Dead code elimination on client

[StorytellerCZ]

Based on #10056 and related to #11164

Heard about this recently and I think this could help a little, so I have decided to revive the code.
I would like to hear what people think and how we can make this better.

[zodern]

I think this comment still applies - #10056 (comment)
It really should work on the AST instead of using a regex.

Instead of doing it in the minifier, it might be better to do it as either part of the import scanner, or in the babel-compiler package. This way Meteor would also ignore any imports in the removed code. The import scanner would work in more situations but be more difficult to optimize - I was planning to redesign how its caching works to support this, but I probably won't have time in the near future.

[jamauro]

This would be applied to the final bundle right?

If so, could this be viewed as an interim solution until a better solution materializes or the tree shaking pr is merged? Would be great to have Meteor.isServer code removed from the client bundle.

Even if it were opt in only, I think it would be beneficial. It could always be removed when a better solution is ready.

I suppose it also depends on when the tree shaking pr could be conceivably merged. At this point, I'm assuming that's still a ways off given all the Meteor 3 work, but maybe that's a bad assumption and it's right around the corner 🤞.

[StorytellerCZ]

@zodern point well taken, still I'm with @jamauro on this. Once I get around to this again, I will try to add a flag that can turn this on and off and we can turn this off by default until we have a better solution so this could be an interim solution for people who need it or want to experiment with this. Thoughts?