官方实现
2024年03月14日
一、实现
React 中维护着两棵 fiber 树，一棵是正在展示的 UI 对应的那棵树，我们称为 current 树；另一棵通过更新，将要构建的树。那么在更新的过程中，是通过怎么样的对比过程，来决定是复用之前的节点，还是创建新的节点。
1.1 packages/react-reconciler/src/ReactFiberBeginWork.js reconcileChildren()
函数 reconcileChildren() 是 React Diff 入口函数, 用于调和，创建或更新fiber树, 主要逻辑如下:
-
若
current的fiber节点为null，调用mountChildFibers初始化 -
若
current不为空，说明要得到一棵新的fiber树，执行reconcileChildFibers()方法
export function reconcileChildren(
current: Fiber | null,
workInProgress: Fiber,
nextChildren: any,
renderLanes: Lanes,
) {
if (current === null) {
// If this is a fresh new component that hasn't been rendered yet, we
// won't update its child set by applying minimal side-effects. Instead,
// we will add them all to the child before it gets rendered. That means
// we can optimize this reconciliation pass by not tracking side-effects.
workInProgress.child = mountChildFibers(
workInProgress,
null,
nextChildren,
renderLanes,
);
} else {
// If the current child is the same as the work in progress, it means that
// we haven't yet started any work on these children. Therefore, we use
// the clone algorithm to create a copy of all the current children.
// If we had any progressed work already, that is invalid at this point so
// let's throw it out.
workInProgress.child = reconcileChildFibers(
workInProgress,
current.child,
nextChildren,
renderLanes,
);
}
}
1.2 packages/react-reconciler/src/ReactChildFiber.js
export const reconcileChildFibers: ChildReconciler =
createChildReconciler(true); // 需要收集副作用
export const mountChildFibers: ChildReconciler = createChildReconciler(false); // 不用追踪副作用
这两个函数都是 ChildReconciler() 生成，只是参数不一样。可见这两个函数就区别在是否要追踪 fiber 节点的副作用。
1.3 packages/react-reconciler/src/ReactChildFiber.js createChildReconciler()
createChildReconciler() 子元素协调器，即把当前 fiber 节点中的 element 结构转为 fiber 节点
function createChildReconciler(
shouldTrackSideEffects: boolean,
): ChildReconciler {
function deleteChild(returnFiber: Fiber, childToDelete: Fiber): void {
if (!shouldTrackSideEffects) {
// Noop.
return;
}
const deletions = returnFiber.deletions;
if (deletions === null) {
returnFiber.deletions = [childToDelete];
returnFiber.flags |= ChildDeletion;
} else {
deletions.push(childToDelete);
}
}
function deleteRemainingChildren(
returnFiber: Fiber,
currentFirstChild: Fiber | null,
): null {
if (!shouldTrackSideEffects) {
// Noop.
return null;
}
// TODO: For the shouldClone case, this could be micro-optimized a bit by
// assuming that after the first child we've already added everything.
let childToDelete = currentFirstChild;
while (childToDelete !== null) {
deleteChild(returnFiber, childToDelete);
childToDelete = childToDelete.sibling;
}
return null;
}
function mapRemainingChildren(
returnFiber: Fiber,
currentFirstChild: Fiber,
): Map<string | number, Fiber> {
// Add the remaining children to a temporary map so that we can find them by
// keys quickly. Implicit (null) keys get added to this set with their index
// instead.
const existingChildren: Map<string | number, Fiber> = new Map();
let existingChild: null | Fiber = currentFirstChild;
while (existingChild !== null) {
if (existingChild.key !== null) {
existingChildren.set(existingChild.key, existingChild);
} else {
existingChildren.set(existingChild.index, existingChild);
}
existingChild = existingChild.sibling;
}
return existingChildren;
}
function useFiber(fiber: Fiber, pendingProps: mixed): Fiber {
// We currently set sibling to null and index to 0 here because it is easy
// to forget to do before returning it. E.g. for the single child case.
const clone = createWorkInProgress(fiber, pendingProps);
clone.index = 0;
clone.sibling = null;
return clone;
}
function placeChild(
newFiber: Fiber,
lastPlacedIndex: number,
newIndex: number,
): number {
newFiber.index = newIndex;
if (!shouldTrackSideEffects) {
// During hydration, the useId algorithm needs to know which fibers are
// part of a list of children (arrays, iterators).
newFiber.flags |= Forked;
return lastPlacedIndex;
}
const current = newFiber.alternate;
if (current !== null) {
const oldIndex = current.index;
if (oldIndex < lastPlacedIndex) {
// This is a move.
newFiber.flags |= Placement | PlacementDEV;
return lastPlacedIndex;
} else {
// This item can stay in place.
return oldIndex;
}
} else {
// This is an insertion.
newFiber.flags |= Placement | PlacementDEV;
return lastPlacedIndex;
}
}
function placeSingleChild(newFiber: Fiber): Fiber {
// This is simpler for the single child case. We only need to do a
// placement for inserting new children.
if (shouldTrackSideEffects && newFiber.alternate === null) {
newFiber.flags |= Placement | PlacementDEV;
}
return newFiber;
}
function updateTextNode(
returnFiber: Fiber,
current: Fiber | null,
textContent: string,
lanes: Lanes,
) {
if (current === null || current.tag !== HostText) {
// Insert
const created = createFiberFromText(textContent, returnFiber.mode, lanes);
created.return = returnFiber;
return created;
} else {
// Update
const existing = useFiber(current, textContent);
existing.return = returnFiber;
return existing;
}
}
function updateElement(
returnFiber: Fiber,
current: Fiber | null,
element: ReactElement,
lanes: Lanes,
): Fiber {
const elementType = element.type;
if (elementType === REACT_FRAGMENT_TYPE) {
return updateFragment(
returnFiber,
current,
element.props.children,
lanes,
element.key,
);
}
if (current !== null) {
if (
current.elementType === elementType ||
// Keep this check inline so it only runs on the false path:
(__DEV__
? isCompatibleFamilyForHotReloading(current, element)
: false) ||
// Lazy types should reconcile their resolved type.
// We need to do this after the Hot Reloading check above,
// because hot reloading has different semantics than prod because
// it doesn't resuspend. So we can't let the call below suspend.
(typeof elementType === 'object' &&
elementType !== null &&
elementType.$$typeof === REACT_LAZY_TYPE &&
resolveLazy(elementType) === current.type)
) {
// Move based on index
const existing = useFiber(current, element.props);
existing.ref = coerceRef(returnFiber, current, element);
existing.return = returnFiber;
if (__DEV__) {
existing._debugSource = element._source;
existing._debugOwner = element._owner;
}
return existing;
}
}
// Insert
const created = createFiberFromElement(element, returnFiber.mode, lanes);
created.ref = coerceRef(returnFiber, current, element);
created.return = returnFiber;
return created;
}
function updatePortal(
returnFiber: Fiber,
current: Fiber | null,
portal: ReactPortal,
lanes: Lanes,
): Fiber {
if (
current === null ||
current.tag !== HostPortal ||
current.stateNode.containerInfo !== portal.containerInfo ||
current.stateNode.implementation !== portal.implementation
) {
// Insert
const created = createFiberFromPortal(portal, returnFiber.mode, lanes);
created.return = returnFiber;
return created;
} else {
// Update
const existing = useFiber(current, portal.children || []);
existing.return = returnFiber;
return existing;
}
}
function updateFragment(
returnFiber: Fiber,
current: Fiber | null,
fragment: Iterable<React$Node>,
lanes: Lanes,
key: null | string,
): Fiber {
if (current === null || current.tag !== Fragment) {
// Insert
const created = createFiberFromFragment(
fragment,
returnFiber.mode,
lanes,
key,
);
created.return = returnFiber;
return created;
} else {
// Update
const existing = useFiber(current, fragment);
existing.return = returnFiber;
return existing;
}
}
function createChild(
returnFiber: Fiber,
newChild: any,
lanes: Lanes,
): Fiber | null {
if (
(typeof newChild === 'string' && newChild !== '') ||
typeof newChild === 'number'
) {
// Text nodes don't have keys. If the previous node is implicitly keyed
// we can continue to replace it without aborting even if it is not a text
// node.
const created = createFiberFromText(
'' + newChild,
returnFiber.mode,
lanes,
);
created.return = returnFiber;
return created;
}
if (typeof newChild === 'object' && newChild !== null) {
switch (newChild.$$typeof) {
case REACT_ELEMENT_TYPE: {
const created = createFiberFromElement(
newChild,
returnFiber.mode,
lanes,
);
created.ref = coerceRef(returnFiber, null, newChild);
created.return = returnFiber;
return created;
}
case REACT_PORTAL_TYPE: {
const created = createFiberFromPortal(
newChild,
returnFiber.mode,
lanes,
);
created.return = returnFiber;
return created;
}
case REACT_LAZY_TYPE: {
const payload = newChild._payload;
const init = newChild._init;
return createChild(returnFiber, init(payload), lanes);
}
}
if (isArray(newChild) || getIteratorFn(newChild)) {
const created = createFiberFromFragment(
newChild,
returnFiber.mode,
lanes,
null,
);
created.return = returnFiber;
return created;
}
// Usable node types
//
// Unwrap the inner value and recursively call this function again.
if (typeof newChild.then === 'function') {
const thenable: Thenable<any> = (newChild: any);
return createChild(returnFiber, unwrapThenable(thenable), lanes);
}
if (
newChild.$$typeof === REACT_CONTEXT_TYPE ||
newChild.$$typeof === REACT_SERVER_CONTEXT_TYPE
) {
const context: ReactContext<mixed> = (newChild: any);
return createChild(
returnFiber,
readContextDuringReconcilation(returnFiber, context, lanes),
lanes,
);
}
throwOnInvalidObjectType(returnFiber, newChild);
}
if (__DEV__) {
if (typeof newChild === 'function') {
warnOnFunctionType(returnFiber);
}
}
return null;
}
function updateSlot(
returnFiber: Fiber,
oldFiber: Fiber | null,
newChild: any,
lanes: Lanes,
): Fiber | null {
// Update the fiber if the keys match, otherwise return null.
const key = oldFiber !== null ? oldFiber.key : null;
if (
(typeof newChild === 'string' && newChild !== '') ||
typeof newChild === 'number'
) {
// Text nodes don't have keys. If the previous node is implicitly keyed
// we can continue to replace it without aborting even if it is not a text
// node.
if (key !== null) {
return null;
}
return updateTextNode(returnFiber, oldFiber, '' + newChild, lanes);
}
if (typeof newChild === 'object' && newChild !== null) {
switch (newChild.$$typeof) {
case REACT_ELEMENT_TYPE: {
if (newChild.key === key) {
return updateElement(returnFiber, oldFiber, newChild, lanes);
} else {
return null;
}
}
case REACT_PORTAL_TYPE: {
if (newChild.key === key) {
return updatePortal(returnFiber, oldFiber, newChild, lanes);
} else {
return null;
}
}
case REACT_LAZY_TYPE: {
const payload = newChild._payload;
const init = newChild._init;
return updateSlot(returnFiber, oldFiber, init(payload), lanes);
}
}
if (isArray(newChild) || getIteratorFn(newChild)) {
if (key !== null) {
return null;
}
return updateFragment(returnFiber, oldFiber, newChild, lanes, null);
}
// Usable node types
//
// Unwrap the inner value and recursively call this function again.
if (typeof newChild.then === 'function') {
const thenable: Thenable<any> = (newChild: any);
return updateSlot(
returnFiber,
oldFiber,
unwrapThenable(thenable),
lanes,
);
}
if (
newChild.$$typeof === REACT_CONTEXT_TYPE ||
newChild.$$typeof === REACT_SERVER_CONTEXT_TYPE
) {
const context: ReactContext<mixed> = (newChild: any);
return updateSlot(
returnFiber,
oldFiber,
readContextDuringReconcilation(returnFiber, context, lanes),
lanes,
);
}
throwOnInvalidObjectType(returnFiber, newChild);
}
if (__DEV__) {
if (typeof newChild === 'function') {
warnOnFunctionType(returnFiber);
}
}
return null;
}
function updateFromMap(
existingChildren: Map<string | number, Fiber>,
returnFiber: Fiber,
newIdx: number,
newChild: any,
lanes: Lanes,
): Fiber | null {
if (
(typeof newChild === 'string' && newChild !== '') ||
typeof newChild === 'number'
) {
// Text nodes don't have keys, so we neither have to check the old nor
// new node for the key. If both are text nodes, they match.
const matchedFiber = existingChildren.get(newIdx) || null;
return updateTextNode(returnFiber, matchedFiber, '' + newChild, lanes);
}
if (typeof newChild === 'object' && newChild !== null) {
switch (newChild.$$typeof) {
case REACT_ELEMENT_TYPE: {
const matchedFiber =
existingChildren.get(
newChild.key === null ? newIdx : newChild.key,
) || null;
return updateElement(returnFiber, matchedFiber, newChild, lanes);
}
case REACT_PORTAL_TYPE: {
const matchedFiber =
existingChildren.get(
newChild.key === null ? newIdx : newChild.key,
) || null;
return updatePortal(returnFiber, matchedFiber, newChild, lanes);
}
case REACT_LAZY_TYPE:
const payload = newChild._payload;
const init = newChild._init;
return updateFromMap(
existingChildren,
returnFiber,
newIdx,
init(payload),
lanes,
);
}
if (isArray(newChild) || getIteratorFn(newChild)) {
const matchedFiber = existingChildren.get(newIdx) || null;
return updateFragment(returnFiber, matchedFiber, newChild, lanes, null);
}
// Usable node types
//
// Unwrap the inner value and recursively call this function again.
if (typeof newChild.then === 'function') {
const thenable: Thenable<any> = (newChild: any);
return updateFromMap(
existingChildren,
returnFiber,
newIdx,
unwrapThenable(thenable),
lanes,
);
}
if (
newChild.$$typeof === REACT_CONTEXT_TYPE ||
newChild.$$typeof === REACT_SERVER_CONTEXT_TYPE
) {
const context: ReactContext<mixed> = (newChild: any);
return updateFromMap(
existingChildren,
returnFiber,
newIdx,
readContextDuringReconcilation(returnFiber, context, lanes),
lanes,
);
}
throwOnInvalidObjectType(returnFiber, newChild);
}
if (__DEV__) {
if (typeof newChild === 'function') {
warnOnFunctionType(returnFiber);
}
}
return null;
}
/**
* Warns if there is a duplicate or missing key
*/
function warnOnInvalidKey(
child: mixed,
knownKeys: Set<string> | null,
returnFiber: Fiber,
): Set<string> | null {
if (__DEV__) {
if (typeof child !== 'object' || child === null) {
return knownKeys;
}
switch (child.$$typeof) {
case REACT_ELEMENT_TYPE:
case REACT_PORTAL_TYPE:
warnForMissingKey(child, returnFiber);
const key = child.key;
if (typeof key !== 'string') {
break;
}
if (knownKeys === null) {
knownKeys = new Set();
knownKeys.add(key);
break;
}
if (!knownKeys.has(key)) {
knownKeys.add(key);
break;
}
console.error(
'Encountered two children with the same key, `%s`. ' +
'Keys should be unique so that components maintain their identity ' +
'across updates. Non-unique keys may cause children to be ' +
'duplicated and/or omitted — the behavior is unsupported and ' +
'could change in a future version.',
key,
);
break;
case REACT_LAZY_TYPE:
const payload = child._payload;
const init = (child._init: any);
warnOnInvalidKey(init(payload), knownKeys, returnFiber);
break;
default:
break;
}
}
return knownKeys;
}
function reconcileChildrenArray(
returnFiber: Fiber,
currentFirstChild: Fiber | null,
newChildren: Array<any>,
lanes: Lanes,
): Fiber | null {
// This algorithm can't optimize by searching from both ends since we
// don't have backpointers on fibers. I'm trying to see how far we can get
// with that model. If it ends up not being worth the tradeoffs, we can
// add it later.
// Even with a two ended optimization, we'd want to optimize for the case
// where there are few changes and brute force the comparison instead of
// going for the Map. It'd like to explore hitting that path first in
// forward-only mode and only go for the Map once we notice that we need
// lots of look ahead. This doesn't handle reversal as well as two ended
// search but that's unusual. Besides, for the two ended optimization to
// work on Iterables, we'd need to copy the whole set.
// In this first iteration, we'll just live with hitting the bad case
// (adding everything to a Map) in for every insert/move.
// If you change this code, also update reconcileChildrenIterator() which
// uses the same algorithm.
if (__DEV__) {
// First, validate keys.
let knownKeys: Set<string> | null = null;
for (let i = 0; i < newChildren.length; i++) {
const child = newChildren[i];
knownKeys = warnOnInvalidKey(child, knownKeys, returnFiber);
}
}
let resultingFirstChild: Fiber | null = null;
let previousNewFiber: Fiber | null = null;
let oldFiber = currentFirstChild;
let lastPlacedIndex = 0;
let newIdx = 0;
let nextOldFiber = null;
for (; oldFiber !== null && newIdx < newChildren.length; newIdx++) {
if (oldFiber.index > newIdx) {
nextOldFiber = oldFiber;
oldFiber = null;
} else {
nextOldFiber = oldFiber.sibling;
}
const newFiber = updateSlot(
returnFiber,
oldFiber,
newChildren[newIdx],
lanes,
);
if (newFiber === null) {
// TODO: This breaks on empty slots like null children. That's
// unfortunate because it triggers the slow path all the time. We need
// a better way to communicate whether this was a miss or null,
// boolean, undefined, etc.
if (oldFiber === null) {
oldFiber = nextOldFiber;
}
break;
}
if (shouldTrackSideEffects) {
if (oldFiber && newFiber.alternate === null) {
// We matched the slot, but we didn't reuse the existing fiber, so we
// need to delete the existing child.
deleteChild(returnFiber, oldFiber);
}
}
lastPlacedIndex = placeChild(newFiber, lastPlacedIndex, newIdx);
if (previousNewFiber === null) {
// TODO: Move out of the loop. This only happens for the first run.
resultingFirstChild = newFiber;
} else {
// TODO: Defer siblings if we're not at the right index for this slot.
// I.e. if we had null values before, then we want to defer this
// for each null value. However, we also don't want to call updateSlot
// with the previous one.
previousNewFiber.sibling = newFiber;
}
previousNewFiber = newFiber;
oldFiber = nextOldFiber;
}
if (newIdx === newChildren.length) {
// We've reached the end of the new children. We can delete the rest.
deleteRemainingChildren(returnFiber, oldFiber);
if (getIsHydrating()) {
const numberOfForks = newIdx;
pushTreeFork(returnFiber, numberOfForks);
}
return resultingFirstChild;
}
if (oldFiber === null) {
// If we don't have any more existing children we can choose a fast path
// since the rest will all be insertions.
for (; newIdx < newChildren.length; newIdx++) {
const newFiber = createChild(returnFiber, newChildren[newIdx], lanes);
if (newFiber === null) {
continue;
}
lastPlacedIndex = placeChild(newFiber, lastPlacedIndex, newIdx);
if (previousNewFiber === null) {
// TODO: Move out of the loop. This only happens for the first run.
resultingFirstChild = newFiber;
} else {
previousNewFiber.sibling = newFiber;
}
previousNewFiber = newFiber;
}
if (getIsHydrating()) {
const numberOfForks = newIdx;
pushTreeFork(returnFiber, numberOfForks);
}
return resultingFirstChild;
}
// Add all children to a key map for quick lookups.
const existingChildren = mapRemainingChildren(returnFiber, oldFiber);
// Keep scanning and use the map to restore deleted items as moves.
