Unnecessary "observe" warning

[nmalevich]

Description

Warning "An "observe" was called from another "observe" closure, which can lead to over-observation and unintended side effects." was added in version 1.9.3 and become at unnecessary cases
I attach example project where you can see that bug
BadObserveExample.zip

Checklist

• I have determined whether this bug is also reproducible in a vanilla SwiftUI project.
• If possible, I've reproduced the issue using the main branch of this package.
• This issue hasn't been addressed in an existing GitHub issue or discussion.

Expected behavior

Warning doesn't appear

Actual behavior

Warning appears

Steps to reproduce

Just run app and wait. Screens will navigate by themselves

The Composable Architecture version information

1.9.3

Destination operating system

iOS 17.4.1

Xcode version information

15.3

Swift Compiler version information

swift-driver version: 1.90.11.1 Apple Swift version 5.10 (swiftlang-5.10.0.13 clang-1500.3.9.4)

[stephencelis]

@nmalevich We recently added this runtime warning because nested observes can have unintended consequences. In this case, a viewDidLoad is evaluated in the same stack as the presenting view controller's observe, which means all child state evaluated in the child controller's observe will be observed by the parent.

To work around the problem, you can move observe into viewWillAppear instead, and manage the lifetime of the observation token, or you can dispatch the observation a tick in viewDidLoad:

DispatchQueue.main.async {
  observe { [weak self] in
    …
  }
}

We're still deciding if this warning is too heavy-handed, but we don't consider it a bug at the moment. Because of this I'm going to convert this to a discussion.

[nmalevich]

@stephencelis Hi!
Thank you for your fast answer! But I don't understand exactly why it happens. You sad something about same stack, what did you mean? And why it happens only after presenting the third screen, not after the second?

Yeah, I have seen topic about cancellation observing on viewWillDisappear, but we can't do it with navigation, because we wouldn't be able to dismiss presented controller

I will be really grateful for your explanation. Thanks