gecko-dev/servo/components/style/dom_apis.rs

/* 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 http://mozilla.org/MPL/2.0/. */

//! Generic implementations of some DOM APIs so they can be shared between Servo
//! and Gecko.

use Atom;
use context::QuirksMode;
use dom::{TDocument, TElement, TNode, TShadowRoot};
use invalidation::element::invalidator::{DescendantInvalidationLists, Invalidation};
use invalidation::element::invalidator::{InvalidationProcessor, InvalidationVector};
use selectors::{Element, NthIndexCache, SelectorList};
use selectors::attr::CaseSensitivity;
use selectors::matching::{self, MatchingContext, MatchingMode};
use selectors::parser::{Combinator, Component, LocalName};
use smallvec::SmallVec;
use std::borrow::Borrow;

/// <https://dom.spec.whatwg.org/#dom-element-matches>
pub fn element_matches<E>(
    element: &E,
    selector_list: &SelectorList<E::Impl>,
    quirks_mode: QuirksMode,
) -> bool
where
    E: Element,
{
    let mut context = MatchingContext::new(MatchingMode::Normal, None, None, quirks_mode);
    context.scope_element = Some(element.opaque());
    context.current_host = element.containing_shadow_host().map(|e| e.opaque());
    matching::matches_selector_list(selector_list, element, &mut context)
}

/// <https://dom.spec.whatwg.org/#dom-element-closest>
pub fn element_closest<E>(
    element: E,
    selector_list: &SelectorList<E::Impl>,
    quirks_mode: QuirksMode,
) -> Option<E>
where
    E: Element,
{
    let mut nth_index_cache = NthIndexCache::default();

    let mut context = MatchingContext::new(
        MatchingMode::Normal,
        None,
        Some(&mut nth_index_cache),
        quirks_mode,
    );
    context.scope_element = Some(element.opaque());
    context.current_host = element.containing_shadow_host().map(|e| e.opaque());

    let mut current = Some(element);
    while let Some(element) = current.take() {
        if matching::matches_selector_list(selector_list, &element, &mut context) {
            return Some(element);
        }
        current = element.parent_element();
    }

    return None;
}

/// A selector query abstraction, in order to be generic over QuerySelector and
/// QuerySelectorAll.
pub trait SelectorQuery<E: TElement> {
    /// The output of the query.
    type Output;

    /// Whether the query should stop after the first element has been matched.
    fn should_stop_after_first_match() -> bool;

    /// Append an element matching after the first query.
    fn append_element(output: &mut Self::Output, element: E);

    /// Returns true if the output is empty.
    fn is_empty(output: &Self::Output) -> bool;
}

/// The result of a querySelectorAll call.
pub type QuerySelectorAllResult<E> = SmallVec<[E; 128]>;

/// A query for all the elements in a subtree.
pub struct QueryAll;

impl<E: TElement> SelectorQuery<E> for QueryAll {
    type Output = QuerySelectorAllResult<E>;

    fn should_stop_after_first_match() -> bool {
        false
    }

    fn append_element(output: &mut Self::Output, element: E) {
        output.push(element);
    }

    fn is_empty(output: &Self::Output) -> bool {
        output.is_empty()
    }
}

/// A query for the first in-tree match of all the elements in a subtree.
pub struct QueryFirst;

impl<E: TElement> SelectorQuery<E> for QueryFirst {
    type Output = Option<E>;

    fn should_stop_after_first_match() -> bool {
        true
    }

    fn append_element(output: &mut Self::Output, element: E) {
        if output.is_none() {
            *output = Some(element)
        }
    }

    fn is_empty(output: &Self::Output) -> bool {
        output.is_none()
    }
}

struct QuerySelectorProcessor<'a, E, Q>
where
    E: TElement + 'a,
    Q: SelectorQuery<E>,
    Q::Output: 'a,
{
    results: &'a mut Q::Output,
    matching_context: MatchingContext<'a, E::Impl>,
    selector_list: &'a SelectorList<E::Impl>,
}

impl<'a, E, Q> InvalidationProcessor<'a, E> for QuerySelectorProcessor<'a, E, Q>
where
    E: TElement + 'a,
    Q: SelectorQuery<E>,
    Q::Output: 'a,
{
    fn light_tree_only(&self) -> bool {
        true
    }