for (; newIdx < newChildren.length; newIdx++) {
const newFiber = updateFromMap(
existingChildren,
returnFiber,
newIdx,
newChildren[newIdx],
lanes,
);
if (newFiber !== null) {
if (shouldTrackSideEffects) {
if (newFiber.alternate !== null) {
// The new fiber is a work in progress, but if there exists a
// current, that means that we reused the fiber. We need to delete
// it from the child list so that we don't add it to the deletion
// list.
existingChildren.delete(
newFiber.key === null ? newIdx : newFiber.key,
);
}
}
lastPlacedIndex = placeChild(newFiber, lastPlacedIndex, newIdx);
if (previousNewFiber === null) {
resultingFirstChild = newFiber;
} else {
previousNewFiber.sibling = newFiber;
}
previousNewFiber = newFiber;
}
}
if (shouldTrackSideEffects) {
// Any existing children that weren't consumed above were deleted. We need
// to add them to the deletion list.
existingChildren.forEach(child => deleteChild(returnFiber, child));
}
if (getIsHydrating()) {
const numberOfForks = newIdx;
pushTreeFork(returnFiber, numberOfForks);
}
return resultingFirstChild;
}
function reconcileChildrenIterator(
returnFiber: Fiber,
currentFirstChild: Fiber | null,
newChildrenIterable: Iterable<mixed>,
lanes: Lanes,
): Fiber | null {
// This is the same implementation as reconcileChildrenArray(),
// but using the iterator instead.
const iteratorFn = getIteratorFn(newChildrenIterable);
if (typeof iteratorFn !== 'function') {
throw new Error(
'An object is not an iterable. This error is likely caused by a bug in ' +
'React. Please file an issue.',
);
}
if (__DEV__) {
// We don't support rendering Generators because it's a mutation.
// See https://github.com/facebook/react/issues/12995
if (
typeof Symbol === 'function' &&
// $FlowFixMe[prop-missing] Flow doesn't know about toStringTag
newChildrenIterable[Symbol.toStringTag] === 'Generator'
) {
if (!didWarnAboutGenerators) {
console.error(
'Using Generators as children is unsupported and will likely yield ' +
'unexpected results because enumerating a generator mutates it. ' +
'You may convert it to an array with `Array.from()` or the ' +
'`[...spread]` operator before rendering. Keep in mind ' +
'you might need to polyfill these features for older browsers.',
);
}
didWarnAboutGenerators = true;
}
// Warn about using Maps as children
if ((newChildrenIterable: any).entries === iteratorFn) {
if (!didWarnAboutMaps) {
console.error(
'Using Maps as children is not supported. ' +
'Use an array of keyed ReactElements instead.',
);
}
didWarnAboutMaps = true;
}
// First, validate keys.
// We'll get a different iterator later for the main pass.
const newChildren = iteratorFn.call(newChildrenIterable);
if (newChildren) {
let knownKeys: Set<string> | null = null;
let step = newChildren.next();
for (; !step.done; step = newChildren.next()) {
const child = step.value;
knownKeys = warnOnInvalidKey(child, knownKeys, returnFiber);
}
}
}
const newChildren = iteratorFn.call(newChildrenIterable);
if (newChildren == null) {
throw new Error('An iterable object provided no iterator.');
}
let resultingFirstChild: Fiber | null = null;
let previousNewFiber: Fiber | null = null;
let oldFiber = currentFirstChild;
let lastPlacedIndex = 0;
let newIdx = 0;
let nextOldFiber = null;
let step = newChildren.next();
for (
;
oldFiber !== null && !step.done;
newIdx++, step = newChildren.next()
) {
if (oldFiber.index > newIdx) {
nextOldFiber = oldFiber;
oldFiber = null;
} else {
nextOldFiber = oldFiber.sibling;
}
const newFiber = updateSlot(returnFiber, oldFiber, step.value, lanes);
if (newFiber === null) {
// TODO: This breaks on empty slots like null children. That's
// unfortunate because it triggers the slow path all the time. We need
// a better way to communicate whether this was a miss or null,
// boolean, undefined, etc.
if (oldFiber === null) {
oldFiber = nextOldFiber;
}
break;
}
if (shouldTrackSideEffects) {
if (oldFiber && newFiber.alternate === null) {
// We matched the slot, but we didn't reuse the existing fiber, so we
// need to delete the existing child.
deleteChild(returnFiber, oldFiber);
}
}
lastPlacedIndex = placeChild(newFiber, lastPlacedIndex, newIdx);
if (previousNewFiber === null) {
// TODO: Move out of the loop. This only happens for the first run.
resultingFirstChild = newFiber;
} else {
// TODO: Defer siblings if we're not at the right index for this slot.
