Immutable middleware is not being tree-shaken in production

[markerikson]

Per recent Twitter discussion with @mweststrate and @Andarist , it turns out all my attempts to ensure that redux-immutable-invariant-middleware isn't being included in prod builds... didn't work out:

https://twitter.com/acemarke/status/1228092154830098432

So, RTK users are currently getting an extra couple K in their prod bundles that shouldn't be there.

Per #78 , it seems that RISM doesn't shake right because it's not a proper module or something like that.

Looking at https://github.com/leoasis/redux-immutable-state-invariant , it hasn't been updated in 3 years. If I look at the author's Github profile, they're not entirely inactive, as there's a few one-off commits in the last few months, but the lack of activity on the repo suggests we're unlikely to be able to poke them and get an improved version published.

Given that, I'm planning to fork redux-immutable-state-invariant, copy it completely into the RTK codebase, and ensure that it's getting shaken properly in production.

Other related notes:

• Michel Weststrate just published a utility that can help check sizes of different exports in prod (https://twitter.com/mweststrate/status/1228805162871017477, https://github.com/mweststrate/import-size)
• Looks like a new version of Immer may be much-better shakeable ( https://twitter.com/mweststrate/status/1228056670447730688 ), and thus worth upgrading to. At the same time, Immer 5.3 requires TS 3.7+, and we've been supporting back through 3.3.
• We probably want to look at maybe doing something similar for the redux-devtools-extension package, as that's also not a correct ES module and might also be preventing us from shaking right.

[markerikson]

Resolved in the 1.3 alphas by #381 .