# Oxlint
### 💥 BREAKING CHANGES

- 88f4455 str: [**BREAKING**] `Str` and `Ident` methods take
`&GetAllocator` (#23781) (overlookmotel)

### 🚀 Features

- f2091b3 ast: Unify old and new `AstBuilder`s (#23875) (overlookmotel)
- 1c8f50c linter: Add schema for `eslint/no-restricted-import` (#23642)
(Sysix)

### 🐛 Bug Fixes

- 7cb85c4 linter/eslint/no-negated-condition: Add autofix for negated
conditions (#23825) (Yagiz Nizipli)
- f7d1f50 oxlint, oxfmt: Enable `disable_old_builder` Cargo feature for
`oxc_ast` crate (#23886) (overlookmotel)
- d891990 linter/jsx-a11y/role-supports-aria-props: Ignore nullish prop
values (#23865) (Mikhail Baev)
- 94b6599 linter: Deduplicate missing plugin errors (#23853) (camc314)
- eff3eff linter/oxc/branches-sharing-code: Avoid else-if false
positives (#23843) (camc314)
- 2a2d3b9 linter/eslint/prefer-destructuring: Skip
`AssignmentExpression` autofixes (#23818) (camc314)
- ddc24ae linter/eslint/id-length: Respect checkGeneric for mapped type
keys (#23802) (bab)
- cd89202 linter/react/exhaustive-deps: Skip wrapper expression when
analyzing hook initializers (#23793) (camc314)
- 20e8285 linter/unicorn/prefer-native-coercion-function: Allow ts type
predicates (#23774) (camc314)
- d86f60b lsp: Normalize user config path to watch pattern (#23723)
(Sysix)
- 52032cf linter: Newline-terminate tsgolint errors (#23762) (Mikhail
Baev)
- 368fda7 linter/eslint/no-warning-comments: Avoid dropping generated
regex patterns (#23741) (camc314)
- ce44fbd linter/valid-title: Escape disallowed words regex (#23742)
(camc314)
- 3100d11 linter/prefer-called-exactly-once-with: Avoid out-of-bounds
slice panic at end of file (#23625) (Jerry Zhao)
- 742be36 refactor/node/handle-callback-err: Reject invalid regex config
(#23740) (camc314)
- d7be179 linter/eslint/no-restricted-globals: Handle shadowed locals
(#23736) (camc314)
- b3b1ff8 linter/vitest/expect-expect: Handle global vitest detection
correctly (#23734) (camc314)

### ⚡ Performance

- 68f9472 linter/jsx-a11y: Skip lowercasing non-aria attribute names
(#23906) (Lawrence Lin)
- b9312b4 linter/unicorn/prefer-export-from: Use keyed binding lookup
(#23893) (Marius Schulz)
- cd5204e linter/typescript/no-unsafe-declaration-merging: Use keyed
binding lookup (#23894) (Marius Schulz)
- e948498 linter/eslint/prefer-named-capture-group: Only dispatch for
relevant node types (#23868) (Connor Shea)
- 4ac7a8e linter/eslint/max-depth: Derive node types (#23896) (Connor
Shea)
- daeed09 linter/eslint/no-restricted-globals: Only scan unresolved
references (#23890) (camc314)
- e808514 linter/jest-vitest: Speed up no-standalone-expect (#23883)
(camc314)
- 8b165e5 linter/react/exhaustive-deps: Skip non-reactive calls early
(#23882) (camc314)
- 54005e7 linter/eslint/no-unused-vars: Precompute exported bindings
(#23881) (camc314)
- 9bc2f8c linter/unicorn/prefer-number-properties: Speed up global
checks (#23880) (camc314)
- 4ff104f linter: Optimize `require-hook` and `prefer-mock-*` rules to
run on specific node types (#23871) (Connor Shea)
- cc2213b linter: Run `no-underscore-dangle` only when relevant node
types are present (#23867) (Connor Shea)
- 3e55c21 linter/promise/always-return: Narrow to function node types
(#23878) (Connor Shea)
- 7136182 linter/jest-vitest: Speed up no-commented-out-tests (#23864)
(camc314)
- f138264 linter/eslint/no-script-url: Match javascript: prefix without
allocating (#23861) (Lawrence Lin)
- 7ef6895 linter/react/no-array-index-key: Delay index symbol lookup
(#23857) (camc314)
- 26bc171 linter/react/no-array-index-key: Match callback methods
directly (#23856) (camc314)
- 44fbbda linter/jsx-a11y/interactive-supports-focus: Check cheap
conditions first (#23854) (camc314)
- 84a5aa3 linter/eslint/no-extend-native: Skip lowercase references
early (#23851) (camc314)
- 88a74b2 linter/eslint/no-nonoctal-decimal-escape: Scan decimal escapes
as bytes (#23850) (camc314)
- fca69a8 linter: Skip traversal without this expressions (#23845)
(camc314)
- 838fd63 linter: Reduce preallocation for per-file diagnostics `Vec`
(#23705) (Marius Schulz)
- 417b506 linter/typescript/array-type: Remove full source text clone
(#23751) (Marius Schulz)

