Packages that import XCTest break generated playgrounds

[vzsg]

As we've discussed on Discord, using Arena 1.0.0 to make a playground for RxSwift (5.1.1 at the time of writing) results in a seemingly valid workspace playground that Xcode loads successfully, with autocomplete to boot.

However, running the playground fails with errors such as:

error: MyPlayground.playground:8:15: error: cannot find type 'Observable' in scope
let triggers: Observable<Int> = Observable.merge(
              ^~~~~~~~~~

error: MyPlayground.playground:15:29: error: cannot find type 'Observable' in scope
    .flatMapLatest { max -> Observable<Int> in
                            ^~~~~~~~~~

An example repo is available here (GH link), or here (ZIP).

---

As a workaround, editing Dependencies/Package.swift and removing all product dependencies except RxSwift makes the playground work.

From:

package.targets = [
    .target(name: "Dependencies",
        dependencies: [
            .product(name: "RxSwift", package: "RxSwift"),
.product(name: "RxCocoa", package: "RxSwift"),
.product(name: "RxRelay", package: "RxSwift"),
.product(name: "RxBlocking", package: "RxSwift"),
.product(name: "RxTest", package: "RxSwift")
        ]
    )
]

To:

package.targets = [
    .target(name: "Dependencies",
        dependencies: [
            .product(name: "RxSwift", package: "RxSwift")
        ]
    )
]

[vzsg]

I did some tests, it seems the RxTest product is the one that kills the mood. The other four, in any combination, work fine.

I wonder what's so special about it... The only thing I see is this symlink.

That symlink is a red herring, Xcode could clone it just fine and it appeared as a regular file at the proper place. In fact, the complete Sources folder in RxSwift is just a bunch of symlinks.

There was another red herring in the build logs:

Changing the deployment target in Dependencies/Package.swift to macOS 10.15 made the warning go away, but did not change the original error.

---

My next suspicion is the fact that RxTest is pulling in XCTest, and that might somehow be illegal for a playground.

[vzsg]

It's definitely the XCTest import! There is a single file inside RxTest that imports it. After removing this file from the project, the playground started working.

---

On a whim, I tried to make a playground for Nimble, and that resulted in the same kind of errors.

[finestructure]

Thanks a lot for raising this and finding out about XCTest!

I know XCTest didn't work in playgrounds in the past but I thought that wasn't a problem anymore. I'll see what I can do.

[finestructure]

Raised as FB8882995. From what I gather this might be a problem with playgrounds.

[Peter-Schorn]

A similar issue occurs when you try to add a SPM package product that imports XCTest to a command line project. In order for the project to build you must make certain changes to the build settings:

For the project build settings, search for "Runpath Search Paths" and add the following paths:

• /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/Library/Frameworks/
• /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/usr/lib/

For the project build settings, set "Enable Testing Search Paths" to "Yes"

You don't have access to these settings in a playground, so there's probably nothing you can do.

[finestructure]

@pointfreeco have come up with a workaround to ship XCTFail in library code and I wonder if this would work in a playground as well.

It's using their new package XCTest Dynamic Overlay. I'll need to try this but perhaps adding this package and import XCTestDynamicOverlay at the top might work?

[finestructure]

This might require defining all the other XCTest symbols though - the library only declares XCTFail.

[finestructure]

I wonder if conditional linking of XCTest would be a workable solution (upstream): https://github.com/apple/swift-collections/blob/main/Package.swift#L72-L81

[finestructure]

I've just tried this with RxSwift 6.5.0 and Xcode 14.1 and this seems to be fixed now: