Named tslib imports cause webpack bundle size increase

TypeScript Version: 3.6.1-rc

Search Terms: tslib

Expected behavior: #32742, which changes all tslib imports from namespace imports to named imports, would have decreased bundle size in webpack builds from typescript code

Actual behavior: Due to a quirky workaround in webpack, all function invocations of named harmony imports are wrapped in an Object() constructor; as a result, #32742 actually increases bundle size (to the tune of ~9kB in Outlook Web boot bundles)

Since the PR was an attempt specifically to help webpack, and @sokra claims that tree-shaking works even with namespace imports, I think the change should be reverted.

Related Issues: webpack/webpack#9615

[sokra]

import * as ns from "module";
import { abc } from "module";

console.log(ns.abc, abc);

Both can be tree-shaken equally. This has always been the case.

Some claims say that namespace objects are not tree-shake-able, but this is only true when using the namespace object directly, without accessing a property of it.

import * as ns from "module";

console.log(ns); // <- all exports of module are included, tree-shaking disabled

[tommytroylin]

according to @sokra and my test based on @RikkiGibson 's demo

latest webpack@4 has already support tree-shaking something like tslib_1.__assign

@sokra I could barely remember when tree-shaking comes out on webpack@2or3, namespace imports are not shakeable. I’m not sure.

back to #16999, I can’t reproduce that build now but we actually notice that behaviour years ago.

IMO, if tests confirm that on webpack@3or4 with proper configs tree-shaking works as expected. Reverting that outdated optimization is acceptable.