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 // First up, we diff all the nodes with the same key at the beginning of the
281 // `shared_prefix_count` is the count of how many nodes at the start of
282 // `new` and `old` share the same keys.
283 let shared_prefix_count =
284 match diff_keyed_prefix(cached_set, change_list, registry, old, new, cached_roots) {
285 KeyedPrefixResult::Finished => return,
286 KeyedPrefixResult::MoreWorkToDo(count) => count,
289 // Next, we find out how many of the nodes at the end of the children have
290 // the same key. We do _not_ diff them yet, since we want to emit the change
291 // list instructions such that they can be applied in a single pass over the
292 // DOM. Instead, we just save this information for later.
294 // `shared_suffix_count` is the count of how many nodes at the end of `new`
295 // and `old` share the same keys.
296 let shared_suffix_count = old[shared_prefix_count..]
299 .zip(new[shared_prefix_count..].iter().rev())
300 .take_while(|&(old, new)| old.key() == new.key())
303 let old_shared_suffix_start = old.len() - shared_suffix_count;
304 let new_shared_suffix_start = new.len() - shared_suffix_count;
306 // Ok, we now hopefully have a smaller range of children in the middle
307 // within which to re-order nodes with the same keys, remove old nodes with
308 // now-unused keys, and create new nodes with fresh keys.
313 &old[shared_prefix_count..old_shared_suffix_start],
314 &new[shared_prefix_count..new_shared_suffix_start],
318 old_shared_suffix_start,
321 // Finally, diff the nodes at the end of `old` and `new` that share keys.
322 let old_suffix = &old[old_shared_suffix_start..];
323 let new_suffix = &new[new_shared_suffix_start..];
324 debug_assert_eq!(old_suffix.len(), new_suffix.len());
325 if !old_suffix.is_empty() {
333 new_shared_suffix_start,
338enum KeyedPrefixResult {
339 // Fast path: we finished diffing all the children just by looking at the
340 // prefix of shared keys!
342 // There is more diffing work to do. Here is a count of how many children at
343 // the beginning of `new` and `old` we already processed.
347// Diff the prefix of children in `new` and `old` that share the same keys in
350// Upon entry of this function, the stack must be:
354// Upon exit, the stack is the same.
356 cached_set: &CachedSet,
357 change_list: &mut ChangeListBuilder,
358 registry: &mut EventsRegistry,
361 cached_roots: &mut FxHashSet<CacheId>,
362) -> KeyedPrefixResult {
363 let mut pushed = false;
364 let mut shared_prefix_count = 0;
366 for (old, new) in old.iter().zip(new.iter()) {
367 if old.key() != new.key() {
372 debug_assert!(shared_prefix_count > 0);
373 change_list.pop_push_next_sibling();
375 debug_assert_eq!(shared_prefix_count, 0);
376 change_list.push_first_child();
380 diff(cached_set, change_list, registry, old, new, cached_roots);
381 shared_prefix_count += 1;
383 // At the end of the loop, the stack looks like
385 // [... parent child_we_just_diffed]
386 debug_assert!(pushed);
389 // If that was all of the old children, then create and append the remaining
390 // new children and we're finished.
391 if shared_prefix_count == old.len() {
394 "we handle the case of empty children before calling this method, so
395 `shared_prefix_count` must be greater than zero, and therefore we
396 must have pushed in the above loop"
399 create_and_append_children(
403 &new[shared_prefix_count..],
406 return KeyedPrefixResult::Finished;
409 // And if that was all of the new children, then remove all of the remaining
410 // old children and we're finished.
411 if shared_prefix_count == new.len() {
413 debug_assert!(pushed);
414 change_list.pop_push_next_sibling();
415 change_list.remove_self_and_next_siblings();
416 return KeyedPrefixResult::Finished;
420 debug_assert!(shared_prefix_count > 0);
423 KeyedPrefixResult::MoreWorkToDo(shared_prefix_count)
426// The most-general, expensive code path for keyed children diffing.
428// We find the longest subsequence within `old` of children that are relatively
429// ordered the same way in `new` (via finding a longest-increasing-subsequence
430// of the old child's index within `new`). The children that are elements of
431// this subsequence will remain in place, minimizing the number of DOM moves we
434// Upon entry to this function, the stack must be:
438// Upon exit from this function, it will be restored to that same state.
440 cached_set: &CachedSet,
441 change_list: &mut ChangeListBuilder,
442 registry: &mut EventsRegistry,
445 cached_roots: &mut FxHashSet<CacheId>,
446 shared_prefix_count: usize,
447 shared_suffix_count: usize,
448 old_shared_suffix_start: usize,
450 // Should have already diffed the shared-key prefixes and suffixes.
451 debug_assert_ne!(new.first().map(|n| n.key()), old.first().map(|o| o.key()));
452 debug_assert_ne!(new.last().map(|n| n.key()), old.last().map(|o| o.key()));
454 // The algorithm below relies upon using `u32::MAX` as a sentinel
455 // value, so if we have that many new nodes, it won't work. This
456 // check is a bit academic (hence only enabled in debug), since
457 // wasm32 doesn't have enough address space to hold that many nodes
459 debug_assert!(new.len() < u32::MAX as usize);
461 // Map from each `old` node's key to its index within `old`.
462 let mut old_key_to_old_index = FxHashMap::default();
463 old_key_to_old_index.reserve(old.len());
464 old_key_to_old_index.extend(old.iter().enumerate().map(|(i, o)| (o.key(), i)));
466 // The set of shared keys between `new` and `old`.
467 let mut shared_keys = FxHashSet::default();
468 // Map from each index in `new` to the index of the node in `old` that
470 let mut new_index_to_old_index = Vec::with_capacity(new.len());
471 new_index_to_old_index.extend(new.iter().map(|n| {
473 if let Some(&i) = old_key_to_old_index.get(&key) {
474 shared_keys.insert(key);
481 // If none of the old keys are reused by the new children, then we
482 // remove all the remaining old children and create the new children
484 if shared_suffix_count == 0 && shared_keys.is_empty() {
485 if shared_prefix_count == 0 {
486 remove_all_children(change_list, registry, old);
488 change_list.pop_push_next_sibling();
489 remove_self_and_next_siblings(change_list, registry, &old[shared_prefix_count..]);
491 create_and_append_children(cached_set, change_list, registry, new, cached_roots);
495 // The longest increasing subsequence within `new_index_to_old_index` in
496 // reverse order (since `lis_with` adds the indices in reverse
497 // order). We will leave these nodes in place in the DOM, and only move
498 // nodes that are not part of the LIS. This results in the minimum
499 // number of DOM nodes moved.
500 let mut reverse_lis = Vec::with_capacity(new_index_to_old_index.len());
501 let mut predecessors = vec![0; new_index_to_old_index.len()];
502 let mut starts = vec![0; new_index_to_old_index.len()];
503 longest_increasing_subsequence::lis_with(
504 &new_index_to_old_index,
511 // Save each of the old children whose keys are reused in the new
513 let mut old_index_to_temp = vec![u32::MAX; old.len()];
516 let end = (start..old.len())
518 let key = old[i].key();
519 !shared_keys.contains(&key)
521 .unwrap_or(old.len());
524 let mut t = change_list.save_children_to_temporaries(
525 shared_prefix_count + start,
526 shared_prefix_count + end,
528 for i in start..end {
529 old_index_to_temp[i] = t;
534 debug_assert!(end <= old.len());
535 if end == old.len() {
542 // Remove any old children whose keys were not reused in the new
543 // children. Remove from the end first so that we don't mess up indices.
544 let mut removed_count = 0;
545 for (i, old_child) in old.iter().enumerate().rev() {
546 if !shared_keys.contains(&old_child.key()) {
547 change_list.remove_child(i + shared_prefix_count);
552 // Whether we have pushed a child onto the stack or not.
553 let mut pushed = false;
555 // Now iterate from the end of the new children back to the beginning,
556 // moving old children to their new destination, diffing them, and
557 // creating new children as necessary. Note that iterating in reverse
558 // order lets us use `Node.prototype.insertBefore` to move/insert
560 if shared_suffix_count > 0 {
561 change_list.push_child(old_shared_suffix_start - removed_count);
564 let mut segment_end = new.len();
565 for lis_index in reverse_lis {
566 // Because we use `u32::MAX` as a sentinel value representing "a child
567 // with this key is not a member of `new`", we filter that out here.
568 let old_index = new_index_to_old_index[lis_index];
569 if old_index == u32::MAX as usize {
573 // A segment begins with a member of the LIS, which will remain in
574 // place in the DOM, followed by zero or more new children that are
575 // not members of the LIS. If one of these new children shares a key
576 // with one of the old children, then we will move that old child in
577 // the DOM. Otherwise, we create the new child afresh.
578 debug_assert!(segment_end - lis_index > 0);
580 // Go through each of the non-LIS child and move-and-diff or create
582 diff_and_move_or_create_segment(
589 lis_index + 1..segment_end,
590 &new_index_to_old_index,
595 // Now we push the member of the LIS and diff it with its
596 // correspondingly-keyed new child.
597 let new_child = &new[lis_index];
598 let temp = old_index_to_temp[old_index];
599 debug_assert_ne!(temp, u32::MAX);
603 change_list.push_temporary(temp);
614 segment_end = lis_index;
617 // And now diff-and-move or create each of the non-LIS children that
618 // appear before the first LIS-member.
619 diff_and_move_or_create_segment(
627 &new_index_to_old_index,
637// Diff-and-then-move or create each new node in the given segment. The
638// segment's nodes must _not_ be members of the LIS (those nodes we will diff in
639// place elsewhere, and we should not move them nor create them afresh).
641// On entering this function, the stack has the parent and optionally the next
642// sibling after this segment of children:
644// [... parent next_sibling] if *pushed == true
645// [... parent] otherwise
647// After exiting, if any children were moved or created, then `pushed` is set to
648// true and the stack has the first child in this segment on top. Otherwise the
649// stack is left as it was on entering.
