PSA: If you're using Approachable Concurrency and MainActor isolation…

[ryanbooker]

The feature that seems to actually cause drama is: NonisolatedNonsendingByDefault.

If you have everything in packages, not enabling this seems to work smoothly.

i.e. I have the following enabled:

• MainActor isolation default for UI packages
• InferIsolatedConformances for all packages
• Swift v6 mode for all packages

This is equivalent to Approachable Concurrency and MainActor default isolation except for NonisolatedNonsendingByDefault.

Beta season ends soon, I don't know where that will leave us. It's been a very rough year.

[mbrandonw]

Hi @ryanbooker, thanks for the info!

Can you provide more info of what was failing to build before you switched to these settings? And can you confirm that even enum reducers work with this set up? This issue #3768 states some problems with enum reducers that we need to look into soon.

[ryanbooker]

Ah sorry. Not failing to build. I was seeing a crash in a .run {}. I'll set up a simple project example and link to it. It's also possible it's me holding it wrong. 😅

[ryanbooker]

Because I haven't got around to it yet, the basics:

• Nonisolated service with Sendable FooClient (services package)
• MainActor Reducer and View (UI package)
• .run { client.dosomething } in the reducer blows up

[ryanbooker]

I worked out the issue… I had completely forgotten about the new @concurrent option…

With NonisolatedNonsendingByDefault enabled, .e.g. when using Approachable Concurrency, you need to make nonisolated client closures @concurrent @Sendable.

No more crashes.

[mbrandonw]

If something crashes that seems like a swift bug. Are you compiling in swift 6 mode?

[ryanbooker]

Yeah, Swift 6. Maybe it is a Swift bug, all I know for sure is that with the Approachable Concurrency changes all enabled, a nonisolated client, and a MainActor reducer, you have to make the client closures @concurrent @Sendable.