### 📚 Documentation

- 57e4469 linter/unicorn: Update prefer-dom-node-text-content rationale
(#23933) (Mikhail Baev)
- 3d61dea all: Correct capitalization in comments (#23887)
(overlookmotel)

### 🛡️ Security

- 3cdd18f deps: Update npm packages (#23690) (renovate[bot])
# Oxfmt
### 💥 BREAKING CHANGES

- 259e0cd oxfmt,formatter_graphql: [**BREAKING**] Support draft syntax
with removing prettier fallback (#23326) (leaysgur)
- accbc49 oxfmt: [**BREAKING**] Format `parser:css,less,scss` files +
css-in-js by `oxc_formatter_css` (#23321) (leaysgur)

### 🚀 Features

- dffa4b3 formatter_css: Implement `oxc_formatter_css` (#23320)
(leaysgur)
- 01de9ec oxfmt: Format `parser:graphql` files by
`oxc_formatter_graphql` (#23318) (leaysgur)
- 4e66212 formatter_graphql: Implement oxc_formatter_graphql (#23317)
(leaysgur)

### 🐛 Bug Fixes

- 67325ae formatter_css: Handle frontmatter language (#23819) (leaysgur)
- 3f355e5 formatter_graphql: Improve major prettier diffs (#23419)
(leaysgur)
- 48e2d78 formatter_css: Improve major prettier diffs (#23327)
(leaysgur)
- 8c07cad all: Enable `disable_old_builder` Cargo feature for `oxc_ast`
crate in tests (#23888) (overlookmotel)
- f7d1f50 oxlint, oxfmt: Enable `disable_old_builder` Cargo feature for
`oxc_ast` crate (#23886) (overlookmotel)
- d86f60b lsp: Normalize user config path to watch pattern (#23723)
(Sysix)

### ⚡ Performance

- 4ddcba0 formatter_core: Add printable-ASCII fast path to TextWidth
(#23913) (Lawrence Lin)

### 📚 Documentation

- b4d0dc9 oxfmt,formatter,formatter_css,formatter_core: Update AGENTS.md
(#23814) (leaysgur)

Co-authored-by: Boshen <[email protected]>
Co-authored-by: Cameron <[email protected]>

…3751)

## What

`check_and_report_error_generic` in the `typescript/array-type` rule
cloned the entire source file via `ctx.source_text().to_string()` on
every `TSArrayType` violation, only to use the result as a `&str`
(passed to `get_message_type` and sliced in the fixer closure).
`ctx.source_text()` already returns `&'a str` tied to the arena
lifetime, so the heap copy is pure waste.

## Change

Drop `.to_string()`; use the borrowed `&str` directly.

```diff
-    let source_text = ctx.source_text().to_string();
+    let source_text = ctx.source_text();
     ...
-    let message_type = get_message_type(type_param, &source_text);
+    let message_type = get_message_type(type_param, source_text);
```

## Impact

Around **1.61 GB** of heap allocations saved when running against the
`microsoft/vscode` repo (10,572 files).

Measured by linting with `{"typescript/array-type": ["error",
{"default": "generic"}]}` as the only enabled rule — 40,426 violations
across 5,744 files. Release build, glibc system allocator, 3 interleaved
runs after warmup, medians reported.