    fn collect_invalidations(
        &mut self,
        element: E,
        self_invalidations: &mut InvalidationVector<'a>,
        descendant_invalidations: &mut DescendantInvalidationLists<'a>,
        _sibling_invalidations: &mut InvalidationVector<'a>,
    ) -> bool {
        // TODO(emilio): If the element is not a root element, and
        // selector_list has any descendant combinator, we need to do extra work
        // in order to handle properly things like:
        //
        //   <div id="a">
        //     <div id="b">
        //       <div id="c"></div>
        //     </div>
        //   </div>
        //
        // b.querySelector('#a div'); // Should return "c".
        //
        // For now, assert it's a root element.
        debug_assert!(element.parent_element().is_none());

        let target_vector = if self.matching_context.scope_element.is_some() {
            &mut descendant_invalidations.dom_descendants
        } else {
            self_invalidations
        };

        for selector in self.selector_list.0.iter() {
            target_vector.push(Invalidation::new(selector, 0))
        }

        false
    }

    fn matching_context(&mut self) -> &mut MatchingContext<'a, E::Impl> {
        &mut self.matching_context
    }

    fn should_process_descendants(&mut self, _: E) -> bool {
        if Q::should_stop_after_first_match() {
            return Q::is_empty(&self.results);
        }

        true
    }

    fn invalidated_self(&mut self, e: E) {
        Q::append_element(self.results, e);
    }

    fn recursion_limit_exceeded(&mut self, _e: E) {}
    fn invalidated_descendants(&mut self, _e: E, _child: E) {}
}

fn collect_all_elements<E, Q, F>(root: E::ConcreteNode, results: &mut Q::Output, mut filter: F)
where
    E: TElement,
    Q: SelectorQuery<E>,
    F: FnMut(E) -> bool,
{
    for node in root.dom_descendants() {
        let element = match node.as_element() {
            Some(e) => e,
            None => continue,
        };

        if !filter(element) {
            continue;
        }

        Q::append_element(results, element);
        if Q::should_stop_after_first_match() {
            return;
        }
    }
}

/// Returns whether a given element connected to `root` is descendant of `root`.
///
/// NOTE(emilio): if root == element, this returns false.
fn connected_element_is_descendant_of<E>(element: E, root: E::ConcreteNode) -> bool
where
    E: TElement,
{
    // Optimize for when the root is a document or a shadow root and the element
    // is connected to that root.
    if root.as_document().is_some() {
        debug_assert!(element.as_node().is_in_document(), "Not connected?");
        debug_assert_eq!(
            root,
            root.owner_doc().as_node(),
            "Where did this element come from?",
        );
        return true;
    }

    if root.as_shadow_root().is_some() {
        debug_assert_eq!(
            element.containing_shadow().unwrap().as_node(),
            root,
            "Not connected?"
        );
        return true;
    }

    let mut current = element.as_node().parent_node();
    while let Some(n) = current.take() {
        if n == root {
            return true;
        }

        current = n.parent_node();
    }
    false
}

/// Fast path for iterating over every element with a given id in the document
/// or shadow root that `root` is connected to.
fn fast_connected_elements_with_id<'a, N>(
    root: N,
    id: &Atom,
    quirks_mode: QuirksMode,
) -> Result<&'a [N::ConcreteElement], ()>
where
    N: TNode + 'a,
{
    let case_sensitivity = quirks_mode.classes_and_ids_case_sensitivity();
    if case_sensitivity != CaseSensitivity::CaseSensitive {
        return Err(());
    }

    if root.is_in_document() {
        return root.owner_doc().elements_with_id(id);
    }

    if let Some(shadow) = root.as_shadow_root() {
        return shadow.elements_with_id(id);
    }

    if let Some(shadow) = root.as_element().and_then(|e| e.containing_shadow()) {
        return shadow.elements_with_id(id);
    }

