make tslib imports shakable

[tommytroylin]

TypeScript Version: 2.4.1
when I use ts with config like:

{
  "compilerOptions": {
    "experimentalDecorators": true,
    "importHelpers": true,
    "module": "esnext",
    "noEmitHelpers": true,
    "target": "esnext"
  }
}

I notice that it come out with code like this

import * as tslib_1 from "tslib";

It is not good enough for tree-shaking by webpack.
Webpack actually bundle with the entire tslib.es6.js

And it's a bit heavy in my bundle

Expected behavior:

import { __decorate } from "tslib"; 
// depends on funcitons that actually used with in this file

[bfricka]

It should be shakable, as the package.json defines "module": "tslib.es6.js", and uses es6 exports rather than exporting an object. From this perspective, it seems more like a Webpack issue. Have you tried reproducing with Rollup?

[RichiCoder1]

@bfricka I think the issue is that import * as tslib_1 from "tslib"; is what is being generated by tsc. Webpack (currently) doesn't know how to shake this. Typescript should emit an import that only includes what that module is actually using.

[bfricka]

Totally. I should have read the ticket closer.

[TheLarkInn]

That is correct!!! import * is very hard for webpack to try and analyze.

However something like import foo from "tslib/lib/foo" would be far easier to analyze.

[RikkiGibson]

Is there anything that would make this unfeasible? It would really be ideal to have only the actually used helpers get bundled by tools like webpack.

[DanielRosenwasser]

@TheLarkInn, just curious, where can users track better tree-shaking for namespace imports in Webpack?