// TODO - add some convenient way to visit the files of the tree without collecting them into a set
                files.addAll(fileTree.getFiles());
            }

            @Override
            public void visitFileTree(File root, PatternSet patterns, FileTreeInternal fileTree) {
                addTreeContents(fileTree);
            }

            @Override

            return fileTrees.get(0);
        } else {
            return new DefaultCompositeFileTree(taskDependencyFactory, patternSetFactory, ImmutableList.copyOf(fileTrees));
        }
    }

    @Override
    public FileTreeInternal treeOf(MinimalFileTree tree) {
        return new FileTreeAdapter(tree, listener, taskDependencyFactory, patternSetFactory);
    }

    @Override

        }
        where:
        method | path
        "dir"  | "output-file.txt"
        "dirs" | "output-file.txt"
    }

    @Issue("https://github.com/gradle/gradle/issues/15679")
    def "fileTrees with regular file roots cannot be used as output files"() {
        enableProblemsApiCheck()
        expectReindentedValidationMessage()
        buildScript """
            task myTask {

    }

    @Issue("https://github.com/gradle/gradle/issues/2180")
    def "fileTrees can be used as output files"() {
        given:
        buildScript """
            task myTask {
                inputs.file file('input.txt')
                outputs.files fileTree(dir: 'build', include: 'output.txt')
                def layout = project.layout
                doLast {

        def visitor = Mock(MinimalFileTree.MinimalFileTreeStructureVisitor)

        fileTree = new SingleIncludePatternFileTree(tempDir.testDirectory, "pattern", spec)

        when:
        fileTree.visitStructure(visitor, owner)

        then:
        1 * visitor.visitFileTree(tempDir.testDirectory, _, owner) >> { dir, patterns, fileTree ->
            assert patterns.includes == ["pattern"] as Set

        }

        expect:
        fileTree.contains(included1)
        fileTree.contains(included2)
        !fileTree.contains(testDir)
        !fileTree.contains(included1.parentFile)
        !fileTree.contains(included2.parentFile)
        !fileTree.contains(new File(testDir, 'does not exist'))
        !fileTree.contains(testDir.parentFile)
        !fileTree.contains(new File('something'))
    }

    override fun visitFileTree(root: File, patterns: PatternSet, fileTree: FileTreeInternal) =
        unsupportedFileTree(fileTree)

    override fun visitFileTreeBackedByFile(file: File, fileTree: FileTreeInternal, sourceTree: FileSystemMirroringFileTree) =
        unsupportedFileTree(fileTree)

    private
    fun unsupportedFileTree(fileTree: FileTreeInternal): Nothing =
        throw UnsupportedOperationException(

    }

    @Override
    public ConfigurableFileTree fileTree(Object baseDir) {
        ConfigurableFileTree fileTree = fileCollectionFactory.fileTree();
        fileTree.from(baseDir);
        return fileTree;
    }

    @Override
    public ConfigurableFileTree fileTree(Map<String, ?> args) {
        ConfigurableFileTree fileTree = fileCollectionFactory.fileTree();
        ConfigureUtil.configureByMap(args, fileTree);

        delegate.group = group
    }

    override fun fileTree(baseDir: Any): ConfigurableFileTree =
        delegate.fileTree(baseDir)

    override fun fileTree(baseDir: Any, configureClosure: Closure<*>): ConfigurableFileTree =
        delegate.fileTree(baseDir, configureClosure)

    override fun fileTree(baseDir: Any, configureAction: Action<in ConfigurableFileTree>): ConfigurableFileTree =

        given:
        def project = project('root', null, Stub(GradleInternal))
        def action = { fileTree -> fileTree.builtBy('something') } as Action<ConfigurableFileTree>

        when:
        def fileTree = project.fileTree('path', action)

        then:
        fileTree.builtBy == ['something'] as Set
    }

    def "can configure ant tasks with an Action"() {
        given: