Why doesn't typescript narrow types with control flow and never when using arrow functions

Typescript refuses to narrow with a call to fail but will narrow with a call to fail2. Is this a bug in typescript?

const fail = (message?: string): never => {
    throw new Error(message);
};

function fail2(message?: string): never {
    throw new Error(message);
}

const getData = (): string | null => {
    return "the-data";
}



export const loadDataOrError = (): string => {
    const data = getData();

    if (data === null) {
        // Swap the below and see that it works
         
        // fail2();
        fail();
    }

    // This errors
    return data;
};

here is a playground if you want to try switching the comments and seeing the error vanish.

Screenshots for clarity

With an error

Without an error

According to this open GitHub issue this is a limitation of how type narrowing currently works in typescript. If you want to remedy it you can explicitly annotate arrow function types like so:

const fail: (message?: string) => never = (message) => {
    throw new Error(message)
}