perf: hoist transaction violations for MoneyRequestReportTransactionList items

[TMisiukiewicz]

Explanation of Change

On the expense report transaction list, each row called useTransactionViolations, which subscribes to Onyx per transaction 4 times.

With many rows in a virtualized list, that becomes N rows × several subscriptions. Any Onyx update can trigger re-renders across many rows, and list recycling keeps those subscriptions active while scrolling. That matches the general anti-pattern of calling useOnyx inside list item render paths (see PERF-3 in coding standards).

The parent list (MoneyRequestReportTransactionList) already subscribed to the full TRANSACTION_VIOLATIONS collection for RBR sorting, but each row still duplicated work with its own hooks.

This PR hoists transaction violation filtering from per-row useOnyx subscriptions to the report transaction list’s existing bulk violations subscription, reducing list subscription overhead and stabilizing row props for FlashList.

Fixed Issues

$ #91963
PROPOSAL:

Tests

1. Open report with multiple transactions (at least one must have a violation)
2. Verify the transaction shows RBR message

• Verify that no errors appear in the JS console

Offline tests

QA Steps

// TODO: These must be filled out, or the issue title must include "[No QA]."
Same as tests

• Verify that no errors appear in the JS console

PR Author Checklist

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Screenshots/Videos

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iOS: mWeb Safari

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[melvin-bot]

@aimane-chnaif Please 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]

[codecov]

Codecov Report

❌ Looks like you've decreased code coverage for some files. Please write tests to increase, or at least maintain, the existing level of code coverage. See our documentation here for how to interpret this table.

Files with missing lines	Coverage Δ
...stReportView/MoneyRequestReportTransactionItem.tsx	0.00% <ø> (ø)
src/hooks/useTransactionViolations.ts	100.00% <100.00%> (ø)
src/libs/TransactionUtils/index.ts	87.50% <80.00%> (-0.04%)	⬇️
...stReportView/MoneyRequestReportTransactionList.tsx	0.60% <5.88%> (+0.28%)	⬆️
... and 10 files with indirect coverage changes

[MelvinBot]

Code Review

Overview: Hoists per-row useTransactionViolations subscriptions out of MoneyRequestReportTransactionItemBody and reuses the parent list's existing TRANSACTION_VIOLATIONS collection subscription. Extracts the filter+merge logic into a new shared getVisibleTransactionViolations helper so the per-row hook and the bulk path share one implementation.

Verdict: Looks good. The refactor is minimal, behavior‑preserving for other callers, and meaningfully reduces FlashList subscription overhead. A few notes below.

Correctness

• The new shared helper getVisibleTransactionViolations is a verbatim extraction of the original hook body — same filter predicates, same mergeProhibitedViolations wrap, same default for shouldShowRterForSettledReport = true. ✅
• All previous non‑list callers of useTransactionViolations (DebugTransactionViolationPage, IOURequestStepAttendees, MoneyRequestHeader, etc.) go through the new helper and get identical output. ✅
• In the list path, useTransactionViolations(transaction.transactionID) was previously called without the second arg, so shouldShowRterForSettledReport defaulted to true. The new bulk path also implicitly uses true. No behavior change. ✅
• EMPTY_VIOLATIONS is a module‑level constant returned for both the "no raw violations" and "filtered to empty" cases — this preserves stable prop identity for rows without visible violations, which is exactly what FlashList wants. ✅

Potential downsides worth being aware of

• Re-render fanout for rows with violations. Previously, only the row whose TRANSACTION_VIOLATIONS_<id> key changed re-rendered. Now the parent re-renders on any change in the whole TRANSACTION_VIOLATIONS collection, rebuilds violationsByTransactionID, and every row whose violation list is non‑empty gets a freshly‑allocated violations array reference (even when its actual contents are unchanged). Rows with no violations stay stable via EMPTY_VIOLATIONS, but rows with violations will re-render on every collection update across the report.

  This is probably still a net win (no more N × subscriptions on a virtualized recycled list), and it matches what MoneyRequestReportTransactionList was already paying for RBR sorting on line 211. But it's worth checking on a report with many violated transactions to confirm there's no regression. If it shows up, an easy follow‑up is to shallow‑compare the new filtered array against the previous one and reuse the prior reference when equal.

