Expando function declarations cant emit non-identifier properties

Bug Report

🔎 Search Terms

expando properties function declaration symbol computed

🕗 Version & Regression Information

• This is the behavior in every version I tried

⏯ Playground Link

Playground link with relevant code

💻 Code

export const sym = Symbol()
const dashes = 'my-prop'

export function decl() {}
decl.foo = 1
decl[sym] = 2
decl[dashes] = ''
decl[10] = ''
decl["100"] = ''

export const arrow = () => {}
arrow.foo = 1
arrow[sym] = 2
arrow[dashes] = ''
arrow[10] = ''
arrow["100"] = ''

🙁 Actual behavior

export declare const sym: unique symbol;
export declare function decl(): void;
export declare namespace decl {
    var foo: number;
}
export declare const arrow: {
    (): void;
    foo: number;
    10: string;
    "100": string;
    [sym]: number;
    "my-prop": string;
};

🙂 Expected behavior

I'd expect decl to be transformed into an object instead of a namespace. That would allow the same properties to be emitted for decl as the ones that are emitted for arrow.

The object variant was the first choice by @sandersn here but then it got changed to a namespace. I didn't find any reason given for this change/decision in the PR comments though. Is there anything that the namespace can deliver here that the object variant can't?

Start with the linked TypeScript Playground and compare the declaration output for decl with the output for arrow. Review the historical PR linked in the issue for the namespace decision; done means function declarations emit the same non-identifier properties as the reproduced arrow-function case without regressing the other declarations.