Sandbox::https://github.com/babel/babel/pull/17404

liuxingbaoyu · 2025-06-27T18:21:03Z

Q	A
Fixed Issues?	`Fixes #1, Fixes #2`
Patch: Bug Fix?
Major: Breaking Change?
Minor: New Feature?
Tests Added + Pass?	Yes
Documentation PR Link
Any Dependency Changes?
License	MIT

The main change is to distinguish InputOptions from ValidatedOptions, because they have two different fields.

To be honest, I don't want to expose some internal types such as Plugin or even ValidatedOptions details.
But I didn't think of a good way.

liuxingbaoyu · 2025-06-27T18:22:54Z

+  | ((api: PluginAPI, options?: object, dirname?: string) => PluginObject);
 export type PluginItem =
  | ConfigItem<PluginAPI>
-  | Plugin


This is a change, Plugin is our internal class and should not be accepted.

babel-bot · 2025-06-27T18:23:16Z

Build successful! You can test your changes in the REPL here: https://babeljs.io/repl/build/60052

liuxingbaoyu · 2025-06-27T18:24:27Z


      for (let i = 0; i < rawPresets.length; i++) {
        const descriptor = rawPresets[i];
+        // @ts-expect-error TODO: disallow false


What do you think?
Currently Babel accepts ["plugin", false] to disable a plugin, is there any reason for this?

liuxingbaoyu · 2025-06-27T18:26:51Z

To be honest, I don't want to expose some internal types such as Plugin or even ValidatedOptions details.
But I didn't think of a good way.

Currently some private properties are also exposed, I will open a new PR.

pkg-pr-new · 2025-07-28T20:41:08Z

Open in StackBlitz

commit: 030d0c1

liuxingbaoyu · 2025-07-31T07:34:37Z

+  const options: BaseOptions = {
    ...opts,

    parserOpts: {
      sourceType:
        path.extname(filenameRelative) === ".mjs" ? "module" : sourceType,

+      // @ts-expect-error FIXME: should be sourceFilename
      sourceFileName: filename,


This is a bug, but requires a more complex fix, which I'll include in a separate PR.

liuxingbaoyu · 2025-08-22T20:33:24Z

  filepath: string;
  dirname: string;
-  options: ValidatedOptions;
+  options: InputOptions;


This isn't ideal, but I haven't figured out a better solution yet.

JLHwung

I agree that we should probably stop exporting ValidatedOptions, but we still have to export InputOptions and NormalizedOptions, since the latter can be accessed from the return result of the loadPartialConfig API via the .options property.

JLHwung · 2025-08-27T16:03:07Z

+  plugins?: Plugin[];
+};
+
 export type NormalizedOptions = {


Could you add JSDoc description comments on InputOptions, ValidatedOptions and NormalizedOptions?
Based on the shape it seems to me that ValidatedOptions is the option after the plugins / presets are resolved, and NormalizedOptions is the option after targets are resolved. But the their namings currently do not really indicate their lifecycles.

And among them only InputOptions are exported to users right?

I did some refactoring, and it looks much better now.

Renamed ValidatedOptions to ResolvedOptions

Better defined NormalizedOptions so it can now be assigned to InputOptions.

I hesitated about exporting ResolvedOptions; obviously, we don't want users to read or write it, but as a public function return value, exporting it would make caching easier for users.

NormalizedOptions has been exported.

Better defined NormalizedOptions so it can now be assigned to InputOptions.

I don't think it is safe to assign NormalizedOptions to an InputOptions, because:

InputOptions is the options for the API users, we will then provide defaults, enforces validations and resolve plugins/ presets so that it became a ResolvedOptions. Then we resolve targets and it became NormalizedOptions. At this point, the targets are readonly, plugins are resolved, it should not be cast to an InputOptions -- since we are not going to resolve targets / plugins again.

If there are typing errors for doing so, maybe those methods actually expects NormalizedOptions rather than InputOptions and we should then update those methods.

From what I understand, InputOptions will first become NormalizedOptions and then become ResolvedOptions?
We have an existing usage in eslint-parser of passing loadPartialConfigSync().options into parseSync which seems to be acceptable.

Okay. If that's the case, that means ResolvedOptions must be made a subset type of InputOptions, so we should export the internal resolved plugin type, since it is indeed accepted by our API.

Could you explain more, thanks!

Sorry, I don't understand what you mean. The API accepts NormalizedOptions but not ResolvedOptions.

Sorry for the late reply. Let me try to elaborate a bit.

The parseSync accepts InputOptions.

babel/packages/babel-core/src/parse.ts

Line 26 in 900e5d1

opts: InputOptions | undefined | null,

Now if parseSync also supports the return result of loadPartialConfigSync().options, then the NormalizedOptions, returned from loadPartialConfigSync().options,

babel/packages/babel-core/src/config/partial.ts

Line 204 in 900e5d1

options: NormalizedOptions;

should be automatically also a valid InputOptions. This implies that ConfigItem<PluginAPI>[] should be accepted in InputOptions, because of the usage in eslint-parser. And Plugin should be broaden to include ConfigItem<PluginAPI>.

Thanks for the detailed explanation.
It looks like PluginItem already contains ConfigItem<PluginAPI>?

And Plugin should be broaden to include ConfigItem.

