abstract type guard does not narrow when keyed with a unique symbol

[Jamesernator]

🔎 Search Terms

abstract type guard symbol

🕗 Version & Regression Information

• This is the behavior in every version I tried, and I reviewed the FAQ for entries about abstract type guard

⏯ Playground Link

https://www.typescriptlang.org/play/?ts=6.0.0-dev.20250810&ssl=28&ssc=2&pln=1&pc=1#code/FAYw9gdgzgLgBASygIQIYCc4F44GUCeAtgEZgA2AFAERJrpUCUA3MMKsbOqiPCGalChwAYmDBwA3sDgy47Tt3i0MFBgC44MABZJEQui1lyOMLjzgBtZegC6qjdt26DrI4QCm2sABN7cAG5gCN6S0kayCABmcBSOUFYoGHYMDKHh6XAA9JlwACo6QlBaYACuZCEQYPDE7nIQcO7o6GDoYRmycQB0xBgAsp7Fvsxt4QC+DWRQtVExXdaqqVLtRl096P1eQ4YZoyO7u6D8gnB0DQAeMO4Q3kKi4kuyYP6N6MHTieh+cXonGGkZ6E8JXQ9VMJXc2xkByMTxeb0s1mSDgKP1OD3SgJgwNB6HBkLg0Nkaw2gz8gWCkn2QA

💻 Code

const isBar = Symbol("isBar");

abstract class Foo {
    abstract isBar(): this is Bar;
    abstract [isBar](): this is Bar;

    method(): void {
        if (this[isBar]()) {
            // This should not be an error, it should work the same as .isBar()
            this.barMethod();
        } else if (this.isBar()) {
            this.barMethod();
        }
    }
}

class Bar extends Foo {
    override isBar(): this is Bar {
        return true;
    }

    override [isBar](): this is Bar {
        return true;
    }

    barMethod(): void {}
}

🙁 Actual behavior

TS reports an error:

Property 'barMethod' does not exist on type 'Foo'. Did you mean 'method'?(2551)

🙂 Expected behavior

No error should happen here, the type guard should work the same as the non-symbol version of the method.

Additional information about the issue

No response