// I.e. if we had null values before, then we want to defer this
// for each null value. However, we also don't want to call updateSlot
// with the previous one.
previousNewFiber.sibling = newFiber;
}
previousNewFiber = newFiber;
oldFiber = nextOldFiber;
}
if (step.done) {
// We've reached the end of the new children. We can delete the rest.
deleteRemainingChildren(returnFiber, oldFiber);
if (getIsHydrating()) {
const numberOfForks = newIdx;
pushTreeFork(returnFiber, numberOfForks);
}
return resultingFirstChild;
}
if (oldFiber === null) {
// If we don't have any more existing children we can choose a fast path
// since the rest will all be insertions.
for (; !step.done; newIdx++, step = newChildren.next()) {
const newFiber = createChild(returnFiber, step.value, lanes);
if (newFiber === null) {
continue;
}
lastPlacedIndex = placeChild(newFiber, lastPlacedIndex, newIdx);
if (previousNewFiber === null) {
// TODO: Move out of the loop. This only happens for the first run.
resultingFirstChild = newFiber;
} else {
previousNewFiber.sibling = newFiber;
}
previousNewFiber = newFiber;
}
if (getIsHydrating()) {
const numberOfForks = newIdx;
pushTreeFork(returnFiber, numberOfForks);
}
return resultingFirstChild;
}
// Add all children to a key map for quick lookups.
const existingChildren = mapRemainingChildren(returnFiber, oldFiber);
// Keep scanning and use the map to restore deleted items as moves.
for (; !step.done; newIdx++, step = newChildren.next()) {
const newFiber = updateFromMap(
existingChildren,
returnFiber,
newIdx,
step.value,
lanes,
);
if (newFiber !== null) {
if (shouldTrackSideEffects) {
if (newFiber.alternate !== null) {
// The new fiber is a work in progress, but if there exists a
// current, that means that we reused the fiber. We need to delete
// it from the child list so that we don't add it to the deletion
// list.
existingChildren.delete(
newFiber.key === null ? newIdx : newFiber.key,
);
}
}
lastPlacedIndex = placeChild(newFiber, lastPlacedIndex, newIdx);
if (previousNewFiber === null) {
resultingFirstChild = newFiber;
} else {
previousNewFiber.sibling = newFiber;
}
previousNewFiber = newFiber;
}
}
if (shouldTrackSideEffects) {
// Any existing children that weren't consumed above were deleted. We need
// to add them to the deletion list.
existingChildren.forEach(child => deleteChild(returnFiber, child));
}
if (getIsHydrating()) {
const numberOfForks = newIdx;
pushTreeFork(returnFiber, numberOfForks);
}
return resultingFirstChild;
}
function reconcileSingleTextNode(
returnFiber: Fiber,
currentFirstChild: Fiber | null,
textContent: string,
lanes: Lanes,
): Fiber {
// There's no need to check for keys on text nodes since we don't have a
// way to define them.
if (currentFirstChild !== null && currentFirstChild.tag === HostText) {
// We already have an existing node so let's just update it and delete
// the rest.
deleteRemainingChildren(returnFiber, currentFirstChild.sibling);
const existing = useFiber(currentFirstChild, textContent);
existing.return = returnFiber;
return existing;
}
// The existing first child is not a text node so we need to create one
// and delete the existing ones.
deleteRemainingChildren(returnFiber, currentFirstChild);
const created = createFiberFromText(textContent, returnFiber.mode, lanes);
created.return = returnFiber;
return created;
}
function reconcileSingleElement(
returnFiber: Fiber,
currentFirstChild: Fiber | null,
element: ReactElement,
lanes: Lanes,
): Fiber {
const key = element.key;
let child = currentFirstChild;
while (child !== null) {
// TODO: If key === null and child.key === null, then this only applies to
// the first item in the list.
if (child.key === key) {
const elementType = element.type;
if (elementType === REACT_FRAGMENT_TYPE) {
if (child.tag === Fragment) {
deleteRemainingChildren(returnFiber, child.sibling);
const existing = useFiber(child, element.props.children);
existing.return = returnFiber;
if (__DEV__) {
existing._debugSource = element._source;
existing._debugOwner = element._owner;
}
return existing;
}
} else {
if (
child.elementType === elementType ||
// Keep this check inline so it only runs on the false path:
(__DEV__
? isCompatibleFamilyForHotReloading(child, element)
: false) ||
// Lazy types should reconcile their resolved type.
// We need to do this after the Hot Reloading check above,
// because hot reloading has different semantics than prod because
// it doesn't resuspend. So we can't let the call below suspend.
(typeof elementType === 'object' &&
elementType !== null &&
elementType.$$typeof === REACT_LAZY_TYPE &&
resolveLazy(elementType) === child.type)
) {
deleteRemainingChildren(returnFiber, child.sibling);
const existing = useFiber(child, element.props);
existing.ref = coerceRef(returnFiber, child, element);
existing.return = returnFiber;
if (__DEV__) {
existing._debugSource = element._source;
existing._debugOwner = element._owner;
}
return existing;
}
}
// Didn't match.
