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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/. */
//! The structure that contains the custom properties of a given element.
use crate::custom_properties::Name;
use crate::properties_and_values::value::ComputedValue as ComputedRegisteredValue;
use crate::selector_map::PrecomputedHasher;
use indexmap::IndexMap;
use servo_arc::Arc;
use std::hash::BuildHasherDefault;
/// A map for a set of custom properties, which implements copy-on-write behavior on insertion with
/// cheap copying.
#[derive(Clone, Debug, PartialEq)]
pub struct CustomPropertiesMap(Arc<Inner>);
impl Default for CustomPropertiesMap {
fn default() -> Self {
Self(EMPTY.clone())
}
}
/// We use None in the value to represent a removed entry.
type OwnMap =
IndexMap<Name, Option<ComputedRegisteredValue>, BuildHasherDefault<PrecomputedHasher>>;
lazy_static! {
static ref EMPTY: Arc<Inner> = {
Arc::new_leaked(Inner {
own_properties: Default::default(),
parent: None,
len: 0,
ancestor_count: 0,
})
};
}
#[derive(Debug, Clone)]
struct Inner {
own_properties: OwnMap,
parent: Option<Arc<Inner>>,
/// The number of custom properties we store. Note that this is different from the sum of our
/// own and our parent's length, since we might store duplicate entries.
len: usize,
/// The number of ancestors we have.
ancestor_count: u8,
}
/// A not-too-large, not too small ancestor limit, to prevent creating too-big chains.
const ANCESTOR_COUNT_LIMIT: usize = 4;
/// An iterator over the custom properties.
pub struct Iter<'a> {
current: &'a Inner,
current_iter: indexmap::map::Iter<'a, Name, Option<ComputedRegisteredValue>>,
descendants: smallvec::SmallVec<[&'a Inner; ANCESTOR_COUNT_LIMIT]>,
}
impl<'a> Iterator for Iter<'a> {
type Item = (&'a Name, &'a Option<ComputedRegisteredValue>);
fn next(&mut self) -> Option<Self::Item> {
loop {
let (name, value) = match self.current_iter.next() {
Some(v) => v,
None => {
let parent = self.current.parent.as_deref()?;
self.descendants.push(self.current);
self.current = parent;
self.current_iter = parent.own_properties.iter();
continue;
},
};
// If the property is overridden by a descendant we've already visited it.
for descendant in &self.descendants {
if descendant.own_properties.contains_key(name) {
continue;
}
}
return Some((name, value));
}
}
}
impl PartialEq for Inner {
fn eq(&self, other: &Self) -> bool {
if self.len != other.len {
return false;
}
// NOTE(emilio): In order to speed up custom property comparison when tons of custom
// properties are involved, we return false in some cases where the ordering might be
// different, but the computed values end up being the same.
//
// This is a performance trade-off, on the assumption that if the ordering is different,
// there's likely a different value as well, but might over-invalidate.
//
// Doing the slow thing (checking all the keys) shows up a lot in profiles, see
// bug 1926423.
//
// Note that self.own_properties != other.own_properties is not the same, as by default
// IndexMap comparison is not order-aware.
if self.own_properties.as_slice() != other.own_properties.as_slice() {
return false;
}
self.parent == other.parent
}
}
impl Inner {
fn iter(&self) -> Iter<'_> {
Iter {
current: self,
current_iter: self.own_properties.iter(),
descendants: Default::default(),
}
}
fn is_empty(&self) -> bool {
self.len == 0
}
fn len(&self) -> usize {
self.len
}
fn get(&self, name: &Name) -> Option<&ComputedRegisteredValue> {
if let Some(p) = self.own_properties.get(name) {
return p.as_ref();
}
self.parent.as_ref()?.get(name)
}
fn insert(&mut self, name: &Name, value: Option<ComputedRegisteredValue>) {
let new = self.own_properties.insert(name.clone(), value).is_none();
if new && self.parent.as_ref().map_or(true, |p| p.get(name).is_none()) {
self.len += 1;
}
}
/// Whether we should expand the chain, or just copy-on-write.
fn should_expand_chain(&self) -> bool {
const SMALL_THRESHOLD: usize = 8;
if self.own_properties.len() <= SMALL_THRESHOLD {
return false; // Just copy, to avoid very long chains.
}
self.ancestor_count < ANCESTOR_COUNT_LIMIT as u8
}
}
impl CustomPropertiesMap {
/// Returns whether the map has no properties in it.
pub fn is_empty(&self) -> bool {
self.0.is_empty()
}
/// Returns the amount of different properties in the map.
pub fn len(&self) -> usize {
self.0.len()
}
/// Returns the property name and value at a given index.
pub fn get_index(&self, index: usize) -> Option<(&Name, &Option<ComputedRegisteredValue>)> {
if index >= self.len() {
return None;
}
// FIXME: This is O(n) which is a bit unfortunate.
self.0.iter().nth(index)
}
/// Returns a given property value by name.
pub fn get(&self, name: &Name) -> Option<&ComputedRegisteredValue> {
self.0.get(name)
}
fn do_insert(&mut self, name: &Name, value: Option<ComputedRegisteredValue>) {
if let Some(inner) = Arc::get_mut(&mut self.0) {
return inner.insert(name, value);
}
if self.get(name) == value.as_ref() {
return;
}
if !self.0.should_expand_chain() {
return Arc::make_mut(&mut self.0).insert(name, value);
}
let len = self.0.len;
let ancestor_count = self.0.ancestor_count + 1;
let mut new_inner = Inner {
own_properties: Default::default(),
// FIXME: Would be nice to avoid this clone.
parent: Some(self.0.clone()),
len,
ancestor_count,
};
new_inner.insert(name, value);
self.0 = Arc::new(new_inner);
}
/// Inserts an element in the map.
pub fn insert(&mut self, name: &Name, value: ComputedRegisteredValue) {
self.do_insert(name, Some(value))
}
/// Removes an element from the map.
pub fn remove(&mut self, name: &Name) {
self.do_insert(name, None)
}
/// Shrinks the map as much as possible.
pub fn shrink_to_fit(&mut self) {
if let Some(inner) = Arc::get_mut(&mut self.0) {
inner.own_properties.shrink_to_fit()
}
}
/// Return iterator to go through all properties.
pub fn iter(&self) -> Iter<'_> {
self.0.iter()
}
}