[ts] Add support for `expr satisfies Type` expressions #14211

nicolo-ribaudo · 2022-01-27T22:40:17Z

Q	A
Fixed Issues?	Fixes: #15067
Patch: Bug Fix?
Major: Breaking Change?
Minor: New Feature?
Tests Added + Pass?	Yes
Documentation PR Link
Any Dependency Changes?
License	MIT

microsoft/TypeScript#46827 is in the TypeScript 4.6 iteration plan: I'm opening this PR so that we are ready in case it gets merged before Babel 7.17.0. However, I'm marking this PR as a draft because that one is still marked as a draft (@DanielRosenwasser, do you think that there is any chance that that PR will be actually included in 4.6, even if you already released a beta without it?).

I'm not convinced by the new AST node I introduced for expr satisfies Type expressions. It feels like it should be the same node as TSAsExpression, similarly to how in and instanceof both are BinaryExpressions. Ideally, something like this:

type TSBinaryExpression = { // or TSTypeExpression
  type: "TSBinaryExpression",
  operator: "as" | "satisfies",
  expression: Expression,
  typeAnnotation: TSType,
}

however, that would be a breaking change. I also considered just adding operator to TSAsExpression, but { type: "TSAsExpression", operator: "satisfies" } looks wrong.

Maybe we could go for the breaking change in Babel 8, and for now provide a TSBinaryExpression alias in @babel/types?

TSBinaryExpression or TSTypeExpression? The new node would not cover <Type> expr, because it needs to visit its childrens in a different order (type before expression).

babel-bot · 2022-01-27T22:42:45Z

Build successful! You can test your changes in the REPL here: https://babeljs.io/repl/build/53224/

JLHwung · 2022-01-28T15:30:57Z

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

+          this.next(); // "as" or "satisfies"
+          if (this.match(tt._const)) {
+            if (isSatisfies) {
+              this.raise(


I think we don't have to specialize tt._const after tt._satisfies: tsParseType should throw when const is seen.

DanielRosenwasser · 2022-01-28T18:42:17Z

do you think that there is any chance that that PR will be actually included in 4.6, even if you already released a beta without it?

This feature won't make its way into TypeScript 4.6 - it's still being iterated on, so if we can figure out the issues with it, 4.7 will be the earliest it can land.

nicolo-ribaudo · 2022-01-29T07:44:11Z

Thank you!

nicolo-ribaudo · 2022-08-27T16:07:15Z

The TS pull request has been merged, I'll rebase this.

nicolo-ribaudo · 2022-08-31T19:28:39Z

Depending on the 7.19 timing, we might need to postpone this to 7.20.

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

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

liuxingbaoyu · 2022-10-22T05:14:53Z

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

-      // name, since const isn't allowed as a type name. So in this instance we
-      // get to pretend we're the type checker.
-      if (typeReference.typeParameters) {
-        this.raise(TSErrors.CannotFindName, {


CannotFindName seems to be used only here.

liuxingbaoyu · 2022-10-22T05:38:18Z

packages/babel-types/src/builders/generated/index.ts

+    typeAnnotation,
+  });
+}
+export { tsSatisfiesExpression as tSSatisfiesExpression };


This seems to be a bug.😕

edited: No, just a little ugly.🙃

thorn0 · 2022-10-24T17:17:50Z

"Type expression" sounds like something that operates on types only whereas in as and satisfies one operand is a value and the other one a type.

ngregory-rbi · 2022-10-24T19:00:52Z

"Type expression" sounds like something that operates on types only...

I disagree. An adjective does not describe an operand but a property of the thing itself. In math, we don't call the addition symbol a "number expression". It operates on numbers, it itself is not a number.

This is a "type expression" because it expresses a type to either:

cast the operand value to, or
ensure the operand value satisfies

Makes sense to me.

nicolo-ribaudo · 2022-10-24T20:30:44Z

The exposed names are TSAsExpression and TSSatisfiesExpression; TSTypeExpression is just an internal variable name.

thorn0 · 2022-10-24T20:31:41Z

@ngregory-rbi You have a point, but in TypeScript there is this dichotomy between values and types. And when it's needed to specify one of these contexts, this kind of wording is used. E.g. "type operators" here.

On the other hand, I just noticed that the TS team strictly avoids using the word "expression" for type-only things, which makes TSTypeExpression a better choice than I thought.

we don't call the addition symbol a "number expression". It operates on numbers, it itself is not a number.

Can't help myself, excuse me :) , but what about "dog food" then? Is it a dog?

ngregory-rbi · 2022-10-24T21:03:24Z

You have a point, but in TypeScript there is this dichotomy between values and types. And when it's needed to specify one of these contexts, this kind of wording is used. E.g. "type operators" here.

Fair enough.

On the other hand, I just noticed that the TS team strictly avoids using the word "expression" for type-only things, which makes TSTypeExpression a better choice than I thought.

Not sure how your conclusion connects to the preceding statement.

Can't help myself, excuse me :) , but what about "dog food" then? Is it a dog?

Fair point as well. Touché.

