Adding upstream version 110.0.1.upstream/110.0.1upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 364 insertions, 0 deletions

diff --git a/servo/components/selectors/builder.rs b/servo/components/selectors/builder.rs
new file mode 100644
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+++ b/servo/components/selectors/builder.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/. */
+
+//! Helper module to build up a selector safely and efficiently.
+//!
+//! Our selector representation is designed to optimize matching, and has
+//! several requirements:
+//! * All simple selectors and combinators are stored inline in the same buffer
+//!   as Component instances.
+//! * We store the top-level compound selectors from right to left, i.e. in
+//!   matching order.
+//! * We store the simple selectors for each combinator from left to right, so
+//!   that we match the cheaper simple selectors first.
+//!
+//! Meeting all these constraints without extra memmove traffic during parsing
+//! is non-trivial. This module encapsulates those details and presents an
+//! easy-to-use API for the parser.
+
+use crate::parser::{Combinator, Component, Selector, SelectorImpl};
+use crate::sink::Push;
+use servo_arc::{Arc, HeaderWithLength, ThinArc};
+use smallvec::{self, SmallVec};
+use std::cmp;
+use std::iter;
+use std::ptr;
+use std::slice;
+
+/// Top-level SelectorBuilder struct. This should be stack-allocated by the
+/// consumer and never moved (because it contains a lot of inline data that
+/// would be slow to memmov).
+///
+/// After instantation, callers may call the push_simple_selector() and
+/// push_combinator() methods to append selector data as it is encountered
+/// (from left to right). Once the process is complete, callers should invoke
+/// build(), which transforms the contents of the SelectorBuilder into a heap-
+/// allocated Selector and leaves the builder in a drained state.
+#[derive(Debug)]
+pub struct SelectorBuilder<Impl: SelectorImpl> {
+    /// The entire sequence of simple selectors, from left to right, without combinators.
+    ///
+    /// We make this large because the result of parsing a selector is fed into a new
+    /// Arc-ed allocation, so any spilled vec would be a wasted allocation. Also,
+    /// Components are large enough that we don't have much cache locality benefit
+    /// from reserving stack space for fewer of them.
+    simple_selectors: SmallVec<[Component<Impl>; 32]>,
+    /// The combinators, and the length of the compound selector to their left.
+    combinators: SmallVec<[(Combinator, usize); 16]>,
+    /// The length of the current compount selector.
+    current_len: usize,
+}
+
+impl<Impl: SelectorImpl> Default for SelectorBuilder<Impl> {
+    #[inline(always)]
+    fn default() -> Self {
+        SelectorBuilder {
+            simple_selectors: SmallVec::new(),
+            combinators: SmallVec::new(),
+            current_len: 0,
+        }
+    }
+}
+
+impl<Impl: SelectorImpl> Push<Component<Impl>> for SelectorBuilder<Impl> {
+    fn push(&mut self, value: Component<Impl>) {
+        self.push_simple_selector(value);
+    }
+}
+
+impl<Impl: SelectorImpl> SelectorBuilder<Impl> {
+    /// Pushes a simple selector onto the current compound selector.
+    #[inline(always)]
+    pub fn push_simple_selector(&mut self, ss: Component<Impl>) {
+        assert!(!ss.is_combinator());
+        self.simple_selectors.push(ss);
+        self.current_len += 1;
+    }
+
+    /// Completes the current compound selector and starts a new one, delimited
+    /// by the given combinator.
+    #[inline(always)]
+    pub fn push_combinator(&mut self, c: Combinator) {
+        self.combinators.push((c, self.current_len));
+        self.current_len = 0;
+    }
+
+    /// Returns true if combinators have ever been pushed to this builder.
+    #[inline(always)]
+    pub fn has_combinators(&self) -> bool {
+        !self.combinators.is_empty()
+    }
+
+    /// Consumes the builder, producing a Selector.
+    #[inline(always)]
+    pub fn build(
+        &mut self,
+        parsed_pseudo: bool,
+        parsed_slotted: bool,
+        parsed_part: bool,
+    ) -> ThinArc<SpecificityAndFlags, Component<Impl>> {
+        // Compute the specificity and flags.
+        let specificity = specificity(self.simple_selectors.iter());
+        let mut flags = SelectorFlags::empty();
+        if parsed_pseudo {
+            flags |= SelectorFlags::HAS_PSEUDO;
+        }
+        if parsed_slotted {
+            flags |= SelectorFlags::HAS_SLOTTED;
+        }
+        if parsed_part {
+            flags |= SelectorFlags::HAS_PART;
+        }
+        self.build_with_specificity_and_flags(SpecificityAndFlags { specificity, flags })
+    }
+
+    /// Builds with an explicit SpecificityAndFlags. This is separated from build() so
+    /// that unit tests can pass an explicit specificity.
