Bundle introduces a type that references to itself

[notaphplover]

The bundler seems to be removing type aliases that leads to circularly referenced types.

Checklist

• I can reproduce this issue when running this plugin on its own.
  Other plugins, such as node-resolve are known to cause issues.
• I am running this plugin on .d.ts files generated by TypeScript.
  The plugin can consume .ts and even .js files (with allowJs: true), but this is known to cause issues.
• This issue is not related to rolling up @types.
  The plugin ignores these by default, unless respectExternal is set. @types can contain hand-crafted code which is known to cause issues.

Code Snipped

import { foo as namedFoo } from '@foo/package';

namespace myAwesomeNamespace {
  export type foo = namedFoo;
}

Error Message

The bundled code is the following one:

import { foo } from '@foo/package'; // Unused import

declare namespace myAwesomeNamespace {
  export type foo = foo; // Type alias 'foo' circularly references itself.ts(2456)
}

[notaphplover]

For those experiencing this issue, you can workaround it introducing some redundacy the bundler cannot detect. An example to workaround my sample code would be:

import { foo } from '@foo/package';

// This type has the only purpose of introducing a redundancy
type Identity<T> = T

type namedFoo = Identity<foo>;

namespace myAwesomeNamespace {
  export type foo = namedFoo;
}

Thanks to the undetected redundacy, namedFoo is not removed and there will be no circular dependencies in the bundled types. It's sort of ugly, but works. Any other undetected redundancy might be use to workaround this issue.