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fix: invalidate derived stores deeply #10575

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fix: invalidate derived stores deeply #10575

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91f5b84
add test to exercise semi-diamond dependency problem
Feb 11, 2024
f52adbc
Allow deep invalidation for stores
Feb 15, 2024
c5db044
Correct type docs
Feb 20, 2024
4e666de
Add revalidation logic to cover final test case
Feb 20, 2024
1e62e94
alternative fix
Rich-Harris Feb 20, 2024
78dc776
changeset
Rich-Harris Feb 20, 2024
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5 changes: 5 additions & 0 deletions .changeset/tender-pants-run.md
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@@ -0,0 +1,5 @@
---
'svelte': patch
---

fix: invalidate derived stores deeply
59 changes: 42 additions & 17 deletions packages/svelte/src/store/index.js
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@@ -1,6 +1,8 @@
import { noop, run } from '../internal/common.js';
import { subscribe_to_store } from './utils.js';

const SUBSCRIBERS_SYMBOL = Symbol('subscribers');

/**
* @type {Array<import('./private').SubscribeInvalidateTuple<any> | any>}
*/
Expand All @@ -16,8 +18,11 @@ const subscriber_queue = [];
* @returns {import('./public').Readable<T>}
*/
export function readable(value, start) {
const w = writable(value, start);
return {
subscribe: writable(value, start).subscribe
// @ts-expect-error we don't want this to be on the public types
[SUBSCRIBERS_SYMBOL]: w[SUBSCRIBERS_SYMBOL],
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Should this be made non-enumerable then?

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symbols are already non-enumerable, no?

obj = {
  [Symbol()]: 1,
  foo: 2
};

for (const key in obj) {
  console.log(key, obj[key]); // logs `foo 2`
}

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@trueadm trueadm Feb 20, 2024 •
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Object.assign() copies enumerable symbols as does object spreading.

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I think it's probably harmless — people aren't really spreading or assigning the results of calling writable and readable, and there's not much damage that could be caused by people inadvertently getting a reference to the subscriber list. Feels like overkill to use Object.defineProperty here

subscribe: w.subscribe
};
}

Expand Down Expand Up @@ -55,21 +60,19 @@ export function writable(value, start = noop) {
* @returns {void}
*/
function set(new_value) {
if (safe_not_equal(value, new_value)) {
value = new_value;
if (stop) {
// store is ready
const run_queue = !subscriber_queue.length;
for (const subscriber of subscribers) {
subscriber[1]();
subscriber_queue.push(subscriber, value);
}
if (run_queue) {
for (let i = 0; i < subscriber_queue.length; i += 2) {
subscriber_queue[i][0](subscriber_queue[i + 1]);
}
subscriber_queue.length = 0;
value = new_value;
if (stop) {
// store is ready
const run_queue = !subscriber_queue.length;
for (const subscriber of subscribers) {
subscriber[1]();
subscriber_queue.push(subscriber, value);
}
if (run_queue) {
for (let i = 0; i < subscriber_queue.length; i += 2) {
subscriber_queue[i][0](subscriber_queue[i + 1]);
}
subscriber_queue.length = 0;
}
}
}
Expand Down Expand Up @@ -103,7 +106,23 @@ export function writable(value, start = noop) {
}
};
}
return { set, update, subscribe };

/** @param {T} new_value */
function set_if_changed(new_value) {
if (safe_not_equal(value, new_value)) {
set(new_value);
}
}

return {
// @ts-expect-error
[SUBSCRIBERS_SYMBOL]: subscribers,
set: set_if_changed,
update: (fn) => {
set_if_changed(fn(/** @type {T} */ (value)));
},
subscribe
};
}

/**
Expand Down Expand Up @@ -156,7 +175,7 @@ export function derived(stores, fn, initial_value) {
throw new Error('derived() expects stores as input, got a falsy value');
}
const auto = fn.length < 2;
return readable(initial_value, (set, update) => {
const r = readable(initial_value, (set, update) => {
let started = false;
/** @type {T[]} */
const values = [];
Expand Down Expand Up @@ -186,6 +205,11 @@ export function derived(stores, fn, initial_value) {
},
() => {
pending |= 1 << i;

// @ts-expect-error
for (const s of r[SUBSCRIBERS_SYMBOL]) {
s[1]();
}
}
)
);
Expand All @@ -200,6 +224,7 @@ export function derived(stores, fn, initial_value) {
started = false;
};
});
return r;
}

/**
Expand Down
30 changes: 30 additions & 0 deletions packages/svelte/tests/store/test.ts
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Expand Up @@ -97,6 +97,20 @@ describe('writable', () => {
unsubscribe();
assert.doesNotThrow(() => unsubscribe());
});

it('ignores no-op sets', () => {
const store = writable(0);

let count = 0;
const unsubscribe = store.subscribe(() => {
count += 1;
});

store.set(0);
assert.equal(count, 1);

unsubscribe();
});
});

describe('readable', () => {
Expand Down Expand Up @@ -551,6 +565,22 @@ describe('derived', () => {
});
});
});

it('only updates once dependents are resolved', () => {
const a = writable(1);
const b = derived(a, (a) => a * 2);
const c = derived([a, b], ([a, b]) => a + b);

const values: number[] = [];

const unsubscribe = c.subscribe((c) => {
values.push(c);
});

a.set(2);
a.set(3);
assert.deepEqual(values, [3, 6, 9]);
});
});

describe('get', () => {
Expand Down