This change would allow users to explicitly type check preset options: For example,

import babelPresetEnv from "@babel/preset-env";
import type { Options as BabelPresetEnvOptions } from "@babel/preset-env";
import type { PresetTarget } from "@babel/core";

export default {
  presets: [
    // TS will throw `foo` is not defined in BabelPresetEnvOptions
    [babelPresetEnv, { targets: "chrome 123", foo: "string" }] satisifies PresetTarget<BabelPresetEnvOptions>
  ]
} 

But I didn't figure out how to make it an implicit constraint.

Would something like

export default {
  presets: [
    // TS will throw `foo` is not defined in BabelPresetEnvOptions
    [babelPresetEnv, { targets: "chrome 123", foo: "string" }]
  ]
} as BabelConfig

work, or not because TS cannot infer from babelPresetEnv to the second element of the list?

AFAIK TS calculates the constraints for the generics only when it's a type parameter. So it would require a function call.

import * as babel from '@babel/core';

function p<Option>(p: babel.PresetTarget<Option>, o: Partial<Option>) {
  return [p, o];
}

babel.transformSync('', {
    p(babelPresetEnv, {
      bugfixes: true,
      modules: false,
      // input suggestion works here
    }),
  ],
});

I guess the input suggestion doesn't work with transformSync because type InputOptions has plugins?: PluginItem[], which is the same as plugins?: PluginItem<object>[].

This is a very good point, we could consider exporting two type-aware utilities pluginWithOptions, presetWithOptions such that the plugin/preset option can be properly type checked.

@nicolo-ribaudo @liuxingbaoyu WDYT?

Why are the Options partial?

Good question, this is to workaround the current preset-env option definition:

The options here should have marked every property as optional, but the non-optional one is also handy to type the normalized options.

Could we move Partial<...> to the preset-env export in the index file, rather than just re-exporting Options as-is?

It'd be great to be able to get type errors when required options are missing.