Extensions for subtype of a class marked @Observable generate compile error

[virasio]

Description
I cannot add a subtype (class, enum, struct) to a class marked with @Observable macro. If I add an extension to this subtype, I get compile error:

Circular reference resolving attached macro 'Observable'

Steps to reproduce

@Observable
class MyObservableClass {
    var property1 = ""
    var property2 = MyClass()
}

extension MyObservableClass {
    class MyClass {
        var property = ""
    }
}

extension MyObservableClass.MyClass {
    var test: String { "test \(property)" }
}

Expected behavior
It must be compilable because the following version is compilible:

@Observable
class MyObservableClass {
    var property1 = ""
    var property2 = MyClass()
}

extension MyObservableClass {
    class MyClass {
        var property = ""
        var test: String { "test \(property)" }
    }
}

Environment
Xcode 15.0 beta (15A5160n)
Swift 5.9
Target: iOS 17.0

[JessyCatterwaul]

@Model has the same problem. Do all macros exhibit it?

[ugoArangino]

@JessyCatterwaul Yes. It's always the same pattern.
TypeA with a Macro
extension type B nested in type A
extension for type B → compile error

[yermukhanbet]

Are there any workarounds for this issue?

[nekno]

One workaround is to place the extension(s) in a separate file.

[juliand665]

Just ran into this as well; here's a perhaps even more minimal example:

@Observable
final class Outer {
    struct Inner {}
}

extension Outer.Inner {}

[mbrandonw]

+1 to this issue being a problem that definitely comes up quite a bit in every day work.

Also, regarding this:

One workaround is to place the extension(s) in a separate file.

This can work most of the time, but sometimes it can be difficult. For example a macro applied to a generic type that needs to conditionally conform to Equatable:

@SomeMacro
struct Wrapper<T> { var value: T }

extension Model: Equatable where T: Equatable {}  // 🛑 Circular reference

If this extension is moved into a separate file then you lose the automatic synthesis of Equatable, and so that is unfortunate.

[li3zhen1]

Add a new case:

enum Namespace {
    @SomeMacro
    struct SomeStruct { }
}

extension Namespace.SomeStruct { }  // 🛑 Circular reference

Hello, any progress here?

[stephencelis]

We shipped a few macros this week and have had about a dozen folks report this bug to us. Would be nice to have the issue triaged.

[DevYeom]

It seems that this issue has been fixed in Xcode 15.1 Beta 3.

[mbrandonw]

Hi @DevYeom, I am not able to confirm this. Both the example provided in this issue still fails to compile:

---

As does a simpler repro of the problem:

---

I am using Xcode 15.1 beta 3 (15C5059c) to test this. Can anyone else confirm that it is fixed?

[DevYeom]

I'm so sorry for my misleading.

The issue I had was not related to @Observable, but rather with the custom member macro I created.
The message I encountered was as follows, and it was resolved in Xcode 15.1 Beta 3.

Circular reference expanding member attribute macros on 'Something'