deleteRemainingChildren(returnFiber, child);
break;
} else {
deleteChild(returnFiber, child);
}
child = child.sibling;
}
if (element.type === REACT_FRAGMENT_TYPE) {
const created = createFiberFromFragment(
element.props.children,
returnFiber.mode,
lanes,
element.key,
);
created.return = returnFiber;
return created;
} else {
const created = createFiberFromElement(element, returnFiber.mode, lanes);
created.ref = coerceRef(returnFiber, currentFirstChild, element);
created.return = returnFiber;
return created;
}
}
function reconcileSinglePortal(
returnFiber: Fiber,
currentFirstChild: Fiber | null,
portal: ReactPortal,
lanes: Lanes,
): Fiber {
const key = portal.key;
let child = currentFirstChild;
while (child !== null) {
// TODO: If key === null and child.key === null, then this only applies to
// the first item in the list.
if (child.key === key) {
if (
child.tag === HostPortal &&
child.stateNode.containerInfo === portal.containerInfo &&
child.stateNode.implementation === portal.implementation
) {
deleteRemainingChildren(returnFiber, child.sibling);
const existing = useFiber(child, portal.children || []);
existing.return = returnFiber;
return existing;
} else {
deleteRemainingChildren(returnFiber, child);
break;
}
} else {
deleteChild(returnFiber, child);
}
child = child.sibling;
}
const created = createFiberFromPortal(portal, returnFiber.mode, lanes);
created.return = returnFiber;
return created;
}
// This API will tag the children with the side-effect of the reconciliation
// itself. They will be added to the side-effect list as we pass through the
// children and the parent.
function reconcileChildFibersImpl(
returnFiber: Fiber,
currentFirstChild: Fiber | null,
newChild: any,
lanes: Lanes,
): Fiber | null {
// This function is not recursive.
// If the top level item is an array, we treat it as a set of children,
// not as a fragment. Nested arrays on the other hand will be treated as
// fragment nodes. Recursion happens at the normal flow.
// Handle top level unkeyed fragments as if they were arrays.
// This leads to an ambiguity between <>{[...]}</> and <>...</>.
// We treat the ambiguous cases above the same.
// TODO: Let's use recursion like we do for Usable nodes?
const isUnkeyedTopLevelFragment =
typeof newChild === 'object' &&
newChild !== null &&
newChild.type === REACT_FRAGMENT_TYPE &&
newChild.key === null;
if (isUnkeyedTopLevelFragment) {
newChild = newChild.props.children;
}
// Handle object types
if (typeof newChild === 'object' && newChild !== null) {
switch (newChild.$$typeof) {
case REACT_ELEMENT_TYPE:
return placeSingleChild(
reconcileSingleElement(
returnFiber,
currentFirstChild,
newChild,
lanes,
),
);
case REACT_PORTAL_TYPE:
return placeSingleChild(
reconcileSinglePortal(
returnFiber,
currentFirstChild,
newChild,
lanes,
),
);
case REACT_LAZY_TYPE:
const payload = newChild._payload;
const init = newChild._init;
// TODO: This function is supposed to be non-recursive.
return reconcileChildFibers(
returnFiber,
currentFirstChild,
init(payload),
lanes,
);
}
if (isArray(newChild)) {
return reconcileChildrenArray(
returnFiber,
currentFirstChild,
newChild,
lanes,
);
}
if (getIteratorFn(newChild)) {
return reconcileChildrenIterator(
returnFiber,
currentFirstChild,
newChild,
lanes,
);
}
// Usables are a valid React node type. When React encounters a Usable in
// a child position, it unwraps it using the same algorithm as `use`. For
// example, for promises, React will throw an exception to unwind the
// stack, then replay the component once the promise resolves.
//
// A difference from `use` is that React will keep unwrapping the value
// until it reaches a non-Usable type.
//
// e.g. Usable<Usable<Usable<T>>> should resolve to T
//
// The structure is a bit unfortunate. Ideally, we shouldn't need to
// replay the entire begin phase of the parent fiber in order to reconcile
// the children again. This would require a somewhat significant refactor,
// because reconcilation happens deep within the begin phase, and
// depending on the type of work, not always at the end. We should
// consider as an future improvement.
if (typeof newChild.then === 'function') {
const thenable: Thenable<any> = (newChild: any);
return reconcileChildFibersImpl(
returnFiber,
currentFirstChild,
unwrapThenable(thenable),
lanes,
);
}
if (
newChild.$$typeof === REACT_CONTEXT_TYPE ||
newChild.$$typeof === REACT_SERVER_CONTEXT_TYPE
) {
const context: ReactContext<mixed> = (newChild: any);
return reconcileChildFibersImpl(
returnFiber,
currentFirstChild,
readContextDuringReconcilation(returnFiber, context, lanes),
lanes,
);
}
throwOnInvalidObjectType(returnFiber, newChild);
}
if (
(typeof newChild === 'string' && newChild !== '') ||
typeof newChild === 'number'
) {
return placeSingleChild(
reconcileSingleTextNode(
returnFiber,
currentFirstChild,
'' + newChild,
lanes,
),
);
}
if (__DEV__) {
if (typeof newChild === 'function') {
warnOnFunctionType(returnFiber);
}
}
// Remaining cases are all treated as empty.
return deleteRemainingChildren(returnFiber, currentFirstChild);
}
function reconcileChildFibers(
returnFiber: Fiber,
currentFirstChild: Fiber | null,
newChild: any,
lanes: Lanes,
): Fiber | null {
// This indirection only exists so we can reset `thenableState` at the end.
