[Oleksandr Tarasiuk (a-tarasyuk)]

Fixes #63704

[Copilot]

Pull request overview

Adds ES2026 compiler-target and standard-library support, including the APIs requested by #63704.

Changes:

• Registers es2026 as a target, default standard target, and library.
• Adds ES2026 API declarations and preserves esnext.* aliases.
• Adds conformance tests and refreshes generated baselines.

Reviewed changes

Copilot reviewed 136 out of 540 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
packages/typescript/src/enums/scriptTarget*.ts	Exposes ES2026 publicly.
packages/typescript/test/{async,sync}/api.test.ts	Updates target diagnostics.
tsc/internal/core/{compileroptions,scripttarget_stringer_generated}.go	Defines and formats the target.
tsc/internal/tsoptions/enummaps.go	Registers target, libraries, and compatibility aliases.
tsc/internal/transformers/estransforms/definitions.go	Selects the ES2026 transform pipeline.
tsc/internal/checker/utilities.go	Adds ES2026 library suggestions.
tsc/internal/bundled/libs/lib.es2026*.d.ts	Defines the ES2026 library and APIs.
tsc/internal/bundled/libs/lib.esnext.d.ts	Makes ESNext inherit ES2026.
tsc/internal/bundled/{embed_generated,libs_generated}.go	Embeds and registers new libraries.
tsc/internal/compiler/program_test.go	Updates expected ESNext library ordering.
tsc/testdata/fixtures/compiler/*.ts	Synchronizes compiler fixtures.
tsc/testdata/tests/cases/conformance/es2026/*.ts	Tests ES2026 APIs and diagnostics.
tsc/testdata/baselines/reference/**	Refreshes generated compiler, build, watch, API, and conformance baselines.

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[Copilot]

🔵 Needs a closer look

The public target and library surface spans hundreds of generated baselines and warrants final human validation against the ES2026 specification.

Review details

• Files reviewed: 136/540 changed files
• Comments generated: 0 new
• Review effort level: Balanced

[Copilot]

🟡 Changes recommended

The jsonRawJSON2 source and checked-in baselines disagree, causing baseline tests to fail.

Once you've addressed the issues Copilot identified, you can request another Copilot review.

Review details

• Files reviewed: 146/553 changed files
• Comments generated: 1
• Review effort level: Balanced

[Copilot]

Copilot review overview

🟢 Approval recommended

The target, libraries, API surface, and conformance coverage are coherent; only a non-blocking JSDoc typo remains.

Review effort: Balanced
Findings: None

[Copilot]

Copilot review overview

🟢 Approval recommended

The target registration, library declarations, API exposure, and corresponding baselines are consistent and adequately tested.

Review effort: Balanced
Findings: None

[Copilot]

Copilot review overview

🟢 Approval recommended

Target registration, library declarations, compatibility mappings, and conformance coverage are consistent.

Review effort: Balanced
Findings: None

[Jake Bailey (jakebailey)]

I don't think we typically add a slew of tests for lib files but, it's fine

[Daniel Rosenwasser (DanielRosenwasser)]

I am happy to have lib tests to be honest.

Separately, it looks like we have some baseline merge conflicts though.

[Philipp B. (Phil2812)]

Hello,

Regarding the JSON change, shouldn't the reviver parameter of JSON.parse remain optional in the definition?

Including the changed definition (just lib.es2026.json.d.ts), JSON.parse works fine, but Parameters<JSON["parse"]> returns the wrong type (reviver parameter non-optional).

I am not set up to contribute to the project, so my apologies if this is not the right place to report this.

Cheers,
Philipp

[Jake Bailey (jakebailey)]

Philipp B. (@Phil2812) please file an issue