`final` local variables and static immutability are related via closures

I'm not sure what's the best place to record this is, so just opening an issue to point it out.

**tl;dr** `final` local variables and static immutability are related concerns via closures

The [static immutability proposal](https://github.com/dart-lang/language/blob/master/working/0125-static-immutability/feature-specification.md) introduces objects that are deeply immutable and can be shared across isolates. Top-level and static function tear-offs should be shareable too as they have no internal shared mutable state. In fact, you can already spawn an isolate from a top-level function reference today. The static immutability provides an opportunity to expand this capability by allowing _closures_ to be passed to other isolates along with immutable objects, perhaps as fields of those objects. In fact, a lot of Flutter widgets take closures as arguments, such as `onTap`. However, such closures must only close over deeply immutable `final` local variables.

It would make the developer experience of using shared closures more pleasant if the ergonomics of `final` variable was better. This is discussed in https://github.com/dart-lang/language/issues/136.

Start with the static immutability proposal in working/0125-static-immutability/feature-specification.md, then read issue #136 about final-variable ergonomics. Trace how the proposal relates immutable closures, isolate sharing, and final locals; the issue does not define a concrete implementation or acceptance test, so done would require an agreed language-design scope.

Written by the indexing model from the issue text.