servo/components/style/invalidation/stylesheets.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/. */

//! A collection of invalidations due to changes in which stylesheets affect a
//! document.

#![deny(unsafe_code)]

use Atom;
use LocalName as SelectorLocalName;
use dom::{TElement, TNode};
use fnv::FnvHashSet;
use invalidation::element::restyle_hints::{RESTYLE_SELF, RestyleHint};
use media_queries::Device;
use selector_parser::SelectorImpl;
use selectors::attr::CaseSensitivity;
use selectors::parser::{Component, LocalName, Selector};
use shared_lock::SharedRwLockReadGuard;
use stylesheets::{CssRule, StylesheetInDocument};

/// A style sheet invalidation represents a kind of element or subtree that may
/// need to be restyled. Whether it represents a whole subtree or just a single
/// element is determined by whether the invalidation is stored in the
/// StylesheetInvalidationSet's invalid_scopes or invalid_elements table.
#[derive(Debug, Eq, Hash, PartialEq)]
#[cfg_attr(feature = "servo", derive(HeapSizeOf))]
enum Invalidation {
    /// An element with a given id.
    ID(Atom),
    /// An element with a given class name.
    Class(Atom),
    /// An element with a given local name.
    LocalName { name: SelectorLocalName, lower_name: SelectorLocalName },
}

impl Invalidation {
    fn is_id(&self) -> bool {
        matches!(*self, Invalidation::ID(..))
    }

    fn is_id_or_class(&self) -> bool {
        matches!(*self, Invalidation::ID(..) | Invalidation::Class(..))
    }

    fn matches<E>(&self, element: E) -> bool
        where E: TElement,
    {
        match *self {
            Invalidation::Class(ref class) => {
                // FIXME This should look at the quirks mode of the document to
                // determine case sensitivity.
                element.has_class(class, CaseSensitivity::CaseSensitive)
            }
            Invalidation::ID(ref id) => {
                match element.get_id() {
                    // FIXME This should look at the quirks mode of the document
                    // to determine case sensitivity.
                    Some(element_id) => element_id == *id,
                    None => false,
                }
            }
            Invalidation::LocalName { ref name, ref lower_name } => {
                // This could look at the quirks mode of the document, instead
                // of testing against both names, but it's probably not worth
                // it.
                let local_name = element.get_local_name();
                *local_name == **name || *local_name == **lower_name
            }
        }
    }
}

/// A set of invalidations due to stylesheet additions.
///
/// TODO(emilio): We might be able to do the same analysis for media query
/// changes too (or even selector changes?).
#[cfg_attr(feature = "servo", derive(HeapSizeOf))]
pub struct StylesheetInvalidationSet {
    /// The subtrees we know we have to restyle so far.
    invalid_scopes: FnvHashSet<Invalidation>,
    /// The elements we know we have to restyle so far.
    invalid_elements: FnvHashSet<Invalidation>,
    /// Whether the whole document should be restyled.
    fully_invalid: bool,
}

impl StylesheetInvalidationSet {
    /// Create an empty `StylesheetInvalidationSet`.
    pub fn new() -> Self {
        Self {
            invalid_scopes: FnvHashSet::default(),
            invalid_elements: FnvHashSet::default(),
            fully_invalid: false,
        }
    }

    /// Mark the DOM tree styles' as fully invalid.
    pub fn invalidate_fully(&mut self) {
        debug!("StylesheetInvalidationSet::invalidate_fully");
        self.invalid_scopes.clear();
        self.invalid_elements.clear();
        self.fully_invalid = true;
    }

    /// Analyze the given stylesheet, and collect invalidations from their
    /// rules, in order to avoid doing a full restyle when we style the document
    /// next time.
    pub fn collect_invalidations_for<S>(
        &mut self,
        device: &Device,
        stylesheet: &S,
        guard: &SharedRwLockReadGuard
    )
    where
        S: StylesheetInDocument,
    {
        debug!("StylesheetInvalidationSet::collect_invalidations_for");
        if self.fully_invalid {
            debug!(" > Fully invalid already");
            return;
        }

        if !stylesheet.enabled() ||
           !stylesheet.is_effective_for_device(device, guard) {
            debug!(" > Stylesheet was not effective");
            return; // Nothing to do here.
        }

        for rule in stylesheet.effective_rules(device, guard) {
            self.collect_invalidations_for_rule(rule, guard);
            if self.fully_invalid {
                self.invalid_scopes.clear();
                self.invalid_elements.clear();
                break;
            }
        }

        debug!(" > resulting subtree invalidations: {:?}", self.invalid_scopes);
        debug!(" > resulting self invalidations: {:?}", self.invalid_elements);
        debug!(" > fully_invalid: {}", self.fully_invalid);
    }

    /// Clears the invalidation set, invalidating elements as needed if
    /// `document_element` is provided.
    ///
    /// Returns true if any invalidations ocurred.
    pub fn flush<E>(&mut self, document_element: Option<E>) -> bool
        where E: TElement,
    {
        let have_invalidations = match document_element {
            Some(e) => self.process_invalidations(e),
            None => false,
        };
        self.clear();
        have_invalidations
    }

    /// Clears the invalidation set without processing.
    pub fn clear(&mut self) {
        self.invalid_scopes.clear();
        self.invalid_elements.clear();
        self.fully_invalid = false;
    }

    fn process_invalidations<E>(&self, element: E) -> bool
        where E: TElement,
    {
        {
            let mut data = match element.mutate_data() {
                Some(data) => data,
                None => return false,
            };

            if self.fully_invalid {
                debug!("process_invalidations: fully_invalid({:?})",
                       element);
                data.hint.insert(RestyleHint::restyle_subtree());
                return true;
            }
        }

        if self.invalid_scopes.is_empty() && self.invalid_elements.is_empty() {
            debug!("process_invalidations: empty invalidation set");
            return false;
        }

        self.process_invalidations_in_subtree(element)
    }

    /// Process style invalidations in a given subtree. This traverses the
    /// subtree looking for elements that match the invalidations in
    /// invalid_scopes and invalid_elements.
    ///
    /// Returns whether it invalidated at least one element's style.
    #[allow(unsafe_code)]
    fn process_invalidations_in_subtree<E>(&self, element: E) -> bool
        where E: TElement,
    {
        let mut data = match element.mutate_data() {
            Some(data) => data,
            None => return false,
        };

        if !data.has_styles() {
            return false;
        }

        if data.hint.contains_subtree() {
            debug!("process_invalidations_in_subtree: {:?} was already invalid",
                   element);
            return false;
        }

        for invalidation in &self.invalid_scopes {
            if invalidation.matches(element) {
                debug!("process_invalidations_in_subtree: {:?} matched subtree {:?}",
                       element, invalidation);
                data.hint.insert(RestyleHint::restyle_subtree());
                return true;
            }
        }

        let mut self_invalid = false;

        if !data.hint.contains(RESTYLE_SELF) {
            for invalidation in &self.invalid_elements {
                if invalidation.matches(element) {
                    debug!("process_invalidations_in_subtree: {:?} matched self {:?}",
                           element, invalidation);
                    data.hint.insert(RESTYLE_SELF);
                    self_invalid = true;
                    break;
                }
            }
        }

        let mut any_children_invalid = false;

        for child in element.traversal_children() {
            let child = match child.as_element() {
                Some(e) => e,
                None => continue,
            };

            any_children_invalid |= self.process_invalidations_in_subtree(child);
        }

        if any_children_invalid {
            debug!("Children of {:?} changed, setting dirty descendants",
                   element);
            unsafe { element.set_dirty_descendants() }
        }

