Typescript compiler prevents tree shaking by removing comments.

[seivan]

TypeScript Version: 2.7.0-dev.201xxxxx

Code
https://www.typescriptlang.org/play/index.html#src=class%20Sample%20%7B%0D%0A%20%20%20%20demo%20%3D%20()%20%3D%3E%20%7B%0D%0A%0D%0A%20%20%20%20%7D%0D%0A%7D%0D%0A%0D%0Aconst%20Button%20%3D%20%2F*%40__PURE__*%2F%20new%20Sample().demo

Expected behavior:
The comment should not be stripped

Actual behavior:
The comment is stripped and tree shaking breaks in production.

Related:
"Tree shaking" works when using ES6 modules and targeting the file directly, e.g

import { Button } from "lib/Button"

But if you want, what I want, the glorious way of doing

import { Button } from "lib"

Then it's no good. UNLESS the transpiled code (the output before minifying) in the exported file looks like

const Button = /*@__PURE__*/ whateverFunctionThatCreatesButton { }

In other words, it's a no go with Typescripts compiler as it will remove that comment.

[weswigham]

Duplicates #17606 (but it is worth remembering that new expressions should be tested for, too)

[seivan]

@weswigham Should this be closed since its a dupe?
From my point of view, this is a decent sized issue since it prevents tree shaking to work, thus creates larger than necessary bundles that need workarounds to prevent.

[weswigham]

@seivan Yes. You should track #17606 instead of this issue.