Support TypeScript 4.5 type-only import/export specifiers #13802

sosukesuzuki · 2021-09-30T17:04:30Z

Q	A
Fixed Issues?	Fixes #13799
Minor: New Feature?	Y
Tests Added + Pass?	Yes
License	MIT

Support type-only import/export specifiers will be landed in TS 4.5.

import { type Foo } from "foo";
export { type Foo } from "foo";

Todo:

babel-parser
babel-generator
babel-types
babel-plugin-transform-typescript

AST change:

/cc @bradzacher What do you think?

Add importKind: "value" | "type" to ImportSpecifier.
Add exportKind: "value" | "type" to ExportSpecifier

References:

Type-only import specifiers microsoft/TypeScript#45998

codesandbox-ci · 2021-09-30T17:07:06Z

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babel-bot · 2021-09-30T17:09:52Z

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bradzacher · 2021-09-30T19:17:45Z

I'd personally have preferred if the AST was just kind to match the top-level names - but considering we're matching flow here - I think it's okay for us to align with them

JLHwung · 2021-10-02T03:17:29Z

packages/babel-plugin-transform-typescript/src/index.ts

@@ -229,9 +229,23 @@ export default declare((api, opts) => {
                continue;


Can you rebase on latest main? We should also register global type for type-only import specifiers so they can be removed in the following case:

import { type A } from "module"; export { A }

nicolo-ribaudo

Can you add a test for import { type A } from "x" with onlyRemoveTypeImports? import "x" should not be removed.

nicolo-ribaudo · 2021-10-10T10:42:44Z

packages/babel-generator/src/generators/modules.ts

@@ -40,6 +40,11 @@ export function ExportDefaultSpecifier(
 }

 export function ExportSpecifier(this: Printer, node: t.ExportSpecifier) {
+  if (node.exportKind === "type") {
+    this.word(node.exportKind);


Suggested change

this.word(node.exportKind);

this.word("type");

d337f69 👍

nicolo-ribaudo · 2021-10-10T10:52:40Z

packages/babel-plugin-transform-typescript/src/index.ts

-                  } else {
-                    allElided = false;
-                    NEEDS_EXPLICIT_ESM.set(path.node, false);
+                  if (!importsToRemove.includes(binding.path)) {


We can use a Set for importsToRemove, since .has() is O(1) while .includes is O(n).

8cb6dc0 👍

sosukesuzuki · 2021-10-11T10:40:13Z

@nicolo-ribaudo Thank you for your review! I've addressed your comments. 4d1cde6

JLHwung · 2021-10-12T13:03:13Z

packages/babel-plugin-transform-typescript/src/index.ts

@@ -288,7 +288,7 @@ export default declare((api, opts) => {
                }
              }

-              if (isAllSpecifiersElided()) {
+              if (!onlyRemoveTypeImports && isAllSpecifiersElided()) {


Why should we keep import statements when onlyRemoveTypeImports is true?

TS removes them anyway.

@nicolo-ribaudo You said #13802 (review). What do you think?

Whoops, I assumed that import { type X } from "x" would have been equivalent to import {} from "x" and thus not removed. I'm sorry!

Hmm, interesting. TS removes import {} from "x", too. It preserves only import "x".

According to behavior of TypeScript, it is better to remove the Import Statement in such cases. 6b79fd1

packages/babel-parser/src/plugins/typescript/index.js

packages/babel-parser/src/parser/statement.js

packages/babel-parser/src/plugins/typescript/index.js

nicolo-ribaudo · 2021-10-24T15:09:13Z

packages/babel-parser/src/parser/statement.js

-      const local = this.parseModuleExportName();
-      node.local = local;
-      if (this.eatContextual(tt._as)) {
+      node.local = this.parseModuleExportName();


I'd like to avoid mixing TS/flow-specific code in the main parser, when possible.

Would it be possible to move type handling in parseModuleExportName()? Or maybe we reorganize it like this:

parseExportSpecifiers() { while () { // loop to parse all the specifiers const local = this.parseModuleExportName(); nodes.push(this.parseExportSpecifier(local)); } } parseExportSpecifier(local) { // ... }

and in typescript/index.js

parseExportSpecifier(local) { if (local.type === "Identifier" && local.name === "type") { const node = this.startNodeAtNode(local); // if this is a type export, parse it as such return node; } return super.parseExprtSpecifier(local); }

This is similar to what we do for imports.

It's a little different from the interface you suggested, but I modified it based on that. Please review again.

commits:

(Sorry for many commits..)

d459c8b

519f977

cb0f943

91918b7

d074010

JLHwung · 2021-10-25T18:57:43Z

packages/babel-parser/src/plugins/typescript/index.js

+      node[rightOfAsKey] = rightOfAs;
+
+      const kindKey = isImport ? "importKind" : "exportKind";
+      node[kindKey] = hasTypeSpecifier ? "type" : "value";


Can you also update packages/babel-parser/src/types.js?

c44171a 👍

JLHwung · 2021-10-25T19:27:40Z

packages/babel-parser/src/plugins/typescript/index.js

+              // { type as as something }
+              hasTypeSpecifier = true;
+              leftOfAs = firstAs;
+              rightOfAs = this.parseIdentifier();


When we are parsing export, the right-of-as is a liberal identifier (should be parsed by parseIdentifier(true)), otherwise it should throw unexpected reserved word:

export { type a as if } from "x"; // valid import { type a as if } from "x"; // invalid

We can use parseIdentifier(true/false) for those specifiers. But Babel doesn't check reserved word for TypeScript. Should we still fix for that?

babel/packages/babel-parser/src/plugins/typescript/index.js

Lines 2237 to 2247 in 248aa9d

checkReservedWord(

word: string, // eslint-disable-line no-unused-vars

startLoc: number, // eslint-disable-line no-unused-vars

checkKeywords: boolean, // eslint-disable-line no-unused-vars

// eslint-disable-next-line no-unused-vars

isBinding: boolean,

): void {

// Don't bother checking for TypeScript code.