        return self_invalid || any_children_invalid
    }

    fn scan_component(
        component: &Component<SelectorImpl>,
        invalidation: &mut Option<Invalidation>)
    {
        match *component {
            Component::LocalName(LocalName { ref name, ref lower_name }) => {
                if invalidation.as_ref().map_or(true, |s| !s.is_id_or_class()) {
                    *invalidation = Some(Invalidation::LocalName {
                        name: name.clone(),
                        lower_name: lower_name.clone(),
                    });
                }
            }
            Component::Class(ref class) => {
                if invalidation.as_ref().map_or(true, |s| !s.is_id()) {
                    *invalidation = Some(Invalidation::Class(class.clone()));
                }
            }
            Component::ID(ref id) => {
                if invalidation.is_none() {
                    *invalidation = Some(Invalidation::ID(id.clone()));
                }
            }
            _ => {
                // Ignore everything else, at least for now.
            }
        }
    }

    /// Collect invalidations for a given selector.
    ///
    /// We look at the outermost local name, class, or ID selector to the left
    /// of an ancestor combinator, in order to restyle only a given subtree.
    ///
    /// If the selector has no ancestor combinator, then we do the same for
    /// the only sequence it has, but record it as an element invalidation
    /// instead of a subtree invalidation.
    ///
    /// We prefer IDs to classs, and classes to local names, on the basis
    /// that the former should be more specific than the latter. We also
    /// prefer to generate subtree invalidations for the outermost part
    /// of the selector, to reduce the amount of traversal we need to do
    /// when flushing invalidations.
    fn collect_invalidations(&mut self, selector: &Selector<SelectorImpl>) {
        debug!("StylesheetInvalidationSet::collect_invalidations({:?})", selector);

        let mut element_invalidation: Option<Invalidation> = None;
        let mut subtree_invalidation: Option<Invalidation> = None;

        let mut scan_for_element_invalidation = true;
        let mut scan_for_subtree_invalidation = false;

        let mut iter = selector.iter();

        loop {
            for component in &mut iter {
                if scan_for_element_invalidation {
                    Self::scan_component(component, &mut element_invalidation);
                } else if scan_for_subtree_invalidation {
                    Self::scan_component(component, &mut subtree_invalidation);
                }
            }
            match iter.next_sequence() {
                None => break,
                Some(combinator) => {
                    scan_for_subtree_invalidation = combinator.is_ancestor();
                }
            }
            scan_for_element_invalidation = false;
        }

        if let Some(s) = subtree_invalidation {
            debug!(" > Found subtree invalidation: {:?}", s);
            self.invalid_scopes.insert(s);
        } else if let Some(s) = element_invalidation {
            debug!(" > Found element invalidation: {:?}", s);
            self.invalid_elements.insert(s);
        } else {
            // The selector was of a form that we can't handle. Any element
            // could match it, so let's just bail out.
            debug!(" > Can't handle selector, marking fully invalid");
            self.fully_invalid = true;
        }
    }

    /// Collects invalidations for a given CSS rule.
    fn collect_invalidations_for_rule(
        &mut self,
        rule: &CssRule,
        guard: &SharedRwLockReadGuard)
    {
        use stylesheets::CssRule::*;
        debug!("StylesheetInvalidationSet::collect_invalidations_for_rule");
        debug_assert!(!self.fully_invalid, "Not worth to be here!");

        match *rule {
            Style(ref lock) => {
                let style_rule = lock.read_with(guard);
                for selector in &style_rule.selectors.0 {
                    self.collect_invalidations(selector);
                    if self.fully_invalid {
                        return;
                    }
                }
            }
            Document(..) |
            Namespace(..) |
            Import(..) |
            Media(..) |
            Supports(..) => {
                // Do nothing, relevant nested rules are visited as part of the
                // iteration.
            }
            FontFace(..) |
            CounterStyle(..) |
            Keyframes(..) |
            Page(..) |
            Viewport(..) |
            FontFeatureValues(..) => {
                debug!(" > Found unsupported rule, marking the whole subtree \
                       invalid.");

                // TODO(emilio): Can we do better here?
                //
                // At least in `@page`, we could check the relevant media, I
                // guess.
                self.fully_invalid = true;
            }
        }
    }
}