Selecting the root of a Tree does not highlight descendants.

[davep]

The Tree widget will highlight the lines that descend from the selected node, but at the moment it doesn't seem to do it from the top level. For example, consider this:

where the topmost node is selected but no lines are highlighted, against this:

where a node one level down is highlighted and all the line below are highlighted.

We should review this, decide exactly what is supposed to happen, and have it be the same for all levels.

Also @darrenburns has raised the extra question of if it might be an idea to have it such that it only highlights the immediate lines vs all the lines in the tree below.

[willmcgugan]

The expected behaviour is to highlight all descendants, including the root.

Let's fix that first.

[davep]

While building up some test code for this, I think I've either uncovered three problems here, or three symptoms of an underlying problem. Using this code:

from textual.app          import App, ComposeResult
from textual.containers   import Horizontal
from textual.widgets      import Header, Footer, Tree
from textual.widgets.tree import TreeNode

class TreeLinesTestApp( App[ None ] ):

    CSS = """
    Tree {
        border: round red;
    }

    Tree:focus {
        border: double green;
    }
    """

    def compose( self ) -> ComposeResult:
        yield Header()
        with Horizontal():
            yield Tree("Root", id="root")
            yield Tree("Root", id="no-root")
        yield Footer()

    def populate( self, node: TreeNode, limit: int=3 ) -> Tree:
        for n in range( limit ):
            self.populate( node.add( str( n ) ), limit-1 )
        return node.tree

    def on_mount( self ) -> None:
        self.query_one( "#no-root", Tree ).show_root = False
        self.populate( self.query_one( "#root", Tree ).root ).root.expand_all()
        self.populate( self.query_one( "#no-root", Tree ).root ).root.expand_all()

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

I get this effect:

Screen.Recording.2023-05-03.at.14.15.37.mov

Note the following things:

• The tree that is showing the root does highlight all of the lines when the root is selected
• But... it doesn't do this by default, only if you move off the root and back onto it again
• The tree that doesn't show the root never highlights from the top-level down, only from the second level.

[davep]

Should also be noted that, within the bounds of what it means to hover, the same issue affects the style of lines and mouse hover too.

[davep]

Possibly related, or at least related to one of the effects shown above: the shows-root Tree not showing a selected colour for all line when first focused might make some sense, in that selected in _render_line is predicated on self.has_focus. I'm still not 100% sure what would cause the lines to be drawn in regards to focus change (need to dig into that), but an attempt to force it to change with the addition of _on_focus that invalidates and redraws the tree seem to have no difference because, as best as I can tell, when _on_focus fires self.has_focus isn't yet true.

Need to keep this in mind as I dive deeper.

[davep]

Just to clarify for myself here, as far as I can tell there are two distinct issues at play here:

1. Tree doesn't handle showing lines as being selected when focus is first received.
2. Tree doesn't properly show lines as being selected from the top level when show_root is False

It's been a bit too easy to be distracted by one while trying to reason about the other.

[github-actions]

Don't forget to star the repository!

Follow @textualizeio for Textual updates.