linter: rule fixer improvements

[DonIsaac]

I've been adding and repairing fixers to a lot of rules, but my ad-hoc approach
is not sustainable. This issue is a call for assistance, and tracks fixer
progress for each rule.

Prerequisites

• refactor(linter): Let fixer functions decide whether to apply a fix or not #4187
• feat(linter): Support potentially dangerous fixes behind a --fix-dangerously flag #4211
• Add idempotence test to --fix oxlint-ecosystem-ci#19

Rules

For rules with an existing fixer:

• If the rule has a fixer (using diagnostic_with_fix), ensure that there are
  no cases where the fixer could create a syntax error or semantically different
  code.
• If the fix could be correct in some cases, but could produce semantically
  differently different code in others, use diagnostic_with_fix_dangerous.
• Link this issue to your PR updating the rule's fixer, and a maintainer will
  update this table. If no changes are needed, leave a comment here and we'll
  also update the table.

For rules without a fixer:

• Check if a fixer could be safely added in some cases. If so, create a PR with
  a fixer implementation that links to this issue.
• If no fixer can (or should) be created for the rule, leave a comment below and
  a maintainer will update the table.

Legend

• : Not checked
• ✅ Has a working fixer
• 🚧 No fixer, but one could be added
• 🚫 No fixer, and one cannot be added

Correctness (159):

Code that is outright wrong or useless.

Rule name	Source	Status
for-direction	eslint
no-async-promise-executor	eslint
no-caller	eslint
no-class-assign	eslint
no-compare-neg-zero	eslint
no-cond-assign	eslint
no-const-assign	eslint
no-constant-binary-expression	eslint
no-constant-condition	eslint
no-control-regex	eslint
no-debugger	eslint	✅
no-delete-var	eslint
no-dupe-class-members	eslint
no-dupe-else-if	eslint
no-dupe-keys	eslint
no-duplicate-case	eslint
no-empty-character-class	eslint
no-empty-pattern	eslint
no-empty-static-block	eslint
no-ex-assign	eslint
no-extra-boolean-cast	eslint
no-func-assign	eslint
no-global-assign	eslint
no-import-assign	eslint
no-irregular-whitespace	eslint
no-loss-of-precision	eslint
no-new-native-nonconstructor	eslint
no-nonoctal-decimal-escape	eslint
no-obj-calls	eslint
no-self-assign	eslint
no-setter-return	eslint
no-shadow-restricted-names	eslint
no-sparse-arrays	eslint
no-this-before-super	eslint
no-unsafe-finally	eslint
no-unsafe-negation	eslint
no-unused-labels	eslint
no-unused-private-class-members	eslint
no-useless-catch	eslint
no-useless-escape	eslint
no-useless-rename	eslint
no-with	eslint
require-yield	eslint
use-isnan	eslint	✅
valid-typeof	eslint
default	import
named	import
namespace	import
expect-expect	jest
no-conditional-expect	jest
no-disabled-tests	jest
no-export	jest
no-focused-tests	jest
no-standalone-expect	jest
require-to-throw-message	jest
valid-describe-callback	jest
valid-expect	jest
valid-title	jest
check-property-names	jsdoc
check-tag-names	jsdoc
implements-on-classes	jsdoc
no-defaults	jsdoc
require-property	jsdoc
require-property-description	jsdoc
require-property-name	jsdoc
require-property-type	jsdoc
require-yields	jsdoc
alt-text	jsx_a11y
anchor-has-content	jsx_a11y
anchor-is-valid	jsx_a11y
aria-activedescendant-has-tabindex	jsx_a11y
aria-props	jsx_a11y	✅
aria-role	jsx_a11y
aria-unsupported-elements	jsx_a11y
autocomplete-valid	jsx_a11y
click-events-have-key-events	jsx_a11y
heading-has-content	jsx_a11y
html-has-lang	jsx_a11y
iframe-has-title	jsx_a11y
img-redundant-alt	jsx_a11y
lang	jsx_a11y
media-has-caption	jsx_a11y
mouse-events-have-key-events	jsx_a11y
no-access-key	jsx_a11y
no-aria-hidden-on-focusable	jsx_a11y
no-autofocus	jsx_a11y
no-distracting-elements	jsx_a11y
no-redundant-roles	jsx_a11y
prefer-tag-over-role	jsx_a11y
role-has-required-aria-props	jsx_a11y
role-supports-aria-props	jsx_a11y
scope	jsx_a11y
tabindex-no-positive	jsx_a11y
google-font-display	nextjs
google-font-preconnect	nextjs
inline-script-id	nextjs
next-script-for-ga	nextjs
no-assign-module-variable	nextjs
no-async-client-component	nextjs
no-before-interactive-script-outside-document	nextjs
no-css-tags	nextjs
no-document-import-in-page	nextjs
no-duplicate-head	nextjs
no-head-element	nextjs
no-head-import-in-document	nextjs
no-img-element	nextjs
no-page-custom-font	nextjs
no-script-component-in-head	nextjs
no-styled-jsx-in-document	nextjs
no-sync-scripts	nextjs
no-title-in-document-head	nextjs
no-typos	nextjs
no-unwanted-polyfillio	nextjs
bad-array-method-on-arguments	oxc
bad-char-at-comparison	oxc
bad-comparison-sequence	oxc
bad-min-max-func	oxc
bad-object-literal-comparison	oxc
bad-replace-all-arg	oxc
const-comparisons	oxc
double-comparisons	oxc
erasing-op	oxc
missing-throw	oxc
number-arg-out-of-range	oxc
only-used-in-recursion	oxc
uninvoked-array-callback	oxc
jsx-key	react
jsx-no-duplicate-props	react
jsx-no-target-blank	react
jsx-no-undef	react
no-children-prop	react
no-direct-mutation-state	react
no-find-dom-node	react
no-is-mounted	react
no-render-return-value	react
no-string-refs	react
void-dom-elements-no-children	react
no-extra-non-null-assertion	typescript
no-misused-new	typescript
no-namespace	typescript
no-non-null-asserted-optional-chain	typescript
no-this-alias	typescript
no-unsafe-declaration-merging	typescript
no-useless-empty-export	typescript
prefer-as-const	typescript
triple-slash-reference	typescript
no-await-in-promise-methods	unicorn
no-document-cookie	unicorn
no-empty-file	unicorn
no-invalid-remove-event-listener	unicorn
no-new-array	unicorn
no-single-promise-in-promise-methods	unicorn
no-thenable	unicorn
no-unnecessary-await	unicorn
no-useless-fallback-in-spread	unicorn	✅
no-useless-length-check	unicorn
no-useless-spread	unicorn
prefer-set-size	unicorn
prefer-string-starts-ends-with	unicorn	✅

