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Ensure that a state settled hook cant interfere with a signal update #696

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Ensure that a state settled hook cant interfere with a signal update #696

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4ed40ce
Ensure that a state settled hook cant interfere with a signal update
JoviDeCroock Jun 7, 2025
e962124
Add test
JoviDeCroock Jun 7, 2025
4028d6f
Fix type
JoviDeCroock Jun 7, 2025
85b3ca3
Create mighty-ghosts-train.md
JoviDeCroock Jun 7, 2025
dda1ef4
TS is behaving oddly
JoviDeCroock Jun 7, 2025
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6 changes: 6 additions & 0 deletions .changeset/mighty-ghosts-train.md
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Original file line number Diff line number Diff line change
@@ -0,0 +1,6 @@
---
"@preact/signals": minor
---

Ensure that a state settled hook cant interfere with a signal update, this is in
preparation for the Preact v11 release.
37 changes: 34 additions & 3 deletions packages/preact/src/index.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -33,6 +33,9 @@ export {
const HAS_PENDING_UPDATE = 1 << 0;
const HAS_HOOK_STATE = 1 << 1;
const HAS_COMPUTEDS = 1 << 2;
const SHOULD_UPDATE = 1 << 4;

const PREACT_SKIP_CHILDREN = 1 << 3;

let oldNotify: (this: Effect) => void,
effectsQueue: Array<Effect> = [],
Expand Down Expand Up @@ -355,15 +358,24 @@ Component.prototype.shouldComponentUpdate = function (
// @ts-ignore
for (let i in state) return true;

const hasHooksState = this._updateFlags & HAS_HOOK_STATE;
if (this.__f || (typeof this.u == "boolean" && this.u === true)) {
const hasHooksState = this._updateFlags & HAS_HOOK_STATE;
// if this component used no signals or computeds and no hooks state, update:
if (!hasSignals && !hasHooksState && !(this._updateFlags & HAS_COMPUTEDS))
if (!hasSignals && !hasHooksState && !(this._updateFlags & HAS_COMPUTEDS)) {
if (hasHooksState) {
this._updateFlags |= SHOULD_UPDATE;
}
return true;
}

// if there is a pending re-render triggered from Signals,
// or if there is hooks state, update:
if (this._updateFlags & HAS_PENDING_UPDATE) return true;
if (this._updateFlags & HAS_PENDING_UPDATE) {
if (hasHooksState) {
this._updateFlags |= SHOULD_UPDATE;
}
return true;
}
} else {
// if this component used no signals or computeds, update:
if (!hasSignals && !(this._updateFlags & HAS_COMPUTEDS)) return true;
Expand All @@ -383,6 +395,25 @@ Component.prototype.shouldComponentUpdate = function (
return false;
};

hook(OptionsTypes.AFTER_RENDER, (old, vnode: VNode) => {
const component = vnode.__c;
if (component && component._updateFlags & SHOULD_UPDATE) {
// When we have a signal that should update and we see that SKIP_CHILDREN is set,
// we need to clear it so that the children are rendered.
// This is a rare scenario where we both have a signal update as well as
// a hook that updates and settles on the same value.
component._updateFlags &= ~SHOULD_UPDATE;
// @ts-ignore
if (vnode.__u & PREACT_SKIP_CHILDREN) {
// @ts-ignore
vnode.__u &= ~PREACT_SKIP_CHILDREN;
}
}
// This is a Preact 11 only hook and is meant to take care of state-settling in hooks.
// Explained in https://github.com/preactjs/preact/pull/4760
old(vnode);
});

export function useSignal<T>(value: T, options?: SignalOptions<T>): Signal<T>;
export function useSignal<T = undefined>(): Signal<T | undefined>;
export function useSignal<T>(value?: T, options?: SignalOptions<T>) {
Expand Down
2 changes: 2 additions & 0 deletions packages/preact/src/internal.d.ts
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Expand Up @@ -47,13 +47,15 @@ export const enum OptionsTypes {
RENDER = "__r",
CATCH_ERROR = "__e",
UNMOUNT = "unmount",
AFTER_RENDER = "__d",
}

export interface OptionsType {
[OptionsTypes.HOOK](component: Component, index: number, type: number): void;
[OptionsTypes.DIFF](vnode: VNode): void;
[OptionsTypes.DIFFED](vnode: VNode): void;
[OptionsTypes.RENDER](vnode: VNode): void;
[OptionsTypes.AFTER_RENDER](vnode: VNode): void;
[OptionsTypes.CATCH_ERROR](error: any, vnode: VNode, oldVNode: VNode): void;
[OptionsTypes.UNMOUNT](vnode: VNode): void;
}
Expand Down
28 changes: 28 additions & 0 deletions packages/preact/test/index.test.tsx
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Expand Up @@ -761,6 +761,34 @@ describe("@preact/signals", () => {
});
expect(scratch.innerHTML).to.equal("<p>bar baz</p>");
});

it("state settling should not prevent a signal update from being rendered", () => {
let set: any;
const test2 = signal("Foo");
function Test() {
const [test, setTest] = useState("foo");
set = setTest;
return (
<p>
{test} {test2.value}
</p>
);
}

function App() {
return <Test />;
}

render(<App />, scratch);

expect(scratch.innerHTML).to.equal("<p>foo Foo</p>");
act(() => {
set("bar");
test2.value = "Bar";
set("foo");
});
expect(scratch.innerHTML).to.equal("<p>foo Bar</p>");
});
});

describe("useSignalEffect()", () => {
Expand Down