Types in `d.cts` is incorrect when the entry has multiple exports

[sapphi-red]

Environment

Node 22.15.0
unbuild 3.5.0

Reproduction

https://stackblitz.com/edit/node-vefv5aqh?file=package.json,build.config.ts&terminal=build

Describe the bug

The CJS output has

exports.default = d;
exports.foo = foo;

but the types (index.d.cts, index.d.ts) has

export = d;
export { foo };

I think the correct type for this CJS file is:

export = { default: d, foo }

Additional context

I guess the related changes are #458 and #513

Logs

[kricsleo]

cc @userquin 🤔

[userquin]

When using only default cjs export the correct usage is export = d, when mixing default export + named exports we need to create a namespace.

If using default exports, requiring the default export will need an extra .default (const d = require('d').default).

Check this draft pr using oxc-parser to create the namespace userquin/fix-dts-default-cjs-exports#11

// d.cts
declare const d: {};
declare namespace d {
  export const foo: {};
  import _default = d;
  export { _default as default };
}
export = d;

[userquin]

I think the example is wrong, iirc you cannot redeclare a const as a namespace, you can only use namespace with classes and functions.