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fix(linter/unicorn/prefer-at): skip object numeric-key access#23909

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Jun 30, 2026
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fix(linter/unicorn/prefer-at): skip object numeric-key access#23909
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gaurav0107:fix/23870-unicorn-prefer-at-skip-object-numeric-ke

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Summary

Fixes #23870.

With checkAllIndexAccess: true, unicorn/prefer-at reported and auto-fixed numeric-key access on plain objects, rewriting e.g. tokens[60] (where const tokens = { 60: '#666666' }) to tokens.at(60). Plain objects have no .at() method, so the autofix produced code that fails to type-check (TS2339) / throws at runtime.

This skips receivers that are obviously not array-like before reporting under checkAllIndexAccess:

  • object literals — ({ 1: 1 })[1]
  • non-string literals, function expressions, and class expressions
  • identifiers bound to a const whose initializer is one of the above — const o = { 1: 1 }; o[1] — including through TypeScript as / satisfies / ! wrappers

Strings keep .at(), so string receivers are still reported and fixed ("abc"[1] -> "abc".at(1)). The guard runs only under the opt-in checkAllIndexAccess option and short-circuits on a cheap matches! before any symbol-table lookup, so the default-config hot path is unchanged.

Ports the receiver discrimination from eslint-plugin-unicorn (sindresorhus/eslint-plugin-unicorn#2999, issue #2229).

Test plan

  • Added pass cases covering the exact repro plus object-literal, const-bound, TS as const / as / non-null receivers, function/class/non-string-literal receivers, and the addition-index branch.
  • Added a fail + fix case proving string-literal receivers are still reported and fixed.
  • cargo test -p oxc_linter — 1162 passed, 0 failed.

With `checkAllIndexAccess: true`, `unicorn/prefer-at` reported and
auto-fixed numeric-key access on plain objects (e.g. `tokens[60]` where
`const tokens = { 60: ... }`), rewriting it to `tokens.at(60)`. Plain
objects have no `.at()` method, so the autofix produced broken code.

Skip receivers that are obviously not array-like: object literals,
non-string literals, function/class expressions, and identifiers bound
to a `const` initialized to one of those. Strings keep `.at()`, so
string receivers are still reported and fixed. Ports the receiver
discrimination from eslint-plugin-unicorn
(sindresorhus/eslint-plugin-unicorn#2999).

Fixes oxc-project#23870
@codspeed-hq

codspeed-hq Bot commented Jun 28, 2026

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Merging this PR will not alter performance

✅ 5 untouched benchmarks
⏩ 66 skipped benchmarks1


Comparing gaurav0107:fix/23870-unicorn-prefer-at-skip-object-numeric-ke (69e1a39) with main (6ca9125)

Open in CodSpeed

Footnotes

  1. 66 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports.

@gaurav0107
gaurav0107 marked this pull request as ready for review June 28, 2026 21:39
@gaurav0107
gaurav0107 requested a review from camc314 as a code owner June 28, 2026 21:39

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thanks!

@camc314 camc314 added the A-linter Area - Linter label Jun 30, 2026
@camc314 camc314 self-assigned this Jun 30, 2026
@camc314
camc314 merged commit 29c76bf into oxc-project:main Jun 30, 2026
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camc314 added a commit that referenced this pull request Jul 3, 2026
## Summary

Fixes #23870.

With `checkAllIndexAccess: true`, `unicorn/prefer-at` reported and
auto-fixed numeric-key access on plain objects, rewriting e.g.
`tokens[60]` (where `const tokens = { 60: '#666666' }`) to
`tokens.at(60)`. Plain objects have no `.at()` method, so the autofix
produced code that fails to type-check (`TS2339`) / throws at runtime.

This skips receivers that are obviously not array-like before reporting
under `checkAllIndexAccess`:

- object literals — `({ 1: 1 })[1]`
- non-string literals, function expressions, and class expressions
- identifiers bound to a `const` whose initializer is one of the above —
`const o = { 1: 1 }; o[1]` — including through TypeScript `as` /
`satisfies` / `!` wrappers

Strings keep `.at()`, so string receivers are still reported and fixed
(`"abc"[1]` -> `"abc".at(1)`). The guard runs only under the opt-in
`checkAllIndexAccess` option and short-circuits on a cheap `matches!`
before any symbol-table lookup, so the default-config hot path is
unchanged.

Ports the receiver discrimination from eslint-plugin-unicorn
([sindresorhus/eslint-plugin-unicorn#2999](sindresorhus/eslint-plugin-unicorn#2999),
issue #2229).