• useMemo dep churn from report / policy. Line 652 depends on report and policy directly. If either gets a new reference from Onyx (common), the whole map is rebuilt and every "has‑violations" row's prop changes (see point above). Same caveat — likely fine, just flagging.

Minor nits

• Type for allViolations. filterTransactionViolations types the second arg as Record<string, TransactionViolations | undefined> | undefined, but Onyx collections are OnyxCollection<TransactionViolations> which also permits null values. Consider OnyxCollection<OnyxTypes.TransactionViolations> directly so the type matches what useOnyx returns and you can drop the locally‑defined shape.

• policy ?? undefined at call site. Line 649 normalizes null → undefined only at the call site. If you widen filterTransactionViolations's policy param to OnyxEntry<Policy> (matching the helper signature), you can drop the ?? and let the value flow through unchanged.

• Export ordering. New export getVisibleTransactionViolations is added next to mergeProhibitedViolations in the exports block — fine, but the file has many exports; consider alphabetizing if that's the file's convention (the surrounding exports are mixed, so this is just a preference).

• Test mock churn. The test file's mock was refactored from an inline mergeProhibitedViolations literal to a top‑level binding so it can be referenced by both the merge mock and the new getVisibleTransactionViolations mock. Reads fine.

Verification suggestions

• Manual: open a report with a mix of violated and non‑violated transactions, scroll a long list, confirm RBR badges still render and no extra renders show up in React DevTools profiler.
• Automated: the existing tests/unit/useTransactionViolationsTest.ts exercises the hook indirectly via the new helper through the mock — that's good coverage for the extraction, but there's no direct test for the new filterTransactionViolations / violationsByTransactionID path. A small unit test asserting that two identical inputs produce reference‑equal EMPTY_VIOLATIONS for empty rows would lock in the FlashList stability invariant.

Security / data flow

No new data exposed, no API surface changes, no auth/permission logic touched. The user‑visibility filter (isViolationDismissed + shouldShowViolation) is preserved verbatim in the extracted helper.

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[MelvinBot]

Regression scan

I didn't find any correctness regression that should block this PR. The behavior‑preservation argument holds:

• The extracted helper getVisibleTransactionViolations is byte‑for‑byte equivalent to the old useTransactionViolations body (same filter predicates, same mergeProhibitedViolations, same shouldShowRterForSettledReport default of true).
• The bulk‑filter call site in the list passes the same report/policy/email/accountID the per‑row hook would have used. shouldShowRterForSettledReport is left at the default — matching useTransactionViolations(transaction.transactionID) with no second arg.
• Grouped sort mode is safe: groupTransactionsByCategory / groupTransactionsByTag just re‑bucket the same Transaction objects, so transaction.transactionID lookups in violationsByTransactionID hit for every rendered row.
• All non‑list consumers of useTransactionViolations still go through the new helper unchanged.

That said, there are a few performance regression risks worth being aware of, because some of them are subtle and could show up as field issues on large reports.

Potential performance regressions

1) Whole‑map rebuild on any TRANSACTION_VIOLATIONS change. The parent's bulk subscription on line 211 (useOnyx(ONYXKEYS.COLLECTION.TRANSACTION_VIOLATIONS)) has no selector, so it fires whenever any transaction's violations change anywhere in the app. When that happens, the new violationsByTransactionID memo re‑filters all N transactions in the report, not just the one that changed. Before this PR, each row's per‑transaction subscription only re‑ran the filter for the affected transaction. So the CPU profile changes from O(1 row × 1 filter+merge) to O(N rows × 1 filter+merge) per Onyx event, for any unrelated cross‑report violation update. On a 500‑transaction expense report this can be a noticeable burst.

2) Map rebuilds on report / policy reference churn. The memo deps include report and policy directly (line 652). Onyx report/policy collections frequently give new object identities even when the field you care about (e.g. report.policyID, policy.id) didn't change. Each new ref rebuilds the entire map and produces fresh violations array refs for every row that has violations. Rows with no violations stay stable thanks to EMPTY_VIOLATIONS, but violation‑having rows are now coupled to every report/policy update. The per‑row hook had narrower memo deps and didn't suffer the same fanout.