// Strict mode words may be allowed as in `declare namespace N { const static: number; }`.

// And we have a type checker anyway, so don't bother having the parser do it.

}

Hmm, let's fix that in another PR, then.

JLHwung

Awesome work!

nicolo-ribaudo

Thanks!

sosukesuzuki added area: typescript pkg: generator pkg: types PR: New Feature 🚀 A type of pull request used for our changelog categories labels Sep 30, 2021

sosukesuzuki force-pushed the type-only-import-specifier branch from 3cc6c3d to 15392c3 Compare September 30, 2021 22:40

sosukesuzuki marked this pull request as ready for review September 30, 2021 22:46

fedeci added this to the v7.16.0 milestone Sep 30, 2021

fedeci self-requested a review September 30, 2021 22:50

JLHwung reviewed Oct 2, 2021

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sosukesuzuki added 8 commits October 2, 2021 12:33

Implement parser

9b91e84

Add parser tests

1b20596

Implement generator

8daf3bc

Add generator tests

16b4bc1

Implement types

a2edbe3

Implement plugin-transform-typescript

6421008

Add plugin-transform-typescript tests

6a596b9

Remove imported-type from exports

4929209

sosukesuzuki force-pushed the type-only-import-specifier branch from 15392c3 to 4929209 Compare October 2, 2021 07:26

bradzacher mentioned this pull request Oct 3, 2021

TypeScript 4.5 Support typescript-eslint/typescript-eslint#3950

Closed

8 tasks

sosukesuzuki mentioned this pull request Oct 4, 2021

Support TypeScript 4.5 prettier/prettier#11600

Closed

nicolo-ribaudo reviewed Oct 10, 2021

View reviewed changes

sosukesuzuki added 3 commits October 11, 2021 19:22

Use string literal instead of variable

d337f69

Use set instead of array

8cb6dc0

Keep import statement if all of specifiers are type-only one

4d1cde6

sosukesuzuki added the pkg: parser label Oct 11, 2021

JLHwung reviewed Oct 12, 2021

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packages/babel-parser/src/plugins/typescript/index.js Outdated Show resolved Hide resolved

JLHwung reviewed Oct 12, 2021

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packages/babel-parser/src/parser/statement.js Outdated Show resolved Hide resolved

JLHwung reviewed Oct 12, 2021

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sosukesuzuki added 6 commits October 13, 2021 16:09

Rename isTypeOnly to hasTypeSpecifier

05d5183

Use isContextual instead of string comparison

31b273c

Use tokenIsKeywordOrIdentifier instead of match

ec6398e

Remove import statement if all of specifiers are type-only one

6b79fd1

Merge branch 'main' into type-only-import-specifier

72b3c3b

Fix type errors

ebf0a58

nicolo-ribaudo reviewed Oct 24, 2021

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nicolo-ribaudo mentioned this pull request Oct 24, 2021

Regenerate parser fixtures #13882

Merged

Merge branch 'main' into type-only-import-specifier

d5c69eb

JLHwung reviewed Oct 25, 2021

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JLHwung approved these changes Oct 25, 2021

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sosukesuzuki added 9 commits October 26, 2021 21:20

Extract parseExportSpecifier

d459c8b

Extract parameters

519f977

Move the logic for error

cb0f943

Refactor exports

91918b7

Refactor imports

d074010

Fix lint comments

ab1f5c2

Fix babel-parser/types.js

c44171a

Throw error for string local for import

bfd0f9d

check lval

1f933af

nicolo-ribaudo approved these changes Oct 28, 2021

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nicolo-ribaudo merged commit d5ba355 into babel:main Oct 28, 2021

sosukesuzuki deleted the type-only-import-specifier branch October 29, 2021 01:58

snyk-bot mentioned this pull request Dec 14, 2021

[Snyk] Upgrade @babel/core from 7.9.6 to 7.16.0 aml-org/playground#69

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Support TypeScript 4.5 type-only import/export specifiers #13802

Support TypeScript 4.5 type-only import/export specifiers #13802

sosukesuzuki commented Sep 30, 2021 •

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sosukesuzuki commented Oct 11, 2021 •

edited

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nicolo-ribaudo Oct 24, 2021 •

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nicolo-ribaudo left a comment

		@@ -229,9 +229,23 @@ export default declare((api, opts) => {
		continue;

	checkReservedWord(
	word: string, // eslint-disable-line no-unused-vars
	startLoc: number, // eslint-disable-line no-unused-vars
	checkKeywords: boolean, // eslint-disable-line no-unused-vars
	// eslint-disable-next-line no-unused-vars
	isBinding: boolean,
	): void {
	// Don't bother checking for TypeScript code.
	// Strict mode words may be allowed as in `declare namespace N { const static: number; }`.
	// And we have a type checker anyway, so don't bother having the parser do it.
	}

Support TypeScript 4.5 type-only import/export specifiers #13802

Support TypeScript 4.5 type-only import/export specifiers #13802

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sosukesuzuki commented Sep 30, 2021 • edited

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sosukesuzuki commented Sep 30, 2021 •

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