+    #[inline(always)]
+    pub fn build_with_specificity_and_flags(
+        &mut self,
+        spec: SpecificityAndFlags,
+    ) -> ThinArc<SpecificityAndFlags, Component<Impl>> {
+        // First, compute the total number of Components we'll need to allocate
+        // space for.
+        let full_len = self.simple_selectors.len() + self.combinators.len();
+
+        // Create the header.
+        let header = HeaderWithLength::new(spec, full_len);
+
+        // Create the Arc using an iterator that drains our buffers.
+
+        // Use a raw pointer to be able to call set_len despite "borrowing" the slice.
+        // This is similar to SmallVec::drain, but we use a slice here because
+        // we’re gonna traverse it non-linearly.
+        let raw_simple_selectors: *const [Component<Impl>] = &*self.simple_selectors;
+        unsafe {
+            // Panic-safety: if SelectorBuilderIter is not iterated to the end,
+            // some simple selectors will safely leak.
+            self.simple_selectors.set_len(0)
+        }
+        let (rest, current) = split_from_end(unsafe { &*raw_simple_selectors }, self.current_len);
+        let iter = SelectorBuilderIter {
+            current_simple_selectors: current.iter(),
+            rest_of_simple_selectors: rest,
+            combinators: self.combinators.drain(..).rev(),
+        };
+
+        Arc::into_thin(Arc::from_header_and_iter(header, iter))
+    }
+}
+
+struct SelectorBuilderIter<'a, Impl: SelectorImpl> {
+    current_simple_selectors: slice::Iter<'a, Component<Impl>>,
+    rest_of_simple_selectors: &'a [Component<Impl>],
+    combinators: iter::Rev<smallvec::Drain<'a, [(Combinator, usize); 16]>>,
+}
+
+impl<'a, Impl: SelectorImpl> ExactSizeIterator for SelectorBuilderIter<'a, Impl> {
+    fn len(&self) -> usize {
+        self.current_simple_selectors.len() +
+            self.rest_of_simple_selectors.len() +
+            self.combinators.len()
+    }
+}
+
+impl<'a, Impl: SelectorImpl> Iterator for SelectorBuilderIter<'a, Impl> {
+    type Item = Component<Impl>;
+    #[inline(always)]
+    fn next(&mut self) -> Option<Self::Item> {
+        if let Some(simple_selector_ref) = self.current_simple_selectors.next() {
+            // Move a simple selector out of this slice iterator.
+            // This is safe because we’ve called SmallVec::set_len(0) above,
+            // so SmallVec::drop won’t drop this simple selector.
+            unsafe { Some(ptr::read(simple_selector_ref)) }
+        } else {
+            self.combinators.next().map(|(combinator, len)| {
+                let (rest, current) = split_from_end(self.rest_of_simple_selectors, len);
+                self.rest_of_simple_selectors = rest;
+                self.current_simple_selectors = current.iter();
+                Component::Combinator(combinator)
+            })
+        }
+    }
+
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        (self.len(), Some(self.len()))
+    }
+}
+
+fn split_from_end<T>(s: &[T], at: usize) -> (&[T], &[T]) {
+    s.split_at(s.len() - at)
+}
+
+bitflags! {
+    /// Flags that indicate at which point of parsing a selector are we.
+    #[derive(Default, ToShmem)]
+    pub (crate) struct SelectorFlags : u8 {
+        const HAS_PSEUDO = 1 << 0;
+        const HAS_SLOTTED = 1 << 1;
+        const HAS_PART = 1 << 2;
+    }
+}
+
+#[derive(Clone, Copy, Debug, Eq, PartialEq, ToShmem)]
+pub struct SpecificityAndFlags {
+    /// There are two free bits here, since we use ten bits for each specificity
+    /// kind (id, class, element).
+    pub(crate) specificity: u32,
+    /// There's padding after this field due to the size of the flags.
