Will not build in generated Xcode projects

[ckornher]

This may not be a bug in this package, but the following sequence of commands:

swift package init
# ... add dependencies as described in `README.md`
swift package update
swift package generate-xcodeproj

generates an Xcode project that fails to build with this error:

Undefined symbols for architecture x86_64:
  "_swift_release_n", referenced from:
      __sa_release_n in _AtomicsShims.o
  "_swift_retain_n", referenced from:
      __sa_retain_n in _AtomicsShims.o
ld: symbol(s) not found for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)

This is using the code 12 beta 2 toolchain. A project in Xcode 12 beta2 builds correctly when this package is added via the Swift Package tab.

Package.swift:

// swift-tools-version:5.3
// The swift-tools-version declares the minimum version of Swift required to build this package.

import PackageDescription

let package = Package(
    name: "swift_atomic_test",
    products: [
        // Products define the executables and libraries a package produces, and make them visible to other packages.
        .library(
            name: "swift_atomic_test",
            targets: ["swift_atomic_test"]),
    ],
    dependencies: [
        .package(
          url: "https://github.com/apple/swift-atomics.git", 
          from: "0.0.1"
        )
    ],
    targets: [
        // Targets are the basic building blocks of a package. A target can define a module or a test suite.
        // Targets can depend on other targets in this package, and on products in packages this package depends on.
        .target(
            name: "swift_atomic_test",
            dependencies: [
                .product(name: "Atomics", package: "swift-atomics")
            ]
        ),
        .testTarget(
            name: "swift_atomic_testTests",
            dependencies: ["swift_atomic_test"]
        )
    ]
)

[ktoso]

swift package generate-xcodeproj

Nowadays I don't think you should / need to rely on generating an Xcode project since Xcode is capable of just opening the SPM project directly: open Package.swift.

I can confirm that works just fine :)

[lorentey]

The workaround for now is to manually add libswiftCore.dylib to the _AtomicsShims target's linked library list.

The root cause is that the module relies on a couple of symbols exported by the Swift Runtime that aren't part of its public interface.

[ckornher]

swift package generate-xcodeproj

Nowadays I don't think you should / need to rely on generating an Xcode project since Xcode is capable of just opening the SPM project directly: open Package.swift.

I can confirm that works just fine :)

swift package generate-xcodeproj is still a standard command in the SPM and should be supported by Apple packages.

A little bit more detail as to why this is important to me, on the off-chance that someone from the Xcode team is reading this :)

Xcode does not, AFAIK, allow package dependencies to be editable. e.g. https://developer.apple.com/forums/thread/117570

I am working on a project with multiple layers of packages (for good reasons I won't go into here) I use a scripted workflow that puts the dependencies into edit mode with these commands:

swift package edit MRPCommon
swift package edit MRPConfiguration
swift package edit MRPProtocol
swift package edit MRPRuntime
swift package edit MRPInMemoryComponents
swift package edit MRPSwiftBinding

I can edit all of these packages in one Xcode project (in addition to the main multi-platform package), because it is generated after these commands are run. Although there are 7 git repos to deal with, there is only one Xcode project and edits do not have to be committed/pushed/pulled between repos before running.

This is why this support is important to me. Hopefully the need for the workaround is temporary. Ideally Xcode will support editable dependencies someday.

[lorentey]

@ckornher Thanks for reporting this issue! I believe it is now fixed on main. Please reopen if you can still reproduce it with the current head revision.

[lorentey]

Unfortunately the fix triggered a compiler issue (https://bugs.swift.org/browse/SR-13708), so I'll need to revert it.

[troughton]

I can edit all of these packages in one Xcode project (in addition to the main multi-platform package), because it is generated after these commands are run. Although there are 7 git repos to deal with, there is only one Xcode project and edits do not have to be committed/pushed/pulled between repos before running.

@ckornher One solution for this is to use a single Xcode workspace and drag all of the packages into that workspace. Xcode should then use the local copies to satisfy any dependencies rather than fetching them from the remotes.

[lorentey]

In case Xcode project generation is still a thing these days, getting rid of the C module with something along the lines of https://github.com/apple/swift-atomics/pull/74 will likely eliminate these issues.

However, this will require some Swift compiler & stdlib work, so it will take additional time.

[lorentey]

I believe https://github.com/apple/swift-atomics/pull/97 also resolves this (on the off chance the package works with a toolchain version that still supports generate-xcodeproj -- that command has been removed in some release before Swift 5.9.)