2 cached_set::{CacheId, CachedSet},
3 change_list::ChangeListBuilder,
4 events::EventsRegistry,
5 node::{Attribute, ElementNode, Listener, Node, NodeKind, TextNode},
7use fxhash::{FxHashMap, FxHashSet};
12// Diff the `old` node with the `new` node. Emits instructions to modify a
13// physical DOM node that reflects `old` into something that reflects `new`.
15// Upon entry to this function, the physical DOM node must be on the top of the
20// The stack is in the same state when this function exits.
22 cached_set: &CachedSet,
23 change_list: &mut ChangeListBuilder,
24 registry: &mut EventsRegistry,
27 cached_roots: &mut FxHashSet<CacheId>,
29 match (&new.kind, &old.kind) {
31 &NodeKind::Text(TextNode { text: new_text }),
32 &NodeKind::Text(TextNode { text: old_text }),
34 if new_text != old_text {
35 change_list.set_text(new_text);
39 (&NodeKind::Text(_), &NodeKind::Element(_)) => {
40 create(cached_set, change_list, registry, new, cached_roots);
41 registry.remove_subtree(&old);
42 change_list.replace_with();
45 (&NodeKind::Element(_), &NodeKind::Text(_)) => {
46 create(cached_set, change_list, registry, new, cached_roots);
47 // Note: text nodes cannot have event listeners, so we don't need to
48 // remove the old node's listeners from our registry her.
49 change_list.replace_with();
53 &NodeKind::Element(ElementNode {
55 tag_name: new_tag_name,
56 listeners: new_listeners,
57 attributes: new_attributes,
58 children: new_children,
59 namespace: new_namespace,
61 &NodeKind::Element(ElementNode {
63 tag_name: old_tag_name,
64 listeners: old_listeners,
65 attributes: old_attributes,
66 children: old_children,
67 namespace: old_namespace,
70 if new_tag_name != old_tag_name || new_namespace != old_namespace {
71 create(cached_set, change_list, registry, new, cached_roots);
72 registry.remove_subtree(&old);
73 change_list.replace_with();
76 diff_listeners(change_list, registry, old_listeners, new_listeners);
77 diff_attributes(change_list, old_attributes, new_attributes);
88 // Both the new and old nodes are cached.
89 (&NodeKind::Cached(ref new), &NodeKind::Cached(ref old)) => {
90 cached_roots.insert(new.id);
93 // This is the same cached node, so nothing has changed!
97 let new = cached_set.get(new.id);
98 let old = cached_set.get(old.id);
99 diff(cached_set, change_list, registry, old, new, cached_roots);
102 // New cached node when the old node was not cached. In this scenario,
103 // we assume that they are pretty different, and it isn't worth diffing
104 // the subtrees, so we just create the new cached node afresh.
105 (&NodeKind::Cached(ref c), _) => {
106 cached_roots.insert(c.id);
107 let new = cached_set.get(c.id);
108 create(cached_set, change_list, registry, new, cached_roots);
109 registry.remove_subtree(&old);
110 change_list.replace_with();
113 // Old cached node and new non-cached node. Again, assume that they are
114 // probably pretty different and create the new non-cached node afresh.
115 (_, &NodeKind::Cached(_)) => {
116 create(cached_set, change_list, registry, new, cached_roots);
117 registry.remove_subtree(&old);
118 change_list.replace_with();
123// Diff event listeners between `old` and `new`.
125// The listeners' node must be on top of the stack:
129// The stack is left unchanged.
131 change_list: &mut ChangeListBuilder,
132 registry: &mut EventsRegistry,
136 'outer1: for new_l in new {
138 // Safety relies on removing `new_l` from the registry manually at
139 // the end of its lifetime. This happens below in the `'outer2`
140 // loop, and elsewhere in diffing when removing old dom trees.
145 if new_l.event == old_l.event {
146 change_list.update_event_listener(new_l);
151 change_list.new_event_listener(new_l);
154 'outer2: for old_l in old {
155 registry.remove(old_l);
158 if new_l.event == old_l.event {
162 change_list.remove_event_listener(old_l.event);
166// Diff a node's attributes.
168// The attributes' node must be on top of the stack:
172// The stack is left unchanged.
173fn diff_attributes(change_list: &mut ChangeListBuilder, old: &[Attribute], new: &[Attribute]) {
174 // Do O(n^2) passes to add/update and remove attributes, since
175 // there are almost always very few attributes.