### Peak RSS (`getrusage` `ru_maxrss`)

|             |   baseline | this branch |    Δ (abs) |  Δ (%) |
|-------------|-----------:|------------:|-----------:|-------:|
| threads=1   | 362,236 KB |  332,740 KB | −29,496 KB |  −8.1% |
| threads=64  | 489,180 KB |  459,732 KB | −29,448 KB |  −6.0% |

### Total heap bytes allocated (`LD_PRELOAD` malloc/calloc/realloc
counter)

| | baseline | this branch | Δ (abs) | Δ (%) |

|--------------|--------------:|--------------:|---------------:|-------:|
| malloc calls | 4,552,293 | 4,511,867 | −40,426 | −0.9% |
| bytes | 6,502,015,003 | 4,893,067,752 | −1,608,947,251 | −24.7% |

The −40,426 calls exactly equals the diagnostic count (one
`.to_string()` per violation).

### Wall clock

|             | baseline | this branch |  Δ (abs) | Δ (%) |
|-------------|---------:|------------:|---------:|------:|
| threads=1   |  4.152 s |     4.122 s | −0.030 s | −0.7% |
| threads=64  |  2.695 s |     2.588 s | −0.107 s | −4.0% |

## Verification

- `cargo test -p oxc_linter --lib array_type` passes.

This PR was assisted by Claude Code.

Co-authored-by: Cameron <[email protected]>

# Oxlint
### 💥 BREAKING CHANGES

- 88f4455 str: [**BREAKING**] `Str` and `Ident` methods take
`&GetAllocator` (#23781) (overlookmotel)

### 🚀 Features

- f2091b3 ast: Unify old and new `AstBuilder`s (#23875) (overlookmotel)
- 1c8f50c linter: Add schema for `eslint/no-restricted-import` (#23642)
(Sysix)

### 🐛 Bug Fixes

- 7cb85c4 linter/eslint/no-negated-condition: Add autofix for negated
conditions (#23825) (Yagiz Nizipli)
- f7d1f50 oxlint, oxfmt: Enable `disable_old_builder` Cargo feature for
`oxc_ast` crate (#23886) (overlookmotel)
- d891990 linter/jsx-a11y/role-supports-aria-props: Ignore nullish prop
values (#23865) (Mikhail Baev)
- 94b6599 linter: Deduplicate missing plugin errors (#23853) (camc314)
- eff3eff linter/oxc/branches-sharing-code: Avoid else-if false
positives (#23843) (camc314)
- 2a2d3b9 linter/eslint/prefer-destructuring: Skip
`AssignmentExpression` autofixes (#23818) (camc314)
- ddc24ae linter/eslint/id-length: Respect checkGeneric for mapped type
keys (#23802) (bab)
- cd89202 linter/react/exhaustive-deps: Skip wrapper expression when
analyzing hook initializers (#23793) (camc314)
- 20e8285 linter/unicorn/prefer-native-coercion-function: Allow ts type
predicates (#23774) (camc314)
- d86f60b lsp: Normalize user config path to watch pattern (#23723)
(Sysix)
- 52032cf linter: Newline-terminate tsgolint errors (#23762) (Mikhail
Baev)
- 368fda7 linter/eslint/no-warning-comments: Avoid dropping generated
regex patterns (#23741) (camc314)
- ce44fbd linter/valid-title: Escape disallowed words regex (#23742)
(camc314)
- 3100d11 linter/prefer-called-exactly-once-with: Avoid out-of-bounds
slice panic at end of file (#23625) (Jerry Zhao)
- 742be36 refactor/node/handle-callback-err: Reject invalid regex config
(#23740) (camc314)
- d7be179 linter/eslint/no-restricted-globals: Handle shadowed locals
(#23736) (camc314)
- b3b1ff8 linter/vitest/expect-expect: Handle global vitest detection
correctly (#23734) (camc314)

