[No QA] Add PERF-17 coding-standards rule: Avoid intermediate lookup layers by kacper-mikolajczak · Pull Request #94220 · Expensify/App

kacper-mikolajczak · 2026-06-22T21:50:16Z

Explanation of Change

Adds coding-standards reviewer rule PERF-17 (.claude/skills/coding-standards/rules/perf-17-avoid-intermediate-lookup.md) and indexes it in SKILL.md. The rule flags eager construction of intermediate lookup layers from already-keyed data and recommends passing raw sources with on-demand lookup. Docs-only; no runtime code changes.

Fixed Issues

$ #94219
PROPOSAL:

Tests

Verify that no errors appear in the JS console
Verify the new rule file exists with the standard sections and is linked from SKILL.md.

Verify that no errors appear in the JS console

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N/A

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N/A - docs-only change.

Verify that no errors appear in the JS console

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Android: Native

Android: mWeb Chrome

iOS: Native

iOS: mWeb Safari

MacOS: Chrome / Safari

kacper-mikolajczak · 2026-06-22T21:57:39Z

@codex pls review

kacper-mikolajczak · 2026-06-22T22:01:59Z

@TMisiukiewicz curious what you think and whether I grasped the problem space good enough. Also if you happen to have more concrete real examples then shoot them at me ❤️

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TMisiukiewicz

Some concerns from my side:

The rule points at the wrong villain. #94146's whole win came from replacing the precomputed archivedReportsIDSet digest with the raw reportNameValuePairs collection and doing O(1) lookups inside findLastAccessedReport. Passing the collection was the fix. The actual lesson is: don't eagerly build an expensive data structure from data you already hold to satisfy a conditional/per-element check; pass the raw source and index it on demand. That's a different principle than "don't pass collections to lazy callees."
The "correct" fix recommends a deprecated, staleness-prone path. It relies on the module-scoped Onyx.connectWithoutView fallback inside the util which is the pattern we've been removing for months because those values can be stale or not-yet-hydrated

If you need any help in reframing this rule, let me know 😊

kacper-mikolajczak · 2026-06-24T20:48:27Z

Thanks @TMisiukiewicz, this are exactly the remarks I was looking for ❤️ Let me know what you think of the rule now and if you have more examples, I am more than happy to add those. Thanks!

TMisiukiewicz

Looks good 👍 leaving two more concerns

TMisiukiewicz · 2026-06-26T09:44:49Z

+
+**DO NOT flag if:**
+
+- The digest is reused across many lookups in a hot path and is built once (memoized/stable, not rebuilt every render) - a genuine precompute win.


I think AI might have problems to decide whether a memoized part is a precompute win since from the diff it's difficult to reason about the call frequency. Any ideas how we could improve this? 🤔

Right call. Improved the instructions to search via Grep outside a diff for marks of this, too.

TMisiukiewicz · 2026-06-26T09:51:04Z

+
+### Reasoning
+
+Building a derived lookup structure (`new Set`/`new Map`/`Object.fromEntries` or a hand-built index) from a collection you already hold - just to answer membership/per-element checks downstream - is O(n) construction, often re-run every render, for something the callee can index O(1) straight from the raw source. Pass the raw collection and do the lookup on demand inside the callee instead. In [#94146], replacing a precomputed archived-IDs `Set` with the raw `reportNameValuePairs` collection plus O(1) lookups inside `findLastAccessedReport` cut ~14s on a 100k-report account. This is extra wasteful when the callee runs conditionally/lazily, since the digest is built even when it's never used.


This is extra wasteful when the callee runs conditionally/lazily, since the digest is built even when it's never used

this might be actually translated into a Flag when... condition, wdyt?

- Replace the memoization carve-out with a diff-observable test (repeated/visible lookups), defaulting to flag when usage isn't visible. - Promote the conditional/lazy-callee note into an explicit higher-confidence flag signal. - Add lazy-callee search-pattern hints.

mountiny · 2026-07-02T14:20:53Z

How is this looking?

Clarify when to flag eager lookup construction, tighten confidence criteria, and reduce over-triggering patterns so review signals are more actionable. Co-authored-by: Cursor <cursoragent@cursor.com>

kacper-mikolajczak · 2026-07-07T13:48:23Z

Hi folks! Sorry for the pause here - got involved with higher prio items.

All the review comments are now addressed. Also, refined a bit flags, title and added better examples (in my opinion).

@TMisiukiewicz happy to get your final review on this one. Thanks!

melvin-bot · 2026-07-07T13:50:04Z

@ikevin127 @mountiny One of you needs to copy/paste the Reviewer Checklist from here into a new comment on this PR and complete it. If you have the K2 extension, you can simply click: [this button]

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ikevin127 · 2026-07-07T20:36:47Z

@mountiny I'm assuming this doesn't need C+ review, let me know otherwise!

