fix: remove false tslib requirement for native #private fields at ES2022+

[Erfan (ErfanBagheri404)]

Closed

This PR targets the JavaScript-based TypeScript codebase, which is in maintenance mode. The fix has been ported to microsoft/typescript-go in PR #4841 by astegmaier.

Closing in favor of the Go-based fix.

[Erfan (ErfanBagheri404)]

@microsoft-github-policy-service agree

[Ryan Cavanaugh (RyanCavanaugh)]

The TypeScript repo is closed for development; PR should be in the typescript-go repo. Please see the top section of CONTRIBUTING.md and pinned issue #62963.

[Copilot]

Pull request overview

This PR fixes an incorrect TS2354 (“requires an imported helper… tslib”) being reported for native #private class member usage when importHelpers: true and target >= ES2022, even though the emitter doesn’t downlevel those constructs or emit tslib helpers at those targets.

Changes:

• Simplifies three private-identifier checkExternalEmitHelpers gate conditions in checker.ts to depend only on PrivateNamesAndClassStaticBlocks (ES2022).
• Adds new compiler test cases for ES2022 (including static blocks and auto-accessors) and an ES2022 + useDefineForClassFields: false variant.
• Adds baselines verifying JS output contains no tslib imports/helpers for these scenarios.

Reviewed changes

Copilot reviewed 9 out of 9 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
src/compiler/checker.ts	Removes always-true (for dated targets) helper-gating terms so ES2022+ native private members don’t spuriously require tslib.
tests/cases/compiler/importHelpersNoHelpersForPrivateFieldsAtES2022.ts	New regression test covering many ES2022-native/private-member forms under importHelpers: true.
tests/cases/compiler/importHelpersNoHelpersForPrivateFieldsAtES2022UseDefineForClassFieldsFalse.ts	New regression test ensuring ES2022 behavior remains correct with useDefineForClassFields: false.
tests/baselines/reference/importHelpersNoHelpersForPrivateFieldsAtES2022.js	Baseline confirming no tslib import/helper usage for the ES2022 test.
tests/baselines/reference/importHelpersNoHelpersForPrivateFieldsAtES2022.types	Type baseline for the ES2022 test.
tests/baselines/reference/importHelpersNoHelpersForPrivateFieldsAtES2022.symbols	Symbol baseline for the ES2022 test.
tests/baselines/reference/importHelpersNoHelpersForPrivateFieldsAtES2022UseDefineForClassFieldsFalse.js	Baseline confirming no tslib import/helper usage for the ES2022 + useDefineForClassFields: false test.
tests/baselines/reference/importHelpersNoHelpersForPrivateFieldsAtES2022UseDefineForClassFieldsFalse.types	Type baseline for the ES2022 + useDefineForClassFields: false test.
tests/baselines/reference/importHelpersNoHelpersForPrivateFieldsAtES2022UseDefineForClassFieldsFalse.symbols	Symbol baseline for the ES2022 + useDefineForClassFields: false test.

Suppressed comments (1)

src/compiler/checker.ts:34899

• The tslib-helper check for private-field writes is still unconditional for destructuring assignments: checkReferenceAssignment calls checkExternalEmitHelpers(..., ClassPrivateFieldSet) whenever the target is a private-identifier property access, without checking languageVersion. This can still produce TS2354 at target >= ES2022 for patterns like ({ a: this.#x } = obj) even though the emitter only needs __classPrivateFieldSet when downleveling private elements (target < ES2022). Consider gating that call with the same languageVersion < LanguageFeatureMinimumTarget.PrivateNamesAndClassStaticBlocks condition, and adding a regression test that assigns into this.#field via destructuring under target: es2022 + importHelpers: true.

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