## Test plan

- Added `pass` cases covering the exact repro plus object-literal,
`const`-bound, TS `as const` / `as` / non-null receivers,
function/class/non-string-literal receivers, and the addition-index
branch.
- Added a `fail` + `fix` case proving string-literal receivers are still
reported and fixed.
- `cargo test -p oxc_linter` — 1162 passed, 0 failed.

Co-authored-by: Cameron <cameron.clark@hey.com>
Boshen added a commit that referenced this pull request Jul 6, 2026
# Oxlint
### 🚀 Features

- 7db7a29 allocator: Add `ReplaceWith` trait (#24012) (overlookmotel)
- a2c97f3 linter/unicorn: Implement `explicit-timer-delay` rule (#23612)
(Mikhail Baev)
- 85735cb linter/unicorn: Implement `no-confusing-array-with` rule
(#23638) (Shekhu☺️)
- cb4fbb9 linter/eslint: Implement no-unreachable-loop rule (#23975)
(Todor Andonov)
- dc32112 linter/eslint/no-constant-binary-expression: Check relational
comparisons (#24088) (camc314)
- 439c344 linter/jsdoc: Added missing options to `jsdoc/require-param`
rule (#23364) (kapobajza)
- 62af717 linter/unicorn/filename-case: Add `lowercase` and
`screamingSnakeCase` (#24045) (Boshen)
- d963967 linter/unicorn/no-array-sort: Add `allowAfterSpread` option
(#24043) (Boshen)
- 0a75682 linter: Add per-rule timings for type-aware linting (#22488)
(camchenry)
- 743e222 linter/react: Add `disallowedValues` option for
`forbid-dom-props` rule (#23970) (Mikhail Baev)

### 🐛 Bug Fixes

- 7b80010 linter: Use direct binding symbol ids (#24216) (camc314)
- 8f94b49 linter/import/no-duplicates: Don't flag a type-only import
beside a side-effect import (#24030) (Boshen)
- d8c3fee linter/react/rules-of-hooks: Flag `useEffectEvent` escapes
(#23764) (Rayan Salhab)
- 0a7312b linter/no-deprecated-functions: Map `require.requireActual` to
`jest.requireActual` (#23627) (Jerry Zhao)
- d9e3ab3 linter/eslint/no-useless-return: Handle switch case
continuation (#23984) (camc314)
- 0b25582 ast: Type binding node `typeAnnotation` as `TSTypeAnnotation |
null` (#23113) (Boshen)
- 122d112 linter/eslint/no-restricted-imports: Flag dynamic import()
expressions (#24029) (Boshen)
- 59b6b83 linter: Avoid `OnceLock` re-entry on cyclic `export *`
re-exports (#23632) (Jerry Zhao)
- dd09af0 linter/import/namespace: Avoid panic on destructuring of an
unresolvable namespace re-export (#23626) (Jerry Zhao)
- bdb51c7 linter/jest/prefer-ending-with-an-expect: Validate config
patterns (#24122) (camc314)
- e383843 linter/unicorn/prefer-modern-dom-apis: Skip fixer for non
identifier arguments (#23630) (Jerry Zhao)
- 0ac4c83 linter: Detect circular config extends (#24115) (camc314)
- bae1edf linter/import/namespace: Check namespace imports after named
imports (#24094) (camc314)
- cd8fdfe linter/eslint/no-eval: Recognize Array.from family thisArg
(#24091) (camc314)
- 851ee43 linter/eslint/no-eval: Resolve this binding for functions
returned from an IIFE (#23643) (Jerry Zhao)
- 002ab35 linter/unicorn: Avoid prefer-array-find rest destructuring
false positive (#23654) (ColemanDunn)
- 01c8775 linter/unicorn/filename-case: Keep digits attached in
screamingSnakeCase (#24056) (Boshen)
- f256941 linter: Recognize `@effect/vitest` as a vitest import source
(#24025) (Boshen)
- 73eeb1d linter/import/extensions: Honor per-extension `never` for
explicit extensions (#24031) (Boshen)
- d4ebe1f linter: Reject non-object oxlint config files (#24026)
(Boshen)
- 45d607d linter/react/forbid-component-props: Make allow/disallow lists
optional in schema (#24024) (Boshen)
- 54076ad linter/unicorn/no-array-for-each: Suggest entries loop for
index callbacks (#24004) (camc314)
- d057736 linter/jsdoc: Avoid param root underflow (#23945) (camc314)
- 29c76bf linter/unicorn/prefer-at: Skip object numeric-key access
(#23909) (Gaurav Dubey)

