Dynamic method names prevent tree shaking about esbuild HOT 2 CLOSED

I have tried to add various /* @__PURE__ */ annotations, but the class A does not get tree shaken.

The way to add a @__PURE__ annotation for the class A is as follows:

https://esbuild.github.io/try/#dAAwLjE5LjExAC0tdHJlZS1zaGFraW5nPXRydWUAY29uc3QgbWV0aG9kID0gJ21ldGhvZCc7CgpsZXQgQSA9IC8qIEBfX1BVUkVfXyAqLyAoKCkgPT4gY2xhc3MgewogIGdyZWV0KCkgewogICAgY29uc29sZS5sb2coJ2hlbGxvIGZyb20gQScpOwogIH0KICAKICBbbWV0aG9kXSgpIHsKICAgIHJldHVybiAnQSc7CiAgfQp9KSgpCgpjbGFzcyBCIHsKICBncmVldCgpIHsKICAgIGNvbnNvbGUubG9nKCdoZWxsbyBmcm9tIEInKTsKICB9Cn0KCm5ldyBCKCkuZ3JlZXQoKTs

You cannot add the pure annotation to the method variable reference like this because that's annotating the wrong thing. The @__PURE__ annotation says the result can be removed if it's not used. Except it is being used (as the name of the method) so the annotation doesn't have any effect. That's why it has to go around the whole class declaration. Another way to think about it: Just because the evaluation of the expression method has no side effects doesn't necessarily mean the evaluation of the ToString operation on that value also has no side effects.

The above example is deliberately simple to demonstrate the issue, but the context where it came from is that any class that declares a custom inspect function like below prevents treeshaking:

[Symbol.for('nodejs.util.inspect.custom')]() {
  return '...';
}

I appreciate you mentioning the actual use case. It's possible that esbuild could special-case this syntax to still allow tree shaking in this case.

from esbuild.

Thank you ! I appreciate you taking the time to explain the correct way to place the /* @PURE */ annotation !

from esbuild.