Require ECMAScript private class members

[Bharat Middha (bmiddha)]

Summary

• add @rushstack/prefer-ecmascript-private-members
• require native # syntax for private fields, methods, and accessors
• leave private constructors and constructor parameter properties unchanged
• enable the rule in legacy and flat shared ESLint profiles
• document runtime-privacy rationale and unsafe-autofix boundary

Dependency

Draft/stacked on the integration branch for #5939, #5940, #5941, #5942, and #5943. Retarget to main after those migrations merge.

Validation

• rush build --to @rushstack/eslint-config --verbose
• rush test --only @rushstack/eslint-plugin --only @rushstack/eslint-config --verbose
• 208 ESLint plugin tests passed

[Bharat Middha (bmiddha)]

Scope update: the new ESLint rule now enforces ECMAScript #private syntax for private fields, methods, getters, and setters. Private constructors and constructor parameter properties remain excluded because they have no direct native-private equivalent. The refreshed stack passes all 208 ESLint plugin tests.

[Copilot]

Pull request overview

Adds and enables an ESLint rule requiring native ECMAScript private class members.

Changes:

• Implements and tests the new rule.
• Enables it in legacy and flat profiles.
• Documents behavior and release changes.

Reviewed changes

Copilot reviewed 8 out of 8 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
eslint/eslint-plugin/src/prefer-ecmascript-private-members.ts	Implements the rule.
eslint/eslint-plugin/src/test/prefer-ecmascript-private-members.test.ts	Tests supported member forms and exemptions.
eslint/eslint-plugin/src/index.ts	Exports the rule.
eslint/eslint-plugin/README.md	Documents rationale and usage.
eslint/eslint-config/profile/_common.js	Enables the legacy rule.
eslint/eslint-config/flat/profile/_common.js	Enables the flat rule.
common/changes/@rushstack/eslint-plugin/native-private-fields_2026-08-18-12-00-00.json	Records the plugin change.
common/changes/@rushstack/eslint-config/native-private-fields_2026-08-18-12-00-00.json	Records the config change.

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