While this fixes the issue of inferring State when on is used outside createReducer, I would expect that it breaks the deferred contextual inference which was intended by using the conditional type. Do the current tests ensure that State is inferred contextually from on's usage in the parameters of a function like createReducer? Otherwise, I'd expect this could break some intended functionality.

Specifically, this allowed for generic reducers: https://github.com/ngrx/platform/pull/2996/files#diff-b5b61b5c88ce4368769a58df0918602484c6c507e6a6dfad51e4746e470caf26R45

In that last PR, it seems the effect of using the conditional type was not understood. Here's why it worked- https://stackoverflow.com/a/70129630/11087018.

I'm not immediately sure what the correct thing to do would be to support both use cases. Probably a good question for jcalz, StackOverflow's Typescript wizard.

Hey @david-shortman
Yes, we have a test covering a generic reducer as well.
There are number of test still broken, so this is not the final fix.

Well, this was fun :)

@david-shortman this should be now fixed with preserving generic reducers and all the other interesting cases that we were running into.

Here's the playground link

Cool! TS is a blast 😄