// It should get inlined by Closure.
thenableIndexCounter = 0;
const firstChildFiber = reconcileChildFibersImpl(
returnFiber,
currentFirstChild,
newChild,
lanes,
);
thenableState = null;
// Don't bother to reset `thenableIndexCounter` to 0 because it always gets
// set at the beginning.
return firstChildFiber;
}
return reconcileChildFibers;
}
1.4 packages/react-reconciler/src/ReactChildFiber.js reconcileChildFibers()
function reconcileChildFibers(
returnFiber: Fiber,
currentFirstChild: Fiber | null,
newChild: any,
lanes: Lanes,
): Fiber | null {
// This indirection only exists so we can reset `thenableState` at the end.
// It should get inlined by Closure.
thenableIndexCounter = 0;
const firstChildFiber = reconcileChildFibersImpl(
returnFiber,
currentFirstChild,
newChild,
lanes,
);
thenableState = null;
// Don't bother to reset `thenableIndexCounter` to 0 because it always gets
// set at the beginning.
return firstChildFiber;
}
1.5 packages/react-reconciler/src/ReactChildFiber.js reconcileChildFibersImpl()
function reconcileChildFibersImpl(
returnFiber: Fiber,
currentFirstChild: Fiber | null,
newChild: any,
lanes: Lanes,
): Fiber | null {
// This function is not recursive.
// If the top level item is an array, we treat it as a set of children,
// not as a fragment. Nested arrays on the other hand will be treated as
// fragment nodes. Recursion happens at the normal flow.
// Handle top level unkeyed fragments as if they were arrays.
// This leads to an ambiguity between <>{[...]}</> and <>...</>.
// We treat the ambiguous cases above the same.
// TODO: Let's use recursion like we do for Usable nodes?
const isUnkeyedTopLevelFragment =
typeof newChild === 'object' &&
newChild !== null &&
newChild.type === REACT_FRAGMENT_TYPE &&
newChild.key === null;
if (isUnkeyedTopLevelFragment) {
newChild = newChild.props.children;
}
// Handle object types
if (typeof newChild === 'object' && newChild !== null) {
switch (newChild.$$typeof) {
case REACT_ELEMENT_TYPE:
return placeSingleChild(
reconcileSingleElement(
returnFiber,
currentFirstChild,
newChild,
lanes,
),
);
case REACT_PORTAL_TYPE:
return placeSingleChild(
reconcileSinglePortal(
returnFiber,
currentFirstChild,
newChild,
lanes,
),
);
case REACT_LAZY_TYPE:
const payload = newChild._payload;
const init = newChild._init;
// TODO: This function is supposed to be non-recursive.
return reconcileChildFibers(
returnFiber,
currentFirstChild,
init(payload),
lanes,
);
}
if (isArray(newChild)) {
return reconcileChildrenArray(
returnFiber,
currentFirstChild,
newChild,
lanes,
);
}
if (getIteratorFn(newChild)) {
return reconcileChildrenIterator(
returnFiber,
currentFirstChild,
newChild,
lanes,
);
}
// Usables are a valid React node type. When React encounters a Usable in
// a child position, it unwraps it using the same algorithm as `use`. For
// example, for promises, React will throw an exception to unwind the
// stack, then replay the component once the promise resolves.
//
// A difference from `use` is that React will keep unwrapping the value
// until it reaches a non-Usable type.
//
// e.g. Usable<Usable<Usable<T>>> should resolve to T
//
// The structure is a bit unfortunate. Ideally, we shouldn't need to
// replay the entire begin phase of the parent fiber in order to reconcile
// the children again. This would require a somewhat significant refactor,
// because reconcilation happens deep within the begin phase, and
// depending on the type of work, not always at the end. We should
// consider as an future improvement.
if (typeof newChild.then === 'function') {
const thenable: Thenable<any> = (newChild: any);
return reconcileChildFibersImpl(
returnFiber,
currentFirstChild,
unwrapThenable(thenable),
lanes,
);
}
if (
newChild.$$typeof === REACT_CONTEXT_TYPE ||
newChild.$$typeof === REACT_SERVER_CONTEXT_TYPE
) {
const context: ReactContext<mixed> = (newChild: any);
return reconcileChildFibersImpl(
returnFiber,
currentFirstChild,
readContextDuringReconcilation(returnFiber, context, lanes),
lanes,
);
}
throwOnInvalidObjectType(returnFiber, newChild);
}
if (
(typeof newChild === 'string' && newChild !== '') ||
typeof newChild === 'number'
) {
return placeSingleChild(
reconcileSingleTextNode(
returnFiber,
currentFirstChild,
'' + newChild,
lanes,
),
);
}
if (__DEV__) {
if (typeof newChild === 'function') {
warnOnFunctionType(returnFiber);
}
}
// Remaining cases are all treated as empty.
return deleteRemainingChildren(returnFiber, currentFirstChild);
}