@Observable macro fails on Linux: 'shouldNotifyObservers' not covered by macro (Swift 6.2.3)

[guitaripod]

Description

Building any project using @Observable on Linux with Swift 6.2.3 fails with macro expansion errors.

Environment

• OS: Arch Linux (kernel 6.18.3-arch1-1)
• xtool: 1.16.1
• Swift: 6.2.3 (swift-6.2.3-RELEASE)
• iOS SDK: darwin (iOS 18.5 from Xcode)

Error

macro expansion @Observable:16:26: error: declaration name 'shouldNotifyObservers' is not covered by macro 'Observable'

The generated code shows mangled unique names:

private nonisolated func shouldNotifyObservers<$s6A_LIST22JourneysContentManager10ObservablefMm_6MemberfMu1_>(...)

Root Cause Analysis

The @Observable macro uses context.makeUniqueName("Member") for generic parameters. On Linux, these generate names starting with $ that look like Swift symbol manglings, which the compiler then rejects.

The macro declaration in Swift properly declares shouldNotifyObservers in its names: parameter:

@attached(member, names: named(_$observationRegistrar), named(access), named(withMutation), named(shouldNotifyObservers))

But the generated code uses unique mangled names that aren't being accepted.

Related Issues

• makeUniqueName() produces tokens that cannot be used as closure arguments swiftlang/swift-syntax#2256 (makeUniqueName produces $ prefixed names)
• Cross-compiling packages which contain macros doesn't work swiftlang/swift-package-manager#6950 (cross-compile macros)

Question

Is this a known limitation? Is there a workaround like using a different Swift version or toolchain configuration?

[kabiroberai]

Can you try the iOS 26 SDK? Macros for system libraries tend to be tightly coupled between the compiler version and the SDK. The iOS 18 SDK probably expects Swift 6.1, and iOS 26 expects 6.2.

[guitaripod]

Update: Found workaround - Swift 6.1 works

After testing, I can confirm that Swift 6.1 does not have this issue. The @Observable macro works correctly with Swift 6.1 on Linux.

This appears to be a regression in Swift 6.2.x.

However, after getting past this issue with Swift 6.1, I hit another blocker: the Sentry xcframework causes a signing error:

Invalid arch file in fat mach-o file!

This is tracked in #130. So even with the @observable fix, xtool builds fail if the project uses Sentry.

For now, projects using:

• @Observable + Swift 6.2.x → blocked by this issue
• Sentry xcframework → blocked by Issues using the Sentry package #130

I've also filed the underlying Swift bug: swiftlang/swift#86778