// A wrapper of LengthPercentageOrAuto, whose value must be >= 0.
+pub type NonNegativeLengthPercentageOrAuto =
+    generics::LengthPercentageOrAuto<NonNegativeLengthPercentage>;
 
-    #[inline]
-    fn from_computed_value(computed: &LengthPercentageOrNone) -> Self {
-        match *computed {
-            LengthPercentageOrNone::None => specified::LengthPercentageOrNone::None,
-            LengthPercentageOrNone::LengthPercentage(value) => {
-                specified::LengthPercentageOrNone::LengthPercentage(
-                    ToComputedValue::from_computed_value(&value),
-                )
-            },
-        }
-    }
+impl NonNegativeLengthPercentageOrAuto {
+    computed_length_percentage_or_auto!(NonNegativeLengthPercentage);
 }
 
 /// A wrapper of LengthPercentage, whose value must be >= 0.
@@ -630,13 +542,6 @@ impl From<LengthPercentage> for NonNegativeLengthPercentage {
     }
 }
 
-impl From<NonNegativeLengthPercentage> for LengthPercentage {
-    #[inline]
-    fn from(lp: NonNegativeLengthPercentage) -> LengthPercentage {
-        lp.0
-    }
-}
-
 // TODO(emilio): This is a really generic impl which is only needed to implement
 // Animated and co for Spacing<>. Get rid of this, probably?
 impl From<Au> for LengthPercentage {
@@ -650,7 +555,7 @@ impl NonNegativeLengthPercentage {
     /// Get zero value.
     #[inline]
     pub fn zero() -> Self {
-        NonNegative::<LengthPercentage>(LengthPercentage::zero())
+        NonNegative(LengthPercentage::zero())
     }
 
     /// Returns true if the computed value is absolute 0 or 0%.
@@ -662,7 +567,26 @@ impl NonNegativeLengthPercentage {
     /// Returns the used value.
     #[inline]
     pub fn to_used_value(&self, containing_length: Au) -> Au {
-        self.0.to_used_value(containing_length)
+        let resolved = self.0.to_used_value(containing_length);
+        ::std::cmp::max(resolved, Au(0))
+    }
+
+    /// Convert the computed value into used value.
+    #[inline]
+    pub fn maybe_to_used_value(&self, containing_length: Option<Au>) -> Option<Au> {
+        let resolved = self.0.maybe_to_used_value(containing_length)?;
+        Some(::std::cmp::max(resolved, Au(0)))
+    }
+}
+
+#[cfg(feature = "servo")]
+impl MaxLength {
+    /// Convert the computed value into used value.
+    pub fn to_used_value(&self, percentage_basis: Au) -> Option<Au> {
+        match *self {
+            GenericMaxLength::None => None,
+            GenericMaxLength::LengthPercentage(ref lp) => Some(lp.to_used_value(percentage_basis)),
+        }
     }
 }
 
@@ -881,6 +805,8 @@ pub type NonNegativeLengthPercentageOrNormal = Either<NonNegativeLengthPercentag
     Parse,
     PartialEq,
     SpecifiedValueInfo,
+    ToAnimatedValue,
+    ToAnimatedZero,
     ToComputedValue,
     ToCss,
 )]
@@ -895,23 +821,7 @@ pub enum ExtremumLength {
 }
 
 /// A computed value for `min-width`, `min-height`, `width` or `height` property.
-pub type MozLength = GenericMozLength<LengthPercentageOrAuto>;
-
-impl MozLength {
-    /// Returns the `auto` value.
-    #[inline]
-    pub fn auto() -> Self {
-        GenericMozLength::LengthPercentageOrAuto(LengthPercentageOrAuto::Auto)
-    }
-}
+pub type MozLength = GenericMozLength<NonNegativeLengthPercentage>;
 
 /// A computed value for `max-width` or `min-height` property.
-pub type MaxLength = GenericMaxLength<LengthPercentageOrNone>;
-
-impl MaxLength {
-    /// Returns the `none` value.
-    #[inline]
-    pub fn none() -> Self {
-        GenericMaxLength::LengthPercentageOrNone(LengthPercentageOrNone::None)
-    }
-}
+pub type MaxLength = GenericMaxLength<NonNegativeLengthPercentage>;
diff --git a/components/style/values/computed/mod.rs b/components/style/values/computed/mod.rs
index 02ccf01e25e..ab8edd2b746 100644
--- a/components/style/values/computed/mod.rs
+++ b/components/style/values/computed/mod.rs
@@ -62,7 +62,7 @@ pub use self::gecko::ScrollSnapPoint;
 pub use self::image::{Gradient, GradientItem, Image, ImageLayer, LineDirection, MozImageRect};
 pub use self::length::{CSSPixelLength, ExtremumLength, NonNegativeLength};
 pub use self::length::{Length, LengthOrNumber, LengthPercentage};
-pub use self::length::{LengthPercentageOrAuto, LengthPercentageOrNone, MaxLength, MozLength};
+pub use self::length::{LengthPercentageOrAuto, MaxLength, MozLength};
 pub use self::length::{NonNegativeLengthPercentage, NonNegativeLengthPercentageOrAuto};
 #[cfg(feature = "gecko")]
 pub use self::list::ListStyleType;
diff --git a/components/style/values/generics/background.rs b/components/style/values/generics/background.rs
index 4a7ee4b9b95..d739329e4fc 100644
--- a/components/style/values/generics/background.rs
+++ b/components/style/values/generics/background.rs
@@ -4,7 +4,7 @@
 
 //! Generic types for CSS values related to backgrounds.
 
-use crate::values::IsAuto;
+use crate::values::generics::length::LengthPercentageOrAuto;
 use std::fmt::{self, Write};
 use style_traits::{CssWriter, ToCss};
 
@@ -22,13 +22,13 @@ use style_traits::{CssWriter, ToCss};
     ToAnimatedZero,
     ToComputedValue,
 )]
-pub enum BackgroundSize<LengthPercentageOrAuto> {
+pub enum BackgroundSize<LengthPercentage> {
     /// `<width> <height>`
     Explicit {
         /// Explicit width.
-        width: LengthPercentageOrAuto,
+        width: LengthPercentageOrAuto<LengthPercentage>,
         /// Explicit height.
-        height: LengthPercentageOrAuto,
+        height: LengthPercentageOrAuto<LengthPercentage>,
     },
     /// `cover`
     #[animation(error)]
@@ -38,9 +38,9 @@ pub enum BackgroundSize<LengthPercentageOrAuto> {
     Contain,
 }
 
-impl<LengthPercentageOrAuto> ToCss for BackgroundSize<LengthPercentageOrAuto>
+impl<LengthPercentage> ToCss for BackgroundSize<LengthPercentage>
 where
-    LengthPercentageOrAuto: ToCss + IsAuto,
+    LengthPercentage: ToCss,
 {
     fn to_css<W>(&self, dest: &mut CssWriter<W>) -> fmt::Result
     where
diff --git a/components/style/values/generics/length.rs b/components/style/values/generics/length.rs
index 006739462aa..61be27e4fd2 100644
--- a/components/style/values/generics/length.rs
+++ b/components/style/values/generics/length.rs
@@ -4,7 +4,75 @@
 
 //! Generic types for CSS values related to length.
 
