#1311: Start side effects DEFAULT instead of LAZY.

[steve-the-edwards]

See #1311 for more information on the problem.

The first commit is a red test that will test that behaviour on Android with the Main.immediate dispatcher.

The second commit makes that test green!!

It does so by launching side effects with DEFAULT instead of LAZY. That means that with an eager dispatcher like Main.immediate your workers and side effects will be eagerly entered as they are created during render. We want to maintain the distinction that we cannot send to the sink in render() but we need to be able to do so in a worker/side effect. So we freeze the RenderContext whenever we dispatch the coroutine for that side effect (and then unfreeze it as necessary when that is complete) using a ContinuationInterceptor.

Note that this is a pretty significant change to the contract for workers/side effects; we've explored this before without making any significant changes, preferring instead to provide the CoroutineScope of the Workflow with a SessionWorkflow ( #1102, #1093 ).

In this instance our motivation is to enable further optimization and it is a pretty good motivation!

We will want to reflect on ramifications of this semantics change.

[steve-the-edwards]

• I need to use a delegating ContinuationInterceptor so that we still use whatever dispatcher is in the context - just adding the layer of freeze/unfreeze. E.g., see CoroutineDispatchers-compatible ContinuationInterceptor composition Kotlin/kotlinx.coroutines#2478

errr.... if that's possible. Need to do some more reading on that thread.