feat: add es2026 as a valid target and lib by a-tarasyuk · Pull Request #64096 · microsoft/TypeScript

Oleksandr Tarasiuk (a-tarasyuk) · 2026-08-30T10:30:41Z

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

…into feat/63704

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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

typescript-automation · 2026-09-24T22:22:24Z

Daniel Rosenwasser (@DanielRosenwasser) Here are the results of running the user tests with tsc comparing main and refs/pull/64096/merge:

There were infrastructure failures potentially unrelated to your change:

1 instance of "Git clone failed"
1 instance of "Package install failed"

Otherwise...

Something interesting changed - please have a look.

Details

lodash

/mnt/vss/work/1/s/ts_downloads//m/lodash/tsconfig.json

[MISSING] error TS2345: Argument of type '{ castArray: () => any[]; clone: (value: any) => any; cloneDeep: (value: any) => any; cloneDeepWith: (value: any, customizer?: Function | undefined) => any; cloneWith: (value: any, customizer?: Function | undefined) => any; ... 50 more ...; toString: (value: any) => string; }' is not assignable to parameter of type 'string'.
- /mnt/vss/work/1/s/ts_downloads//m/lodash/node_modules/lodash/fp/lang.js(2,26)

typescript-automation · 2026-09-24T23:01:00Z

Daniel Rosenwasser (@DanielRosenwasser) Here are the results of running the top 400 repos with tsc comparing main and refs/pull/64096/merge:

Everything looks good!

typescript-automation · 2026-09-25T05:28:55Z

Hey Daniel Rosenwasser (@DanielRosenwasser), the results of running the DT tests are ready.

Everything looks the same!

You can check the log here.

…eat/63704

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) · 2026-09-28T17:08:38Z

I am happy to have lib tests to be honest.

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

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…into feat/63704

typescript-automation Bot added the For Milestone Bug PRs that fix a bug with a specific milestone label Aug 30, 2026

typescript-automation Bot assigned Daniel Rosenwasser (DanielRosenwasser) Aug 30, 2026

feat: add es2026 as a valid target and lib

a022dd9

Oleksandr Tarasiuk (a-tarasyuk) force-pushed the feat/63704 branch from fefecb3 to a022dd9 Compare August 31, 2026 21:08

Oleksandr Tarasiuk (a-tarasyuk) marked this pull request as ready for review August 31, 2026 21:27

Copilot AI balanced review requested due to automatic review settings August 31, 2026 21:27

Copilot started reviewing on behalf of Oleksandr Tarasiuk (a-tarasyuk) August 31, 2026 21:28 View session

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Oleksandr Tarasiuk (a-tarasyuk) added 3 commits September 1, 2026 08:55

Merge branch 'main' into feat/63704

6d0205a

Merge branch 'main' of https://github.com/microsoft/TypeScript into f…

2bba2a4

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Merge branch 'main' into feat/63704

fb73068

Jake Bailey (jakebailey) requested a balanced review from Copilot September 4, 2026 17:54

Jake Bailey (jakebailey) reviewed Sep 4, 2026

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Comment thread tsc/internal/bundled/libs/lib.es2026.error.d.ts Outdated

Copilot started reviewing on behalf of Jake Bailey (jakebailey) September 4, 2026 17:57 View session

Copilot AI reviewed Sep 4, 2026

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restore spec wording for Error.isError

43135e9

Jake Bailey (jakebailey) requested changes Sep 4, 2026

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Comment thread tsc/internal/bundled/libs/lib.es2026.full.d.ts

Comment thread tsc/internal/bundled/libs/lib.es2026.json.d.ts Outdated

Comment thread tsc/internal/bundled/libs/lib.es2026.typedarrays.d.ts

Comment thread tsc/testdata/fixtures/compiler/commandLineParser.ts

Oleksandr Tarasiuk (a-tarasyuk) added 4 commits September 4, 2026 21:45

clean up es2026 lib

2099baf

Merge branch 'feat/63704' of https://github.com/a-tarasyuk/TypeScript …

97f4eae

…into feat/63704

update baseline

bba9bbb

Merge branch 'main' of https://github.com/microsoft/TypeScript into f…

4e61768

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Oleksandr Tarasiuk (a-tarasyuk) requested a review from Jake Bailey (jakebailey) September 4, 2026 19:25

Oleksandr Tarasiuk (a-tarasyuk) added 2 commits September 8, 2026 09:42

add a private field to RawJSON

3d4c1c1

Merge branch 'main' of https://github.com/microsoft/TypeScript into f…

acabd00

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Oleksandr Tarasiuk (a-tarasyuk) requested a balanced review from Copilot September 8, 2026 06:46

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Comment thread tsc/testdata/tests/cases/conformance/es2026/jsonRawJSON2.ts

update baseline

5af4a72

Oleksandr Tarasiuk (a-tarasyuk) requested a balanced review from Copilot September 8, 2026 06:56

Copilot started reviewing on behalf of Oleksandr Tarasiuk (a-tarasyuk) September 8, 2026 06:56 View session

Oleksandr Tarasiuk (a-tarasyuk) added 2 commits September 25, 2026 10:34

use a module-local class for RawJSON

074a75f

Merge branch 'main' of https://github.com/microsoft/TypeScript into f…

3d5e091

…eat/63704

Oleksandr Tarasiuk (a-tarasyuk) requested review from Daniel Rosenwasser (DanielRosenwasser) and a balanced review from Copilot September 25, 2026 07:35

Copilot started reviewing on behalf of Oleksandr Tarasiuk (a-tarasyuk) September 25, 2026 07:37 View session

Copilot AI reviewed Sep 25, 2026

View reviewed changes

fix typos

b31c0e2

Oleksandr Tarasiuk (a-tarasyuk) requested a balanced review from Copilot September 25, 2026 08:06

Copilot started reviewing on behalf of Oleksandr Tarasiuk (a-tarasyuk) September 25, 2026 08:07 View session

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Daniel Rosenwasser (DanielRosenwasser) approved these changes Sep 25, 2026

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Daniel Rosenwasser (DanielRosenwasser) requested a balanced review from Copilot September 25, 2026 20:27

Copilot started reviewing on behalf of Daniel Rosenwasser (DanielRosenwasser) September 25, 2026 20:28 View session

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Jake Bailey (jakebailey) approved these changes Sep 25, 2026

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Oleksandr Tarasiuk (a-tarasyuk) added 2 commits September 28, 2026 20:24

Merge branch 'main' of https://github.com/microsoft/TypeScript into f…

4385042

…eat/63704

Merge branch 'main' into feat/63704

1ca4422

Jake Bailey (jakebailey) approved these changes Sep 28, 2026

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Oleksandr Tarasiuk (a-tarasyuk) added 2 commits September 28, 2026 21:10

update baseline

cce3619

Merge branch 'feat/63704' of https://github.com/a-tarasyuk/TypeScript …

bd8adf1

…into feat/63704

Jake Bailey (jakebailey) approved these changes Sep 28, 2026

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Daniel Rosenwasser (DanielRosenwasser) enabled auto-merge September 28, 2026 18:18

Daniel Rosenwasser (DanielRosenwasser) added this pull request to the merge queue Sep 28, 2026

Merged via the queue into microsoft:main with commit 75e50a4 Sep 28, 2026
29 checks passed

Vedant Madane (VedantMadane) mentioned this pull request Oct 1, 2026

Add lib types for JSON.rawJSON, JSON.isRawJSON, and reviver context #63248

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Oleksandr Tarasiuk (a-tarasyuk) commented Aug 30, 2026

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Pull request overview

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🔵 Needs a closer look

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🟡 Changes recommended

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typescript-automation Bot commented Sep 24, 2026

lodash

/mnt/vss/work/1/s/ts_downloads//m/lodash/tsconfig.json

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🟢 Approval recommended

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🟢 Approval recommended

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Daniel Rosenwasser (DanielRosenwasser) commented Sep 28, 2026

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