+use crate::parser::{Parse, ParserContext};
 use crate::values::computed::ExtremumLength;
+use cssparser::Parser;
+use style_traits::ParseError;
+
+/// A `<length-percentage> | auto` value.
+#[allow(missing_docs)]
+#[derive(
+    Animate,
+    Clone,
+    ComputeSquaredDistance,
+    Copy,
+    Debug,
+    MallocSizeOf,
+    PartialEq,
+    SpecifiedValueInfo,
+    ToAnimatedValue,
+    ToAnimatedZero,
+    ToComputedValue,
+    ToCss,
+)]
+#[repr(C, u8)]
+pub enum GenericLengthPercentageOrAuto<LengthPercent> {
+    LengthPercentage(LengthPercent),
+    Auto,
+}
+
+pub use self::GenericLengthPercentageOrAuto as LengthPercentageOrAuto;
+
+impl<LengthPercentage> LengthPercentageOrAuto<LengthPercentage> {
+    /// `auto` value.
+    #[inline]
+    pub fn auto() -> Self {
+        LengthPercentageOrAuto::Auto
+    }
+
+    /// Whether this is the `auto` value.
+    #[inline]
+    pub fn is_auto(&self) -> bool {
+        matches!(*self, LengthPercentageOrAuto::Auto)
+    }
+
+    /// A helper function to parse this with quirks or not and so forth.
+    pub fn parse_with<'i, 't>(
+        context: &ParserContext,
+        input: &mut Parser<'i, 't>,
+        parser: impl FnOnce(
+            &ParserContext,
+            &mut Parser<'i, 't>,
+        ) -> Result<LengthPercentage, ParseError<'i>>,
+    ) -> Result<Self, ParseError<'i>> {
+        if input.try(|i| i.expect_ident_matching("auto")).is_ok() {
+            return Ok(LengthPercentageOrAuto::Auto);
+        }
+
+        Ok(LengthPercentageOrAuto::LengthPercentage(parser(
+            context, input,
+        )?))
+    }
+}
+
+impl<LengthPercentage: Parse> Parse for LengthPercentageOrAuto<LengthPercentage> {
+    fn parse<'i, 't>(
+        context: &ParserContext,
+        input: &mut Parser<'i, 't>,
+    ) -> Result<Self, ParseError<'i>> {
+        Self::parse_with(context, input, LengthPercentage::parse)
+    }
+}
 
 /// A generic value for the `width`, `height`, `min-width`, or `min-height` property.
 ///
@@ -13,25 +81,35 @@ use crate::values::computed::ExtremumLength;
 ///
 /// Note that it only accepts non-negative values.
 #[allow(missing_docs)]
-#[cfg_attr(feature = "servo", derive(MallocSizeOf))]
 #[derive(
     Animate,
     Clone,
     ComputeSquaredDistance,
     Copy,
     Debug,
+    MallocSizeOf,
     PartialEq,
     SpecifiedValueInfo,
+    ToAnimatedValue,
     ToAnimatedZero,
     ToComputedValue,
     ToCss,
 )]
-pub enum MozLength<LengthPercentageOrAuto> {
-    LengthPercentageOrAuto(LengthPercentageOrAuto),
+pub enum MozLength<LengthPercentage> {
+    LengthPercentage(LengthPercentage),
+    Auto,
     #[animation(error)]
     ExtremumLength(ExtremumLength),
 }
 
+impl<LengthPercentage> MozLength<LengthPercentage> {
+    /// `auto` value.
+    #[inline]
+    pub fn auto() -> Self {
+        MozLength::Auto
+    }
+}
+
 /// A generic value for the `max-width` or `max-height` property.
 #[allow(missing_docs)]
 #[cfg_attr(feature = "servo", derive(MallocSizeOf))]
@@ -43,12 +121,23 @@ pub enum MozLength<LengthPercentageOrAuto> {
     Debug,
     PartialEq,
     SpecifiedValueInfo,
+    ToAnimatedValue,
     ToAnimatedZero,
     ToComputedValue,
     ToCss,
 )]
-pub enum MaxLength<LengthPercentageOrNone> {
-    LengthPercentageOrNone(LengthPercentageOrNone),
+pub enum MaxLength<LengthPercentage> {
+    LengthPercentage(LengthPercentage),
+    None,
+    #[cfg(feature = "gecko")]
     #[animation(error)]
     ExtremumLength(ExtremumLength),
 }
+
+impl<LengthPercentage> MaxLength<LengthPercentage> {
+    /// `none` value.
+    #[inline]
+    pub fn none() -> Self {
+        MaxLength::None
+    }
+}
diff --git a/components/style/values/specified/background.rs b/components/style/values/specified/background.rs
index 47c66feaef6..b53669abfa8 100644
--- a/components/style/values/specified/background.rs
+++ b/components/style/values/specified/background.rs
@@ -6,14 +6,16 @@
 
 use crate::parser::{Parse, ParserContext};
 use crate::values::generics::background::BackgroundSize as GenericBackgroundSize;
-use crate::values::specified::length::NonNegativeLengthPercentageOrAuto;
+use crate::values::specified::length::{
+    NonNegativeLengthPercentage, NonNegativeLengthPercentageOrAuto,
+};
 use cssparser::Parser;
 use selectors::parser::SelectorParseErrorKind;
 use std::fmt::{self, Write};
 use style_traits::{CssWriter, ParseError, ToCss};
 
