Unbundle mode does not emit reachable transitive facade module

[amanmahajan7]

Reproduction link or steps

This description is generated using codex. I thought I created an issue but I cannot find it so this may be a duplicate.

I am trying to use tsdown with unbundle: true for a package that has an aggregate entry file and separate public subpath/facade entry files.

The simplified setup looks like this:

packages/
  ui/
    index.js
  card/
    index.js
    components/
      card.js
      content-card.js

The aggregate entry is packages/ui/index.js:

export * from '../card';

The card package has its own public facade file at packages/card/index.js:

export { default as Card } from './components/card.js';
export { BigCard } from './components/content-card.js';

The package export map points ./card at the generated facade path:

{
  "exports": {
    ".": "./dist/packages/ui/index.mjs",
    "./card": "./dist/packages/card/index.mjs"
  }
}

I have attached a sample project

tsdown-unbundle-facade-repro.zip

What is expected?

With unbundle: true, I expected tsdown to transform the reachable module graph while preserving file-level public entry/facade modules. In this case, I expected the build output to include:

dist/packages/ui/index.mjs
dist/packages/card/index.mjs
dist/packages/card/components/card.mjs
dist/packages/card/components/content-card.mjs

The important file is dist/packages/card/index.mjs. I expected it to preserve the public facade exports

What is actually happening?

Instead, tsdown emits the aggregate root and the implementation files, but does not emit the transitive facade module:

dist/packages/ui/index.mjs
dist/packages/card/components/card.mjs
dist/packages/card/components/content-card.mjs

The generated root file directly imports the implementation modules:

import Card from "../card/components/card.mjs";
import { BigCard } from "../card/components/content-card.mjs";
export { BigCard, Card };

So the root package import works but the subpath export is broken because dist/packages/card/index.mjs does not exist:

import { Card } from 'tsdown-unbundle-facade-repro/card';

Any additional comments?

This is surprising because packages/card/index.js is directly reachable from the aggregate entry and is also a public package facade/subpath target. Since unbundle mode is described as focusing on code transformation without combining files, I expected the reachable facade module to remain present in the output rather than being bypassed.

The workaround is to add packages/card/index.js as an explicit entry, but that does not scale well for a package that has many public facade/subpath modules reachable from a single aggregate entry.

[amanmahajan7]

Possible replated #881

[sxzz]

Please track rolldown/rolldown#9209