Re-export from a .d.ts file is not removed when compiling ES modules

TypeScript Version: 2.9.x

When you have a file types.d.ts

export interface IComponent {
}

export const enum Test {
    Foo,
    Bar
}

and re-export this in another module index.ts

export * from "./types";

and you compile this to ES modules, index.js will contain the export from types even though types.d.ts did not result in a module.

export * from "./types";

Code https://github.com/cschleiden/ts-module-repro

Expected behavior types export is not output in index.js

Actual behavior It is.

[mhegazy]

The current design is that export or re-exports of type only declarations are elided. the rational here is the same as that of eliding imports that are only used in type positions.

For this bug, the issue is const enum. if the file only included type or interface declarations it would have behaved as intended.

This is bug that we need to fix.

[Alxandr]

With imports you can guarantee to be right though. With export * from (which I argue should probably be a special case), you are stating that “I want everything in X to be available”, but the typescript compiler can’t guarantee that it knows what “everything” is. If I have typings that are only partyally covering a js library for instance, this could result in the export being removed from the output, changing the result.