1 files changed, 239 insertions, 0 deletions
diff --git a/servo/components/style/stylesheets/layer_rule.rs b/servo/components/style/stylesheets/layer_rule.rs
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+++ b/servo/components/style/stylesheets/layer_rule.rs
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+/* 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/. */
+
+//! A [`@layer`][layer] rule.
+//!
+//! [layer]: https://drafts.csswg.org/css-cascade-5/#layering
+
+use crate::parser::{Parse, ParserContext};
+use crate::shared_lock::{DeepCloneParams, DeepCloneWithLock, Locked};
+use crate::shared_lock::{SharedRwLock, SharedRwLockReadGuard, ToCssWithGuard};
+use crate::values::AtomIdent;
+
+use super::CssRules;
+
+use cssparser::{Parser, SourceLocation, Token};
+use servo_arc::Arc;
+use smallvec::SmallVec;
+use std::fmt::{self, Write};
+use style_traits::{CssWriter, ParseError, ToCss};
+
+/// The order of a given layer. We use 16 bits so that we can pack LayerOrder
+/// and CascadeLevel in a single 32-bit struct. If we need more bits we can go
+/// back to packing CascadeLevel in a single byte as we did before.
+#[derive(Clone, Copy, Debug, Eq, Hash, MallocSizeOf, PartialEq, PartialOrd, Ord)]
+pub struct LayerOrder(u16);
+
+impl LayerOrder {
+    /// The order of the root layer.
+    pub const fn root() -> Self {
+        Self(std::u16::MAX - 1)
+    }
+
+    /// The order of the style attribute layer.
+    pub const fn style_attribute() -> Self {
+        Self(std::u16::MAX)
+    }
+
+    /// Returns whether this layer is for the style attribute, which behaves
+    /// differently in terms of !important, see
+    /// https://github.com/w3c/csswg-drafts/issues/6872
+    ///
+    /// (This is a bit silly, mind-you, but it's needed so that revert-layer
+    /// behaves correctly).
+    #[inline]
+    pub fn is_style_attribute_layer(&self) -> bool {
+        *self == Self::style_attribute()
+    }
+
+    /// The first cascade layer order.
+    pub const fn first() -> Self {
+        Self(0)
+    }
+
+    /// Increment the cascade layer order.
+    #[inline]
+    pub fn inc(&mut self) {
+        if self.0 != std::u16::MAX - 1 {
+            self.0 += 1;
+        }
+    }
+}
+
+/// A `<layer-name>`: https://drafts.csswg.org/css-cascade-5/#typedef-layer-name
+#[derive(Clone, Debug, Eq, Hash, MallocSizeOf, PartialEq, ToShmem)]
+pub struct LayerName(pub SmallVec<[AtomIdent; 1]>);
+
+impl LayerName {
+    /// Returns an empty layer name (which isn't a valid final state, so caller
+    /// is responsible to fill up the name before use).
+    pub fn new_empty() -> Self {
+        Self(Default::default())
+    }
+
+    /// Returns a synthesized name for an anonymous layer.
+    pub fn new_anonymous() -> Self {
+        use std::sync::atomic::{AtomicUsize, Ordering};
+        static NEXT_ANONYMOUS_LAYER_NAME: AtomicUsize = AtomicUsize::new(0);
+
+        let mut name = SmallVec::new();
+        let next_id = NEXT_ANONYMOUS_LAYER_NAME.fetch_add(1, Ordering::Relaxed);
+        // The parens don't _technically_ prevent conflicts with authors, as
+        // authors could write escaped parens as part of the identifier, I
+        // think, but highly reduces the possibility.
+        name.push(AtomIdent::from(&*format!("-moz-anon-layer({})", next_id)));
+
+        LayerName(name)
+    }
+
+    /// Returns the names of the layers. That is, for a layer like `foo.bar`,
+    /// it'd return [foo, bar].
