WIP: batch commit callbacks from all components in the render queue

compat/test/browser/useSyncExternalStore.test.js

@@ -658,10 +658,7 @@ describe('useSyncExternalStore', () => {
 			await act(() => {
 				store.set(1);
 			});
-			// Preact logs differ from React here cuz of how we do rerendering. We
-			// rerender subtrees and then commit effects so Child2 never sees the
-			// update to 1 cuz Child1 rerenders and runs its layout effects first.
-			assertLog([1, /*1,*/ 'Reset back to 0', 0, 0]);
+			assertLog([1, 1, 'Reset back to 0', 0, 0]);
 			expect(container.textContent).to.equal('00');
 		});
 

src/component.js

@@ -2,7 +2,7 @@ import { assign } from './util';
 import { diff, commitRoot } from './diff/index';
 import options from './options';
 import { Fragment } from './create-element';
-import { MODE_HYDRATE } from './constants';
+import { EMPTY_ARR, MODE_HYDRATE } from './constants';
 
 /**
  * Base Component class. Provides `setState()` and `forceUpdate()`, which
@@ -120,12 +120,10 @@ export function getDomSibling(vnode, childIndex) {
  * Trigger in-place re-rendering of a component.
  * @param {Component} component The component to rerender
  */
-function renderComponent(component) {
+function renderComponent(component, commitQueue, refQueue) {
 	let oldVNode = component._vnode,
 		oldDom = oldVNode._dom,
-		parentDom = component._parentDom,
-		commitQueue = [],
-		refQueue = [];
+		parentDom = component._parentDom;
 
 	if (parentDom) {
 		const newVNode = assign({}, oldVNode);
@@ -146,11 +144,14 @@ function renderComponent(component) {
 		);
 
 		newVNode._parent._children[newVNode._index] = newVNode;
-		commitRoot(commitQueue, newVNode, refQueue);
+
+		newVNode._nextDom = undefined;
 
 		if (newVNode._dom != oldDom) {
 			updateParentDomPointers(newVNode);
 		}
+
+		return newVNode;
 	}
 }
 
@@ -220,21 +221,33 @@ const depthSort = (a, b) => a._vnode._depth - b._vnode._depth;
 /** Flush the render queue by rerendering all queued components */
 function process() {
 	let c;
+	let commitQueue = [];
+	let refQueue = [];
+	let root;
 	rerenderQueue.sort(depthSort);
 	// Don't update `renderCount` yet. Keep its value non-zero to prevent unnecessary
 	// process() calls from getting scheduled while `queue` is still being consumed.
 	while ((c = rerenderQueue.shift())) {
 		if (c._dirty) {
 			let renderQueueLength = rerenderQueue.length;
-			renderComponent(c);
-			if (rerenderQueue.length > renderQueueLength) {
+			root = renderComponent(c, commitQueue, refQueue) || root;
+			// If this WAS the last component in the queue, run commit callbacks *before* we exit the tight loop.
+			// This is required in order for `componentDidMount(){this.setState()}` to be batched into one flush.
+			// Otherwise, also run commit callbacks if the render queue was mutated.
+			if (renderQueueLength === 0 || rerenderQueue.length > renderQueueLength) {
+				commitRoot(commitQueue, root, refQueue);
+				refQueue.length = commitQueue.length = 0;
+				root = undefined;
 				// When i.e. rerendering a provider additional new items can be injected, we want to
 				// keep the order from top to bottom with those new items so we can handle them in a
 				// single pass
 				rerenderQueue.sort(depthSort);
+			} else if (root) {
+				if (options._commit) options._commit(root, EMPTY_ARR);
 			}
 		}
 	}
+	if (root) commitRoot(commitQueue, root, refQueue);
 	process._rerenderCount = 0;
 }
 

src/diff/index.js

@@ -311,8 +311,6 @@ export function diff(
  * @param {VNode} root
  */
 export function commitRoot(commitQueue, root, refQueue) {
-	root._nextDom = undefined;
-
 	for (let i = 0; i < refQueue.length; i++) {
 		applyRef(refQueue[i], refQueue[++i], refQueue[++i]);
 	}

src/render.js

@@ -59,7 +59,7 @@ export function render(vnode, parentDom, replaceNode) {
 		refQueue
 	);
 
-	// Flush all queued effects
+	vnode._nextDom = undefined;
 	commitRoot(commitQueue, vnode, refQueue);
 }