Incorrect type resolution with nested constructors

🔎 Search Terms

nested constructors type resolution anti-pattern

🕗 Version & Regression Information

• This changed between versions ______ and _______
• This changed in commit or PR _______
• This is the behavior in every version I tried, and I reviewed the FAQ for entries about _________
• I was unable to test this on prior versions because I only report bugs to be helpful, but I don't have time to dive deeper myself.

⏯ Playground Link

https://www.typescriptlang.org/play/?#code/KYDwDg9gTgLgBAE2AYwDYEMrDsiA7AZ3gCF0DgAuOAbwCgBIPYAdwAoBKKu++gawEs8CKgHIAgiIaMWHLnAFDRxEXAC+DdetyF4YuAF44TZjgwECcUDGBCLpcjTW1tROMQNGWpshas2EFnrUTsQAdAoIQA

💻 Code

export declare const Base: {
	new(): {
		kind: 'A'
		new(): { kind: 'B' }
	}
}
const A = new class extends Base { }
const B = new class extends A { }
B.kind // shows 'A', but should be 'B'

🙁 Actual behavior

If a ctor returns another ctor, it repeats the first level. In the above example, B.kind is 'A', but since we extended and instantiated twice, it should be 'B'.

🙂 Expected behavior

After extending twice, it should reach the inner class, instead of repeating the outer one.

Additional information about the issue

I can only reproduce this bug with this weird experimental anti-pattern - so on its own probably not a priority at all, but types should probably reflect the runtime state as much as possible, even in weird edge cases such as this, and it might indicate a deeper underlying issue.

リンクされた TypeScript Playground の再現例から始め、ネストされた2つの new class extends ... 式の型解決を追跡します。2回の拡張とインスタンス化の後、例が B.kind を 'A' ではなく 'B' と報告すれば、作業は完了です。