Various panics when dealing with nested structs about flux HOT 2 CLOSED

@ranjitjhala some of the crashes are spurious (the ones related to evars) with respect to accessing nested fields because they are an instance of #212.

For the rest, it turns out that they are all related to unpacking references. The issue is that the FdMap inside VmCtx is existentially quantified, so even declaring a dummy parameter for VmCtx won't help as the nested field will still have an existentially quantified index.

I implemented a general fix here #301. The fix is to unpack the existential inside references when needed. This will make flux not crash but it makes a nested existential field behind a mutable reference a bit useless as you will only be able to mutate it in a way that doesn't change the index.

from flux.

The remaining issues here are related to #212 or opening of mutable references

from flux.