 /// A specified value for the `background-size` property.
-pub type BackgroundSize = GenericBackgroundSize<NonNegativeLengthPercentageOrAuto>;
+pub type BackgroundSize = GenericBackgroundSize<NonNegativeLengthPercentage>;
 
 impl Parse for BackgroundSize {
     fn parse<'i, 't>(
diff --git a/components/style/values/specified/gecko.rs b/components/style/values/specified/gecko.rs
index 8259430bf20..42ca5e3e2bf 100644
--- a/components/style/values/specified/gecko.rs
+++ b/components/style/values/specified/gecko.rs
@@ -5,8 +5,8 @@
 //! Specified types for legacy Gecko-only properties.
 
 use crate::parser::{Parse, ParserContext};
-use crate::values::computed::{self, LengthPercentage};
 use crate::values::computed::length::CSSPixelLength;
+use crate::values::computed::{self, LengthPercentage};
 use crate::values::generics::gecko::ScrollSnapPoint as GenericScrollSnapPoint;
 use crate::values::generics::rect::Rect;
 use crate::values::specified::length::LengthPercentage as SpecifiedLengthPercentage;
@@ -28,8 +28,8 @@ impl Parse for ScrollSnapPoint {
         }
         input.expect_function_matching("repeat")?;
         // FIXME(emilio): This won't clamp properly when animating.
-        let length =
-            input.parse_nested_block(|i| SpecifiedLengthPercentage::parse_non_negative(context, i))?;
+        let length = input
+            .parse_nested_block(|i| SpecifiedLengthPercentage::parse_non_negative(context, i))?;
         Ok(GenericScrollSnapPoint::Repeat(length))
     }
 }
@@ -49,9 +49,9 @@ fn parse_pixel_or_percent<'i, 't>(
                 _ => Err(()),
             }
         },
-        Token::Percentage { unit_value, .. } => Ok(
-            LengthPercentage::new_percent(computed::Percentage(unit_value))
-        ),
+        Token::Percentage { unit_value, .. } => Ok(LengthPercentage::new_percent(
+            computed::Percentage(unit_value),
+        )),
         _ => Err(()),
     };
     value.map_err(|()| location.new_custom_error(StyleParseErrorKind::UnspecifiedError))
diff --git a/components/style/values/specified/length.rs b/components/style/values/specified/length.rs
index e83abebc37c..9da17990078 100644
--- a/components/style/values/specified/length.rs
+++ b/components/style/values/specified/length.rs
@@ -10,12 +10,14 @@ use super::{AllowQuirks, Number, Percentage, ToComputedValue};
 use crate::font_metrics::FontMetricsQueryResult;
 use crate::parser::{Parse, ParserContext};
 use crate::values::computed::{self, CSSPixelLength, Context, ExtremumLength};
-use crate::values::generics::length::MaxLength as GenericMaxLength;
-use crate::values::generics::length::MozLength as GenericMozLength;
+use crate::values::generics::length as generics;
+use crate::values::generics::length::{
+    MaxLength as GenericMaxLength, MozLength as GenericMozLength,
+};
 use crate::values::generics::transform::IsZeroLength;
 use crate::values::generics::NonNegative;
 use crate::values::specified::calc::CalcNode;
-use crate::values::{Auto, CSSFloat, Either, IsAuto, Normal};
+use crate::values::{Auto, CSSFloat, Either, Normal};
 use app_units::Au;
 use cssparser::{Parser, Token};
 use euclid::Size2D;
@@ -785,6 +787,16 @@ impl From<computed::Percentage> for LengthPercentage {
     }
 }
 
+impl Parse for LengthPercentage {
+    #[inline]
+    fn parse<'i, 't>(
+        context: &ParserContext,
+        input: &mut Parser<'i, 't>,
+    ) -> Result<Self, ParseError<'i>> {
+        Self::parse_quirky(context, input, AllowQuirks::No)
+    }
+}
+
 impl LengthPercentage {
     #[inline]
     /// Returns a `zero` length.
@@ -844,12 +856,26 @@ impl LengthPercentage {
         Ok(LengthPercentage::Calc(Box::new(calc)))
     }
 