176 'outer: for new_attr in new {
177 if new_attr.is_volatile() {
178 change_list.set_attribute(new_attr.name, new_attr.value);
180 for old_attr in old {
181 if old_attr.name == new_attr.name {
182 if old_attr.value != new_attr.value {
183 change_list.set_attribute(new_attr.name, new_attr.value);
188 change_list.set_attribute(new_attr.name, new_attr.value);
192 'outer2: for old_attr in old {
193 for new_attr in new {
194 if old_attr.name == new_attr.name {
198 change_list.remove_attribute(old_attr.name);
202// Diff the given set of old and new children.
204// The parent must be on top of the stack when this function is entered:
208// The stack is in the same state when this function returns.
210 cached_set: &CachedSet,
211 change_list: &mut ChangeListBuilder,
212 registry: &mut EventsRegistry,
215 cached_roots: &mut FxHashSet<CacheId>,
219 remove_all_children(change_list, registry, old);
225 create_and_append_children(cached_set, change_list, registry, new, cached_roots);
229 let new_is_keyed = new[0].key().is_some();
230 let old_is_keyed = old[0].key().is_some();
233 new.iter().all(|n| n.key().is_some() == new_is_keyed),
234 "all siblings must be keyed or all siblings must be non-keyed"
237 old.iter().all(|o| o.key().is_some() == old_is_keyed),
238 "all siblings must be keyed or all siblings must be non-keyed"
241 if new_is_keyed && old_is_keyed {
242 let t = change_list.next_temporary();
243 diff_keyed_children(cached_set, change_list, registry, old, new, cached_roots);
244 change_list.set_next_temporary(t);
246 diff_non_keyed_children(cached_set, change_list, registry, old, new, cached_roots);
250// Diffing "keyed" children.
252// With keyed children, we care about whether we delete, move, or create nodes
253// versus mutate existing nodes in place. Presumably there is some sort of CSS
254// transition animation that makes the virtual DOM diffing algorithm
255// observable. By specifying keys for nodes, we know which virtual DOM nodes
256// must reuse (or not reuse) the same physical DOM nodes.
258// This is loosely based on Inferno's keyed patching implementation. However, we
259// have to modify the algorithm since we are compiling the diff down into change
260// list instructions that will be executed later, rather than applying the
261// changes to the DOM directly as we compare virtual DOMs.
263// https://github.com/infernojs/inferno/blob/36fd96/packages/inferno/src/DOM/patching.ts#L530-L739
265// When entering this function, the parent must be on top of the stack:
269// Upon exiting, the stack is in the same state.
270fn diff_keyed_children(
271 cached_set: &CachedSet,
272 change_list: &mut ChangeListBuilder,
273 registry: &mut EventsRegistry,
276 cached_roots: &mut FxHashSet<CacheId>,
278 if cfg!(debug_assertions) {
279 let mut keys = FxHashSet::default();
280 let mut assert_unique_keys = |children: &[Node]| {
282 for child in children {
283 let key = child.key();
286 "if any sibling is keyed, all siblings must be keyed"
293 "keyed siblings must each have a unique key"
296 assert_unique_keys(old);
297 assert_unique_keys(new);
300 // First up, we diff all the nodes with the same key at the beginning of the
303 // `shared_prefix_count` is the count of how many nodes at the start of
304 // `new` and `old` share the same keys.
305 let shared_prefix_count =
306 match diff_keyed_prefix(cached_set, change_list, registry, old, new, cached_roots) {
307 KeyedPrefixResult::Finished => return,
308 KeyedPrefixResult::MoreWorkToDo(count) => count,
311 // Next, we find out how many of the nodes at the end of the children have
312 // the same key. We do _not_ diff them yet, since we want to emit the change
313 // list instructions such that they can be applied in a single pass over the
314 // DOM. Instead, we just save this information for later.
316 // `shared_suffix_count` is the count of how many nodes at the end of `new`
317 // and `old` share the same keys.
318 let shared_suffix_count = old[shared_prefix_count..]
321 .zip(new[shared_prefix_count..].iter().rev())
322 .take_while(|&(old, new)| old.key() == new.key())
325 let old_shared_suffix_start = old.len() - shared_suffix_count;
326 let new_shared_suffix_start = new.len() - shared_suffix_count;
328 // Ok, we now hopefully have a smaller range of children in the middle
329 // within which to re-order nodes with the same keys, remove old nodes with
330 // now-unused keys, and create new nodes with fresh keys.
335 &old[shared_prefix_count..old_shared_suffix_start],
336 &new[shared_prefix_count..new_shared_suffix_start],
340 old_shared_suffix_start,
343 // Finally, diff the nodes at the end of `old` and `new` that share keys.