3) Fresh array reference for unchanged violation rows. Even within the same memo run, every transaction whose filter result is non‑empty gets a brand‑new array allocated by mergeProhibitedViolations. So when the memo recomputes, every violation‑bearing row receives a new violations prop ref — React Compiler memoization of the row will see a prop change and re‑render that row, even if the underlying violation contents are identical to what was passed last render. Before this PR, the per‑row useMemo inside the hook only invalidated when that row's slice actually changed. Easy mitigation if this shows up: cache the previous filtered result per transactionID and reuse the prior ref when the new filter result is shallow‑equal.

4) EMPTY_VIOLATIONS is a shared mutable array. Line 89 declares it as []. If anything downstream mutates violations (e.g. .push, .sort in place), it would corrupt the shared sentinel across all rows. TransactionItemRow looks to read‑only its consumption, so this is theoretical — but it would be safer as a readonly type or Object.freeze([]) to make the contract explicit.

Other regression‑adjacent observations

• useMemo body builds a Map via mutating loop. React Compiler can be picky about in‑place mutation inside hooks/components. If it ever bails on the file, the memo will recompute every render. Worth running npm run react-compiler-compliance-check check-changed to confirm it still compiles cleanly.
• No backstop for transactionID collisions. If two Transaction objects in resolvedTransactions share a transactionID (shouldn't happen, but the old per‑row hook would have just queried Onyx and got the same answer), the new Map.set overwrites. Same effective result, just noting the assumption is now load‑bearing.
• Memo allocates a Map. Minor: a plain object keyed by transactionID would have the same O(1) lookup with a bit less allocator pressure on FlashList scroll. Probably negligible.

Verification suggestions

• Profile a long expense report (~200+ transactions, mix of violated and clean) while another tab edits violations on an unrelated report. Watch for re‑render churn on the list rows.
• Run the existing Reassure perf suite around MoneyRequestReportView if there's one in tests/perf-test/; otherwise add a baseline for the new path.
• Confirm React Compiler still compiles MoneyRequestReportTransactionList.tsx with react-compiler-compliance-check check-changed.

Overall: the change is a net win for steady‑state subscription cost on a virtualized list, but it trades narrower per‑row updates for broader parent re‑renders. The risks above are unlikely to be deal‑breakers, but worth knowing so you can react quickly if perf telemetry regresses post‑deploy.

[aimane-chnaif]

Reviewer Checklist

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

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[MelvinBot]

Help site review: no changes required

I reviewed the changes in this PR and no updates to the help site (App/docs/articles) are required. I did not create a draft docs PR.

Why: This is a pure performance refactor with no user-facing behavior change. It hoists transaction-violation filtering out of per-row useOnyx subscriptions and into a single bulk computation at the parent list level (MoneyRequestReportTransactionList), and extracts the existing filter logic into a shared getVisibleTransactionViolations helper. The RBR (violation) messages a user sees on an expense report's transaction list are computed identically — only how they're computed changed (bulk vs. per-row), which is invisible to end users.

The help site documents user-facing features, settings, and workflows. Since none of those changed here — no new feature, no renamed labels/tabs/buttons, no altered behavior — there is nothing to document.

Files reviewed

• src/components/MoneyRequestReportView/MoneyRequestReportTransactionItem.tsx — now receives violations as a prop instead of calling the hook per-row
• src/components/MoneyRequestReportView/MoneyRequestReportTransactionList.tsx — computes violations in bulk via a memoized map
• src/hooks/useTransactionViolations.ts — refactored to use the new shared helper
• src/libs/TransactionUtils/index.ts — adds getVisibleTransactionViolations (extraction of existing logic)
• tests/unit/useTransactionViolationsTest.ts — updated mocks

All five files are internal implementation/test changes with no user-facing surface.

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🚀 Deployed to production by https://github.com/lakchote in version: 9.3.90-3 🚀

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