TMisiukiewicz

left one NIT :)

kacper-mikolajczak · 2026-07-08T10:30:29Z

Thanks @TMisiukiewicz, adjusted to Avoid intermediate lookup layers and perf-17-avoid-intermediate-lookup

kacper-mikolajczak · 2026-07-08T10:34:22Z

Also needed to fix commits signing but the PR should be ready now :)

CC @ikevin127 @mountiny

Addresses codex P2: Set/Map built from an array to avoid O(n) .includes is a real O(1) win, not a violation. Restrict rule to already-keyed raw sources and drop the .includes search pattern.

kacper-mikolajczak · 2026-07-09T16:25:21Z

Hey 👋 Wanted to let you know that I'll be out of office tomorrow. The PR should be ready for merge - if anything happens otherwise, I will resolve when I am back 🫡

mountiny · 2026-07-09T19:04:54Z

Reviewer Checklist

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OSBotify · 2026-07-10T16:17:50Z

🚀 Deployed to staging by https://github.com/mountiny in version: 9.4.33-0 🚀

platform	result
🕸 web 🕸	success ✅
🤖 android 🤖	success ✅
🍎 iOS 🍎	cancelled 🔪

OSBotify · 2026-07-14T11:15:58Z

🚀 Deployed to production by https://github.com/lakchote in version: 9.4.33-8 🚀

platform	result
🕸 web 🕸	success ✅
🤖 android 🤖	success ✅
🍎 iOS 🍎	success ✅

Bundle Size Analysis (Sentry):

Android

Add PERF-17 coding-standards rule: no eager args for lazy callees

3a3110a

melvin-bot Bot assigned kacper-mikolajczak Jun 22, 2026

Make PERF-17 concise for agentic reviewer

f42e940

chatgpt-codex-connector Bot reviewed Jun 22, 2026

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Comment thread .claude/skills/coding-standards/rules/perf-17-no-eager-args-for-lazy-callees.md Outdated

Align PERF-17 metadata headings with other rules

b21472f

TMisiukiewicz suggested changes Jun 23, 2026

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Comment thread .claude/skills/coding-standards/rules/perf-17-no-eager-args-for-lazy-callees.md Outdated

Comment thread .claude/skills/coding-standards/rules/perf-17-no-eager-args-for-lazy-callees.md Outdated

Reframe PERF-17 around eager pre-aggregation per review

3e445bd

kacper-mikolajczak changed the title ~~[No QA] Add PERF-17 coding-standards rule: no eager args for lazy callees~~ [No QA] Add PERF-17 coding-standards rule: pass raw source, index on demand Jun 24, 2026

kacper-mikolajczak requested a review from TMisiukiewicz June 24, 2026 20:47

TMisiukiewicz reviewed Jun 26, 2026

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kacper-mikolajczak and others added 2 commits July 7, 2026 15:37

Refine PERF-17 guidance for intermediate lookup layers.

6312e00

Clarify when to flag eager lookup construction, tighten confidence criteria, and reduce over-triggering patterns so review signals are more actionable. Co-authored-by: Cursor <cursoragent@cursor.com>

adjust examples and outside diff behaviour

f414825

kacper-mikolajczak requested a review from TMisiukiewicz July 7, 2026 13:48

kacper-mikolajczak marked this pull request as ready for review July 7, 2026 13:49

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Comment thread .claude/skills/coding-standards/rules/perf-17-pass-raw-index-on-demand.md Outdated

TMisiukiewicz reviewed Jul 8, 2026

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Comment thread .claude/skills/coding-standards/rules/perf-17-pass-raw-index-on-demand.md Outdated

TMisiukiewicz approved these changes Jul 8, 2026

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kacper-mikolajczak changed the title ~~[No QA] Add PERF-17 coding-standards rule: pass raw source, index on demand~~ [No QA] Add PERF-17 coding-standards rule: Avoid intermediate lookup layers Jul 8, 2026

kacper-mikolajczak and others added 2 commits July 8, 2026 12:34

Scope PERF-17 to keyed sources; exempt array-backed indexes

d00eaec

Addresses codex P2: Set/Map built from an array to avoid O(n) .includes is a real O(1) win, not a violation. Restrict rule to already-keyed raw sources and drop the .includes search pattern.

update title

f2a2079

kacper-mikolajczak force-pushed the reviewer-rule-lazy-args branch from a377431 to f2a2079 Compare July 8, 2026 10:34

mountiny approved these changes Jul 9, 2026

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mountiny merged commit a7fb506 into Expensify:main Jul 9, 2026
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melvin-bot Bot mentioned this pull request Jul 14, 2026

[Due for payment 2026-07-21] Add coding-standards rule to prevent eager component-level args for conditionally/lazily-used callees #94219

Open


		DO NOT flag if:

		- The digest is reused across many lookups in a hot path and is built once (memoized/stable, not rebuilt every render) - a genuine precompute win.


		### Reasoning

		Building a derived lookup structure (`new Set`/`new Map`/`Object.fromEntries` or a hand-built index) from a collection you already hold - just to answer membership/per-element checks downstream - is O(n) construction, often re-run every render, for something the callee can index O(1) straight from the raw source. Pass the raw collection and do the lookup on demand inside the callee instead. In [#94146], replacing a precomputed archived-IDs `Set` with the raw `reportNameValuePairs` collection plus O(1) lookups inside `findLastAccessedReport` cut ~14s on a 100k-report account. This is extra wasteful when the callee runs conditionally/lazily, since the digest is built even when it's never used.

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