344 let old_suffix = &old[old_shared_suffix_start..];
345 let new_suffix = &new[new_shared_suffix_start..];
346 debug_assert_eq!(old_suffix.len(), new_suffix.len());
347 if !old_suffix.is_empty() {
355 new_shared_suffix_start,
360enum KeyedPrefixResult {
361 // Fast path: we finished diffing all the children just by looking at the
362 // prefix of shared keys!
364 // There is more diffing work to do. Here is a count of how many children at
365 // the beginning of `new` and `old` we already processed.
369// Diff the prefix of children in `new` and `old` that share the same keys in
372// Upon entry of this function, the stack must be:
376// Upon exit, the stack is the same.
378 cached_set: &CachedSet,
379 change_list: &mut ChangeListBuilder,
380 registry: &mut EventsRegistry,
383 cached_roots: &mut FxHashSet<CacheId>,
384) -> KeyedPrefixResult {
385 let mut pushed = false;
386 let mut shared_prefix_count = 0;
388 for (old, new) in old.iter().zip(new.iter()) {
389 if old.key() != new.key() {
394 debug_assert!(shared_prefix_count > 0);
395 change_list.pop_push_next_sibling();
397 debug_assert_eq!(shared_prefix_count, 0);
398 change_list.push_first_child();
402 diff(cached_set, change_list, registry, old, new, cached_roots);
403 shared_prefix_count += 1;
405 // At the end of the loop, the stack looks like
407 // [... parent child_we_just_diffed]
408 debug_assert!(pushed);
411 // If that was all of the old children, then create and append the remaining
412 // new children and we're finished.
413 if shared_prefix_count == old.len() {
416 "we handle the case of empty children before calling this method, so
417 `shared_prefix_count` must be greater than zero, and therefore we
418 must have pushed in the above loop"
421 create_and_append_children(
425 &new[shared_prefix_count..],
428 return KeyedPrefixResult::Finished;
431 // And if that was all of the new children, then remove all of the remaining
432 // old children and we're finished.
433 if shared_prefix_count == new.len() {
435 debug_assert!(pushed);
436 change_list.pop_push_next_sibling();
437 change_list.remove_self_and_next_siblings();
438 return KeyedPrefixResult::Finished;
442 debug_assert!(shared_prefix_count > 0);
445 KeyedPrefixResult::MoreWorkToDo(shared_prefix_count)
448// The most-general, expensive code path for keyed children diffing.
450// We find the longest subsequence within `old` of children that are relatively
451// ordered the same way in `new` (via finding a longest-increasing-subsequence
452// of the old child's index within `new`). The children that are elements of
453// this subsequence will remain in place, minimizing the number of DOM moves we
456// Upon entry to this function, the stack must be:
460// Upon exit from this function, it will be restored to that same state.
462 cached_set: &CachedSet,
463 change_list: &mut ChangeListBuilder,
464 registry: &mut EventsRegistry,
467 cached_roots: &mut FxHashSet<CacheId>,
468 shared_prefix_count: usize,
469 shared_suffix_count: usize,
470 old_shared_suffix_start: usize,
472 // Should have already diffed the shared-key prefixes and suffixes.
473 debug_assert_ne!(new.first().map(|n| n.key()), old.first().map(|o| o.key()));
474 debug_assert_ne!(new.last().map(|n| n.key()), old.last().map(|o| o.key()));
476 // The algorithm below relies upon using `u32::MAX` as a sentinel
477 // value, so if we have that many new nodes, it won't work. This
478 // check is a bit academic (hence only enabled in debug), since
479 // wasm32 doesn't have enough address space to hold that many nodes
481 debug_assert!(new.len() < u32::MAX as usize);
483 // Map from each `old` node's key to its index within `old`.
484 let mut old_key_to_old_index = FxHashMap::default();
485 old_key_to_old_index.reserve(old.len());
486 old_key_to_old_index.extend(old.iter().enumerate().map(|(i, o)| (o.key(), i)));
488 // The set of shared keys between `new` and `old`.
489 let mut shared_keys = FxHashSet::default();
490 // Map from each index in `new` to the index of the node in `old` that
492 let mut new_index_to_old_index = Vec::with_capacity(new.len());
493 new_index_to_old_index.extend(new.iter().map(|n| {
495 if let Some(&i) = old_key_to_old_index.get(&key) {
496 shared_keys.insert(key);
503 // If none of the old keys are reused by the new children, then we
504 // remove all the remaining old children and create the new children
506 if shared_suffix_count == 0 && shared_keys.is_empty() {
507 if shared_prefix_count == 0 {
508 remove_all_children(change_list, registry, old);
510 change_list.pop_push_next_sibling();
511 remove_self_and_next_siblings(change_list, registry, &old[shared_prefix_count..]);
513 create_and_append_children(cached_set, change_list, registry, new, cached_roots);
517 // The longest increasing subsequence within `new_index_to_old_index` in
518 // reverse order (since `lis_with` adds the indices in reverse
519 // order). We will leave these nodes in place in the DOM, and only move
520 // nodes that are not part of the LIS. This results in the minimum
521 // number of DOM nodes moved.