### ⚡ Performance

- 657a8fc linter/oxc/bad-array-method-on-arguments: Only run on member
expressions instead of all identifiers (#24164) (camchenry)
- 073d9e7 linter/eslint/prefer-rest-params: Run on functions instead of
all identifiers (#24163) (camchenry)
- e5a4162 linter/jest/no-confusing-set-timeout: Early exit fast path
(#24092) (camc314)
- bca7ce5 linter: Only run react-perf rules on JSX attribute nodes
(#24083) (camchenry)
- 6881bf6 linter: Compute `apply_overrides` rule set lazily (#23648)
(Jerry Zhao)
- 911c106 linter/eslint/no-obj-calls: Use resolved reference instead of
scope walk (#23895) (Marius Schulz)
- dc8fd9a linter/unicorn/prefer-dom-node-text-content: Change dispatch
to run only on less common node types (#23897) (Connor Shea)
- fdbd34d linter/eslint/no-useless-call: Fast-path static callees
(#24077) (camc314)
- b1be114 linter/import/extensions: Skip empty config and borrow
extensions (#24075) (camc314)
- 4781b2d linter/eslint/no-obj-calls: Use direct global matches (#24076)
(camc314)
- e6cee89 linter: Avoid node-chain allocation for non-Jest calls
(#23907) (Yagiz Nizipli)
- 30dc517 linter/typescript/no-restricted-types: O(1) banned-type
lookups (#23827) (Yagiz Nizipli)

### 📚 Documentation

- 6ca9125 linter/typescript: Clarify consistent-type-imports behavior
(#23972) (camc314)
# Oxfmt
### 🚀 Features

- 4f4313e formatter_css: Update oxc-css-parser 0.0.5 (#24120) (leaysgur)
- 0ccd8a1 formatter_graphql: Update oxc-graphql-parser 0.0.5 (#24106)
(leaysgur)
- 89ec3d9 formatter_core: Add literal line and root indention primitives
(#24051) (leaysgur)
- 213a96b formatter_core: Add no-expand-parent for multiline text
(#24050) (leaysgur)
- 0e5bcc9 formatter_graphql: Update oxc-graphql-parser 0.0.4 (#24039)
(leaysgur)
- e0b35a1 formatter_css: Update `oxc-css-parser@0.0.3` (#23974)
(leaysgur)

### 🐛 Bug Fixes

- 1fe6546 formatter: Omit unneeded `;` for type members with `no-semi`
(#24212) (leaysgur)
- 0ad7316 formatter: Print space for `ForStatement`.`update` only if
exists (#24211) (leaysgur)
- 3abbed5 formatter: Print `;` before jsdoc type-cast parens with
no-semi (#24208) (leaysgur)
- 9af3833 formatter_css: Make scss formatter consistent (#24207)
(leaysgur)
- 46d7194 formatter_css: Use fill IR for `@forward` members (#24206)
(leaysgur)
- e31038f formatter_css: Keep comment inside sass config list (#24205)
(leaysgur)
- d3b9591 formatter: Add parens around `await/yield` with `<T>` (#24202)
(leaysgur)
- 2121a55 oxfmt: Reuse tinypool process during the same LSP process
(#24197) (leaysgur)
- 9bf4b4a formatter_css: Align CSS output to Prettier 3.9.1 (#24100)
(leaysgur)
- cd2452e formatter_css: Align SCSS output to Prettier 3.9.1 (#24097)
(leaysgur)
- 4ee8745 formatter_css: Keep selector value contain line-break without
breaking line (#24055) (leaysgur)
- e1ece97 formatter_graphql: Break `implements` list by print-width
(#23997) (leaysgur)
- 0a6b16c formatter_json: Preserve key and literal value for
json-stringify (#23996) (leaysgur)
- 903ab6e formatter_css: Preserve newlines in css-in-js selector list
(#23992) (leaysgur)
- ea5d095 oxfmt: Update `--migrate prettier` (#23963) (leaysgur)

### ⚡ Performance

- 468e1e3 formatter_core: Make printer queues cursor-based (#24098)
(Boshen)
- c59f2fe rust: Return impl ExactSizeIterator from slice-backed
accessors (#24144) (Boshen)
- c292fb2 formatter: Inline fits element dispatcher (#23982) (camc314)

Co-authored-by: Boshen <1430279+Boshen@users.noreply.github.com>
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unicorn/prefer-at: skip object numeric-key access (upstream #2999)

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