    Err(())
}

/// Collects elements with a given id under `root`, that pass `filter`.
fn collect_elements_with_id<E, Q, F>(
    root: E::ConcreteNode,
    id: &Atom,
    results: &mut Q::Output,
    quirks_mode: QuirksMode,
    mut filter: F,
) where
    E: TElement,
    Q: SelectorQuery<E>,
    F: FnMut(E) -> bool,
{
    let elements = match fast_connected_elements_with_id(root, id, quirks_mode) {
        Ok(elements) => elements,
        Err(()) => {
            let case_sensitivity = quirks_mode.classes_and_ids_case_sensitivity();

            collect_all_elements::<E, Q, _>(root, results, |e| {
                e.has_id(id, case_sensitivity) && filter(e)
            });

            return;
        },
    };

    for element in elements {
        // If the element is not an actual descendant of the root, even though
        // it's connected, we don't really care about it.
        if !connected_element_is_descendant_of(*element, root) {
            continue;
        }

        if !filter(*element) {
            continue;
        }

        Q::append_element(results, *element);
        if Q::should_stop_after_first_match() {
            break;
        }
    }
}

/// Fast paths for querySelector with a single simple selector.
fn query_selector_single_query<E, Q>(
    root: E::ConcreteNode,
    component: &Component<E::Impl>,
    results: &mut Q::Output,
    quirks_mode: QuirksMode,
) -> Result<(), ()>
where
    E: TElement,
    Q: SelectorQuery<E>,
{
    match *component {
        Component::ExplicitUniversalType => {
            collect_all_elements::<E, Q, _>(root, results, |_| true)
        },
        Component::ID(ref id) => {
            collect_elements_with_id::<E, Q, _>(root, id, results, quirks_mode, |_| true);
        },
        Component::Class(ref class) => {
            let case_sensitivity = quirks_mode.classes_and_ids_case_sensitivity();
            collect_all_elements::<E, Q, _>(root, results, |element| {
                element.has_class(class, case_sensitivity)
            })
        },
        Component::LocalName(LocalName {
            ref name,
            ref lower_name,
        }) => collect_all_elements::<E, Q, _>(root, results, |element| {
            if element.is_html_element_in_html_document() {
                element.local_name() == lower_name.borrow()
            } else {
                element.local_name() == name.borrow()
            }
        }),
        // TODO(emilio): More fast paths?
        _ => return Err(()),
    }

    Ok(())
}

/// Fast paths for a given selector query.
///
/// FIXME(emilio, nbp): This may very well be a good candidate for code to be
/// replaced by HolyJit :)
fn query_selector_fast<E, Q>(
    root: E::ConcreteNode,
    selector_list: &SelectorList<E::Impl>,
    results: &mut Q::Output,
    matching_context: &mut MatchingContext<E::Impl>,
) -> Result<(), ()>
where
    E: TElement,
    Q: SelectorQuery<E>,
{
    // We need to return elements in document order, and reordering them
    // afterwards is kinda silly.
    if selector_list.0.len() > 1 {
        return Err(());
    }

    let selector = &selector_list.0[0];
    let quirks_mode = matching_context.quirks_mode();

    // Let's just care about the easy cases for now.
    if selector.len() == 1 {
        return query_selector_single_query::<E, Q>(
            root,
            selector.iter().next().unwrap(),
            results,
            quirks_mode,
        );
    }

    let mut iter = selector.iter();
    let mut combinator: Option<Combinator> = None;

    loop {
        debug_assert!(combinator.map_or(true, |c| !c.is_sibling()));

        'component_loop: for component in &mut iter {
            match *component {
                Component::ID(ref id) => {
                    if combinator.is_none() {
                        // In the rightmost compound, just find descendants of
                        // root that match the selector list with that id.
                        collect_elements_with_id::<E, Q, _>(root, id, results, quirks_mode, |e| {
                            matching::matches_selector_list(selector_list, &e, matching_context)
                        });

                        return Ok(());
                    }

                    let elements =
                        fast_connected_elements_with_id(root, id, quirks_mode)?;
                    if elements.is_empty() {
                        return Ok(());
                    }

