feat(lint/js): add `useThisForClassMethods` by dyc3 · Pull Request #9807 · biomejs/biome

dyc3 · 2026-04-05T15:56:20Z

Summary

This PR adds useThisForClassMethods which is a port of https://eslint.org/docs/latest/rules/class-methods-use-this

I chose to implement these options because they're pretty trivial, and they are useful escape hatches.

Generated by gpt 5.4

Test Plan

snapshots

Docs

changeset-bot · 2026-04-05T15:56:29Z

🦋 Changeset detected

Latest commit: 76e94e3

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 13 packages

Name	Type
@biomejs/biome	Patch
@biomejs/cli-win32-x64	Patch
@biomejs/cli-win32-arm64	Patch
@biomejs/cli-darwin-x64	Patch
@biomejs/cli-darwin-arm64	Patch
@biomejs/cli-linux-x64	Patch
@biomejs/cli-linux-arm64	Patch
@biomejs/cli-linux-x64-musl	Patch
@biomejs/cli-linux-arm64-musl	Patch
@biomejs/wasm-web	Patch
@biomejs/wasm-bundler	Patch
@biomejs/wasm-nodejs	Patch
@biomejs/backend-jsonrpc	Patch

Not sure what this means? Click here to learn what changesets are.

Click here if you're a maintainer who wants to add another changeset to this PR

codspeed-hq · 2026-04-05T16:04:17Z

Merging this PR will not alter performance

✅ 59 untouched benchmarks
⏩ 195 skipped benchmarks¹

_{Comparing dyc3/useThisForClassMethods (76e94e3) with main (3dce737)}

195 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. ↩

coderabbitai · 2026-04-05T19:46:39Z

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: CHILL

Plan: Pro

Run ID: 28f37e95-5e40-4e12-af55-c81ada361e25

📥 Commits

Reviewing files that changed from the base of the PR and between 3e5b87d and 76e94e3.

⛔ Files ignored due to path filters (4)

crates/biome_cli/src/execute/migrate/eslint_any_rule_to_biome.rs is excluded by !**/migrate/eslint_any_rule_to_biome.rs and included by **
crates/biome_cli/tests/snapshots/main_commands_migrate_eslint/migrate_eslintrcjson_class_methods_use_this_options.snap is excluded by !**/*.snap and included by **
crates/biome_configuration/src/analyzer/linter/rules.rs is excluded by !**/rules.rs and included by **
crates/biome_configuration/src/generated/linter_options_check.rs is excluded by !**/generated/**, !**/generated/** and included by **

📒 Files selected for processing (5)

.changeset/rich-cases-cheat.md
.claude/skills/lint-rule-development/SKILL.md
crates/biome_cli/src/execute/migrate/eslint_eslint.rs
crates/biome_cli/src/execute/migrate/eslint_to_biome.rs
crates/biome_cli/tests/commands/migrate_eslint.rs

✅ Files skipped from review due to trivial changes (3)

.claude/skills/lint-rule-development/SKILL.md
.changeset/rich-cases-cheat.md
crates/biome_cli/tests/commands/migrate_eslint.rs

Walkthrough

This pull request adds support for migrating ESLint's class-methods-use-this rule to Biome's new useThisInClassMethods nursery rule. Changes include a changeset entry, ESLint configuration deserialization logic with option mapping (exceptMethods, enforceForClassFields, ignoreOverrideMethods, ignoreClassesWithImplements), conversion from ESLint options to Biome options, migration logic to apply the rule under the nursery ruleset, test coverage with fixture files, and a module export in the rule options crate.

Possibly related PRs

biomejs/biome#9836 – Shares ESLint migration infrastructure modifications in crates/biome_cli and test updates for the migration pipeline.

🚥 Pre-merge checks | ✅ 2

✅ Passed checks (2 passed)

Check name	Status	Explanation
Title check	✅ Passed	The PR title accurately describes the main change: adding a new linter rule `useThisForClassMethods` for JavaScript.
Description check	✅ Passed	The description clearly explains the motivation (porting ESLint's class-methods-use-this rule), mentions implementation details, and includes appropriate test plan and AI disclosure.

_{✏️ Tip: You can configure your own custom pre-merge checks in the settings.}

✨ Finishing Touches

🧪 Generate unit tests (beta)

Create PR with unit tests
Commit unit tests in branch dyc3/useThisForClassMethods

_{Comment @coderabbitai help to get the list of available commands and usage tips.}

coderabbitai

Actionable comments posted: 1

🤖 Prompt for all review comments with AI agents

Verify each finding against the current code and only fix it if needed.

Inline comments:
In `@crates/biome_cli/src/execute/migrate/eslint_eslint.rs`:
- Around line 625-648: The code in
ClassMethodsUseThisOptions::into_biome_options currently ignores the
enforce_for_class_fields field (the let _ = self.enforce_for_class_fields;)
which silently tightens behaviour; update into_biome_options to handle
enforce_for_class_fields: if
biome_rule_options::use_this_for_class_methods::UseThisForClassMethodsOptions
supports an equivalent toggle, map self.enforce_for_class_fields into the
options (e.g., set a matching field or invert as needed), otherwise emit a
migration diagnostic/warning when enforce_for_class_fields is present (false) so
users are informed of the behavioural change; locate ClassMethodsUseThisOptions,
the enforce_for_class_fields field and the into_biome_options function and
either add mapping into
biome_rule_options::use_this_for_class_methods::UseThisForClassMethodsOptions or
add a diagnostic emission path when that field is Some(false).

🪄 Autofix (Beta)

Fix all unresolved CodeRabbit comments on this PR:

Push a commit to this branch (recommended)
Create a new PR with the fixes

ℹ️ Review info

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: CHILL

Plan: Pro

Run ID: 15b1a5b1-206b-480c-8dc5-2ae3b92c43d1

📥 Commits

Reviewing files that changed from the base of the PR and between 1d09f0f and 3e5b87d.

⛔ Files ignored due to path filters (17)

.opencode/package-lock.json is excluded by !**/package-lock.json and included by **
crates/biome_cli/src/execute/migrate/eslint_any_rule_to_biome.rs is excluded by !**/migrate/eslint_any_rule_to_biome.rs and included by **
crates/biome_cli/tests/snapshots/main_commands_migrate_eslint/migrate_eslintrcjson_class_methods_use_this_options.snap is excluded by !**/*.snap and included by **
crates/biome_configuration/src/analyzer/linter/rules.rs is excluded by !**/rules.rs and included by **
crates/biome_configuration/src/generated/linter_options_check.rs is excluded by !**/generated/**, !**/generated/** and included by **
crates/biome_diagnostics_categories/src/categories.rs is excluded by !**/categories.rs and included by **
crates/biome_js_analyze/tests/specs/nursery/useThisForClassMethods/invalid.js.snap is excluded by !**/*.snap and included by **
crates/biome_js_analyze/tests/specs/nursery/useThisForClassMethods/invalid.ts.snap is excluded by !**/*.snap and included by **
crates/biome_js_analyze/tests/specs/nursery/useThisForClassMethods/invalidClassFields.ts.snap is excluded by !**/*.snap and included by **
crates/biome_js_analyze/tests/specs/nursery/useThisForClassMethods/invalidExceptMethods.js.snap is excluded by !**/*.snap and included by **
crates/biome_js_analyze/tests/specs/nursery/useThisForClassMethods/invalidIgnoreClassesWithImplementsPublicFields.ts.snap is excluded by !**/*.snap and included by **
crates/biome_js_analyze/tests/specs/nursery/useThisForClassMethods/valid.js.snap is excluded by !**/*.snap and included by **
crates/biome_js_analyze/tests/specs/nursery/useThisForClassMethods/validClassFields.ts.snap is excluded by !**/*.snap and included by **
crates/biome_js_analyze/tests/specs/nursery/useThisForClassMethods/validIgnoreClassesWithImplementsAll.ts.snap is excluded by !**/*.snap and included by **
crates/biome_js_analyze/tests/specs/nursery/useThisForClassMethods/validIgnoreOverrideMethods.ts.snap is excluded by !**/*.snap and included by **
packages/@biomejs/backend-jsonrpc/src/workspace.ts is excluded by !**/backend-jsonrpc/src/workspace.ts and included by **
packages/@biomejs/biome/configuration_schema.json is excluded by !**/configuration_schema.json and included by **

📒 Files selected for processing (20)

.changeset/rich-cases-cheat.md
crates/biome_cli/src/execute/migrate/eslint_eslint.rs
crates/biome_cli/src/execute/migrate/eslint_to_biome.rs
crates/biome_cli/tests/commands/migrate_eslint.rs
crates/biome_js_analyze/src/lint/nursery/use_this_for_class_methods.rs
crates/biome_js_analyze/tests/specs/nursery/useThisForClassMethods/invalid.js
crates/biome_js_analyze/tests/specs/nursery/useThisForClassMethods/invalid.ts
crates/biome_js_analyze/tests/specs/nursery/useThisForClassMethods/invalidClassFields.ts
crates/biome_js_analyze/tests/specs/nursery/useThisForClassMethods/invalidExceptMethods.js
crates/biome_js_analyze/tests/specs/nursery/useThisForClassMethods/invalidExceptMethods.options.json
crates/biome_js_analyze/tests/specs/nursery/useThisForClassMethods/invalidIgnoreClassesWithImplementsPublicFields.options.json
crates/biome_js_analyze/tests/specs/nursery/useThisForClassMethods/invalidIgnoreClassesWithImplementsPublicFields.ts
crates/biome_js_analyze/tests/specs/nursery/useThisForClassMethods/valid.js
crates/biome_js_analyze/tests/specs/nursery/useThisForClassMethods/validClassFields.ts
crates/biome_js_analyze/tests/specs/nursery/useThisForClassMethods/validIgnoreClassesWithImplementsAll.options.json
crates/biome_js_analyze/tests/specs/nursery/useThisForClassMethods/validIgnoreClassesWithImplementsAll.ts
crates/biome_js_analyze/tests/specs/nursery/useThisForClassMethods/validIgnoreOverrideMethods.options.json
crates/biome_js_analyze/tests/specs/nursery/useThisForClassMethods/validIgnoreOverrideMethods.ts
crates/biome_rule_options/src/lib.rs
crates/biome_rule_options/src/use_this_for_class_methods.rs

coderabbitai · 2026-04-05T19:46:42Z

+    #[deserializable(rename = "enforceForClassFields")]
+    enforce_for_class_fields: Option<bool>,
+    #[deserializable(rename = "ignoreOverrideMethods")]
+    ignore_override_methods: Option<bool>,
+    #[deserializable(rename = "ignoreClassesWithImplements")]
+    ignore_classes_with_implements: Option<EslintIgnoreClassesWithImplements>,
+}
+impl ClassMethodsUseThisOptions {
+    pub(crate) fn into_biome_options(
+        self,
+    ) -> Option<biome_rule_options::use_this_for_class_methods::UseThisForClassMethodsOptions> {
+        let options =
+            biome_rule_options::use_this_for_class_methods::UseThisForClassMethodsOptions {
+                except_methods: (!self.except_methods.is_empty()).then_some(self.except_methods),
+                ignore_override_methods: self.ignore_override_methods,
+                ignore_classes_with_implements: self.ignore_classes_with_implements.map(Into::into),
+            };
+
+        let _ = self.enforce_for_class_fields;
+
+        (options.except_methods.is_some()
+            || options.ignore_override_methods.is_some()
+            || options.ignore_classes_with_implements.is_some())
+        .then_some(options)


⚠️ Potential issue | 🟠 Major

🧩 Analysis chain

🌐 Web query:

In ESLint's class-methods-use-thisrule, what doesenforceForClassFieldsdo, what is its default, and what behaviour changes when it is set tofalse?

💡 Result:

The enforceForClassFields option in ESLint's class-methods-use-this rule enforces that arrow functions and function expressions used as instance field initializers (class fields) utilize this. It also applies to auto-accessor fields declared with the accessor keyword. Its default value is true. When set to false, the rule does not check class fields for this usage, allowing functions in class field initializers that do not reference this without flagging them as violations. With the default true, such fields are flagged unless this is used.

Citations:

1: https://eslint.org/docs/latest/rules/class-methods-use-this

2: https://archive.eslint.org/docs/rules/class-methods-use-this

🏁 Script executed:

#!/bin/bash set -euo pipefail # Check where the option is parsed, dropped, or asserted in migration/tests. rg -n -C3 '\benforceForClassFields\b|\benforce_for_class_fields\b|class-methods-use-this|useThisForClassMethods' \ crates/biome_cli/src/execute/migrate \ crates/biome_cli/tests \ crates/biome_js_analyze/src/lint/nursery/use_this_for_class_methods.rs \ crates/biome_js_analyze/tests/specs/nursery/useThisForClassMethods # Check whether migration currently emits diagnostics/warnings for unsupported option semantics. rg -n -C3 'unsupported|not supported|cannot migrate|warning|diagnostic' crates/biome_cli/src/execute/migrate

Repository: biomejs/biome

Length of output: 50371

Silently dropping enforceForClassFields changes rule behaviour.

When a user sets enforceForClassFields: false in ESLint (disabling class field checks), the migration discards this option without warning. Biome's useThisForClassMethods always checks class fields, so users unknowingly get stricter enforcement post-migration—behaviour tightening disguised as migration.