+    /// Parses allowing the unitless length quirk.
+    /// <https://quirks.spec.whatwg.org/#the-unitless-length-quirk>
+    #[inline]
+    pub fn parse_quirky<'i, 't>(
+        context: &ParserContext,
+        input: &mut Parser<'i, 't>,
+        allow_quirks: AllowQuirks,
+    ) -> Result<Self, ParseError<'i>> {
+        Self::parse_internal(context, input, AllowedNumericType::All, allow_quirks)
+    }
+
     /// Parse a non-negative length.
+    ///
+    /// FIXME(emilio): This should be not public and we should use
+    /// NonNegativeLengthPercentage instead.
     #[inline]
     pub fn parse_non_negative<'i, 't>(
         context: &ParserContext,
         input: &mut Parser<'i, 't>,
-    ) -> Result<LengthPercentage, ParseError<'i>> {
+    ) -> Result<Self, ParseError<'i>> {
         Self::parse_non_negative_quirky(context, input, AllowQuirks::No)
     }
 
@@ -859,7 +885,7 @@ impl LengthPercentage {
         context: &ParserContext,
         input: &mut Parser<'i, 't>,
         allow_quirks: AllowQuirks,
-    ) -> Result<LengthPercentage, ParseError<'i>> {
+    ) -> Result<Self, ParseError<'i>> {
         Self::parse_internal(
             context,
             input,
@@ -869,29 +895,6 @@ impl LengthPercentage {
     }
 }
 
-impl Parse for LengthPercentage {
-    #[inline]
-    fn parse<'i, 't>(
-        context: &ParserContext,
-        input: &mut Parser<'i, 't>,
-    ) -> Result<Self, ParseError<'i>> {
-        Self::parse_quirky(context, input, AllowQuirks::No)
-    }
-}
-
-impl LengthPercentage {
-    /// Parses a length or a percentage, allowing the unitless length quirk.
-    /// <https://quirks.spec.whatwg.org/#the-unitless-length-quirk>
-    #[inline]
-    pub fn parse_quirky<'i, 't>(
-        context: &ParserContext,
-        input: &mut Parser<'i, 't>,
-        allow_quirks: AllowQuirks,
-    ) -> Result<Self, ParseError<'i>> {
-        Self::parse_internal(context, input, AllowedNumericType::All, allow_quirks)
-    }
-}
-
 impl IsZeroLength for LengthPercentage {
     #[inline]
     fn is_zero_length(&self) -> bool {
@@ -903,189 +906,64 @@ impl IsZeroLength for LengthPercentage {
     }
 }
 
-/// Either a `<length>`, a `<percentage>`, or the `auto` keyword.
-#[allow(missing_docs)]
-#[derive(Clone, Debug, MallocSizeOf, PartialEq, SpecifiedValueInfo, ToCss)]
-pub enum LengthPercentageOrAuto {
-    LengthPercentage(LengthPercentage),
-    Auto,
-}
+/// A specified type for `<length-percentage> | auto`.
+pub type LengthPercentageOrAuto = generics::LengthPercentageOrAuto<LengthPercentage>;
 
