Type is not referred correctly in the while loop

🔎 Search Terms

incorrect type while loop

🕗 Version & Regression Information

Worked correctly in version 4.2.3.
It doesn't work since 4.3.5.

⏯ Playground Link

https://www.typescriptlang.org/play/?ts=5.5.4#code/MYGwhgzhAEDCAWBLEATaBTAHgF3QOxRgAkAVAWQBkBREdAW322gG8AoASAHN0mAHMAE6MAFAEoWHdsAD2eCE2bR+QvNhr1G0AL7QAvNGxIIAblaTEAM2jCAhMOWN1DVdERzsYPMHTSrABUFGUXE2djChbABXATxoPEiQEFMwrTNwnmjYh1UnRmTU1NZQSBgAlSYsXAJicmpaZwUObj5A1TEJMJl3FiVWtXrNHX1DRBM09ktrO2z+jRc3eU9vX2gAcQFPFDKgkMl2CMy4hKTJQvSomN7y3NV81kLiqDWNgm2XSvxCaFJKG8auHhXES7TqyeQ9GZ-bR6AxGUzmKy2ex9KELDxeHxWdboMDYdabN7YYIdc6HeKJZLsM77DKXSEDW4cApmR4wbG4-GvPoYHCfGq-Bn-ZpAtogmkXWLkk5U+4syLyaR0P4QAB0KHQFjc6GEACJgABaYBIVA6gA0cGNKFEpmA8uwiuVao1Wt1BpmZughOtRTtDsFqvVmrw2r1+s4LxQ+vd5s5Wz63ttCqV-qdQZDBvDOOwYYjUb6HvZeIjXvh2AAnrx0J6Uf6YYXY4ToAAfZ4E7ktwnwrrgo3IND6YMAdwtfbE8NoTFtAnKhIAXNXrrWW1KYb3UCqZvDB8aq8IpzP4x1u9JaCqQNJOHvogfytboAB6e-QCDwaQJNAAIyr9eL7dbXPKZsF0YNJ90YRt9DA1RCQ3PpTFSIA

💻 Code

class Child extends HTMLElement {
	get parent() {
		const { parentElement } = this;

		if (!(parentElement instanceof Parent)) {
			return null;
		}

		return parentElement;
	}
}

class Parent extends HTMLElement {
	get parent() {
		const { parentElement } = this;

		if (!(parentElement instanceof GrandParent)) {
			return null;
		}

		return parentElement;
	}
}

class GrandParent extends HTMLElement {
	get parent() {
		const { parentElement } = this;

		if (!(parentElement instanceof GreatGrandParent)) {
			return null;
		}

		return parentElement;
	}
}

class GreatGrandParent extends HTMLElement {
	get parent() {
		return null;
	}
}

// irrelevant code
customElements.define("c-child", Child);
customElements.define("c-parent", Parent);
customElements.define("c-grand-parent", GrandParent);
customElements.define("c-great-grand-parent", GreatGrandParent);

type ParentElements = GreatGrandParent | GrandParent | Parent;

const child = new Child();

let currentParent: ParentElements | null = child.parent;

while (currentParent) {
	console.log(currentParent); // should be GreatGrandParent | GrandParent | Parent

	currentParent = currentParent.parent;
}

🙁 Actual behavior

The curerntParent's type is not referred correctly. It became Parent | GrandParent.

🙂 Expected behavior

The currentParent's type should be Parent | GrandParent | GreatGrandParent.

Additional information about the issue

No response

Start with the linked TypeScript Playground reproduction and compare its behavior with version 4.2.3, 4.3.5, and the current version. Trace how type narrowing is retained across the while loop and its reassignment. Done means currentParent remains typed as Parent | GrandParent | GreatGrandParent without regressing the earlier behavior.