Support sideEffects configuration for tree-shaking

[Matthew Phillips]

WebPack has a sideEffects configuration that is used to control what modules can be tree-shaken.

In steal-tools@pre we don't use this. In WebPack, iirc, it will only tree shaken modules explicitly marked as sideEffects: false. We don't want to support that part, but we do want to support this form:

{
  "sideEffects": ["some-module"]
}

Which will prevent some-module from being tree-shaken.

[Matthew Phillips]

I can't remember why we need this... I think maybe we don't. Going to remove this from the 2.0 epic, can add later in a minor release if there becomes a need.

[Justin Meyer]

For something like can-stache-bindings?

[Matthew Phillips]

It depends on how you import it. If you do:

import "can-stache-bindings";

It will be included in the build. However if you do:

import stacheBindings from "can-stache-bindings";
// stacheBindings is never used

Then it would be tree-shaken currently. This configuration would prevent that.

[Justin Meyer]

What about

import {stacheBindings} from “can”

But stacheBindings isn’t used in the file.

[Matthew Phillips]

Would be tree shaken. However, if you're using Component as well then it will be included since that depends on it.

So with this configuration a user could do:

{
  "sideEffects": ["can-stache-bindings"]
}

And then it would be included. Unfortunately canjs couldn't add this config, otherwise it would be included in the bundle whether someone used it or not.