refactor(store): replace array with set in __depsThatHaveWrittenThisTick

[gwansikk]

🎯 Changes

I'm using TanStack Form for a large-scale form application. The project manages user-addable table rows (each row containing multiple inputs) along with 20-30 additional fields on a single page. During form submission, UI blocking of 2.7 seconds, and in some cases 8-10 seconds, was occurring.

After profiling, I identified that the __flush_internals function in @tanstack/store was causing a performance bottleneck due to excessive recursive calls.

Change the data structure of __depsThatHaveWrittenThisTick from Array to Set, replacing O(n) includes() with O(1) has() for duplicate checking.

- current: [] as Array<Derived<unknown> | Store<unknown>>,
+ current: new Set<Derived<unknown> | Store<unknown>>(),

- if (__depsThatHaveWrittenThisTick.current.includes(derived)) {
+ if (__depsThatHaveWrittenThisTick.current.has(derived)) {

- __depsThatHaveWrittenThisTick.current.push(derived)
+ __depsThatHaveWrittenThisTick.current.add(derived)

- __depsThatHaveWrittenThisTick.current = []
+ __depsThatHaveWrittenThisTick.current.clear()

Benchmark

Scale	Stores	Deriveds	Winner	Improvement
Small	20	60	Array	1.98x faster
Medium	50	200	Set	1.13x faster
Large	100	500	Set	2.16x faster
Very Large	200	1000	Set	3.66x faster
Extreme	500	2500	Set	8.43x faster

Detailed Results

Scale	Method	hz	mean (ms)	min (ms)	max (ms)	p99 (ms)	rme	samples
Small	Array.includes()	35,907.52	0.0278	0.0262	0.2352	0.0365	±0.22%	17,954
Small	Set.has()	18,101.88	0.0552	0.0501	2.1192	0.0736	±1.14%	9,051
Medium	Array.includes()	3,044.06	0.3285	0.3119	0.5857	0.3871	±0.29%	1,523
Medium	Set.has()	3,450.28	0.2898	0.2742	0.5368	0.3285	±0.24%	1,726
Large	Array.includes()	398.89	2.5070	2.4501	2.7756	2.7168	±0.34%	200
Large	Set.has()	861.65	1.1606	1.0971	1.5831	1.2923	±0.39%	431
Very Large	Array.includes()	112.81	8.8648	8.7488	9.1669	9.1669	±0.25%	57
Very Large	Set.has()	413.38	2.4191	2.2845	2.9173	2.6126	±0.44%	207
Extreme	Array.includes()	20.31	49.2265	47.9097	51.6416	51.6416	±1.41%	11
Extreme	Set.has()	171.27	5.8386	5.5525	6.4998	6.4998	±0.55%	86

✅ Checklist

• I have followed the steps in the Contributing guide.
• I have tested this code locally with pnpm test:pr.

🚀 Release Impact

• This change affects published code, and I have generated a changeset.
• This change is docs/CI/dev-only (no release).

[gwansikk]

This is the first in a series of performance improvement PRs.
All tests pass, but feedback is welcome if I've missed anything.

I'd like to better understand the internals and help solve the pyramid dependency problem more elegantly.