Should preserve unique symbols when re‑assigning `module.exports`

[ExE-Boss]

TypeScript Version:

3.9.0-dev.20200315

Search Terms:

• object property preserve unique symbol
• module.exports preserve unique symbol

Code

// @target: ES2015
// @module: CommonJS
// @allowJs
// @checkJs
// @noEmit
// @filename: index.js
const customSymbol = Symbol("custom");
//              ^?

// This is a common pattern in Node’s built-in modules:
module.exports = {
	customSymbol,
	//        ^?
};

Workbench Repro

Also, the following requires a // @ts‑ignore comment, but otherwise works:

// some-module.js
const customSymbol = Symbol("custom");

// This is a common pattern in Node’s built-in modules:
module.exports = {
	/** @type {typeof customSymbol} */
	// @ts-ignore
	customSymbol,
// 	~~~~~~~~~~~~ TS2322: Type 'symbol' is not assignable to type 'unique symbol'.
};

Expected behavior:

// some-module.d.ts
declare const customSymbol: unique symbol;
declare const _default: {
	customSymbol: typeof customSymbol;
};
export = _default;

Actual behavior:

// some-module.d.ts
declare const _default: {
	customSymbol: symbol;
};
export = _default;

Playground Link:

https://www.typescriptlang.org/play?module=1#code/MYewdgzgLgBMCu0QFsDKBPZAjEAbGAvDBtngBQBECSyFAlANwCwAUAKYAeADiAE6xEA3qxii4iKChI5cAGlYBfZiyA

Related Issues:

• unique symbol incorrectly widens to symbol when assigning to a const or readonly property #23263
• Should create unique symbols when creating properties on module.exports #37404

[ExE-Boss]

Also, the following requires a // @ts‑ignore comment, but otherwise works:

// some-module.js
const customSymbol = Symbol("custom");

// This is a common pattern in Node’s built-in modules:
module.exports = {
	/** @type {typeof customSymbol} */
	// @ts-ignore
	customSymbol,
// 	~~~~~~~~~~~~ TS2322: Type 'symbol' is not assignable to type 'unique symbol'.
};