Regardless of anything, wording may be a tangential subject to this PR.

thorn0 · 2022-10-24T21:38:50Z

Not sure how your conclusion connects to the preceding statement.

The preceding statement was against applying the wording "type expression" to as and satisfies whereas the following one was in support. Both statements are a result of checking what wording is used in the TS docs.

upd: an example where "type expression" has the meaning I expected.

@nicolo-ribaudo There are your questions about naming in the first post here, so I thought they were still relevant.

nicolo-ribaudo · 2022-10-24T21:41:25Z

Oh thanks, I forgot about it 🙃

Re-reading my original post, I don't like TSBinaryExpression because it feels like it should be an expression between two TS things, but this one is between a JS value and a type. For Babel 8, TSTypeExpression might be fine, however I'm open to alternative suggestions!

ngregory-rbi · 2022-10-25T13:29:37Z

@thorn0 I meant more the two segments here:

On the other hand, I just noticed that the TS team strictly avoids using the word "expression" for type-only things, which makes TSTypeExpression a better choice than I thought.

If the TS team "strictly avoids" using the word "expression", why does it make Babel using the term a "better choice than [you] thought"? Would you not want to keep the same wording as the TS team?

thorn0 · 2022-10-25T14:44:06Z

@ngregory-rbi They avoid it for type-only things. as and satisfies aren't type-only.

ngregory-rbi · 2022-10-26T14:14:32Z

Please merge this as soon as possible :)

nicolo-ribaudo · 2022-10-26T19:33:52Z

Release tomorrow!

nicolo-ribaudo added PR: New Feature 🚀 A type of pull request used for our changelog categories area: typescript labels Jan 27, 2022

nicolo-ribaudo changed the title ~~Avoid lookahead when parsing TS type casts~~ [ts] Add support for expr satisfies Type expressions Jan 27, 2022

nicolo-ribaudo marked this pull request as draft January 27, 2022 22:43

JLHwung reviewed Jan 28, 2022

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IanVS mentioned this pull request Feb 2, 2022

Why CSF Args Type is Partial type ? storybookjs/storybook#13747

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nicolo-ribaudo added this to the 7.19.0 milestone Aug 31, 2022

nicolo-ribaudo force-pushed the ts-parse-satisfies branch from ffc98e5 to ec54229 Compare August 31, 2022 19:23

nicolo-ribaudo marked this pull request as ready for review August 31, 2022 19:28

nicolo-ribaudo modified the milestones: 7.19.0, 7.20.0 Aug 31, 2022

JLHwung self-requested a review September 1, 2022 01:24

sosukesuzuki mentioned this pull request Sep 24, 2022

Support TypeScript 4.9 prettier/prettier#13516

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nicolo-ribaudo force-pushed the ts-parse-satisfies branch from ec54229 to 036704f Compare October 4, 2022 16:58

nicolo-ribaudo force-pushed the ts-parse-satisfies branch from 036704f to 110b104 Compare October 16, 2022 14:17

JLHwung approved these changes Oct 16, 2022

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packages/babel-generator/src/generators/typescript.ts Show resolved Hide resolved

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nicolo-ribaudo added 4 commits October 19, 2022 22:36

Avoid lookahead when parsing TS type casts

9719bb1

Add parser support for satisfies operator

607a5b9

Add TSSatisfiesExpression to types and generator

397dc0f

Add to transform plugins

28c8a0b

nicolo-ribaudo force-pushed the ts-parse-satisfies branch from 110b104 to 28c8a0b Compare October 19, 2022 20:39

liuxingbaoyu mentioned this pull request Oct 22, 2022

[Bug]: Babel TypeScript transformer does not support satisfies operator #15067

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liuxingbaoyu reviewed Oct 22, 2022

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liuxingbaoyu approved these changes Oct 22, 2022

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nicolo-ribaudo added 3 commits October 24, 2022 23:37

Ensure no line terminator

34c91be

Remove unused parser error

307708c

Update comment

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nicolo-ribaudo added the PR: Ready to be Merged A pull request with already two approvals, but waiting for the next minor release label Oct 24, 2022

JLHwung approved these changes Oct 25, 2022

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nicolo-ribaudo merged commit df733b1 into babel:main Oct 26, 2022

nicolo-ribaudo deleted the ts-parse-satisfies branch October 26, 2022 19:34

fisker mentioned this pull request Oct 30, 2022

Support TS4.9 satisfies operator prettier/prettier#13764

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aaronadamsCA mentioned this pull request Nov 7, 2022

Presets need new releases to fix TS 4.9 support #15157

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[Snyk] Upgrade @babel/runtime from 7.12.5 to 7.20.0 shaneomatz/video.js#1

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lenovouser mentioned this pull request Jan 17, 2023

Breaks when using satisfies operator in TypeScript depcheck/depcheck#768

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[ts] Add support for `expr satisfies Type` expressions #14211

[ts] Add support for `expr satisfies Type` expressions #14211

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[ts] Add support for expr satisfies Type expressions #14211

[ts] Add support for expr satisfies Type expressions #14211

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[ts] Add support for `expr satisfies Type` expressions #14211

[ts] Add support for `expr satisfies Type` expressions #14211

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