Perf (6):

Code that can be written to run faster.

Rule name	Source	Status
no-await-in-loop	eslint
no-accumulating-spread	oxc
jsx-no-jsx-as-prop	react_perf
jsx-no-new-array-as-prop	react_perf
jsx-no-new-function-as-prop	react_perf
jsx-no-new-object-as-prop	react_perf

Restriction (49):

Lints which prevent the use of language and library features. Must not be enabled as a whole, should be considered on a case-by-case basis before enabling.

Rule name	Source	Status
default-case	eslint
no-bitwise	eslint
no-console	eslint
no-div-regex	eslint
no-empty	eslint
no-empty-function	eslint
no-eq-null	eslint
no-eval	eslint
no-iterator	eslint
no-proto	eslint
no-regex-spaces	eslint
no-restricted-globals	eslint
no-undefined	eslint
no-unsafe-optional-chaining	eslint
no-var	eslint
no-void	eslint
unicode-bom	eslint
no-amd	import
no-cycle	import
no-default-export	import
check-access	jsdoc
empty-tags	jsdoc
bad-bitwise-operator	oxc
no-async-await	oxc
no-barrel-file	oxc
no-const-enum	oxc
no-optional-chaining	oxc
no-rest-spread-properties	oxc
button-has-type	react
no-danger	react
no-unknown-property	react
explicit-function-return-type	typescript
no-dynamic-delete	typescript
no-explicit-any	typescript
no-import-type-side-effects	typescript
no-non-null-asserted-nullish-coalescing	typescript
no-non-null-assertion	typescript
no-var-requires	typescript
prefer-literal-enum-member	typescript
no-abusive-eslint-disable	unicorn
no-anonymous-default-export	unicorn
no-array-for-each	unicorn
no-array-reduce	unicorn
no-magic-array-flat-depth	unicorn
no-nested-ternary	unicorn
no-process-exit	unicorn
prefer-modern-math-apis	unicorn
prefer-node-protocol	unicorn
prefer-number-properties	unicorn

Suspicious (14):

code that is most likely wrong or useless.

Rule name	Source	Status
no-new	eslint
no-useless-concat	eslint
no-useless-constructor	eslint	✅
no-duplicates	import
no-named-as-default	import
no-named-as-default-member	import
no-self-import	import
no-commented-out-tests	jest
approx-constant	oxc
misrefactored-assign-op	oxc
jsx-no-comment-textnodes	react
react-in-jsx-scope	react
no-unnecessary-type-constraint	typescript
prefer-add-event-listener	unicorn

Pedantic (66):

Lints which are rather strict or have occasional false positives.

Rule name	Source	Status
array-callback-return	eslint
eqeqeq	eslint
max-classes-per-file	eslint
max-lines	eslint
no-array-constructor	eslint
no-case-declarations	eslint
no-constructor-return	eslint
no-fallthrough	eslint
no-inner-declarations	eslint
no-new-wrappers	eslint
no-prototype-builtins	eslint
no-redeclare	eslint
no-self-compare	eslint
radix	eslint
require-await	eslint
symbol-description	eslint
max-dependencies	import
require-param	jsdoc
require-param-description	jsdoc
require-param-name	jsdoc
require-param-type	jsdoc
require-returns	jsdoc
require-returns-description	jsdoc
require-returns-type	jsdoc
checked-requires-onchange-or-readonly	react
jsx-no-useless-fragment	react
no-unescaped-entities	react
ban-ts-comment	typescript
ban-types	typescript
no-duplicate-enum-values	typescript
prefer-enum-initializers	typescript
prefer-ts-expect-error	typescript
escape-case	unicorn
explicit-length-check	unicorn
new-for-builtins	unicorn
no-hex-escape	unicorn
no-instanceof-array	unicorn
no-lonely-if	unicorn
no-negated-condition	unicorn
no-negation-in-equality-check	unicorn
no-new-buffer	unicorn
no-object-as-default-parameter	unicorn
no-static-only-class	unicorn
no-this-assignment	unicorn
no-typeof-undefined	unicorn
no-unreadable-iife	unicorn
no-useless-promise-resolve-reject	unicorn
no-useless-switch-case	unicorn
prefer-array-flat	unicorn
prefer-array-some	unicorn
prefer-blob-reading-methods	unicorn
prefer-code-point	unicorn	✅
prefer-date-now	unicorn
prefer-dom-node-append	unicorn
prefer-dom-node-dataset	unicorn
prefer-dom-node-remove	unicorn
prefer-event-target	unicorn
prefer-math-trunc	unicorn
prefer-native-coercion-functions	unicorn
prefer-prototype-methods	unicorn
prefer-query-selector	unicorn
prefer-regexp-test	unicorn
prefer-string-replace-all	unicorn
prefer-string-slice	unicorn
prefer-type-error	unicorn
require-number-to-fixed-digits-argument	unicorn

Style (80):

Code that should be written in a more idiomatic way.

Rule name	Source	Status
default-case-last	eslint
default-param-last	eslint
guard-for-in	eslint
max-params	eslint
no-continue	eslint
no-multi-str	eslint
no-script-url	eslint
no-template-curly-in-string	eslint
no-ternary	eslint
prefer-exponentiation-operator	eslint
sort-imports	eslint	✅
consistent-test-it	jest
max-expects	jest
max-nested-describe	jest
no-alias-methods	jest
no-confusing-set-timeout	jest
no-deprecated-functions	jest
no-done-callback	jest
no-duplicate-hooks	jest
no-hooks	jest
no-identical-title	jest
no-interpolation-in-snapshots	jest
no-jasmine-globals	jest
no-large-snapshots	jest
no-mocks-import	jest
no-restricted-jest-methods	jest
no-restricted-matchers	jest
no-test-prefixes	jest
no-test-return-statement	jest
no-untyped-mock-factory	jest
prefer-called-with	jest
prefer-comparison-matcher	jest
prefer-equality-matcher	jest
prefer-expect-resolves	jest
prefer-hooks-on-top	jest
prefer-jest-mocked	jest
prefer-lowercase-title	jest
prefer-mock-promise-shorthand	jest
prefer-spy-on	jest
prefer-strict-equal	jest
prefer-to-be	jest
prefer-to-contain	jest
prefer-to-have-length	jest
prefer-todo	jest
require-hook	jest
require-top-level-describe	jest
no-set-state	react
prefer-es-6-class	react
adjacent-overload-signatures	typescript
array-type	typescript
ban-tslint-comment	typescript
consistent-indexed-object-style	typescript
consistent-type-definitions	typescript
no-empty-interface	typescript
prefer-for-of	typescript
prefer-function-type	typescript
catch-error-name	unicorn
empty-brace-spaces	unicorn	✅
error-message	unicorn
filename-case	unicorn
no-await-expression-member	unicorn
no-console-spaces	unicorn
no-null	unicorn
no-unreadable-array-destructuring	unicorn
no-zero-fractions	unicorn	✅
number-literal-case	unicorn
numeric-separators-style	unicorn
prefer-array-flat-map	unicorn
prefer-dom-node-text-content	unicorn
prefer-includes	unicorn
prefer-logical-operator-over-ternary	unicorn
prefer-modern-dom-apis	unicorn
prefer-optional-catch-binding	unicorn
prefer-reflect-apply	unicorn
prefer-spread	unicorn
prefer-string-trim-start-end	unicorn	✅
require-array-join-separator	unicorn
switch-case-braces	unicorn
text-encoding-identifier-case	unicorn
throw-new-error	unicorn

Nursery (9):

New lints that are still under development.

Rule name	Source	Status
constructor-super	eslint
getter-return	eslint
no-undef	eslint
no-unreachable	eslint
export	import
require-render-return	react
rules-of-hooks	react
no-side-effects-in-initialization	tree_shaking
consistent-type-imports	typescript

These tables were created by running oxlint --rules on commit ca0b4fa0.

[jordan-boyer]

no-const-assign cannot have a fixer because we cannot infer the intend of the user .

Or we can add a dangerous fix that will replace the const with a let.
Tell me what you want on this and in can try to implement it

[jelly]

Related to fixes, can oxlint's diagnostic also print that a fix is available. Ruff for example shows:

[jelle@natrium][~/projects/oxc]%ruff check foo.py
foo.py:2:8: F401 [*] `os` imported but unused
  |
1 | #/usr/bin/python
2 | import os
  |        ^^ F401
  |
  = help: Remove unused import: `os`

Found 1 error.
[*] 1 fixable with the `--fix` option.

oxlint prints no information at the moment:

[jelle@natrium][~/projects/oxc]%cargo run --bin oxlint --  -A all -D prefer-string-trim-start-end foo.js
   Compiling oxc_linter v0.6.0 (/home/jelle/projects/oxc/crates/oxc_linter)
   Compiling oxlint v0.6.0 (/home/jelle/projects/oxc/apps/oxlint)
    Finished `dev` profile [unoptimized] target(s) in 3.69s
     Running `target/debug/oxlint -A all -D prefer-string-trim-start-end foo.js`

  × eslint-plugin-unicorn(prefer-string-trim-start-end): Prefer `trimStart` over `trimLeft`
    ╭─[foo.js:34:5]
 33 │ const foo = "lol";
 34 │ foo.trimLeft();
    ·     ────────
    ╰────
  help: Replace with `trimStart`

Finished in 4ms on 1 file with 1 rules using 16 threads.
Found 0 warnings and 1 error.

[DonIsaac]

@jelly check out my PR with suggestions; it does this.

[DonIsaac]

@jelly check out my PR with suggestions; it does this.

#4223

[jelly]

I think another task should be added, rules with fixers without tests. Last night I discovered no-zero-fractions currently produces broken code. See the test cases ff72fcd

  × eslint-plugin-unicorn(no-zero-fractions): Don't use a dangling dot in the number.
   ╭─[bar.js:7:14]
 6 │ const foo4 = -1.e+10;
 7 │ const foo5 = 1.e10;
   ·              ─────
 8 │ const foo6 = .0;
   ╰────
  help: Replace the number literal with `110`

While:

> 1.e10
10000000000

I simply copied some of the failing test cases into a JS file, made a backup and ran eslint fix on it as unicorn sadly has no tests for the fixer it seems.

