Preserve computed property in `--isolatedDeclarations` emit

[acutmore]

🔍 Search Terms

isolated declarations, computed properties

✅ Viability Checklist

• [x] This wouldn't be a breaking change in existing TypeScript/JavaScript code
• [x] This wouldn't change the runtime behavior of existing JavaScript code
• [x] This could be implemented without emitting different JS based on the types of the expressions
• [x] This isn't a runtime feature (e.g. library functionality, non-ECMAScript syntax with JavaScript output, new syntax sugar for JS, etc.)
• [x] This isn't a request to add a new utility type: https://github.com/microsoft/TypeScript/wiki/No-New-Utility-Types
• [x] This feature would agree with the rest of our Design Goals: https://github.com/Microsoft/TypeScript/wiki/TypeScript-Design-Goals

⭐ Suggestion

Now that #60052 allows for (some) computed properties in in .d.ts files I think the next step is for --isolatedDeclaration to be updated to not error and to emit the computed properties. Opening this issue if helpful to track this work.

I believe the previous plan (#58800) to introduce a new syntactic marker is no longer required.

Related issues: #58533 #60818 #61068

📃 Motivating Example

export const prop: unique symbol = Symbol();

export class MyClass {
    [prop] = () => Math.random();
}

@isolatedDeclarations: false

playground

export declare const prop: unique symbol;
export declare class MyClass {
    [prop]: () => number;
}

@isolatedDeclarations: true (current 🙁)

playground

ts(9038) Computed property names on class or object literals cannot be inferred with --isolatedDeclarations.

export declare const prop: unique symbol;
export declare class MyClass {
}

@isolatedDeclarations: true (future 🚀 )

No error and same emit as @isolatedDeclarations: false

export declare const prop: unique symbol;
export declare class MyClass {
    [prop]: () => number;
}

💻 Use Cases

The primary use case is enabling isolated declarations at scale on large codebases that make heavy use of computed properties.