swift: fail to build Observable extenion method on RxSwift

Description in Xcode 15 beta 6,RxSwiftExt Package is starting to fail building. It turns out that specific method declaration extension is problematic.

Steps to reproduce

I made a simple example to reproduce. or you can try to build RxSwiftExt Package.

import RxSwift

extension Observable {
    func test() -> Observable<Bool> {
        // error: Cannot convert return expression of type 'Observable<Element>' to return type 'Observable<Bool>'
        // error: Cannot specialize non-generic type 'Observable<Element>'
        return Observable<Bool>.empty()
    }
}

but this two code is passing without error.

// fully unqualified
extension Observable {
    func test() -> Observable<Bool> {
        return .empty()
    }
}

// fully qualified
extension Observable {
    func test() -> Observable<Bool> {
        return RxSwift.Observable<Bool>.empty()
    }
}

Expected behavior

build success without error

Environment

Swift compiler version info

swift-driver version: 1.87.1 Apple Swift version 5.9 (swiftlang-5.9.0.128.2 clang-1500.0.40.1) Target: arm64-apple-macosx13.0

Xcode version info

Xcode 15.0 Build version 15A5219j

Deployment target: N/A

About this issue

Original URL
State: closed
Created a year ago
Reactions: 14
Comments: 29 (24 by maintainers)

Commits related to this issue

Don't fully spec the return values. Needed because Xcode 15beta6 has a conflict between RxSwift.Observable and Foundation.Observable. By using the static member names, swift is able to infer the corr... — committed to FountainheadMobileSolutions/RxSwiftExt by rudedogdhc a year ago
[PreCheck] Filter out macro declarations from result set Move logic from `ConstraintGenerator::visitOverloadedDeclRefExpr` to pre-check to avoid including macro declarations referenced without `#`. T... — committed to xedin/swift by xedin 10 months ago
[PreCheck] Filter out macro declarations from result set Move logic from `ConstraintGenerator::visitOverloadedDeclRefExpr` to pre-check to avoid including macro declarations referenced without `#`. T... — committed to xedin/swift by xedin 10 months ago
Add RxSwift to remove ambiguity imports Foundation which causes issue described here: https://github.com/apple/swift/issues/67815#issuecomment-1701944076 — committed to barkinglabs/RxBluetoothKit by philfi 9 months ago
Add RxSwift to remove ambiguity imports Foundation which causes issue described here: https://github.com/apple/swift/issues/67815#issuecomment-1701944076 — committed to barkinglabs/RxBluetoothKit by philfi 9 months ago
Xcode 15/Swift 5.9 (#3) * Add RxSwift to remove ambiguity imports Foundation which causes issue described here: https://github.com/apple/swift/issues/67815#issuecomment-1701944076 * Create cont... — committed to barkinglabs/RxBluetoothKit by philfi 9 months ago
Xcode 15/Swift 5.9 에서 발생하는 Observable Ambiguity 대응 https://github.com/apple/swift/issues/67815 — committed to socar-inc/RxBluetoothKit by socar-narr 8 months ago

Most upvoted comments

FYI this is a regression from Xcode 15 Beta 5 where this worked with no issues

+15

freak4pc on Aug 9, 2023

Still an issue in Beta 7

+13

noypi-dev on Aug 23, 2023

I believe this is a constraint system bug that was introduced by https://github.com/apple/swift/pull/66657, and this bug manifested with RxSwift when Foundation started exporting the Observation library in Xcode 15 Beta 6. The bug is specific to writing an explicitly specialized Observable<X> in expressions in a situation where the constraint system has to perform overload resolution in order to determine what the type refers to (e.g. because there’s an import Foundation that also surfaces an Observable declaration), which is why explicitly specifying RxSwift.Observable<X>.empty works around the problem. Regular type annotations should be unaffected, which is why removing Observable<X> from the expression and using the leading dot syntax works around the issue. Removing the specialization may also workaround the problem, though I have not attempted that yet to confirm whether or not it works.

@xedin is working on a fix.

+10

hborla on Sep 1, 2023

Still an issue in Xcode 15 Beta 8

MontakOleg on Aug 29, 2023

Any chance we could get some clarity about this by anyone from the Core Team? The release date is right around the corner and this was already fixed and then regressed during the beta itself. @DougGregor

freak4pc on Aug 23, 2023

The release/5.9 branch corresponds to potential point releases of Swift 5.9. The fix is not in Swift 5.9.0.

Thank you:)

Sorry to go over my last question again but I truly don’t understand the semantics🥲

Will a point release of 5.9.1 necessarily only come in the 15.1 version of Xcode itself? Or is there no way to tell?

Thanks for the patience and pardon my ignorance on the topic 😃

freak4pc on Sep 14, 2023

In my case, after updating RxSwiftExt to 6.2.1 the issue was gone

Yup, we added a workaround, but it would be nice if the breakage wouldn’t be happened from the get go

Would be interesting to test after the next public release of Swift

freak4pc on Sep 20, 2023

In my case, after updating RxSwiftExt to 6.2.1 the issue was gone

frndev on Sep 20, 2023

I think this is worse opening is a separate issue, might be a bug on main that is only reproducible in assert builds. I am going to build a 5.9 toolchain, let’s see if it’s reproducible there as well.

xedin on Sep 2, 2023