### ⚡ Performance

- 68f9472 linter/jsx-a11y: Skip lowercasing non-aria attribute names
(#23906) (Lawrence Lin)
- b9312b4 linter/unicorn/prefer-export-from: Use keyed binding lookup
(#23893) (Marius Schulz)
- cd5204e linter/typescript/no-unsafe-declaration-merging: Use keyed
binding lookup (#23894) (Marius Schulz)
- e948498 linter/eslint/prefer-named-capture-group: Only dispatch for
relevant node types (#23868) (Connor Shea)
- 4ac7a8e linter/eslint/max-depth: Derive node types (#23896) (Connor
Shea)
- daeed09 linter/eslint/no-restricted-globals: Only scan unresolved
references (#23890) (camc314)
- e808514 linter/jest-vitest: Speed up no-standalone-expect (#23883)
(camc314)
- 8b165e5 linter/react/exhaustive-deps: Skip non-reactive calls early
(#23882) (camc314)
- 54005e7 linter/eslint/no-unused-vars: Precompute exported bindings
(#23881) (camc314)
- 9bc2f8c linter/unicorn/prefer-number-properties: Speed up global
checks (#23880) (camc314)
- 4ff104f linter: Optimize `require-hook` and `prefer-mock-*` rules to
run on specific node types (#23871) (Connor Shea)
- cc2213b linter: Run `no-underscore-dangle` only when relevant node
types are present (#23867) (Connor Shea)
- 3e55c21 linter/promise/always-return: Narrow to function node types
(#23878) (Connor Shea)
- 7136182 linter/jest-vitest: Speed up no-commented-out-tests (#23864)
(camc314)
- f138264 linter/eslint/no-script-url: Match javascript: prefix without
allocating (#23861) (Lawrence Lin)
- 7ef6895 linter/react/no-array-index-key: Delay index symbol lookup
(#23857) (camc314)
- 26bc171 linter/react/no-array-index-key: Match callback methods
directly (#23856) (camc314)
- 44fbbda linter/jsx-a11y/interactive-supports-focus: Check cheap
conditions first (#23854) (camc314)
- 84a5aa3 linter/eslint/no-extend-native: Skip lowercase references
early (#23851) (camc314)
- 88a74b2 linter/eslint/no-nonoctal-decimal-escape: Scan decimal escapes
as bytes (#23850) (camc314)
- fca69a8 linter: Skip traversal without this expressions (#23845)
(camc314)
- 838fd63 linter: Reduce preallocation for per-file diagnostics `Vec`
(#23705) (Marius Schulz)
- 417b506 linter/typescript/array-type: Remove full source text clone
(#23751) (Marius Schulz)

### 📚 Documentation

- 57e4469 linter/unicorn: Update prefer-dom-node-text-content rationale
(#23933) (Mikhail Baev)
- 3d61dea all: Correct capitalization in comments (#23887)
(overlookmotel)

### 🛡️ Security

- 3cdd18f deps: Update npm packages (#23690) (renovate[bot])
# Oxfmt
### 💥 BREAKING CHANGES

- 259e0cd oxfmt,formatter_graphql: [**BREAKING**] Support draft syntax
with removing prettier fallback (#23326) (leaysgur)
- accbc49 oxfmt: [**BREAKING**] Format `parser:css,less,scss` files +
css-in-js by `oxc_formatter_css` (#23321) (leaysgur)

### 🚀 Features

- dffa4b3 formatter_css: Implement `oxc_formatter_css` (#23320)
(leaysgur)
- 01de9ec oxfmt: Format `parser:graphql` files by
`oxc_formatter_graphql` (#23318) (leaysgur)
- 4e66212 formatter_graphql: Implement oxc_formatter_graphql (#23317)
(leaysgur)

### 🐛 Bug Fixes

- 67325ae formatter_css: Handle frontmatter language (#23819) (leaysgur)
- 3f355e5 formatter_graphql: Improve major prettier diffs (#23419)
(leaysgur)
- 48e2d78 formatter_css: Improve major prettier diffs (#23327)
(leaysgur)
- 8c07cad all: Enable `disable_old_builder` Cargo feature for `oxc_ast`
crate in tests (#23888) (overlookmotel)
- f7d1f50 oxlint, oxfmt: Enable `disable_old_builder` Cargo feature for
`oxc_ast` crate (#23886) (overlookmotel)
- d86f60b lsp: Normalize user config path to watch pattern (#23723)
(Sysix)

### ⚡ Performance

- 4ddcba0 formatter_core: Add printable-ASCII fast path to TextWidth
(#23913) (Lawrence Lin)

### 📚 Documentation

- b4d0dc9 oxfmt,formatter,formatter_css,formatter_core: Update AGENTS.md
(#23814) (leaysgur)

