Package Manager Conditional Target Dependencies

Karl · December 4, 2019, 10:25pm

Yeah, so after you do that, "it just works".

Thanks a lot

eskimo · December 5, 2019, 8:53am

Cool.

I’ve recently been helping a developer who’s shipping a custom toolchain (s. 723651342), so I’ve spent a bunch of time looking into this. The issue here is that Xcode toolchains kinda look like a bundle but aren’t really, and that causes them to slip through a crack between Gatekeeper and the notary service. This is something that Apple needs to investigate (I don’t yet have a bug number because I only just asked the developer to file one).

Share and Enjoy

Quinn “The Eskimo!” @ DTS @ Apple

Samasaur · December 8, 2019, 10:25pm

Just to clarify — this will not allow me to declare an entire dependency only for debug, correct?

(I'm +1 either way, as I think it'll be useful)

hartbit · December 9, 2019, 3:32pm

Correct. You can't directly declare a dependency only for debug: it will just indirectly only be for debug if it is only depended on by targets with a conditional configuration of Debug.

SDGGiesbrecht · December 9, 2019, 9:07pm

Which only means nothing from it will be built when you do swift build --configuration debug.

Such a dependency will still be fetched and still participate in the resolution of the package graph; all its own version constraints will still be relevant. This is important so that Package.resolved plays nice, and so you cannot accidentally end up with a package graph that works in debug but is unsolvable in release.

crspybits · August 29, 2020, 5:03pm

I'm using this new SE-0273 feature in Xcode 12 beta 6-- thanks for it! It really is important in a package I'm using between an iOS client and a Swift-based server. The package uses Kitura on the server, but I don't want that built on the client.

I have a syntax question-- From what I've seen of the documentation on this feature, we should use something like:

.product(name: "BluetoothLinux", condition: .when(platforms: [.linux])),

However, Xcode 12 beta 6 gives a syntax error unless I add a package parameter. E.g.,

.product(name: "Kitura", package: "Kitura", condition: .when(platforms: [.linux])),

Is this change documented somewhere?

Thanks!

SDGGiesbrecht · August 29, 2020, 10:55pm

The error message is due to SE‐0262. As an unrelated change that hadn’t been implemented yet when SE‐0273 was drafted, the examples in the text did not take it into account.

crspybits · August 30, 2020, 10:22pm

Thanks! Is there some comprehensive documentation, or is this waiting on the actual Swift 5.3 release?

SDGGiesbrecht · August 30, 2020, 11:24pm

The comprehensive API documentation of the latest release can be found here. It will be updated when 5.3 is officially released.

Michael_Brown · October 19, 2020, 2:53pm

Just found this, nice improvement to SPM

One question though, it's not 100% clear to me if this will resolve the need for the hack I had to do here:

github.com

trading-point/reactiveswift-composable-architecture/blob/master/Package.swift#L73-L78


      
          // swift-tools-version:5.5
          
          
import PackageDescription
          
          
let package = Package(
            name: "reactiveswift-composable-architecture",
            platforms: [
              .iOS(.v13),
              .macOS(.v10_15),
              .tvOS(.v13),
              .watchOS(.v6),
            ],
            products: [
              .library(
                name: "ComposableArchitecture",
                targets: ["ComposableArchitecture"]
              )
            ],
            dependencies: [
              .package(name: "Benchmark", url: "https://github.com/google/swift-benchmark", from: "0.1.0"),

This file has been truncated. show original

The problem I had, specifically, was that when running CI on Linux I had no way to ensure that swift test would only run the tests for ComposableArchitecture, and not the other two libraries which are specific to Apple platforms. Even when using --filter to restrict the tests, the other two Apple specific libraries would still attempt to get built and fail.

I guess that only having .linux in the platform conditions for ComposableArchitecture would work. When I switch to 5.3 tooling I will give it a try.

SDGGiesbrecht · October 19, 2020, 5:43pm

No, this does not prevent products from existing for a particular platform. It only prevents them from being included in the dependency graph by a higher‐level target. swift build will still attempt to build all the targets in the main package.

Hence it is only really useful across package boundaries, where unused dependencies are ignored. What it allows is for anyone who uses your ComposableArchitecture product as a dependency to declare it as a macOS‐only dependency in their manifest, and thus avoid having to duplicate your hack at each level.

I have oft wished for the type of platform exclusion you are trying to accomplish. But until then, I have found the best way for now is to wrap each source file in #if. That way the whole package can safely be built no matter how convoluted the cross‐compilation. (Attempting to cross‐compile from macOS to Linux will fail with your hack, because the manifest will compile for macOS, but the target will attempt to compile for Linux.)

Michael_Brown · October 20, 2020, 9:17am

The package declares 3 libraries as products, only one of which is ever going to be compatible with Linux. That library has the necessary #if os(Linux) or #if canImport(Combine) guards so it will compile properly for all platforms.

My problem is really just for running CI for Linux. I wanted a way to tell SwiftPM: just run ComposableArchitecture tests, and ignore any other products or targets in the package. Unfortunately swift test doesn't have the --target option that swift build does. Even using swift test --filter to restrict tests to a specific test target doesn't help, as SwiftPM will still try to build all the non-test targets first, even the ones that the filtered tests don't depend on.

SDGGiesbrecht · October 20, 2020, 5:03pm

For the other two libraries, I literally meant enclosing every single file entirely in #if so that they successfully build as empty libraries:

#if os(macOS)
  // All library content here.
#endif

Otherwise your hack is still necessary, and there is no proposal in the evolution process yet that would make it otherwise. If you want to improve your hack to also support cross‐compilation, see this post: