feat(parser): support import defer #6949

fireairforce · 2025-07-20T12:57:57Z

Summary

closes: #4215

Typescript 5.9 Beta support import defer, which is a stage-3 proposal: https://devblogs.microsoft.com/typescript/announcing-typescript-5-9-beta/#support-for-import-defer

The implement we can refer to: https://github.com/microsoft/TypeScript/pull/60757/files

This PR support import defer, the syntax looks like:

import defer * as foo from "<specifier>";

And the syntax import defer foo from "<specifier>" or import defer { foo } from "<specifier>" is invalid.

In this pr, I use defer as a keyword just like what TypeScript do.

Test Plan

I add test case for biome_js_parser and biome_js_formatter.

Docs

changeset-bot · 2025-07-20T12:58:01Z

🦋 Changeset detected

Latest commit: 0c74466

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

github-actions · 2025-07-20T13:06:55Z

Parser conformance results on

js/262

Test result	`main` count	This PR count	Difference
Total	50627	50627	0
Passed	49303	49357	✅ ⏫ +54
Failed	1324	1270	✅ ⏬ -54
Panics	0	0	0
Coverage	97.38%	97.49%	+0.11%

🎉 Fixed (54):

test/language/import/import-defer/deferred-namespace-object/exotic-object-behavior.js
test/language/import/import-defer/deferred-namespace-object/to-string-tag.js
test/language/import/import-defer/errors/get-self-while-defer-evaluating/main.js
test/language/import/import-defer/errors/get-self-while-evaluating-async/main.js
test/language/import/import-defer/errors/get-self-while-evaluating.js
test/language/import/import-defer/errors/module-throws/third-party-evaluation-after-defer-import.js
test/language/import/import-defer/errors/module-throws/trigger-evaluation.js
test/language/import/import-defer/evaluation-sync/import-defer-does-not-evaluate.js
test/language/import/import-defer/evaluation-sync/module-imported-defer-and-eager.js
test/language/import/import-defer/evaluation-top-level-await/flattening-order/main.js
test/language/import/import-defer/evaluation-top-level-await/import-defer-async-module/main.js
test/language/import/import-defer/evaluation-top-level-await/import-defer-transitive-async-module/main.js
test/language/import/import-defer/evaluation-top-level-await/sync-dependency-of-deferred-async-module/main.js
test/language/import/import-defer/evaluation-triggers/ignore-exported-then-defineOwnProperty.js
test/language/import/import-defer/evaluation-triggers/ignore-exported-then-delete.js
test/language/import/import-defer/evaluation-triggers/ignore-exported-then-get.js
test/language/import/import-defer/evaluation-triggers/ignore-exported-then-getOwnProperty.js
test/language/import/import-defer/evaluation-triggers/ignore-exported-then-hasProperty.js
test/language/import/import-defer/evaluation-triggers/ignore-getPrototypeOf.js
test/language/import/import-defer/evaluation-triggers/ignore-isExtensible.js
test/language/import/import-defer/evaluation-triggers/ignore-not-exported-then-defineOwnProperty.js
test/language/import/import-defer/evaluation-triggers/ignore-not-exported-then-delete.js
test/language/import/import-defer/evaluation-triggers/ignore-not-exported-then-get.js
test/language/import/import-defer/evaluation-triggers/ignore-not-exported-then-getOwnProperty.js
test/language/import/import-defer/evaluation-triggers/ignore-not-exported-then-hasProperty.js
test/language/import/import-defer/evaluation-triggers/ignore-preventExtensions.js
test/language/import/import-defer/evaluation-triggers/ignore-set-string-exported.js
test/language/import/import-defer/evaluation-triggers/ignore-set-string-not-exported.js
test/language/import/import-defer/evaluation-triggers/ignore-setPrototypeOf.js
test/language/import/import-defer/evaluation-triggers/ignore-symbol-other-defineOwnProperty.js
test/language/import/import-defer/evaluation-triggers/ignore-symbol-other-delete.js
test/language/import/import-defer/evaluation-triggers/ignore-symbol-other-get.js
test/language/import/import-defer/evaluation-triggers/ignore-symbol-other-getOwnProperty.js
test/language/import/import-defer/evaluation-triggers/ignore-symbol-other-hasProperty.js
test/language/import/import-defer/evaluation-triggers/ignore-symbol-toStringTag-defineOwnProperty.js
test/language/import/import-defer/evaluation-triggers/ignore-symbol-toStringTag-delete.js
test/language/import/import-defer/evaluation-triggers/ignore-symbol-toStringTag-get.js
test/language/import/import-defer/evaluation-triggers/ignore-symbol-toStringTag-getOwnProperty.js
test/language/import/import-defer/evaluation-triggers/ignore-symbol-toStringTag-hasProperty.js
test/language/import/import-defer/evaluation-triggers/trigger-exported-string-defineOwnProperty.js
test/language/import/import-defer/evaluation-triggers/trigger-exported-string-delete.js
test/language/import/import-defer/evaluation-triggers/trigger-exported-string-get.js
test/language/import/import-defer/evaluation-triggers/trigger-exported-string-getOwnProperty.js
test/language/import/import-defer/evaluation-triggers/trigger-exported-string-hasProperty.js
test/language/import/import-defer/evaluation-triggers/trigger-not-exported-string-defineOwnProperty.js
test/language/import/import-defer/evaluation-triggers/trigger-not-exported-string-delete.js
test/language/import/import-defer/evaluation-triggers/trigger-not-exported-string-get.js
test/language/import/import-defer/evaluation-triggers/trigger-not-exported-string-getOwnProperty.js
test/language/import/import-defer/evaluation-triggers/trigger-not-exported-string-hasProperty.js
test/language/import/import-defer/evaluation-triggers/trigger-ownPropertyKey-names.js
test/language/import/import-defer/evaluation-triggers/trigger-ownPropertyKeys-symbols.js
test/language/import/import-defer/evaluation-triggers/trigger-ownPropertyKeys.js
test/language/import/import-defer/syntax/import-attributes.js
test/language/import/import-defer/syntax/valid-defer-namespace.js