+    pub(crate) flags: SelectorFlags,
+}
+
+impl SpecificityAndFlags {
+    #[inline]
+    pub fn specificity(&self) -> u32 {
+        self.specificity
+    }
+
+    #[inline]
+    pub fn has_pseudo_element(&self) -> bool {
+        self.flags.intersects(SelectorFlags::HAS_PSEUDO)
+    }
+
+    #[inline]
+    pub fn is_slotted(&self) -> bool {
+        self.flags.intersects(SelectorFlags::HAS_SLOTTED)
+    }
+
+    #[inline]
+    pub fn is_part(&self) -> bool {
+        self.flags.intersects(SelectorFlags::HAS_PART)
+    }
+}
+
+const MAX_10BIT: u32 = (1u32 << 10) - 1;
+
+#[derive(Add, AddAssign, Clone, Copy, Default, Eq, Ord, PartialEq, PartialOrd)]
+struct Specificity {
+    id_selectors: u32,
+    class_like_selectors: u32,
+    element_selectors: u32,
+}
+
+impl From<u32> for Specificity {
+    #[inline]
+    fn from(value: u32) -> Specificity {
+        assert!(value <= MAX_10BIT << 20 | MAX_10BIT << 10 | MAX_10BIT);
+        Specificity {
+            id_selectors: value >> 20,
+            class_like_selectors: (value >> 10) & MAX_10BIT,
+            element_selectors: value & MAX_10BIT,
+        }
+    }
+}
+
+impl From<Specificity> for u32 {
+    #[inline]
+    fn from(specificity: Specificity) -> u32 {
+        cmp::min(specificity.id_selectors, MAX_10BIT) << 20 |
+            cmp::min(specificity.class_like_selectors, MAX_10BIT) << 10 |
+            cmp::min(specificity.element_selectors, MAX_10BIT)
+    }
+}
+
+fn specificity<Impl>(iter: slice::Iter<Component<Impl>>) -> u32
+where
+    Impl: SelectorImpl,
+{
+    complex_selector_specificity(iter).into()
+}
+
+fn complex_selector_specificity<Impl>(iter: slice::Iter<Component<Impl>>) -> Specificity
+where
+    Impl: SelectorImpl,
+{
+    fn simple_selector_specificity<Impl>(
+        simple_selector: &Component<Impl>,
+        specificity: &mut Specificity,
+    ) where
+        Impl: SelectorImpl,
+    {
+        match *simple_selector {
+            Component::Combinator(..) => {
+                unreachable!("Found combinator in simple selectors vector?");
+            },
+            Component::Part(..) | Component::PseudoElement(..) | Component::LocalName(..) => {
+                specificity.element_selectors += 1
+            },
+            Component::Slotted(ref selector) => {
+                specificity.element_selectors += 1;
+                // Note that due to the way ::slotted works we only compete with
+                // other ::slotted rules, so the above rule doesn't really
+                // matter, but we do it still for consistency with other
+                // pseudo-elements.
+                //
+                // See: https://github.com/w3c/csswg-drafts/issues/1915
+                *specificity += Specificity::from(selector.specificity());
+            },
+            Component::Host(ref selector) => {
+                specificity.class_like_selectors += 1;
+                if let Some(ref selector) = *selector {
+                    // See: https://github.com/w3c/csswg-drafts/issues/1915
+                    *specificity += Specificity::from(selector.specificity());
+                }
+            },
+            Component::ID(..) => {
+                specificity.id_selectors += 1;
+            },
+            Component::Class(..) |
+            Component::AttributeInNoNamespace { .. } |
+            Component::AttributeInNoNamespaceExists { .. } |
+            Component::AttributeOther(..) |
+            Component::Root |
+            Component::Empty |
+            Component::Scope |
+            Component::Nth(..) |
+            Component::NonTSPseudoClass(..) => {
+                specificity.class_like_selectors += 1;
+            },
+            Component::NthOf(ref nth_of_data) => {
+                // https://drafts.csswg.org/selectors/#specificity-rules:
+                //
+                //     The specificity of the :nth-last-child() pseudo-class,
+                //     like the :nth-child() pseudo-class, combines the
+                //     specificity of a regular pseudo-class with that of its
+                //     selector argument S.
+                specificity.class_like_selectors += 1;
+                *specificity += max_selector_list_specificity(nth_of_data.selectors());
+            },
+            Component::Negation(ref list) | Component::Is(ref list) | Component::Has(ref list) => {
+                // https://drafts.csswg.org/selectors/#specificity-rules:
+                //
+                //     The specificity of an :is(), :not(), or :has() pseudo-class
+                //     is replaced by the specificity of the most specific complex
+                //     selector in its selector list argument.
+                *specificity += max_selector_list_specificity(list);
+            },
+            Component::Where(..) |
+            Component::ExplicitUniversalType |
+            Component::ExplicitAnyNamespace |
+            Component::ExplicitNoNamespace |
+            Component::DefaultNamespace(..) |
+            Component::Namespace(..) => {
+                // Does not affect specificity
+            },
+        }
+    }
+
+    /// Finds the maximum specificity of elements in the list and returns it.
+    fn max_selector_list_specificity<Impl: SelectorImpl>(list: &[Selector<Impl>]) -> Specificity {
+        let max = list
+            .iter()
+            .map(|selector| selector.specificity())
+            .max()
+            .unwrap_or(0);
+        Specificity::from(max)
+    }
+
+    let mut specificity = Default::default();
+    for simple_selector in iter {
+        simple_selector_specificity(&simple_selector, &mut specificity);
+    }
+    specificity
+}