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.

Start with the linked TypeScript Playground reproduction and trace type resolution for the two nested new class extends ... expressions. The work is done when the example reports B.kind as 'B' instead of 'A' after the two extensions and instantiations.