Line 643 silently discards the value. Consider either:

Emitting a diagnostic informing users of the behaviour change

Mapping the option (if Biome's rule supports runtime disabling)

Check whether Biome's rule can support a similar toggle.

🤖 Prompt for AI Agents

Verify each finding against the current code and only fix it if needed. In `@crates/biome_cli/src/execute/migrate/eslint_eslint.rs` around lines 625 - 648, The code in ClassMethodsUseThisOptions::into_biome_options currently ignores the enforce_for_class_fields field (the let _ = self.enforce_for_class_fields;) which silently tightens behaviour; update into_biome_options to handle enforce_for_class_fields: if biome_rule_options::use_this_for_class_methods::UseThisForClassMethodsOptions supports an equivalent toggle, map self.enforce_for_class_fields into the options (e.g., set a matching field or invert as needed), otherwise emit a migration diagnostic/warning when enforce_for_class_fields is present (false) so users are informed of the behavioural change; locate ClassMethodsUseThisOptions, the enforce_for_class_fields field and the into_biome_options function and either add mapping into biome_rule_options::use_this_for_class_methods::UseThisForClassMethodsOptions or add a diagnostic emission path when that field is Some(false).

ematipico

I am a bit biased against this rule (their semantics and name), let me know what you think about the suggestion I gave.

Apart from that, the docs need more work, and code can be improved.

dyc3 force-pushed the dyc3/useThisForClassMethods branch from db3e74a to 0408706 Compare April 5, 2026 15:56

github-actions Bot added A-CLI Area: CLI A-Project Area: project A-Linter Area: linter L-JavaScript Language: JavaScript and super languages A-Diagnostic Area: diagnostocis labels Apr 5, 2026

dyc3 force-pushed the dyc3/useThisForClassMethods branch from 0408706 to 3551362 Compare April 5, 2026 15:59

dyc3 force-pushed the dyc3/useThisForClassMethods branch from 1248d3a to 3e5b87d Compare April 5, 2026 16:36

dyc3 marked this pull request as ready for review April 5, 2026 19:37

dyc3 requested review from a team April 5, 2026 19:37

coderabbitai Bot reviewed Apr 5, 2026

View reviewed changes

ematipico requested changes Apr 17, 2026

View reviewed changes

dyc3 commented Apr 18, 2026

View reviewed changes

Comment thread .opencode/package-lock.json Outdated

Comment thread crates/biome_js_analyze/src/lint/nursery/use_this_for_class_methods.rs Outdated

feat(lint/js): add useThisInClassMethods

76e94e3

dyc3 force-pushed the dyc3/useThisForClassMethods branch from 3e5b87d to 76e94e3 Compare April 18, 2026 17:07

dyc3 requested a review from ematipico April 18, 2026 17:07

Provide feedback

Saved searches

Use saved searches to filter your results more quickly

Uh oh!

feat(lint/js): add `useThisForClassMethods`#9807

feat(lint/js): add `useThisForClassMethods`#9807
dyc3 wants to merge 1 commit intomainfrom
dyc3/useThisForClassMethods

dyc3 commented Apr 5, 2026

Uh oh!

changeset-bot Bot commented Apr 5, 2026 •

edited

Loading

Uh oh!

codspeed-hq Bot commented Apr 5, 2026 •

edited

Loading

Uh oh!

coderabbitai Bot commented Apr 5, 2026 •

edited

Loading

Uh oh!

coderabbitai Bot left a comment

Uh oh!

coderabbitai Bot Apr 5, 2026

Uh oh!

ematipico left a comment

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

2 participants

Uh oh!

Conversation

dyc3 commented Apr 5, 2026

Summary

Test Plan

Docs

Uh oh!

changeset-bot Bot commented Apr 5, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

🦋 Changeset detected

Uh oh!

codspeed-hq Bot commented Apr 5, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Merging this PR will not alter performance

Footnotes

Uh oh!

coderabbitai Bot commented Apr 5, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Walkthrough

Possibly related PRs

Uh oh!

coderabbitai Bot left a comment

Choose a reason for hiding this comment

Uh oh!

coderabbitai Bot Apr 5, 2026

Choose a reason for hiding this comment

Uh oh!

ematipico left a comment

Choose a reason for hiding this comment

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

2 participants

changeset-bot Bot commented Apr 5, 2026 •

edited

Loading

codspeed-hq Bot commented Apr 5, 2026 •

edited

Loading

coderabbitai Bot commented Apr 5, 2026 •

edited

Loading