style: Part 1: Implement @scroll-timeline in style system

Define the data structure for @scroll-timeline rule, the parsing code,
and the serialization.

Differential Revision: https://phabricator.services.mozilla.com/D125764

components/style/stylesheets/mod.rs

@@ -20,6 +20,7 @@ mod page_rule;
 mod rule_list;
 mod rule_parser;
 mod rules_iterator;
+pub mod scroll_timeline_rule;
 mod style_rule;
 mod stylesheet;
 pub mod supports_rule;

components/style/stylesheets/scroll_timeline_rule.rs

@@ -0,0 +1,315 @@
+/* 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 https://mozilla.org/MPL/2.0/. */
+
+//! scroll-timeline-at-rule: https://drafts.csswg.org/scroll-animations/#scroll-timeline-at-rule
+
+use crate::parser::{Parse, ParserContext};
+use crate::shared_lock::{SharedRwLockReadGuard, ToCssWithGuard};
+use crate::str::CssStringWriter;
+use crate::values::specified::{LengthPercentage, Number};
+use crate::values::{AtomIdent, TimelineName};
+use cssparser::{AtRuleParser, CowRcStr, DeclarationParser, Parser, SourceLocation, Token};
+use selectors::parser::SelectorParseErrorKind;
+use std::fmt::{self, Debug, Write};
+use style_traits::{CssWriter, ParseError, StyleParseErrorKind, ToCss};
+
+/// A [`@scroll-timeline`][descriptors] rule.
+///
+/// [descriptors] https://drafts.csswg.org/scroll-animations/#scroll-timeline-descriptors
+#[derive(Clone, Debug, ToShmem)]
+pub struct ScrollTimelineRule {
+    /// The name of the current scroll timeline.
+    pub name: TimelineName,
+    /// The descriptors.
+    pub descriptors: ScrollTimelineDescriptors,
+    /// The line and column of the rule's source code.
+    pub source_location: SourceLocation,
+}
+
+impl ToCssWithGuard for ScrollTimelineRule {
+    fn to_css(&self, _guard: &SharedRwLockReadGuard, dest: &mut CssStringWriter) -> fmt::Result {
+        let mut dest = CssWriter::new(dest);
+        dest.write_str("@scroll-timeline ")?;
+        self.name.to_css(&mut dest)?;
+        dest.write_str(" { ")?;
+        self.descriptors.to_css(&mut dest)?;
+        dest.write_str("}")
+    }
+}
+
+/// The descriptors of @scroll-timeline.
+///
+/// https://drafts.csswg.org/scroll-animations/#scroll-timeline-descriptors
+#[derive(Clone, Debug, Default, ToShmem)]
+pub struct ScrollTimelineDescriptors {
+    /// The source of the current scroll timeline.
+    pub source: Option<Source>,
+    /// The orientation of the current scroll timeline.
+    pub orientation: Option<Orientation>,
+    /// The scroll timeline's scrollOffsets.
+    pub offsets: Option<ScrollOffsets>,
+}
+
+impl Parse for ScrollTimelineDescriptors {
+    fn parse<'i, 't>(
+        context: &ParserContext,
+        input: &mut Parser<'i, 't>,
+    ) -> Result<Self, ParseError<'i>> {
+        use crate::cssparser::DeclarationListParser;
+        use crate::error_reporting::ContextualParseError;
+
+        let mut descriptors = ScrollTimelineDescriptors::default();
+        let parser = ScrollTimelineDescriptorsParser {
+            context,
+            descriptors: &mut descriptors,
+        };
+        let mut iter = DeclarationListParser::new(input, parser);
+        while let Some(declaration) = iter.next() {
+            if let Err((error, slice)) = declaration {
+                let location = error.location;
+                let error = ContextualParseError::UnsupportedRule(slice, error);
+                context.log_css_error(location, error)
+            }
+        }
+
+        Ok(descriptors)
+    }
+}
+
+// Basically, this is used for the serialization of CSSScrollTimelineRule, so we follow the
+// instructions in https://drafts.csswg.org/scroll-animations-1/#serialize-a-cssscrolltimelinerule.
+impl ToCss for ScrollTimelineDescriptors {
+    fn to_css<W>(&self, dest: &mut CssWriter<W>) -> fmt::Result
+    where
+        W: Write,
+    {
+        if let Some(ref value) = self.source {