522 let mut reverse_lis = Vec::with_capacity(new_index_to_old_index.len());
523 let mut predecessors = vec![0; new_index_to_old_index.len()];
524 let mut starts = vec![0; new_index_to_old_index.len()];
525 longest_increasing_subsequence::lis_with(
526 &new_index_to_old_index,
533 // Save each of the old children whose keys are reused in the new
535 let mut old_index_to_temp = vec![u32::MAX; old.len()];
538 let end = (start..old.len())
540 let key = old[i].key();
541 !shared_keys.contains(&key)
543 .unwrap_or(old.len());
546 let mut t = change_list.save_children_to_temporaries(
547 shared_prefix_count + start,
548 shared_prefix_count + end,
550 for i in start..end {
551 old_index_to_temp[i] = t;
556 debug_assert!(end <= old.len());
557 if end == old.len() {
564 // Remove any old children whose keys were not reused in the new
565 // children. Remove from the end first so that we don't mess up indices.
566 let mut removed_count = 0;
567 for (i, old_child) in old.iter().enumerate().rev() {
568 if !shared_keys.contains(&old_child.key()) {
569 change_list.remove_child(i + shared_prefix_count);
574 // Whether we have pushed a child onto the stack or not.
575 let mut pushed = false;
577 // Now iterate from the end of the new children back to the beginning,
578 // moving old children to their new destination, diffing them, and
579 // creating new children as necessary. Note that iterating in reverse
580 // order lets us use `Node.prototype.insertBefore` to move/insert
582 if shared_suffix_count > 0 {
583 change_list.push_child(old_shared_suffix_start - removed_count);
586 let mut segment_end = new.len();
587 for lis_index in reverse_lis {
588 // Because we use `u32::MAX` as a sentinel value representing "a child
589 // with this key is not a member of `new`", we filter that out here.
590 let old_index = new_index_to_old_index[lis_index];
591 if old_index == u32::MAX as usize {
595 // A segment begins with a member of the LIS, which will remain in
596 // place in the DOM, followed by zero or more new children that are
597 // not members of the LIS. If one of these new children shares a key
598 // with one of the old children, then we will move that old child in
599 // the DOM. Otherwise, we create the new child afresh.
600 debug_assert!(segment_end - lis_index > 0);
602 // Go through each of the non-LIS child and move-and-diff or create
604 diff_and_move_or_create_segment(
611 lis_index + 1..segment_end,
612 &new_index_to_old_index,
617 // Now we push the member of the LIS and diff it with its
618 // correspondingly-keyed new child.
619 let new_child = &new[lis_index];
620 let temp = old_index_to_temp[old_index];
621 debug_assert_ne!(temp, u32::MAX);
625 change_list.push_temporary(temp);
636 segment_end = lis_index;
639 // And now diff-and-move or create each of the non-LIS children that
640 // appear before the first LIS-member.
641 diff_and_move_or_create_segment(
649 &new_index_to_old_index,
659// Diff-and-then-move or create each new node in the given segment. The
660// segment's nodes must _not_ be members of the LIS (those nodes we will diff in
661// place elsewhere, and we should not move them nor create them afresh).
663// On entering this function, the stack has the parent and optionally the next
664// sibling after this segment of children:
666// [... parent next_sibling] if *pushed == true
667// [... parent] otherwise
669// After exiting, if any children were moved or created, then `pushed` is set to
670// true and the stack has the first child in this segment on top. Otherwise the
671// stack is left as it was on entering.
673// [... parent child] if *pushed == true
674// [... parent] otherwise
675fn diff_and_move_or_create_segment(
676 cached_set: &CachedSet,
677 change_list: &mut ChangeListBuilder,
678 registry: &mut EventsRegistry,
681 cached_roots: &mut FxHashSet<CacheId>,
682 segment: Range<usize>,
683 new_index_to_old_index: &[usize],
684 old_index_to_temp: &[u32],
687 for new_index in segment.rev() {
688 let new_child = &new[new_index];
689 let old_index = new_index_to_old_index[new_index];
690 if old_index == u32::MAX as usize {
691 // The key is not reused. Create this new child afresh.