 impl LengthPercentageOrAuto {
-    fn parse_internal<'i, 't>(
-        context: &ParserContext,
-        input: &mut Parser<'i, 't>,
-        num_context: AllowedNumericType,
-        allow_quirks: AllowQuirks,
-    ) -> Result<Self, ParseError<'i>> {
-        if input.try(|i| i.expect_ident_matching("auto")).is_ok() {
-            return Ok(LengthPercentageOrAuto::Auto);
-        }
-
-        Ok(LengthPercentageOrAuto::LengthPercentage(
-            LengthPercentage::parse_internal(context, input, num_context, allow_quirks)?,
-        ))
-    }
-
-    /// Parse a non-negative length, percentage, or auto.
-    #[inline]
-    pub fn parse_non_negative<'i, 't>(
-        context: &ParserContext,
-        input: &mut Parser<'i, 't>,
-    ) -> Result<LengthPercentageOrAuto, ParseError<'i>> {
-        Self::parse_non_negative_quirky(context, input, AllowQuirks::No)
-    }
-
-    /// Parse a non-negative length, percentage, or auto.
-    #[inline]
-    pub fn parse_non_negative_quirky<'i, 't>(
-        context: &ParserContext,
-        input: &mut Parser<'i, 't>,
-        allow_quirks: AllowQuirks,
-    ) -> Result<Self, ParseError<'i>> {
-        Self::parse_internal(
-            context,
-            input,
-            AllowedNumericType::NonNegative,
-            allow_quirks,
-        )
-    }
-
-    /// Returns the `auto` value.
-    pub fn auto() -> Self {
-        LengthPercentageOrAuto::Auto
-    }
-
     /// Returns a value representing a `0` length.
     pub fn zero() -> Self {
-        LengthPercentageOrAuto::LengthPercentage(LengthPercentage::zero())
+        generics::LengthPercentageOrAuto::LengthPercentage(LengthPercentage::zero())
     }
 
     /// Returns a value representing `0%`.
     #[inline]
     pub fn zero_percent() -> Self {
-        LengthPercentageOrAuto::LengthPercentage(LengthPercentage::zero_percent())
+        generics::LengthPercentageOrAuto::LengthPercentage(LengthPercentage::zero_percent())
     }
 
-    /// Parses, with quirks.
+    /// Parses a length or a percentage, allowing the unitless length quirk.
+    /// <https://quirks.spec.whatwg.org/#the-unitless-length-quirk>
     #[inline]
     pub fn parse_quirky<'i, 't>(
         context: &ParserContext,
         input: &mut Parser<'i, 't>,
         allow_quirks: AllowQuirks,
     ) -> Result<Self, ParseError<'i>> {
-        Self::parse_internal(context, input, AllowedNumericType::All, allow_quirks)
-    }
-}
-
-impl Parse for LengthPercentageOrAuto {
-    #[inline]
-    fn parse<'i, 't>(
-        context: &ParserContext,
-        input: &mut Parser<'i, 't>,
-    ) -> Result<Self, ParseError<'i>> {
-        Self::parse_quirky(context, input, AllowQuirks::No)
+        Self::parse_with(context, input, |context, input| {
+            LengthPercentage::parse_quirky(context, input, allow_quirks)
+        })
     }
 }
 
 /// A wrapper of LengthPercentageOrAuto, whose value must be >= 0.
-pub type NonNegativeLengthPercentageOrAuto = NonNegative<LengthPercentageOrAuto>;
-
-impl IsAuto for NonNegativeLengthPercentageOrAuto {
-    #[inline]
-    fn is_auto(&self) -> bool {
-        *self == Self::auto()
-    }
-}
+pub type NonNegativeLengthPercentageOrAuto =
+    generics::LengthPercentageOrAuto<NonNegativeLengthPercentage>;
 
 impl NonNegativeLengthPercentageOrAuto {
-    /// 0
-    #[inline]
+    /// Returns a value representing a `0` length.
     pub fn zero() -> Self {
-        NonNegative(LengthPercentageOrAuto::zero())
+        generics::LengthPercentageOrAuto::LengthPercentage(NonNegativeLengthPercentage::zero())
     }
 
