fix(oxlint): skip js-combine-iterations on lazy Iterator helper chains (#205)

[aidenybai]

Summary

Fixes the false positive in js-combine-iterations for chains rooted in lazy Iterator helpers. Previously, this benign single-pass pipeline:

const oddDoubles = numbers
  .values()
  .filter((value) => value % 2 === 1)
  .map((value) => 2 * value)
  .toArray();

…was reported as .filter().map() iterates the array twice — combine into a single loop with .reduce() or for...of. Iterator helpers are lazy and single-pass, so this is incorrect.

Closes #205. Supersedes #212 (which only inspected the immediate inner-call receiver and missed deeper nesting, generators, Iterator.from, Object.values/.toArray() distinctions, etc.).

Approach

Walk the chain inward from the inner call's receiver, classifying each CallExpression:

• Iterator-producing root → skip the rule:
  • <x>.values(), <x>.keys(), <x>.entries() where <x> is not the global Object (Maps, Sets, arrays, URLSearchParams, etc.)
  • Iterator.from(<x>)
  • Identifier callees that resolve to a syntactically-declared generator in the same file (function* gen() {} or const gen = function*() {}, including hoisted use)
• Pass-through → keep walking: any chainable iteration method (map / filter / flatMap / forEach).
• Materializing or unknown → stop walking, leave the rule firing: .toArray(), Array.from(...), plain identifiers, and any other call shape — so eager array chains and Iterator helper chains that have been re-materialized into arrays still get flagged.

Object.values/keys/entries(...) is intentionally treated as eager (returns an array), so Object.values(map).map().filter() still fires.

Cross-file imports of generators, class-method generators, and TS-type-only IterableIterator<T> parameters remain accepted false positives — documented in the test file.

Files

• packages/oxlint-plugin-react-doctor/src/plugin/constants/js.ts — adds ITERATOR_PRODUCING_METHOD_NAMES.
• packages/oxlint-plugin-react-doctor/src/plugin/rules/js-performance/js-combine-iterations.ts — collects per-file generator names on Program enter, then walks the receiver chain to detect iterator-rooted lazy chains before reporting.
• packages/react-doctor/tests/regressions/js-performance-rules.test.ts — 18 new regression cases.

Test matrix (regression tests)

Input	Expectation
arr.filter().map()	flagged (eager)
numbers.values().filter().map().toArray() (issue #205 repro)	not flagged
numbers.values().map().filter() (deeper nesting)	not flagged
mapInstance.entries().map().filter()	not flagged
setInstance.keys().filter().map()	not flagged
Object.values(obj).map().filter()	flagged (Object.* is eager)
Object.entries(obj).filter().map()	flagged
arr.values().toArray().filter().map()	flagged (.toArray() materializes)
Array.from(it).filter().map()	flagged
Iterator.from(arr).map().filter()	not flagged
Hoisted function* countUp(){} then countUp().filter().map()	not flagged
const gen = function*(){}; gen().filter().map()	not flagged
arr?.values()?.filter()?.map() (optional chaining)	not flagged
groups.flatMap(...).filter().map() (eager .flatMap)	flagged (both adjacent pairs)
groups.values().flatMap(...).filter().map().toArray()	not flagged
arr.map(x => x ? x : null).filter(Boolean)	not flagged (existing exclusion preserved)
arr.map(x => x ? x : null).filter(name => name)	not flagged (existing identity-filter exclusion preserved)
Imported gen() from another file then .filter().map()	flagged (documented limitation)

Verification

• pnpm typecheck — green (10/10 tasks).
• pnpm lint — 0 warnings, 0 errors across 542 files.
• pnpm format — clean.
• pnpm test — 998 / 998 tests pass, including all 18 new regression cases under js-combine-iterations.
• pnpm --filter oxlint-plugin-react-doctor gen:check — registry in sync.

Eval Results

Ran against 100-repo corpus (baseline: main @ 529015d, 13,279 diagnostics).

Parity: OK — Zero regressions, zero changes. The fix correctly targets lazy iterator chains without affecting any other diagnostics across the entire corpus.

Metric	Value
Diagnostics added	0
Diagnostics removed	0
Net change	0
Repos changed	0

  

[reactreview]

🔴 React Review — 0/100 (unchanged) · No new issues

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Project	Deployment	Actions	Updated (UTC)
react-doctor-website	Ready	Preview, Comment	May 16, 2026 8:17am