+            dest.write_str("source: ")?;
+            value.to_css(dest)?;
+            dest.write_str("; ")?;
+        }
+
+        if let Some(ref value) = self.orientation {
+            dest.write_str("orientation: ")?;
+            value.to_css(dest)?;
+            dest.write_str("; ")?;
+        }
+
+        // https://github.com/w3c/csswg-drafts/issues/6617
+        if let Some(ref value) = self.offsets {
+            dest.write_str("scroll-offsets: ")?;
+            value.to_css(dest)?;
+            dest.write_str("; ")?;
+        }
+        Ok(())
+    }
+}
+
+struct ScrollTimelineDescriptorsParser<'a, 'b: 'a> {
+    context: &'a ParserContext<'b>,
+    descriptors: &'a mut ScrollTimelineDescriptors,
+}
+
+impl<'a, 'b, 'i> AtRuleParser<'i> for ScrollTimelineDescriptorsParser<'a, 'b> {
+    type Prelude = ();
+    type AtRule = ();
+    type Error = StyleParseErrorKind<'i>;
+}
+
+impl<'a, 'b, 'i> DeclarationParser<'i> for ScrollTimelineDescriptorsParser<'a, 'b> {
+    type Declaration = ();
+    type Error = StyleParseErrorKind<'i>;
+
+    fn parse_value<'t>(
+        &mut self,
+        name: CowRcStr<'i>,
+        input: &mut Parser<'i, 't>,
+    ) -> Result<(), ParseError<'i>> {
+        macro_rules! parse_descriptor {
+            (
+                $( $name: tt / $ident: ident, )*
+            ) => {
+                match_ignore_ascii_case! { &*name,
+                    $(
+                        $name => {
+                            let value = input.parse_entirely(|i| Parse::parse(self.context, i))?;
+                            self.descriptors.$ident = Some(value)
+                        },
+                    )*
+                    _ => {
+                        return Err(input.new_custom_error(
+                            SelectorParseErrorKind::UnexpectedIdent(name.clone()),
+                        ))
+                    }
+                }
+            }
+        }
+        parse_descriptor! {
+            "source" / source,
+            "orientation" / orientation,
+            "scroll-offsets" / offsets,
+        };
+        Ok(())
+    }
+}
+
+/// The scroll-timeline source.
+///
+/// https://drafts.csswg.org/scroll-animations/#descdef-scroll-timeline-source
+#[derive(Clone, Debug, Parse, PartialEq, ToCss, ToShmem)]
+pub enum Source {
+    /// The scroll container.
+    Selector(ScrollTimelineSelector),
+    /// The initial value. The scrollingElement of the Document associated with the Window that is
+    /// the current global object.
+    Auto,
+    /// Null. However, it's not clear what is the expected behavior of this. See the spec issue:
+    /// https://drafts.csswg.org/scroll-animations/#issue-0d1e73bd
+    None,
+}
+
+/// The scroll-timeline orientation.
+/// https://drafts.csswg.org/scroll-animations/#descdef-scroll-timeline-orientation
+///
+/// Note: the initial orientation is auto, and we will treat it as block, the same as the
+/// definition of ScrollTimelineOptions (WebIDL API).
+/// https://drafts.csswg.org/scroll-animations/#dom-scrolltimelineoptions-orientation
+#[derive(Clone, Copy, Debug, MallocSizeOf, Eq, Parse, PartialEq, PartialOrd, ToCss, ToShmem)]
+pub enum Orientation {
+    /// The initial value.
+    Auto,
+    /// The direction along the block axis. This is the default value.
+    Block,
+    /// The direction along the inline axis
+    Inline,
+    /// The physical horizontal direction.
+    Horizontal,
+    /// The physical vertical direction.
+    Vertical,
+}
+
+/// Scroll-timeline offsets. We treat None as an empty vector.
+/// value: none | <scroll-timeline-offset>#
+///
+/// https://drafts.csswg.org/scroll-animations/#descdef-scroll-timeline-scroll-offsets
+#[derive(Clone, Debug, ToCss, ToShmem)]
+#[css(comma)]
+pub struct ScrollOffsets(#[css(if_empty = "none", iterable)] Box<[ScrollTimelineOffset]>);
+
+impl Parse for ScrollOffsets {
+    fn parse<'i, 't>(
+        context: &ParserContext,
+        input: &mut Parser<'i, 't>,
+    ) -> Result<Self, ParseError<'i>> {
+        if input.try_parse(|i| i.expect_ident_matching("none")).is_ok() {
+            return Ok(ScrollOffsets(Box::new([])));
+        }
+
+        Ok(ScrollOffsets(
+            input
+                .parse_comma_separated(|i| ScrollTimelineOffset::parse(context, i))?
+                .into_boxed_slice(),
+        ))
+    }
+}
+
+/// A <scroll-timeline-offset>.
+/// value: auto | <length-percentage> | <element-offset>
+///
+/// https://drafts.csswg.org/scroll-animations/#typedef-scroll-timeline-offset
+#[derive(Clone, Debug, Parse, PartialEq, ToCss, ToShmem)]
+pub enum ScrollTimelineOffset {
+    /// The initial value. A container-based offset.
+    Auto,
+    /// A container-based offset with the distance indicated by the value along source's scroll
+    /// range in orientation.
+    LengthPercentage(LengthPercentage),
+    /// An element-based offset.
+    ElementOffset(ElementOffset),
+}
+
+/// An <element-offset-edge>.
+///
+/// https://drafts.csswg.org/scroll-animations-1/#typedef-element-offset-edge
+#[derive(Clone, Copy, Debug, MallocSizeOf, Eq, Parse, PartialEq, PartialOrd, ToCss, ToShmem)]
+pub enum ElementOffsetEdge {
+    /// Start edge
+    Start,
+    /// End edge.
+    End,
+}
+
+/// An <element-offset>.
+/// value: selector( <id-selector> ) [<element-offset-edge> || <number>]?
+///
+/// https://drafts.csswg.org/scroll-animations-1/#typedef-element-offset
+#[derive(Clone, Debug, PartialEq, ToCss, ToShmem)]
+pub struct ElementOffset {
+    /// The target whose intersection with source's scrolling box determines the concrete scroll
+    /// offset.
+    target: ScrollTimelineSelector,
+    /// An optional value of <element-offset-edge>. If not provided, the default value is start.
+    edge: Option<ElementOffsetEdge>,
+    /// An optional value of threshold. If not provided, the default value is 0.
+    threshold: Option<Number>,
+}
+
+impl Parse for ElementOffset {
+    fn parse<'i, 't>(
+        context: &ParserContext,
+        input: &mut Parser<'i, 't>,
+    ) -> Result<Self, ParseError<'i>> {
+        let target = ScrollTimelineSelector::parse(context, input)?;
+
+        // Parse `[<element-offset-edge> || <number>]?`
+        let mut edge = input.try_parse(ElementOffsetEdge::parse).ok();
+        let threshold = input.try_parse(|i| Number::parse(context, i)).ok();
+        if edge.is_none() {
+            edge = input.try_parse(ElementOffsetEdge::parse).ok();
+        }
+
+        Ok(ElementOffset {
+            target,
+            edge,
+            threshold,
+        })
+    }
+}
+
+/// The type of the selector ID.
+#[derive(Clone, Eq, PartialEq, ToShmem)]
+pub struct ScrollTimelineSelector(AtomIdent);
+
+impl Parse for ScrollTimelineSelector {
+    fn parse<'i, 't>(
+        _context: &ParserContext,
+        input: &mut Parser<'i, 't>,
+    ) -> Result<Self, ParseError<'i>> {
+        // Parse `selector(<id-selector>)`.
+        input.expect_function_matching("selector")?;
+        input.parse_nested_block(|i| match i.next()? {
+            Token::IDHash(id) => Ok(ScrollTimelineSelector(id.as_ref().into())),
+            _ => Err(i.new_custom_error(StyleParseErrorKind::UnspecifiedError)),
+        })
+    }
+}
+
+impl ToCss for ScrollTimelineSelector {
+    fn to_css<W>(&self, dest: &mut CssWriter<W>) -> fmt::Result
+    where
+        W: Write,
+    {
+        use crate::cssparser::ToCss as CssparserToCss;
+        dest.write_str("selector(")?;
+        dest.write_char('#')?;
+        self.0.to_css(dest)?;
+        dest.write_char(')')
+    }
+}
+
+impl Debug for ScrollTimelineSelector {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        self.to_css(&mut CssWriter::new(f))
+    }
+}

components/style/values/mod.rs

@@ -464,29 +464,33 @@ impl ToCss for CustomIdent {
     }
 }
 
+/// The <timeline-name> or <keyframes-name>.
+/// The definition of these two names are the same, so we use the same type for them.
+///
+/// <https://drafts.csswg.org/css-animations-2/#typedef-timeline-name>
 /// <https://drafts.csswg.org/css-animations/#typedef-keyframes-name>
 #[derive(
     Clone, Debug, MallocSizeOf, SpecifiedValueInfo, ToComputedValue, ToResolvedValue, ToShmem,
 )]
-pub enum KeyframesName {
+pub enum TimelineOrKeyframesName {
     /// <custom-ident>
     Ident(CustomIdent),
     /// <string>
     QuotedString(Atom),
 }
 
-impl KeyframesName {
+impl TimelineOrKeyframesName {
     /// <https://drafts.csswg.org/css-animations/#dom-csskeyframesrule-name>
     pub fn from_ident(value: &str) -> Self {
         let location = SourceLocation { line: 0, column: 0 };
         let custom_ident = CustomIdent::from_ident(location, &value.into(), &["none"]).ok();
         match custom_ident {
-            Some(ident) => KeyframesName::Ident(ident),
-            None => KeyframesName::QuotedString(value.into()),
+            Some(ident) => Self::Ident(ident),
+            None => Self::QuotedString(value.into()),
         }
     }
 
-    /// Create a new KeyframesName from Atom.
+    /// Create a new TimelineOrKeyframesName from Atom.
     #[cfg(feature = "gecko")]
     pub fn from_atom(atom: Atom) -> Self {
         debug_assert_ne!(atom, atom!(""));
@@ -494,19 +498,19 @@ impl KeyframesName {
         // FIXME: We might want to preserve <string>, but currently Gecko
         // stores both of <custom-ident> and <string> into nsAtom, so
         // we can't tell it.
-        KeyframesName::Ident(CustomIdent(atom))
+        Self::Ident(CustomIdent(atom))
     }
 
     /// The name as an Atom
     pub fn as_atom(&self) -> &Atom {
         match *self {
-            KeyframesName::Ident(ref ident) => &ident.0,
-            KeyframesName::QuotedString(ref atom) => atom,
+            Self::Ident(ref ident) => &ident.0,
+            Self::QuotedString(ref atom) => atom,
         }
     }
 }
 
-impl Eq for KeyframesName {}
+impl Eq for TimelineOrKeyframesName {}
 
 /// A trait that returns whether a given type is the `auto` value or not. So far
 /// only needed for background-size serialization, which special-cases `auto`.
@@ -515,13 +519,13 @@ pub trait IsAuto {
     fn is_auto(&self) -> bool;
 }
 
-impl PartialEq for KeyframesName {
+impl PartialEq for TimelineOrKeyframesName {
     fn eq(&self, other: &Self) -> bool {
         self.as_atom() == other.as_atom()
     }
 }
 
-impl hash::Hash for KeyframesName {
+impl hash::Hash for TimelineOrKeyframesName {
     fn hash<H>(&self, state: &mut H)
     where
         H: hash::Hasher,
@@ -530,32 +534,40 @@ impl hash::Hash for KeyframesName {
     }
 }
 
-impl Parse for KeyframesName {
+impl Parse for TimelineOrKeyframesName {
     fn parse<'i, 't>(
         _context: &ParserContext,
         input: &mut Parser<'i, 't>,
     ) -> Result<Self, ParseError<'i>> {
         let location = input.current_source_location();
         match *input.next()? {
-            Token::Ident(ref s) => Ok(KeyframesName::Ident(CustomIdent::from_ident(
+            Token::Ident(ref s) => Ok(Self::Ident(CustomIdent::from_ident(
                 location,
                 s,
                 &["none"],
             )?)),
-            Token::QuotedString(ref s) => Ok(KeyframesName::QuotedString(Atom::from(s.as_ref()))),
+            Token::QuotedString(ref s) => {
+                Ok(Self::QuotedString(Atom::from(s.as_ref())))
+            },
             ref t => Err(location.new_unexpected_token_error(t.clone())),
         }
     }
 }
 
-impl ToCss for KeyframesName {
+impl ToCss for TimelineOrKeyframesName {
     fn to_css<W>(&self, dest: &mut CssWriter<W>) -> fmt::Result
     where
         W: Write,
     {
         match *self {
-            KeyframesName::Ident(ref ident) => ident.to_css(dest),
-            KeyframesName::QuotedString(ref atom) => atom.to_string().to_css(dest),
+            Self::Ident(ref ident) => ident.to_css(dest),
+            Self::QuotedString(ref atom) => atom.to_string().to_css(dest),
         }
     }
 }
+
+/// The typedef of <timeline-name>.
+pub type TimelineName = TimelineOrKeyframesName;
+
+/// The typedef of <keyframes-name>.
+pub type KeyframesName = TimelineOrKeyframesName;