style: Support multiple track sizes for grid-auto-{columns|rows}.

Support `<track-size>+` on the implicit track sizing properties,
grid-auto-columns and grid-auto-rows.

Differential Revision: https://phabricator.services.mozilla.com/D38408

components/style/values/computed/mod.rs

@@ -7,6 +7,7 @@
 use self::transform::DirectionVector;
 use super::animated::ToAnimatedValue;
 use super::generics::grid::GridTemplateComponent as GenericGridTemplateComponent;
+use super::generics::grid::ImplicitGridTracks as GenericImplicitGridTracks;
 use super::generics::grid::{GenericGridLine, GenericTrackBreadth};
 use super::generics::grid::{GenericTrackSize, TrackList as GenericTrackList};
 use super::generics::transform::IsParallelTo;
@@ -696,6 +697,9 @@ pub type TrackBreadth = GenericTrackBreadth<LengthPercentage>;
 /// The computed value of a grid `<track-size>`
 pub type TrackSize = GenericTrackSize<LengthPercentage>;
 
+/// The computed value of a grid `<track-size>+`
+pub type ImplicitGridTracks = GenericImplicitGridTracks<TrackSize>;
+
 /// The computed value of a grid `<track-list>`
 /// (could also be `<auto-track-list>` or `<explicit-track-list>`)
 pub type TrackList = GenericTrackList<LengthPercentage, Integer>;

components/style/values/generics/grid.rs

@@ -290,16 +290,17 @@ impl<L> TrackSize<L> {
     }
 }
 
-impl<L> Default for TrackSize<L> {
-    fn default() -> Self {
-        TrackSize::Breadth(TrackBreadth::Auto)
+impl<L: PartialEq> TrackSize<L> {
+    /// Return true if it is `auto`.
+    #[inline]
+    pub fn is_auto(&self) -> bool {
+        *self == TrackSize::Breadth(TrackBreadth::Auto)
     }
 }
 
-impl<L: PartialEq> TrackSize<L> {
-    /// Returns true if current TrackSize is same as default.
-    pub fn is_default(&self) -> bool {
-        *self == TrackSize::default()
+impl<L> Default for TrackSize<L> {
+    fn default() -> Self {
+        TrackSize::Breadth(TrackBreadth::Auto)
     }
 }
 
@@ -334,6 +335,39 @@ impl<L: ToCss> ToCss for TrackSize<L> {
     }
 }
 
+/// A `<track-size>+`.
+/// We use the empty slice as `auto`, and always parse `auto` as an empty slice.
+/// This means it's impossible to have a slice containing only one auto item.
+#[derive(
+    Clone,
+    Debug,
+    Default,
+    MallocSizeOf,
+    PartialEq,
+    SpecifiedValueInfo,
+    ToComputedValue,
+    ToCss,
+    ToResolvedValue,
+    ToShmem,
+)]
+#[repr(transparent)]
+pub struct GenericImplicitGridTracks<T>(
+    #[css(if_empty = "auto", iterable)] pub crate::OwnedSlice<T>,
+);
+
+pub use self::GenericImplicitGridTracks as ImplicitGridTracks;
+
+impl<T: fmt::Debug + Default + PartialEq> ImplicitGridTracks<T> {
+    /// Returns true if current value is same as its initial value (i.e. auto).
+    pub fn is_initial(&self) -> bool {
+        debug_assert_ne!(
+            *self,
+            ImplicitGridTracks(crate::OwnedSlice::from(vec![Default::default()]))
+        );
+        self.0.is_empty()
+    }
+}
+
 /// Helper function for serializing identifiers with a prefix and suffix, used
 /// for serializing <line-names> (in grid).
 pub fn concat_serialize_idents<W>(

components/style/values/specified/grid.rs

@@ -6,8 +6,8 @@
 //! [grids](https://drafts.csswg.org/css-grid/)
 
 use crate::parser::{Parse, ParserContext};
-use crate::values::generics::grid::{GridTemplateComponent, RepeatCount, TrackBreadth};
-use crate::values::generics::grid::{LineNameList, TrackRepeat, TrackSize};
+use crate::values::generics::grid::{GridTemplateComponent, ImplicitGridTracks, RepeatCount};
+use crate::values::generics::grid::{LineNameList, TrackBreadth, TrackRepeat, TrackSize};
 use crate::values::generics::grid::{TrackList, TrackListValue};
 use crate::values::specified::{Integer, LengthPercentage};
 use crate::values::{CSSFloat, CustomIdent};
@@ -95,6 +95,21 @@ impl Parse for TrackSize<LengthPercentage> {
     }
 }
 
+impl Parse for ImplicitGridTracks<TrackSize<LengthPercentage>> {
+    fn parse<'i, 't>(
+        context: &ParserContext,
+        input: &mut Parser<'i, 't>,
+    ) -> Result<Self, ParseError<'i>> {
+        use style_traits::{Separator, Space};
+        let track_sizes = Space::parse(input, |i| TrackSize::parse(context, i))?;
+        if track_sizes.len() == 1 && track_sizes[0].is_auto() {
+            //`auto`, which is the initial value, is always represented by an empty slice.
+            return Ok(Default::default());
+        }
+        return Ok(ImplicitGridTracks(track_sizes.into()));
+    }
+}
+
 /// Parse the grid line names into a vector of owned strings.
 ///
 /// <https://drafts.csswg.org/css-grid/#typedef-line-names>

components/style/values/specified/mod.rs

@@ -8,6 +8,7 @@
 
 use super::computed::transform::DirectionVector;
 use super::computed::{Context, ToComputedValue};
+use super::generics::grid::ImplicitGridTracks as GenericImplicitGridTracks;
 use super::generics::grid::{GridLine as GenericGridLine, TrackBreadth as GenericTrackBreadth};
 use super::generics::grid::{TrackList as GenericTrackList, TrackSize as GenericTrackSize};
 use super::generics::transform::IsParallelTo;
@@ -626,6 +627,9 @@ pub type TrackBreadth = GenericTrackBreadth<LengthPercentage>;
 /// The specified value of a grid `<track-size>`
 pub type TrackSize = GenericTrackSize<LengthPercentage>;
 
+/// The specified value of a grid `<track-size>+`
+pub type ImplicitGridTracks = GenericImplicitGridTracks<TrackSize>;
+
 /// The specified value of a grid `<track-list>`
 /// (could also be `<auto-track-list>` or `<explicit-track-list>`)
 pub type TrackList = GenericTrackList<LengthPercentage, Integer>;