Collected the list of fixers without expect_fix:

• crates/oxc_linter/src/rules/eslint/no_unsafe_negation.rs
• crates/oxc_linter/src/rules/eslint/valid_typeof.rs
• crates/oxc_linter/src/rules/jest/no_test_prefixes.rs
• crates/oxc_linter/src/rules/jest/valid_title.rs
• crates/oxc_linter/src/rules/typescript/ban_ts_comment.rs
• crates/oxc_linter/src/rules/unicorn/no_null.rs
• crates/oxc_linter/src/rules/unicorn/no_zero_fractions.rs
• crates/oxc_linter/src/rules/unicorn/prefer_dom_node_text_content.rs

[heygsc]

For eslint itself, some rules have fixers, while others do not.
For those eslint without fixers, is it not recommended to do it with oxc, or is it okay to add it as a unique feature of oxc?

[rzvxa]

For eslint itself, some rules have fixers, while others do not. For those eslint without fixers, is it not recommended to do it with oxc, or is it okay to add it as a unique feature of oxc?

I'm not sure if I'm getting it right or not, So feel free to correct me.

---

If you are talking about adding new fixers where there isn't one in eslint(or other linting solutions), It is completely welcomed here, We want backward compatibility with eslint as a drop-in replacement for most parts; But as long as we are adding(and not subtracting) features, It is allowed with no restrictions whatsoever. As long as it makes sense and is useful.

Although for non-exiting fixers/linters, you'd have to write through tests - since there isn't any source to borrow the tests from - and it might need a more rigorous review process to make sure it is doing the intended behavior we have in mind and assess the risks for the fixer(in case it have to be a dangerous fix).

With that said if you ever think the change you have in mind might be controversial it'd be best to create an issue for it beforehand or ask for reviews early in the process to make sure there aren't any strong oppositions against it. The last thing we want is to allow contributors' time to go to waste.

Let me know if I didn't answer your question.

[heygsc]

For itself, some rules have fixers, while others do not. For those without fixers, is it not recommended to do it with , or is it okay to add it as a unique feature of ?eslint``eslint``oxc``oxc

I'm not sure if I'm getting it right or not, So feel free to correct me.

If you are talking about adding new fixers where there isn't one in eslint(or other linting solutions), It is completely welcomed here, We want backward compatibility with eslint as a drop-in replacement for most parts; But as long as we are adding(and not subtracting) features, It is allowed with no restrictions whatsoever. As long as it makes sense and is useful.

Although for non-exiting fixers/linters, you'd have to write through tests - since there isn't any source to borrow the tests from - and it might need a more rigorous review process to make sure it is doing the intended behavior we have in mind and assess the risks for the fixer(in case it have to be a dangerous fix).

With that said if you ever think the change you have in mind might be controversial it'd be best to create an issue for it beforehand or ask for reviews early in the process to make sure there aren't any strong oppositions against it. The last thing we want is to allow contributors' time to go to waste.

Let me know if I didn't answer your question.

Yes, thank you. That's what I wanted to ask.
If we prioritize which one to do first, would it be recommended in Oxc's plan to start with existing fixers (such as in ESLint)?

[DonIsaac]

@heygsc it depends. I'd recommend starting there if you're just getting your feet wet. Porting existing fixers is definitely easier than writing new ones.

In some cases, rules intentionally do not have auto fixes for DX reasons. For example, imagine an unused import getting deleted when your editor saves a file. That would get really annoying quite quickly. For those cases, we've added infrastructure for suggestions and "dangerous" fixes, which do not get applied when --fix is used, but instead get their own CLI flags.

[heygsc]

@heygsc it depends. I'd recommend starting there if you're just getting your feet wet. Porting existing fixers is definitely easier than writing new ones.

In some cases, rules intentionally do not have auto fixes for DX reasons. For example, imagine an unused import getting deleted when your editor saves a file. That would get really annoying quite quickly. For those cases, we've added infrastructure for suggestions and "dangerous" fixes, which do not get applied when --fix is used, but instead get their own CLI flags.

What you said makes sense. Thank you.