jsx/babel

Test result	`main` count	This PR count	Difference
Total	40	40	0
Passed	37	37	0
Failed	3	3	0
Panics	0	0	0
Coverage	92.50%	92.50%	0.00%

symbols/microsoft

Test result	`main` count	This PR count	Difference
Total	6706	6706	0
Passed	2244	2245	✅ ⏫ +1
Failed	4462	4461	✅ ⏬ -1
Panics	0	0	0
Coverage	33.46%	33.48%	+0.01%

🎉 Fixed (1):

importDeferComments.symbols

ts/babel

Test result	`main` count	This PR count	Difference
Total	822	822	0
Passed	731	731	0
Failed	91	91	0
Panics	0	0	0
Coverage	88.93%	88.93%	0.00%

ts/microsoft

Test result	`main` count	This PR count	Difference
Total	18784	18784	0
Passed	14412	14412	0
Failed	4372	4372	0
Panics	0	0	0
Coverage	76.72%	76.72%	0.00%

🔥 Regression (2):

conformance/importDefer/importDeferNamespace.ts
conformance/importDefer/importDeferTypeConflict1.ts

🎉 Fixed (2):

conformance/importDefer/importDeferComments.ts
conformance/importDefer/importDeferDeclaration.ts

codspeed-hq · 2025-07-20T13:12:33Z

CodSpeed Performance Report

Merging #6949 will not alter performance

_{Comparing feat-4215 (0c74466) with main (249306d)}

Summary

✅ 115 untouched benchmarks

crates/biome_js_parser/src/syntax/module.rs

ematipico · 2025-07-20T13:40:36Z

Out of curiosity, is the following syntax allowed?