                    // Results need to be in document order. Let's not bother
                    // reordering or deduplicating nodes, which we would need to
                    // do if one element with the given id were a descendant of
                    // another element with that given id.
                    if !Q::should_stop_after_first_match() && elements.len() > 1 {
                        continue;
                    }

                    for element in elements {
                        // If the element is not a descendant of the root, then
                        // it may have descendants that match our selector that
                        // _are_ descendants of the root, and other descendants
                        // that match our selector that are _not_.
                        //
                        // So we can't just walk over the element's descendants
                        // and match the selector against all of them, nor can
                        // we skip looking at this element's descendants.
                        //
                        // Give up on trying to optimize based on this id and
                        // keep walking our selector.
                        if !connected_element_is_descendant_of(*element, root) {
                            continue 'component_loop;
                        }

                        query_selector_slow::<E, Q>(
                            element.as_node(),
                            selector_list,
                            results,
                            matching_context,
                        );

                        if Q::should_stop_after_first_match() && !Q::is_empty(&results) {
                            break;
                        }
                    }

                    return Ok(());
                },
                _ => {},
            }
        }

        loop {
            let next_combinator = match iter.next_sequence() {
                None => return Err(()),
                Some(c) => c,
            };

            // We don't want to scan stuff affected by sibling combinators,
            // given we scan the subtree of elements with a given id (and we
            // don't want to care about scanning the siblings' subtrees).
            if next_combinator.is_sibling() {
                // Advance to the next combinator.
                for _ in &mut iter {}
                continue;
            }

            combinator = Some(next_combinator);
            break;
        }
    }
}

// Slow path for a given selector query.
fn query_selector_slow<E, Q>(
    root: E::ConcreteNode,
    selector_list: &SelectorList<E::Impl>,
    results: &mut Q::Output,
    matching_context: &mut MatchingContext<E::Impl>,
) where
    E: TElement,
    Q: SelectorQuery<E>,
{
    collect_all_elements::<E, Q, _>(root, results, |element| {
        matching::matches_selector_list(selector_list, &element, matching_context)
    });
}

/// Whether the invalidation machinery should be used for this query.
#[derive(PartialEq)]
pub enum MayUseInvalidation {
    /// We may use it if we deem it useful.
    Yes,
    /// Don't use it.
    No,
}

/// <https://dom.spec.whatwg.org/#dom-parentnode-queryselector>
pub fn query_selector<E, Q>(
    root: E::ConcreteNode,
    selector_list: &SelectorList<E::Impl>,
    results: &mut Q::Output,
    may_use_invalidation: MayUseInvalidation,
) where
    E: TElement,
    Q: SelectorQuery<E>,
{
    use invalidation::element::invalidator::TreeStyleInvalidator;

    let quirks_mode = root.owner_doc().quirks_mode();

    let mut nth_index_cache = NthIndexCache::default();
    let mut matching_context = MatchingContext::new(
        MatchingMode::Normal,
        None,
        Some(&mut nth_index_cache),
        quirks_mode,
    );

    let root_element = root.as_element();
    matching_context.scope_element = root_element.map(|e| e.opaque());
    matching_context.current_host = match root_element {
        Some(root) => root.containing_shadow_host().map(|host| host.opaque()),
        None => root.as_shadow_root().map(|root| root.host().opaque()),
    };

    let fast_result =
        query_selector_fast::<E, Q>(root, selector_list, results, &mut matching_context);

    if fast_result.is_ok() {
        return;
    }

    // Slow path: Use the invalidation machinery if we're a root, and tree
    // traversal otherwise.
    //
    // See the comment in collect_invalidations to see why only if we're a root.
    //
    // The invalidation mechanism is only useful in presence of combinators.
    //
    // We could do that check properly here, though checking the length of the
    // selectors is a good heuristic.
    //
    // A selector with a combinator needs to have a length of at least 3: A
    // simple selector, a combinator, and another simple selector.
    let invalidation_may_be_useful = may_use_invalidation == MayUseInvalidation::Yes &&
        selector_list.0.iter().any(|s| s.len() > 2);

    if root_element.is_some() || !invalidation_may_be_useful {
        query_selector_slow::<E, Q>(root, selector_list, results, &mut matching_context);
    } else {
        let mut processor = QuerySelectorProcessor::<E, Q> {
            results,
            matching_context,
            selector_list,
        };

        for node in root.dom_children() {
            if let Some(e) = node.as_element() {
                TreeStyleInvalidator::new(e, /* stack_limit_checker = */ None, &mut processor)
                    .invalidate();
            }
        }
    }
}