Swift Source Compatibility

Source compatibility is a strong goal for future Swift releases. To aid in this goal, a community owned source compatibility test suite serves to regression test changes to the compiler against a (gradually increasing) corpus of Swift source code. Projects added to this test suite are periodically built against the latest development versions of Swift as part of Swift’s continuous integration system, allowing Swift compiler developers to understand the compatibility impact their changes have on real-world Swift projects.

Current List of Projects

Adding Projects

The Swift source compatibility test suite is community driven, meaning that open source Swift project owners are encouraged to submit their projects that meet the acceptance criteria for inclusion in the test suite. Projects added to the suite serve as general source compatibility tests and are afforded greater protection against unintentional source breakage in future Swift releases.

Acceptance Criteria

To be accepted into the Swift source compatibility test suite, a project must:

Target Linux, macOS, or iOS/tvOS/watchOS device
Be an Xcode or Swift Package Manager project (Carthage and CocoaPods are currently unsupported but are being explored to be supported in the future)
Support building on either Linux or macOS
Be contained in a publicly accessible Git repository
Maintain a project branch that builds against the current Swift GM version compatibility mode and passes any unit tests
Have maintainers who will commit to resolve issues in a timely manner
Be compatible with the latest GM/Beta versions of Xcode and swiftpm
Add value not already included in the suite
Be licensed with one of the following permissive licenses:
- BSD
- MIT
- Apache License, version 2.0
- Eclipse Public License
- Mozilla Public License (MPL) 1.1
- MPL 2.0
- CDDL

Note: Linux compatibility testing in continuous integration is not available yet, but Linux projects are being accepted now.

Adding a Project

To add a project meeting the acceptance criteria to the suite, perform the following steps:

Ensure the project builds successfully at a chosen commit against the current Swift GM version.
Create a pull request against the source compatibility suite repository, modifying projects.json to include a reference to the project being added to the test suite.

The project index is a JSON file that contains a list of repositories containing Xcode and/or Swift Package Manager target actions.

To add a new Swift Package Manager project, use the following template:

{
  "repository": "Git",
  "url": "https://github.com/example/project.git",
  "path": "project",
  "branch": "main",
  "maintainer": "[email protected]",
  "compatibility": {
    "3.0": {
      "commit": "195cd8cde2bb717242b3081f9c367ccd0a2f0121"
    }
  },
  "platforms": [
    "Darwin"
  ],
  "actions": [
    {
      "action": "BuildSwiftPackage",
      "configuration": "release"
    },
    {
      "action": "TestSwiftPackage"
    }
  ]
}

The commit field specifies a commit hash to pin the repository to. It’s contained inside a compatibility field which specifies the version of Swift the commit is known to compile against. Multiple commits compatible with different versions of Swift can be specified.

The platforms field specifies the platforms that can be used to build the project. Linux and Darwin can currently be specified.

If tests aren’t supported, remove the test action entry.

To add a new Swift Xcode workspace, use the following template:

{
  "repository": "Git",
  "url": "https://github.com/example/project.git",
  "path": "project",
  "branch": "main",
  "maintainer": "[email protected]",
  "compatibility": {
    "3.0": {
      "commit": "195cd8cde2bb717242b3081f9c367ccd0a2f0121"
    }
  },
  "platforms": [
    "Darwin"
  ],
  "actions": [
    {
      "action": "BuildXcodeWorkspaceScheme",
      "workspace": "project.xcworkspace",
      "scheme": "project OSX",
      "destination": "platform=macOS",
      "configuration": "Release"
    },
    {
      "action": "BuildXcodeWorkspaceScheme",
      "workspace": "project.xcworkspace",
      "scheme": "project iOS",
      "destination": "generic/platform=iOS",
      "configuration": "Release"
    },
    {
      "action": "BuildXcodeWorkspaceScheme",
      "workspace": "project.xcworkspace",
      "scheme": "project tvOS",
      "destination": "generic/platform=tvOS",
      "configuration": "Release"
    },
    {
      "action": "BuildXcodeWorkspaceScheme",
      "workspace": "project.xcworkspace",
      "scheme": "project watchOS",
      "destination": "generic/platform=watchOS",
      "configuration": "Release"
    },
    {
      "action": "TestXcodeWorkspaceScheme",
      "workspace": "project.xcworkspace",
      "scheme": "project OSX",
      "destination": "platform=macOS"
    },
    {
      "action": "TestXcodeWorkspaceScheme",
      "workspace": "project.xcworkspace",
      "scheme": "project iOS",
      "destination": "platform=iOS Simulator,name=iPhone 7"
    },
    {
      "action": "TestXcodeWorkspaceScheme",
      "workspace": "project.xcworkspace",
      "scheme": "project tvOS",
      "destination": "platform=tvOS Simulator,name=Apple TV 1080p"
    }
  ]
}

To add a new Swift Xcode project, use the following template:

{
  "repository": "Git",
  "url": "https://github.com/example/project.git",
  "path": "project",
  "branch": "main",
  "maintainer": "[email protected]",
  "compatibility": {
    "3.0": {
      "commit": "195cd8cde2bb717242b3081f9c367ccd0a2f0121"
    }
  },
  "platforms": [
    "Darwin"
  ],
  "actions": [
    {
      "action": "BuildXcodeProjectTarget",
      "project": "project.xcodeproj",
      "target": "project",
      "destination": "generic/platform=iOS",
      "configuration": "Release"
    }
  ]
}

After adding a new project to the index, ensure it builds successfully at the pinned commits against the specified versions of Swift. In the examples, the commits are specified as being compatible with Swift 3.0, which is included in Xcode 8.0.

# Select Xcode 8.0 GM
sudo xcode-select -s /Applications/Xcode.app
# Build project at pinned commit against selected Xcode
./check project-path-field

On Linux, you can build against the Swift 3.0 release toolchain:

curl -O https://download.swift.org/swift-3.0-release/ubuntu1510/swift-3.0-RELEASE/swift-3.0-RELEASE-ubuntu15.10.tar.gz
tar xzvf swift-3.0-RELEASE-ubuntu15.10.tar.gz
./check project-path-field --swiftc swift-3.0-RELEASE-ubuntu15.10/usr/bin/swiftc

Maintaining Projects

In the event that Swift introduces a change that breaks source compatibility with a project (e.g., a compiler bug fix that fixes wrong behavior in the compiler), project maintainers are expected to update their projects and submit a new pull request with the updated commit hash within two weeks of being notified. Otherwise, unmaintained projects may be removed from the project index.

Pull Request Testing

Pull request testing against the Swift source compatibility suite can be executed by commenting with @swift-ci Please test source compatibility in a Swift pull request.

Building Projects

To build all projects against a specified Swift compiler locally, use the runner.py utility as shown below.

./runner.py --swift-branch main --projects projects.json --swift-version 3 --include-actions 'action.startswith("Build")' --swiftc path/to/swiftc

Use the --include-repos flag to build a specific project.

./runner.py --swift-branch main --projects projects.json --swift-version 3 --include-actions 'action.startswith("Build")' --include-repos 'path == "Alamofire"' --swiftc path/to/swiftc

By default, build output is redirected to per-action .log files in the current working directory. To change this behavior to output build results to standard out, use the --verbose flag.