692 create(cached_set, change_list, registry, new_child, cached_roots);
694 // The key is reused. Diff it with the old node and then
695 // move the old node into its final destination.
696 let temp = old_index_to_temp[old_index];
697 debug_assert_ne!(temp, u32::MAX);
698 change_list.push_temporary(temp);
709 // At this point the stack can have one of two shapes.
711 // [... parent next_child new_child]
712 change_list.insert_before();
713 // [... parent new_child]
715 // [... parent new_child]
716 change_list.append_child();
718 change_list.push_last_child();
719 // [... parent new_child]
723 // At the end of each loop iteration, the stack looks like:
725 // [... parent new_child]
726 debug_assert!(*pushed);
730// Diff the suffix of keyed children that share the same keys in the same order.
732// The parent must be on the stack when we enter this function:
736// When this function exits, the stack remains the same.
738 cached_set: &CachedSet,
739 change_list: &mut ChangeListBuilder,
740 registry: &mut EventsRegistry,
743 cached_roots: &mut FxHashSet<CacheId>,
744 new_shared_suffix_start: usize,
746 debug_assert_eq!(old.len(), new.len());
747 debug_assert!(!old.is_empty());
750 change_list.push_child(new_shared_suffix_start);
751 // [... parent new_child]
753 for (old_child, new_child) in old.iter().zip(new.iter()) {
763 // [... parent this_new_child]
764 change_list.pop_push_next_sibling();
765 // [... parent next_new_child]
772// Diff children that are not keyed.
774// The parent must be on the top of the stack when entering this function:
778// The stack is in the same state when this function returns.
779fn diff_non_keyed_children(
780 cached_set: &CachedSet,
781 change_list: &mut ChangeListBuilder,
782 registry: &mut EventsRegistry,
785 cached_roots: &mut FxHashSet<CacheId>,
787 // Handled these cases in `diff_children` before calling this function.
788 debug_assert!(!new.is_empty());
789 debug_assert!(!old.is_empty());
791 for (i, (new_child, old_child)) in new.iter().zip(old.iter()).enumerate() {
793 change_list.push_first_child();
795 change_list.pop_push_next_sibling();
808 match old.len().cmp(&new.len()) {
809 Ordering::Greater => {
810 change_list.pop_push_next_sibling();
811 remove_self_and_next_siblings(change_list, registry, &old[new.len()..]);
815 create_and_append_children(
829// Create the given children and append them to the parent node.
831// The parent node must currently be on top of the stack:
835// When this function returns, the stack is in the same state.
836fn create_and_append_children(
837 cached_set: &CachedSet,
838 change_list: &mut ChangeListBuilder,
839 registry: &mut EventsRegistry,
841 cached_roots: &mut FxHashSet<CacheId>,
844 create(cached_set, change_list, registry, child, cached_roots);
845 change_list.append_child();
849// Remove all of a node's children.
851// The stack must have this shape upon entry to this function:
855// When this function returns, the stack is in the same state.
856fn remove_all_children(
857 change_list: &mut ChangeListBuilder,
858 registry: &mut EventsRegistry,
862 registry.remove_subtree(child);
864 // Fast way to remove all children: set the node's textContent to an empty
866 change_list.set_text("");
869// Remove the current child and all of its following siblings.
871// The stack must have this shape upon entry to this function:
875// After the function returns, the child is no longer on the stack:
878fn remove_self_and_next_siblings(
879 change_list: &mut ChangeListBuilder,
880 registry: &mut EventsRegistry,
884 registry.remove_subtree(child);
886 change_list.remove_self_and_next_siblings();
889// Emit instructions to create the given virtual node.
891// The stack may have any shape upon entering this function:
895// When this function returns, the new node is on top of the stack:
899 cached_set: &CachedSet,
900 change_list: &mut ChangeListBuilder,
901 registry: &mut EventsRegistry,
903 cached_roots: &mut FxHashSet<CacheId>,
906 NodeKind::Text(TextNode { text }) => {
907 change_list.create_text_node(text);
909 NodeKind::Element(ElementNode {
917 if let Some(namespace) = namespace {
918 change_list.create_element_ns(tag_name, namespace);
920 change_list.create_element(tag_name);
926 change_list.new_event_listener(l);
928 for attr in attributes {
929 change_list.set_attribute(&attr.name, &attr.value);
931 for child in children {
932 create(cached_set, change_list, registry, child, cached_roots);
933 change_list.append_child();
936 NodeKind::Cached(ref c) => {
937 cached_roots.insert(c.id);
938 let node = cached_set.get(c.id);
939 create(cached_set, change_list, registry, node, cached_roots)
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