Add filtering support to DirectoryTree

[davep]

Something that's come up on Discord this week, and something I could very much do with for what I'm working on at the moment: the ability to flexibly filter what goes into a DirectoryTree.

The idea being that it will allow a very flexible method of filtering, which could be as simple as checking extensions, or something like file permissions, or even more complex things like "exclude directories with files of a certain type in them, and also files over a certain size, and only files that are more than 2 weeks old, and...".

A simple example use of this would be to show the same directory, side-by-side, but the right hand side only shows directories and Markdown files, and also ignores any filesystem entries that start with a .).

from pathlib import Path

from typing import Iterable

from textual.app        import App, ComposeResult
from textual.containers import Horizontal
from textual.widgets    import Header, Footer, DirectoryTree

class MDDirectoryTree(DirectoryTree):

    def filter_paths(self, paths: Iterable[Path]) -> Iterable[Path]:
        """Filter the paths before adding them to the tree.

        Args:
            paths: The paths to be filtered.

        Returns:
            The filtered paths.
        """
        return [
            path for path in paths
            if not path.name.startswith( "." ) and path.is_dir() or (
                    path.is_file() and path.suffix == ".md"
            )
        ]

class DirTreeFilter( App[ None ] ):

    CSS = """
    DirectoryTree {
        width: 1fr;
    }
    """

    def compose( self ) -> ComposeResult:
        yield Header()
        yield Horizontal(
            DirectoryTree("."),
            MDDirectoryTree(".")
        )
        yield Footer()

if __name__ == "__main__":
    DirTreeFilter().run()

[davep]

Another change I'd like to make is to allow the reloading of the tree. It would be handy to be able to ask a directory tree, without needing to remove and mount a fresh one, to start again from a different root location. I notice that DirectoryTree.path seems to get set, is mutable, but is (as far as I can see) never used again. I'm thinking it might be a good idea to turn this into a setter/getter so that if the developer sets DirectoryPath.path it clears the tree, sets the new root, and populates again.

Edit to add: this should go into a followup PR.