if (productReference != null) {
            s.addField("productReference", productReference);
        }
        s.addField("buildPhases", buildPhases);
        if (buildConfigurationList != null) {
            s.addField("buildConfigurationList", buildConfigurationList);
        }
    }

    public enum ProductType {
        INDEXER("org.gradle.product-type.indexer"),

    private final XCConfigurationList buildConfigurationList;
    private final String compatibilityVersion;
    private final String name;

    public PBXProject(String name) {
        this.name = Preconditions.checkNotNull(name);
        this.mainGroup = new PBXGroup("mainGroup", null, PBXReference.SourceTree.GROUP);
        this.targets = new ArrayList<>();
        this.buildConfigurationList = new XCConfigurationList();

            assert target.buildConfigurationList.buildConfigurations.size() == 1

            assert target.buildConfigurationList.buildConfigurations[0].name == "unbuildable"
            assert target.buildConfigurationList.buildConfigurations[0].buildSettings.ARCHS == null
            assert target.buildConfigurationList.buildConfigurations[0].buildSettings.CONFIGURATION_BUILD_DIR == null

        when:
        succeeds("xcode")

        then:
        def project = rootXcodeProject.projectFile
        project.targets.each { target ->
            assert target.buildConfigurationList.buildConfigurations.each {
                it.buildSettings.SWIFT_VERSION == expectedSwiftVersion
            }
        }

        where:
        sourceCompatibility   | expectedSwiftVersion