Sorry for any confusion here. To clarify, Plugin is not an typo of PluginItem. I refer to the Plugin type defined here:

babel/packages/babel-core/src/config/plugin.ts

Line 5 in 61ad855

export default class Plugin {

nested within the ResolvedConfig in packages/babel-core/src/config/full.ts.

Since ResolvedOptions is allowed as an InputOption because of the usage in eslint-parser, we should make typing adjustments to InputOptions such that any ResolvedOptions will also satisfy InputOptions, but not the opposite. Or we provide overload signatures to the API for the ResolvedOptions support.

The goal here is that end users should not cast typings if they only use Babel API, as long as the API accepts such inputs.

I checked and it seems that eslint-parser does not use ResolvedOptions, although there is a function called validateResolvedConfig, it actually returns still InputOptions | NormalizedOptions.

JLHwung · 2025-08-27T16:06:32Z

 export type {
  CallerMetadata,
  NormalizedOptions,
  ValidatedOptions as PresetObject,


Is this type export still used now that we have created PresetObject type in the root index.ts?

JLHwung · 2025-08-27T16:11:27Z

  });

-  const options: NormalizedOptions = {
+  const options: InputOptions = {


We only resolve the targets here, isn't the options here the NormalizedOptions? That is, the targets should be considered read-only because it won't be resolved again if they are somehow modified by plugins.

nicolo-ribaudo · 2025-09-12T10:34:22Z

+  PluginItem,
+} from "./config/validation/options.ts";
 export { loadOptionsSync };
+export type { PluginItem };


Thanks for this, currently for Jest I had to use type PluginItem = NonNullable<BabelOptions['plugins']>[number]; instead 😅

JLHwung

Aside: I also noticed that there is another normalizeOptions routine:

babel/packages/babel-core/src/config/config-chain.ts

Line 739 in 61ad855

function normalizeOptions(opts: ValidatedOptions): ValidatedOptions {

I think this routine can be renamed to createConfigChainOptions and we should create a new ConfigChainOptions type for it, it is also a subset of InputOptions but with quite a few properties removed. This should catch errors if we try to access those properties from the config chain options.

JLHwung · 2025-09-22T15:36:45Z

 export default function normalizeOptions(
  config: ResolvedConfig,
-): NormalizedOptions {
+): ResolvedOptions {


The type NormalizedOptions is named after this routine, it would be very confusing if this routine returns ResolvedOptions. Maybe we can rename it as buildResolvedConfigOptions or something.

JLHwung · 2025-09-22T16:03:12Z

+  plugins?: Plugin[];
+};
+
 export type NormalizedOptions = {


Sorry, I don't understand what you mean. The API accepts NormalizedOptions but not ResolvedOptions.

Sorry for the late reply. Let me try to elaborate a bit.

The parseSync accepts InputOptions.

babel/packages/babel-core/src/parse.ts

Line 26 in 900e5d1

opts: InputOptions | undefined | null,

Now if parseSync also supports the return result of loadPartialConfigSync().options, then the NormalizedOptions, returned from loadPartialConfigSync().options,

babel/packages/babel-core/src/config/partial.ts

Line 204 in 900e5d1

options: NormalizedOptions;

should be automatically also a valid InputOptions. This implies that ConfigItem<PluginAPI>[] should be accepted in InputOptions, because of the usage in eslint-parser. And Plugin should be broaden to include ConfigItem<PluginAPI>.

Co-authored-by: Huáng Jùnliàng <jlhwung@gmail.com>

liuxingbaoyu commented Jun 27, 2025

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Comment thread packages/babel-core/src/index.ts Resolved

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Comment thread packages/babel-preset-typescript/src/index.ts Resolved

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Comment thread packages/babel-preset-react/src/index.ts Resolved

liuxingbaoyu force-pushed the improve-core-types branch from 827283d to 94299e4 Compare July 31, 2025 07:26

liuxingbaoyu commented Jul 31, 2025

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Comment thread packages/babel-core/src/config/index.ts Resolved

liuxingbaoyu mentioned this pull request Jul 31, 2025

Removed incorrect options #17458

Open

liuxingbaoyu force-pushed the improve-core-types branch from 0765993 to e139554 Compare August 22, 2025 19:39

JLHwung reviewed Aug 22, 2025

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Comment thread packages/babel-preset-env/src/index.ts Resolved

liuxingbaoyu commented Aug 22, 2025

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JLHwung reviewed Aug 27, 2025

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liuxingbaoyu force-pushed the improve-core-types branch from f626409 to 900e5d1 Compare August 28, 2025 22:47

liuxingbaoyu added pkg: core PR: Polish (next major) 💅 A type of pull request used for our changelog categories for next major release labels Sep 4, 2025

liuxingbaoyu requested a review from JLHwung September 9, 2025 17:33

nicolo-ribaudo approved these changes Sep 12, 2025

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JLHwung reviewed Sep 22, 2025

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liuxingbaoyu force-pushed the improve-core-types branch from ea0f6bb to 8f32ea5 Compare September 30, 2025 15:00

liuxingbaoyu and others added 7 commits October 3, 2025 17:05

improve types

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Apply suggestions from code review

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Co-authored-by: Huáng Jùnliàng <jlhwung@gmail.com>

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github-actions Bot added the outdated A closed issue/PR that is archived due to age. Recommended to make a new issue label Jan 17, 2026

github-actions Bot locked as resolved and limited conversation to collaborators Jan 17, 2026

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