Co-authored-by: Boshen <[email protected]>
Co-authored-by: Cameron <[email protected]>

…r comment (#24369)

## What

`get_last_comment_line` in the `typescript/prefer-ts-expect-error` rule
heap-allocated a
`String` (`String::from(raw)` / `String::from(raw.lines().last()...)`)
for **every comment in the
file**. It is called unconditionally from `is_valid_ts_ignore_present`,
which `run_once` invokes on
every comment *before* any `@ts-ignore` match — so the allocation
happens once per comment even in
files with zero violations. The returned value is only ever read as
`&str`
(`test_single_line_comment` / `test_multi_line_comment`), never mutated
or stored. `raw` is
`ctx.source_range(...)` → `&'a str` tied to the arena, and
`str::lines().last()` yields a borrowed
slice of it, so the heap copy is pure waste.

## Change

Return a borrowed `&'a str` instead of an owned `String`:

```diff
-fn get_last_comment_line(comment: Comment, raw: &str) -> String {
+fn get_last_comment_line<'a>(comment: Comment, raw: &'a str) -> &'a str {
     if comment.is_line() {
-        return String::from(raw);
+        return raw;
     }
-
-    String::from(raw.lines().last().unwrap_or(raw))
+    raw.lines().last().unwrap_or(raw)
 }
```

(The caller's `test_*` calls take `&str`, so `&line` becomes `line`.)

## Impact

One heap allocation removed per comment. Measured on a synthetic
11k-line TS file with 4,000
comments (`typescript/prefer-ts-expect-error` as the only enabled rule),
counting system-allocator
activity during `Linter::run` only:

| metric      |   baseline |  this branch |        Δ |
|-------------|-----------:|-------------:|---------:|
| allocs/iter |     12,006 |        8,006 | **−4,000 (−33%)** |
| bytes/iter  |  1,479,224 |    1,377,057 | −102,167 |

The −4,000 allocs/iter exactly equals the comment count (one
`String::from` per comment).

### Wall clock

This is a memory/allocation optimization, not a speed one — same class
as #23751 (whose own
wall-clock delta was only −0.7% to −4%). In an isolated single-rule
Criterion benchmark
(release build, `tasks/benchmark`, the repo's deterministic
`NeverGrowInPlace` allocator),
the change trends slightly faster (~−4% median over 40 paired runs,
fixed faster in 57%), but the effect is small and near the noise floor
of a shared
machine, so no end-to-end speedup should be assumed. The reliable,
deterministic win is the
reduced allocation count above (production uses mimalloc, where these
small allocations are
cheap).

## Verification

- `cargo test -p oxc_linter --lib prefer_ts_expect_error` passes.

This PR was assisted by Claude Code.

---------

Co-authored-by: Cameron <[email protected]>

… per violation (#24370)

## What

When `typescript/consistent-type-imports` reports an import whose
specifiers are only used as
types, `run` built **two** `Vec`s per violation:

```rust
let type_names = type_references_without_type_qualifier
    .iter()
    .map(|specifier| specifier.name())          // Vec<Cow<'a, str>>
    .collect::<Vec<_>>();

let type_imports = format_word_list(&type_names);
let type_names =
    type_names.iter().map(std::convert::AsRef::as_ref).collect::<Vec<_>>();  // Vec<&str>
```

`ImportDeclarationSpecifier::name()` always returns
`Cow::Borrowed(self.local().name.as_str())`, so
the first `Vec<Cow>` is never anything but borrowed data, and the second
`collect` allocates an
entire additional `Vec` on every violation just to convert `Cow → &str`
for the fixer. Both the
message builder (`format_word_list`) and the fixer only need `&str`.

## Change

Collect a single `Vec<&str>` directly from the arena-backed names and
drop the second `collect`;
`format_word_list` takes `&[&str]`:

```diff
     let type_names = type_references_without_type_qualifier
         .iter()
-        .map(|specifier| specifier.name())
+        .map(|specifier| specifier.local().name.as_str())
         .collect::<Vec<_>>();

     let type_imports = format_word_list(&type_names);
-    let type_names =
-        type_names.iter().map(std::convert::AsRef::as_ref).collect::<Vec<_>>();
```
```diff
-fn format_word_list<'a>(words: &[Cow<'a, str>]) -> Cow<'a, str> {
+fn format_word_list<'a>(words: &[&'a str]) -> Cow<'a, str> {
     match words.len() {
         0 => Cow::Borrowed(""),
-        1 => words[0].clone(),
+        1 => Cow::Borrowed(words[0]),
         2 => Cow::Owned(format!("{} and {}", words[0], words[1])),
```

## Impact

One `Vec` allocation removed per reported import, and the remaining
`Vec` shrinks from
`Cow<str>` (24 B/elem) to `&str` (16 B/elem). Measured on a synthetic
9k-line TS file with 3,000
type-only import declarations (`typescript/consistent-type-imports` as
the only enabled rule),
counting system-allocator activity during `Linter::run` only:

| metric      |   baseline |  this branch |        Δ |
|-------------|-----------:|-------------:|---------:|
| allocs/iter |     21,006 |       18,006 | **−3,000 (−14%)** |
| bytes/iter  |  2,555,972 |    2,339,972 | −216,000 |

The −3,000 allocs/iter exactly equals the number of reported imports
(one redundant `Vec` each).

### Wall clock

This is a memory/allocation optimization, not a speed one — same class
as #23751 (whose own
wall-clock delta was only −0.7% to −4%). In an isolated single-rule
Criterion benchmark
(release build, `tasks/benchmark`, the repo's deterministic
`NeverGrowInPlace` allocator),
the change trends slightly faster (~−5% median over 40 paired runs,
fixed faster in 57%), but the effect is small and near the noise floor
of a shared
machine, so no end-to-end speedup should be assumed. The reliable,
deterministic win is the
reduced allocation count above (production uses mimalloc, where these
small allocations are
cheap).

## Verification

- `cargo test -p oxc_linter --lib consistent_type_imports` passes.

This PR was assisted by Claude Code.

Co-authored-by: Cameron <[email protected]>

…tifier (#24371)

## What

`NoUnderscoreDangle::is_allowed` heap-allocated a `String`
(`name.to_string()`) on every call, only
to feed `Vec::contains` for a membership test:

```rust
fn is_allowed(&self, name: &str) -> bool {
    is_always_allowed(name) || self.allow.contains(&name.to_string())
}
```

`is_allowed` runs from `report`, which fires for every checked
identifier (bindings, members,
private fields, function/method/property names). `self.allow` is a
`Vec<String>` and `name` is
already `&str`, so the `to_string()` allocates a throwaway `String`
purely to compare it, then drops
it — once per identifier the rule inspects.

## Change

Compare against the existing `String`s by reference; no allocation:

```diff
-    is_always_allowed(name) || self.allow.contains(&name.to_string())
+    is_always_allowed(name) || self.allow.iter().any(|allowed| allowed == name)
```

## Impact

One heap allocation removed per checked identifier. Measured on a
synthetic 8k-line TS file with
8,000 dangling-underscore identifiers (`eslint/no-underscore-dangle` as
the only enabled rule),
counting system-allocator activity during `Linter::run` only:

| metric      |   baseline |  this branch |        Δ |
|-------------|-----------:|-------------:|---------:|
| allocs/iter |     32,006 |       24,006 | **−8,000 (−25%)** |
| bytes/iter  |  5,236,309 |    5,174,529 |  −61,780 |

The −8,000 allocs/iter exactly equals the number of identifiers checked
(one `to_string` each).

### Wall clock

This is a memory/allocation optimization, not a speed one — same class
as #23751 (whose own
wall-clock delta was only −0.7% to −4%). In an isolated single-rule
Criterion benchmark
(release build, `tasks/benchmark`, the repo's deterministic
`NeverGrowInPlace` allocator),
the change trends flat (fixed faster in only 20/40 paired runs — no
measurable wall-clock change; the removed `String` is dwarfed by the
rule's unavoidable per-diagnostic message allocations), but the effect
is small and near the noise floor of a shared
machine, so no end-to-end speedup should be assumed. The reliable,
deterministic win is the
reduced allocation count above (production uses mimalloc, where these
small allocations are
cheap).

## Verification

- `cargo test -p oxc_linter --lib no_underscore_dangle` passes.

This PR was assisted by Claude Code.

Co-authored-by: Cameron <[email protected]>