filter.copyFrom(patterns);
        return new FilteredMinimalFileTree(filter, tree);
    }

    @Override
    public void visitStructure(MinimalFileTreeStructureVisitor visitor, FileTreeInternal owner) {
        tree.visitStructure(new MinimalFileTreeStructureVisitor() {
            @Override
            public void visitFileTree(File root, PatternSet patterns, FileTreeInternal fileTree) {

    /**
     * Visits the elements of this tree, in depth-first prefix order.
     */
    void visit(FileVisitor visitor);

    void visitStructure(MinimalFileTreeStructureVisitor visitor, FileTreeInternal owner);

    interface MinimalFileTreeStructureVisitor {

        /**
         * Visits a file tree at a root file on the file system (potentially filtered).
         */

        def intersectPatterns = Mock(PatternSet)
        def visitor = Mock(MinimalFileTree.MinimalFileTreeStructureVisitor)

        when:
        tree.visitStructure(visitor, owner)

        then:
        1 * source.visitStructure(_, _) >> { MinimalFileTree.MinimalFileTreeStructureVisitor nestedVisitor, FileTreeInternal o ->
            nestedVisitor.visitFileTree(dir, sourcePatterns, o)
        }

    abstract protected Provider<File> getBackingFileProvider();

    private File getBackingFile() {
        return getBackingFileProvider().get();
    }

    @Override
    public void visitStructure(MinimalFileTreeStructureVisitor visitor, FileTreeInternal owner) {
        File backingFile = getBackingFile();
        visitor.visitFileTreeBackedByFile(backingFile, owner, this);
    }

    @Override

    def "visits structure when backing file is known"() {
        def owner = Stub(FileTreeInternal)
        def visitor = Mock(MinimalFileTree.MinimalFileTreeStructureVisitor)
        def backingFile = tmpDir.createFile("thing.bin")

        def fileTree = new TestArchiveFileTree(TestDecompressionCoordinators.decompressionCoordinator(tmpDir.createDir("cache-dir")), backingFile)

    }

    def "visiting structure eagerly generates content when listener requests content but does not use it"() {
        def owner = Stub(FileTreeInternal)
        def visitor = Mock(MinimalFileTree.MinimalFileTreeStructureVisitor)
        def tmpDir = tmpDir.createDir("dir")
        def generatedFile = tmpDir.file("file.bin")
        def generationListener = Mock(Action)
        def contentWriter = Mock(Action)

        visitor.accept(this);
    }

    @Override
    protected void visitContents(FileCollectionStructureVisitor visitor) {
        tree.visitStructure(new MinimalFileTree.MinimalFileTreeStructureVisitor() {

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

    }

    @Override
    public PatternSet getPatterns() {
        return new PatternSet().include(includePattern).exclude(excludeSpec);
    }

    @Override
    public void visitStructure(MinimalFileTreeStructureVisitor visitor, FileTreeInternal owner) {
        visitor.visitFileTree(baseDir, getPatterns(), owner);
    }

    @Override
    public void visit(FileVisitor visitor) {

    }

    @Override
    public DirectoryFileTree getMirror() {
        return new DirectoryFileTree(getFile(), new PatternSet(), fileSystem);
    }

    @Override
    public void visitStructure(MinimalFileTreeStructureVisitor visitor, FileTreeInternal owner) {
        visitor.visitFileTree(getFile(), new PatternSet(), owner);
    }

    @Override
    public void visit(FileVisitor visitor) {

    @Override
    public boolean contains(File file) {
        return DirectoryTrees.contains(fileSystem, this, file) && file.isFile();
    }

    @Override
    public void visitStructure(MinimalFileTreeStructureVisitor visitor, FileTreeInternal owner) {
        visitor.visitFileTree(dir, patternSet, owner);
    }

    @Override
    public void visit(FileVisitor visitor) {