+    pub fn layer_names(&self) -> &[AtomIdent] {
+        &self.0
+    }
+}
+
+impl Parse for LayerName {
+    fn parse<'i, 't>(
+        _: &ParserContext,
+        input: &mut Parser<'i, 't>,
+    ) -> Result<Self, ParseError<'i>> {
+        let mut result = SmallVec::new();
+        result.push(AtomIdent::from(&**input.expect_ident()?));
+        loop {
+            let next_name = input.try_parse(|input| -> Result<AtomIdent, ParseError<'i>> {
+                match input.next_including_whitespace()? {
+                    Token::Delim('.') => {},
+                    other => {
+                        let t = other.clone();
+                        return Err(input.new_unexpected_token_error(t));
+                    },
+                }
+
+                let name = match input.next_including_whitespace()? {
+                    Token::Ident(ref ident) => ident,
+                    other => {
+                        let t = other.clone();
+                        return Err(input.new_unexpected_token_error(t));
+                    },
+                };
+
+                Ok(AtomIdent::from(&**name))
+            });
+
+            match next_name {
+                Ok(name) => result.push(name),
+                Err(..) => break,
+            }
+        }
+        Ok(LayerName(result))
+    }
+}
+
+impl ToCss for LayerName {
+    fn to_css<W>(&self, dest: &mut CssWriter<W>) -> fmt::Result
+    where
+        W: Write,
+    {
+        let mut first = true;
+        for name in self.0.iter() {
+            if !first {
+                dest.write_char('.')?;
+            }
+            first = false;
+            name.to_css(dest)?;
+        }
+        Ok(())
+    }
+}
+
+#[derive(Debug, ToShmem)]
+/// A block `@layer <name>? { ... }`
+/// https://drafts.csswg.org/css-cascade-5/#layer-block
+pub struct LayerBlockRule {
+    /// The layer name, or `None` if anonymous.
+    pub name: Option<LayerName>,
+    /// The nested rules.
+    pub rules: Arc<Locked<CssRules>>,
+    /// The source position where this rule was found.
+    pub source_location: SourceLocation,
+}
+
+impl ToCssWithGuard for LayerBlockRule {
+    fn to_css(
+        &self,
+        guard: &SharedRwLockReadGuard,
+        dest: &mut crate::str::CssStringWriter,
+    ) -> fmt::Result {
+        dest.write_str("@layer")?;
+        if let Some(ref name) = self.name {
+            dest.write_char(' ')?;
+            name.to_css(&mut CssWriter::new(dest))?;
+        }
+        self.rules.read_with(guard).to_css_block(guard, dest)
+    }
+}
+
+impl DeepCloneWithLock for LayerBlockRule {
+    fn deep_clone_with_lock(
+        &self,
+        lock: &SharedRwLock,
+        guard: &SharedRwLockReadGuard,
+        params: &DeepCloneParams,
+    ) -> Self {
+        Self {
+            name: self.name.clone(),
+            rules: Arc::new(
+                lock.wrap(
+                    self.rules
+                        .read_with(guard)
+                        .deep_clone_with_lock(lock, guard, params),
+                ),
+            ),
+            source_location: self.source_location.clone(),
+        }
+    }
+}
+
+/// A statement `@layer <name>, <name>, <name>;`
+///
+/// https://drafts.csswg.org/css-cascade-5/#layer-empty
+#[derive(Clone, Debug, ToShmem)]
+pub struct LayerStatementRule {
+    /// The list of layers to sort.
+    pub names: Vec<LayerName>,
+    /// The source position where this rule was found.
+    pub source_location: SourceLocation,
+}
+
+impl ToCssWithGuard for LayerStatementRule {
+    fn to_css(
+        &self,
+        _: &SharedRwLockReadGuard,
+        dest: &mut crate::str::CssStringWriter,
+    ) -> fmt::Result {
+        let mut writer = CssWriter::new(dest);
+        writer.write_str("@layer ")?;
+        let mut first = true;
+        for name in &*self.names {
+            if !first {
+                writer.write_str(", ")?;
+            }
+            first = false;
+            name.to_css(&mut writer)?;
+        }
+        writer.write_char(';')
+    }
+}
+
+impl DeepCloneWithLock for LayerStatementRule {
+    fn deep_clone_with_lock(
+        &self,
+        _: &SharedRwLock,
+        _: &SharedRwLockReadGuard,
+        _: &DeepCloneParams,
+    ) -> Self {
+        self.clone()
+    }
+}