651// [... parent child] if *pushed == true
652// [... parent] otherwise
653fn diff_and_move_or_create_segment(
654 cached_set: &CachedSet,
655 change_list: &mut ChangeListBuilder,
656 registry: &mut EventsRegistry,
659 cached_roots: &mut FxHashSet<CacheId>,
660 segment: Range<usize>,
661 new_index_to_old_index: &[usize],
662 old_index_to_temp: &[u32],
665 for new_index in segment.rev() {
666 let new_child = &new[new_index];
667 let old_index = new_index_to_old_index[new_index];
668 if old_index == u32::MAX as usize {
669 // The key is not reused. Create this new child afresh.
670 create(cached_set, change_list, registry, new_child, cached_roots);
672 // The key is reused. Diff it with the old node and then
673 // move the old node into its final destination.
674 let temp = old_index_to_temp[old_index];
675 debug_assert_ne!(temp, u32::MAX);
676 change_list.push_temporary(temp);
687 // At this point the stack can have one of two shapes.
689 // [... parent next_child new_child]
690 change_list.insert_before();
691 // [... parent new_child]
693 // [... parent new_child]
694 change_list.append_child();
696 change_list.push_last_child();
697 // [... parent new_child]
701 // At the end of each loop iteration, the stack looks like:
703 // [... parent new_child]
704 debug_assert!(*pushed);
708// Diff the suffix of keyed children that share the same keys in the same order.
710// The parent must be on the stack when we enter this function:
714// When this function exits, the stack remains the same.
716 cached_set: &CachedSet,
717 change_list: &mut ChangeListBuilder,
718 registry: &mut EventsRegistry,
721 cached_roots: &mut FxHashSet<CacheId>,
722 new_shared_suffix_start: usize,
724 debug_assert_eq!(old.len(), new.len());
725 debug_assert!(!old.is_empty());
728 change_list.push_child(new_shared_suffix_start);
729 // [... parent new_child]
731 for (old_child, new_child) in old.iter().zip(new.iter()) {
741 // [... parent this_new_child]
742 change_list.pop_push_next_sibling();
743 // [... parent next_new_child]
750// Diff children that are not keyed.
752// The parent must be on the top of the stack when entering this function:
756// The stack is in the same state when this function returns.
757fn diff_non_keyed_children(
758 cached_set: &CachedSet,
759 change_list: &mut ChangeListBuilder,
760 registry: &mut EventsRegistry,
763 cached_roots: &mut FxHashSet<CacheId>,
765 // Handled these cases in `diff_children` before calling this function.
766 debug_assert!(!new.is_empty());
767 debug_assert!(!old.is_empty());
769 for (i, (new_child, old_child)) in new.iter().zip(old.iter()).enumerate() {
771 change_list.push_first_child();
773 change_list.pop_push_next_sibling();
786 match old.len().cmp(&new.len()) {
787 Ordering::Greater => {
788 change_list.pop_push_next_sibling();
789 remove_self_and_next_siblings(change_list, registry, &old[new.len()..]);
793 create_and_append_children(
807// Create the given children and append them to the parent node.
809// The parent node must currently be on top of the stack:
813// When this function returns, the stack is in the same state.
814fn create_and_append_children(
815 cached_set: &CachedSet,
816 change_list: &mut ChangeListBuilder,
817 registry: &mut EventsRegistry,
819 cached_roots: &mut FxHashSet<CacheId>,
822 create(cached_set, change_list, registry, child, cached_roots);
823 change_list.append_child();
827// Remove all of a node's children.
829// The stack must have this shape upon entry to this function:
833// When this function returns, the stack is in the same state.
834fn remove_all_children(
835 change_list: &mut ChangeListBuilder,
836 registry: &mut EventsRegistry,
840 registry.remove_subtree(child);
842 // Fast way to remove all children: set the node's textContent to an empty
844 change_list.set_text("");
847// Remove the current child and all of its following siblings.
849// The stack must have this shape upon entry to this function:
853// After the function returns, the child is no longer on the stack:
856fn remove_self_and_next_siblings(
857 change_list: &mut ChangeListBuilder,
858 registry: &mut EventsRegistry,
862 registry.remove_subtree(child);
864 change_list.remove_self_and_next_siblings();
867// Emit instructions to create the given virtual node.
869// The stack may have any shape upon entering this function:
873// When this function returns, the new node is on top of the stack:
877 cached_set: &CachedSet,
878 change_list: &mut ChangeListBuilder,
879 registry: &mut EventsRegistry,
881 cached_roots: &mut FxHashSet<CacheId>,
884 NodeKind::Text(TextNode { text }) => {
885 change_list.create_text_node(text);
887 NodeKind::Element(ElementNode {
895 if let Some(namespace) = namespace {
896 change_list.create_element_ns(tag_name, namespace);
898 change_list.create_element(tag_name);
904 change_list.new_event_listener(l);
906 for attr in attributes {
907 change_list.set_attribute(&attr.name, &attr.value);
909 for child in children {
910 create(cached_set, change_list, registry, child, cached_roots);
911 change_list.append_child();
914 NodeKind::Cached(ref c) => {
915 cached_roots.insert(c.id);
916 let node = cached_set.get(c.id);
917 create(cached_set, change_list, registry, node, cached_roots)
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