.willBecomeAnErrorInGradle9()
            .withUpgradeGuideSection(8, "deprecate_self_resolving_dependency")
            .nagUser();

        return source.getFiles();
    }

    @Override
    @Deprecated
    public Set<File> resolve(boolean transitive) {
        DeprecationLogger.deprecate("Directly resolving a file collection dependency's files")

    SourceElement getGreeter() {
        return app.greeter
    }

    SourceElement getLogger() {
        return app.logger
    }

    @Override
    List<SourceFile> getFiles() {
        return Lists.newArrayList(Iterables.concat(super.getFiles(), app.greeter.files, app.logger.files, sum.files, multiply.files))
    }

        when:
        Set<File> files = collection.getFiles()

        then:
        collection.toString() == 'test files'
        files == [tmpDir.file('abc')] as Set
    }

    def 'resolving collection source #description can return null'() {
        def collection = factory.resolving('test files', input)

        when:
        Set<File> files = collection.getFiles()

        then:
        files.isEmpty()

        return collect(getSourceFiles().getFiles(), File::getAbsolutePath);
    }

    @Internal
    public Set<File> getResourceFiles() {
        Set<File> allResources = new LinkedHashSet<File>();
        for (VisualStudioTargetBinary binary : configurations.keySet()) {
            allResources.addAll(binary.getResourceFiles().getFiles());
        }
        return allResources;
    }

        for (int i = 0; i < artifactSets.length; i++) {
            fileCollections[i] = (FileCollectionInternal) artifactSets[i].getFiles();
        }
        files = new UnionFileCollection(taskDependencyFactory, fileCollections);
    }

    @Override
    public FileCollection getFiles() {
        return files;
    }

    final library = new SwiftGreeterWithOptionalFeature()
    final application = new SwiftMainWithOptionalFeature(library.withFeatureDisabled()) {
        @Override
        List<SourceFile> getFiles() {
            return super.getFiles().collect {
                sourceFile(it.path, it.name, "import Greeter\n${it.content}")
            }
        }
    }

    AppElement withFeatureEnabled() {

        } else if (expression == "getFiles { true }") {

    }

    @Override
    public boolean getHasInputs() {
        throw failWithUnsupportedMethod("getHasInputs()");
    }

    @Override
    public FileCollection getFiles() {
        throw failWithUnsupportedMethod("getFiles()");
    }

    @Override
    public TaskInputFilePropertyBuilder files(Object... paths) {
        throw failWithUnsupportedMethod("files(Object...)");
    }

    @Override

        when:
        FileCollection sum = collection1.plus(collection2)

        then:
        assertThat(sum, instanceOf(UnionFileCollection.class))
        assertThat(sum.getFiles(), equalTo(toLinkedSet(file1, file2, file3)))
    }

    def "can add collections using + operator"() {
        File file1 = new File("f1")
        File file2 = new File("f2")
        File file3 = new File("f3")

        left.visitDependencies(context);
    }

    @Override
    protected Set<File> getIntrinsicFiles() {
        Set<File> files = new LinkedHashSet<File>(left.getFiles());
        files.removeAll(right.getFiles());
        return files;
    }

    @Override
    public boolean contains(File file) {
        return left.contains(file) && !right.contains(file);
    }