import defer type * as foo from "bar"

fireairforce · 2025-07-20T13:41:38Z

Out of curiosity, is the following syntax allowed?
import defer type * as foo from "bar"

No, only allow import defer * as foo from "bar", the behaviour is align with https://www.typescriptlang.org/play/?ts=5.9.0-beta#code/JYWwDg9gTgLgBAEwKYDMlTjAnmJcBUcAhgM5woQTlQQhwBEARkVPUA

Co-authored-by: Denis Bezrukov <6227442+denbezrukov@users.noreply.github.com>

fireairforce · 2025-07-20T13:43:12Z

The next step i will support import source: https://github.com/tc39/proposal-source-phase-imports

Syntax like: import.defer() will support in next pr.

fireairforce · 2025-07-20T13:59:47Z

Out of curiosity, is the following syntax allowed?
import defer type * as foo from "bar"

also add test case for this example

denbezrukov · 2025-07-20T14:00:08Z

xtask/codegen/js.ungram

+// import defer * as foo from "mod";
 JsImportNamespaceClause =
-	'type'?
+	'type'? | 'defer'?


I’m wondering if we can reuse the logic from Babel:
https://github.com/babel/babel/blob/ab6de823b3353b2af6d8e163b55fdc763aa840a6/packages/babel-parser/src/types.ts#L751
They have a separate token for it: phase.

What do you think?

you are right here，before i make this pr，i also refer swc and oxc's parser imeplement of the import defer，they do the same things as babel does. I will change here too

fireairforce · 2025-07-20T15:49:06Z

xtask/codegen/js.ungram

+// import defer * as foo from "mod";
 JsImportNamespaceClause =
 	'type'?
+	phase: 'defer'?


@denbezrukov i add a phase field here, i will expand this filed in the next pr when i support phase: 'source', that case will be different from import defer here.

import defer need to support syntax like:

import defer * as x from 'mod';

import source syntax is:

import source x from 'mod';

Do you mean that a 'source' phase doesn't make any sense for a namespace syntax?
I think you're right!

To be honest I have the same feeling for a 'type' token.
It might be also a 'phase' modifier.
But I'm not sure how many changes it might require.

It’s not a big problem. I’ll observe it again when I implement the import source. We will keep the phase here now.

github-actions bot added A-Parser Area: parser A-Formatter Area: formatter A-Tooling Area: internal tools L-JavaScript Language: JavaScript and super languages labels Jul 20, 2025

fireairforce added 2 commits July 20, 2025 21:01

feat(parser): support import defer

223492a

chore: add changeset

67bc710

fireairforce force-pushed the feat-4215 branch from 0b10e15 to 67bc710 Compare July 20, 2025 13:01

fix: clippy

4adeb51

chore: clippy code

b35c9a0

denbezrukov reviewed Jul 20, 2025

View reviewed changes

crates/biome_js_parser/src/syntax/module.rs Outdated Show resolved Hide resolved

Update crates/biome_js_parser/src/syntax/module.rs

fb566b3

Co-authored-by: Denis Bezrukov <6227442+denbezrukov@users.noreply.github.com>

chore: add more test cases

c891c48

denbezrukov reviewed Jul 20, 2025

View reviewed changes

chore: use phase fields

298efac

fireairforce commented Jul 20, 2025

View reviewed changes

chore: add import defer with import-attributes test

0c74466

denbezrukov approved these changes Jul 21, 2025

View reviewed changes

fireairforce merged commit 48462f8 into main Jul 21, 2025
30 checks passed

fireairforce deleted the feat-4215 branch July 21, 2025 07:50

github-actions bot mentioned this pull request Jul 21, 2025

ci: release #6927

Merged

robpalme mentioned this pull request Jul 21, 2025

import defer implementation tracker tc39/proposal-defer-import-eval#73

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fireairforce commented Jul 20, 2025

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Test Plan

Docs

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Parser conformance results on

js/262

jsx/babel

symbols/microsoft

ts/babel

ts/microsoft

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CodSpeed Performance Report

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