Allow class expressions in type declarations

[JoshuaKGoldberg]

Suggestion

🔍 Search Terms

class expression declaration type

✅ Viability Checklist

My suggestion meets these guidelines:

• This wouldn't be a breaking change in existing TypeScript/JavaScript code
• This wouldn't change the runtime behavior of existing JavaScript code
• This could be implemented without emitting different JS based on the types of the expressions
• This isn't a runtime feature (e.g. library functionality, non-ECMAScript syntax with JavaScript output, new syntax sugar for JS, etc.)
• This feature would agree with the rest ofTypeScript's Design Goals.

⭐ Suggestion

When a class is created by a static method, there doesn't seem to be a way to directly use it as a class type.

📃 Motivating Example

Implementation:

class BaseClass {
    static cloneClass() {
        return class extends BaseClass { }
    }
}

How I would expect the declaration to look, with the type error present now:

declare class BaseClass {
    static cloneClass(): class extends BaseClass {};
    //                   ~~~~~
    // Cannot find name 'class'.
}

The declaration actually created:

declare class BaseClass {
    static cloneClass(): {
        new (): {};
        cloneClass(): any;
    };
}

💻 Use Cases

Similar to #45013: it's difficult to represent class "factories" like this one in type declarations.

[fatcerberus]

typeof BaseClass?

[RyanCavanaugh]

Same as #41581 / #41587

[JoshuaKGoldberg]

Super, thank you! Apologies for the issue spam then :)