Suggestion: disallow synthetic imports for ES modules

TypeScript Version: 3.6.3

Search Terms: allowSyntheticDefaultImports esModuleInterop babel synthetic es modules default exports imports commonjs

Code

allowSyntheticDefaultImports is great when you're importing a CommonJS module, where/when Babel/TS will make sure there is a default export/import via their "interop" layers (e.g. esModuleInterop).

// foo.js
exports.foo = () => {}

// foo.d.ts
declare const _default: { foo: () => {} }
export = _default

// main.ts
import Foo from './foo';
Foo.foo(); // all good!

However, it's possible to shoot yourself in the foot by trying to import a non-existent default from an ES module.

// foo.js
export const foo = () => {}

// foo.d.ts
export declare const foo: () => {}

// main.ts
import Foo from './foo'; // no error, but should be `* as Foo`!
// runtime error!!
// TypeError: Cannot read property 'foo' of undefined
Foo.foo();

Ideally it would not be possible to use synthetic default imports with an ES module, so runtime errors such as the one above would not happen.

allowSyntheticDefaultImports が ES モジュールからの default import を受け入れることを示す TypeScript 3.6.3 の再現コードから始め、CommonJS の例と比較してください。ES モジュールからの無効な default import が拒否され、意図された CommonJS の synthetic-default ケースは引き続きサポートされれば完了です。