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.

The current list of projects can be viewed on Swift.org.

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.

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

1. Target Linux, macOS, or iOS/tvOS/watchOS device
2. Be an Xcode or Swift Package Manager project (Carthage and CocoaPods are currently unsupported but are being explored to be supported in the future)
3. Support building on either Linux or macOS
4. Be contained in a publicly accessible git repository
5. Maintain a project branch that builds against Swift 4.2 compatibility mode and passes any unit tests
6. Have maintainers who will commit to resolve issues in a timely manner
7. Be compatible with the latest GM/Beta versions of Xcode and swiftpm
8. Add value not already included in the suite
9. 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.

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

1. Ensure the project builds successfully at a chosen commit against Swift 4.2 GM
2. 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": "master",
  "maintainer": "[email protected]",
  "compatibility": [
    {
      "version": "4.2",
      "commit": "195cd8cde2bb717242b3081f9c367ccd0a2f0121"
    }
  ],
  "platforms": [
    "Darwin"
  ],
  "actions": [
    {
      "action": "BuildSwiftPackage",
      "configuration": "release"
    },
    {
      "action": "TestSwiftPackage"
    }
  ]
}

The compatibility field contains a list of version dictionaries, each containing a Swift version and a commit. Commits are checked out before building a project in the associated Swift version compatibility mode. The Swift version is the earliest version of Swift known to compile the project at the given commit. The goal is to have multiple commits at different points in a project's history that are compatible with all supported Swift version compatibility modes.

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": "master",
  "maintainer": "[email protected]",
  "compatibility": [
    {
      "version": "4.2",
      "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": "master",
  "maintainer": "[email protected]",
  "compatibility": [
    {
      "version": "4.2",
      "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 4.2, which is included in Xcode 10.

# Select Xcode 10 GM
sudo xcode-select -s /Applications/Xcode.app
# Build project at pinned commit against selected Xcode
./project_precommit_check project-path-field --earliest-compatible-swift-version 4.2

On Linux, you can build against the Swift 4.2 release toolchain:

curl -O https://swift.org/builds/swift-4.2-release/ubuntu1604/swift-4.2-RELEASE/swift-4.2-RELEASE-ubuntu16.04.tar.gz
tar xzvf swift-4.2-RELEASE-ubuntu16.04.tar.gz
./project_precommit_check project-path-field --earliest-compatible-swift-version 4.2 --swiftc swift-4.2-RELEASE-ubuntu15.10/usr/bin/swiftc

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

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 --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 --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.

When an action is expected to fail for an extended period of time, it's important to mark the action as an expected failure to make new failures more visible.

To mark an action as an expected failure, add an xfail entry for the correct Swift version and branch to the failing actions, associating each with a link to a JIRA issue reporting the relevant failure. The following is an example of an action that's XFAIL'd when building against Swift main branch in 4.2 compatibility mode.

{
  "repository": "Git",
  "url": "https://github.com/example/project.git",
  "path": "project",
  "branch": "master",
  "maintainer": "[email protected]",
  "compatibility": [
    {
      "version": "4.2",
      "commit": "195cd8cde2bb717242b3081f9c367ccd0a2f0121"
    }
  ],
  "platforms": [
    "Darwin"
  ],
  "actions": [
    {
      "action": "BuildXcodeProjectTarget",
      "project": "project.xcodeproj",
      "target": "project",
      "destination": "generic/platform=iOS",
      "configuration": "Release",
      "xfail": {
        "issue": "https://bugs.swift.org/browse/SR-9999",
        "compatibility": "4.2",
        "branch": "main"
      }
    }
  ]
}

Additional Swift branches and versions can be added to XFAIL different configurations. The currently supported fields for XFAIL entries are:

• "compatibility": the Swift version(s) it fails with, e.g. "4.0"
• "branch": the branch(es) of the swift compiler it fails with, e.g. "swift-5.1-branch"
• "platform": the platform(s) it fails on, e.g. "Darwin" or "Linux"
• "configuration": the build configuration(s) if fails with, i.e. "release" or "debug")

Values can either be a single string literal or a list of alternative string literals to match against. For example the below action is expected to fail on both main and swift-5.1-branch in both 4.0 and 5.1 compatibility modes:

...
{
  "action": "BuildXcodeProjectTarget",
  "project": "project.xcodeproj",
  "target": "project",
  "destination": "generic/platform=iOS",
  "configuration": "Release",
  "xfail": {
    "issue": "https://bugs.swift.org/browse/SR-9999",
    "compatibility": ["4.0", "5.1"],
    "branch": ["main", "swift-5.1-branch"]
  }
}
...

If an action is failing for different reasons in different configurations, the value of the action's "xfail" entry can also become a list rather than a single entry. In this case the "issue" of the first item that matches will be reported. In the below example any failure on Linux would be reported as SR-7777, while a failure on other platforms would be reported as SR-8888 using a toolchain built from the master branch and SR-9999 using a toolchain built from swift-5.1-branch. If the entries were in the reverse order, SR-7777 would only be reported for Linux failures with toolchains built from a branch other than main or swift-5.1-branch.

...
{
  "action": "BuildXcodeProjectTarget",
  "project": "project.xcodeproj",
  "target": "project",
  "destination": "generic/platform=iOS",
  "configuration": "Release",
  "xfail": [
    {
      "issue": "https://bugs.swift.org/browse/SR-7777",
      "platform": "Linux"
    },
    {
      "issue": "https://bugs.swift.org/browse/SR-8888",
      "branch": "main"
    },
    {
      "issue": "https://bugs.swift.org/browse/SR-9999",
      "branch": "swift-5.1-branch"
    }
  ]
}
...