-    /// 0%
+    /// Returns a value representing `0%`.
     #[inline]
     pub fn zero_percent() -> Self {
-        NonNegative(LengthPercentageOrAuto::zero_percent())
-    }
-
-    /// `auto`
-    #[inline]
-    pub fn auto() -> Self {
-        NonNegative(LengthPercentageOrAuto::Auto)
-    }
-}
-
-impl Parse for NonNegativeLengthPercentageOrAuto {
-    #[inline]
-    fn parse<'i, 't>(
-        context: &ParserContext,
-        input: &mut Parser<'i, 't>,
-    ) -> Result<Self, ParseError<'i>> {
-        Ok(NonNegative(LengthPercentageOrAuto::parse_non_negative(
-            context, input,
-        )?))
-    }
-}
-
-/// Either a `<length>`, a `<percentage>`, or the `none` keyword.
-#[derive(Clone, Debug, MallocSizeOf, PartialEq, SpecifiedValueInfo, ToCss)]
-#[allow(missing_docs)]
-pub enum LengthPercentageOrNone {
-    LengthPercentage(LengthPercentage),
-    None,
-}
-
-impl LengthPercentageOrNone {
-    fn parse_internal<'i, 't>(
-        context: &ParserContext,
-        input: &mut Parser<'i, 't>,
-        num_context: AllowedNumericType,
-        allow_quirks: AllowQuirks,
-    ) -> Result<Self, ParseError<'i>> {
-        if input.try(|i| i.expect_ident_matching("none")).is_ok() {
-            return Ok(LengthPercentageOrNone::None);
-        }
-
-        Ok(LengthPercentageOrNone::LengthPercentage(
-            LengthPercentage::parse_internal(context, input, num_context, allow_quirks)?,
-        ))
-    }
-
-    /// Parse a non-negative LengthPercentageOrNone.
-    #[inline]
-    pub fn parse_non_negative<'i, 't>(
-        context: &ParserContext,
-        input: &mut Parser<'i, 't>,
-    ) -> Result<Self, ParseError<'i>> {
-        Self::parse_non_negative_quirky(context, input, AllowQuirks::No)
-    }
-
-    /// Parse a non-negative LengthPercentageOrNone, with quirks.
-    #[inline]
-    pub fn parse_non_negative_quirky<'i, 't>(
-        context: &ParserContext,
-        input: &mut Parser<'i, 't>,
-        allow_quirks: AllowQuirks,
-    ) -> Result<Self, ParseError<'i>> {
-        Self::parse_internal(
-            context,
-            input,
-            AllowedNumericType::NonNegative,
-            allow_quirks,
+        generics::LengthPercentageOrAuto::LengthPercentage(
+            NonNegativeLengthPercentage::zero_percent(),
         )
     }
-}
 
-impl Parse for LengthPercentageOrNone {
+    /// Parses a non-negative length-percentage, allowing the unitless length
+    /// quirk.
     #[inline]
-    fn parse<'i, 't>(
+    pub fn parse_quirky<'i, 't>(
         context: &ParserContext,
         input: &mut Parser<'i, 't>,
+        allow_quirks: AllowQuirks,
     ) -> Result<Self, ParseError<'i>> {
-        Self::parse_internal(context, input, AllowedNumericType::All, AllowQuirks::No)
+        Self::parse_with(context, input, |context, input| {
+            NonNegativeLengthPercentage::parse_quirky(context, input, allow_quirks)
+        })
     }
 }
 
@@ -1101,7 +979,7 @@ pub type NonNegativeLengthPercentageOrNormal = Either<NonNegativeLengthPercentag
 impl From<NoCalcLength> for NonNegativeLengthPercentage {
     #[inline]
     fn from(len: NoCalcLength) -> Self {
-        NonNegative::<LengthPercentage>(LengthPercentage::from(len))
+        NonNegative(LengthPercentage::from(len))
     }
 }
 
@@ -1111,7 +989,7 @@ impl Parse for NonNegativeLengthPercentage {
         context: &ParserContext,
         input: &mut Parser<'i, 't>,
     ) -> Result<Self, ParseError<'i>> {
-        LengthPercentage::parse_non_negative(context, input).map(NonNegative::<LengthPercentage>)
+        Self::parse_quirky(context, input, AllowQuirks::No)
     }
 }
 
@@ -1119,7 +997,13 @@ impl NonNegativeLengthPercentage {
     #[inline]
     /// Returns a `zero` length.
     pub fn zero() -> Self {
-        NonNegative::<LengthPercentage>(LengthPercentage::zero())
+        NonNegative(LengthPercentage::zero())
+    }
+
+    #[inline]
+    /// Returns a `0%` value.
+    pub fn zero_percent() -> Self {
+        NonNegative(LengthPercentage::zero_percent())
     }
 
     /// Parses a length or a percentage, allowing the unitless length quirk.
@@ -1130,8 +1014,7 @@ impl NonNegativeLengthPercentage {
         input: &mut Parser<'i, 't>,
         allow_quirks: AllowQuirks,
     ) -> Result<Self, ParseError<'i>> {
-        LengthPercentage::parse_non_negative_quirky(context, input, allow_quirks)
-            .map(NonNegative::<LengthPercentage>)
+        LengthPercentage::parse_non_negative_quirky(context, input, allow_quirks).map(NonNegative)
     }
 }
 
@@ -1168,7 +1051,7 @@ impl LengthOrNumber {
 }
 
 /// A specified value for `min-width`, `min-height`, `width` or `height` property.
-pub type MozLength = GenericMozLength<LengthPercentageOrAuto>;
+pub type MozLength = GenericMozLength<NonNegativeLengthPercentage>;
 
 impl Parse for MozLength {
     fn parse<'i, 't>(
@@ -1190,26 +1073,23 @@ impl MozLength {
             return Ok(GenericMozLength::ExtremumLength(l));
         }
 
-        let length =
-            LengthPercentageOrAuto::parse_non_negative_quirky(context, input, allow_quirks)?;
-        Ok(GenericMozLength::LengthPercentageOrAuto(length))
-    }
+        if input.try(|i| i.expect_ident_matching("auto")).is_ok() {
+            return Ok(GenericMozLength::Auto);
+        }
 
-    /// Returns `auto`.
-    #[inline]
-    pub fn auto() -> Self {
-        GenericMozLength::LengthPercentageOrAuto(LengthPercentageOrAuto::auto())
+        let length = NonNegativeLengthPercentage::parse_quirky(context, input, allow_quirks)?;
+        Ok(GenericMozLength::LengthPercentage(length))
     }
 
     /// Returns `0%`.
     #[inline]
     pub fn zero_percent() -> Self {
-        GenericMozLength::LengthPercentageOrAuto(LengthPercentageOrAuto::zero_percent())
+        GenericMozLength::LengthPercentage(NonNegativeLengthPercentage::zero_percent())
     }
 }
 
 /// A specified value for `max-width` or `max-height` property.
-pub type MaxLength = GenericMaxLength<LengthPercentageOrNone>;
+pub type MaxLength = GenericMaxLength<NonNegativeLengthPercentage>;
 
 impl Parse for MaxLength {
     fn parse<'i, 't>(
@@ -1227,12 +1107,18 @@ impl MaxLength {
         input: &mut Parser<'i, 't>,
         allow_quirks: AllowQuirks,
     ) -> Result<Self, ParseError<'i>> {
-        if let Ok(l) = input.try(ExtremumLength::parse) {
-            return Ok(GenericMaxLength::ExtremumLength(l));
+        #[cfg(feature = "gecko")]
+        {
+            if let Ok(l) = input.try(ExtremumLength::parse) {
+                return Ok(GenericMaxLength::ExtremumLength(l));
+            }
+        }
+
+        if input.try(|i| i.expect_ident_matching("none")).is_ok() {
+            return Ok(GenericMaxLength::None);
         }
 
-        let length =
-            LengthPercentageOrNone::parse_non_negative_quirky(context, input, allow_quirks)?;
-        Ok(GenericMaxLength::LengthPercentageOrNone(length))
+        let length = NonNegativeLengthPercentage::parse_quirky(context, input, allow_quirks)?;
+        Ok(GenericMaxLength::LengthPercentage(length))
     }
 }
diff --git a/components/style/values/specified/mod.rs b/components/style/values/specified/mod.rs
index 2cb267045ac..b37d2554c34 100644
--- a/components/style/values/specified/mod.rs
+++ b/components/style/values/specified/mod.rs
@@ -59,7 +59,7 @@ pub use self::image::{GradientItem, GradientKind, Image, ImageLayer, MozImageRec
 pub use self::length::{AbsoluteLength, CalcLengthPercentage, CharacterWidth};
 pub use self::length::{FontRelativeLength, Length, LengthOrNumber};
 pub use self::length::{LengthPercentage, LengthPercentageOrAuto};
-pub use self::length::{LengthPercentageOrNone, MaxLength, MozLength};
+pub use self::length::{MaxLength, MozLength};
 pub use self::length::{NoCalcLength, ViewportPercentageLength};
 pub use self::length::{NonNegativeLengthPercentage, NonNegativeLengthPercentageOrAuto};
 #[cfg(feature = "gecko")]