Tree.scroll_to_line() off-by-2 error in x coordinate?

[rcrowell]

Have you checked closed issues? https://github.com/Textualize/textual/issues?q=is%3Aissue+is%3Aclosed

Yes.

Description

Pressing up/down to change the highlighted row in a Tree widget will scroll to strange x-offsets when node labels are wide.

For instance, render this Tree:

And then press the down key to highlight the first leaf of root:

Expected: Content scrolled so that "a" is the first visible character in the first leaf
Observed: Content scrolled so that "c" is the first visible character in the first leaf

Here is my example app:

from textual.app import App
from textual.widgets import Tree


class ExampleApp(App):
    CSS = '''
    Tree {
        width: 16;
    }
    '''

    def compose(self):
        tree = Tree(label='root')
        tree.root.add_leaf('abcdefghijklmnopqrstuvwxyz')
        child = tree.root.add('antidisestablishmentarianism')
        child.add_leaf('interesting')
        child.add_leaf('very interesting')
        child.add_leaf('very very interesting')
        tree.root.add_leaf('not long')
        tree.root.add_leaf('looooooooooooooooong')
        # Expand nodes.
        tree.root.expand()
        child.expand()
        yield tree

    
if __name__ == '__main__':
    app = ExampleApp()
    app.run()

Possible Cause

This is the function in question:

class _TreeLine(Generic[TreeDataType]):
    def _get_guide_width(self, guide_depth: int, show_root: bool) -> int:                                                                                                                                                                                                                      
        if show_root:
            return 2 + (max(0, len(self.path) - 1)) * guide_depth
        else:
            guides = 2
            if len(self.path) > 1:
                guides += (len(self.path) - 1) * guide_depth

        return guides

Questions:

1. What is the significance of "2" in the above? Was this intended to ensure the down arrow is visible for non-leaf nodes? Or perhaps the DirectoryTree widget relies on this to show the file/folder icons?
2. Kind of an aside, but is there any case where the boolean value of show_root changes the result? Is the calculation not the same in either case?

Fix?

rcrowell@ec2207c seems to fix the off-by-two error in my testing. I may be missing something super obvious though, as this is my first weekend using textual...

Diagnostic

$ textual diagnose
<!-- This is valid Markdown, please paste the following directly in to a GitHub issue -->
# Textual Diagnostics

## Versions

| Name    | Value  |
|---------|--------|
| Textual | 0.71.0 |
| Rich    | 13.7.1 |

## Python

| Name           | Value                                     |
|----------------|-------------------------------------------|
| Version        | 3.10.4                                    |
| Implementation | CPython                                   |
| Compiler       | GCC 11.2.0                                |
| Executable     | /home/rcrowell/bemix/bemix-env/bin/python |

## Operating System

| Name    | Value                                                   |
|---------|---------------------------------------------------------|
| System  | Linux                                                   |
| Release | 6.5.11-8-pve                                            |
| Version | #1 SMP PREEMPT_DYNAMIC PMX 6.5.11-8 (2024-01-30T12:27Z) |

## Terminal

| Name                 | Value          |
|----------------------|----------------|
| Terminal Application | *Unknown*      |
| TERM                 | xterm-256color |
| COLORTERM            | *Not set*      |
| FORCE_COLOR          | *Not set*      |
| NO_COLOR             | *Not set*      |

## Rich Console options

| Name           | Value               |
|----------------|---------------------|
| size           | width=80, height=24 |
| legacy_windows | False               |
| min_width      | 1                   |
| max_width      | 80                  |
| is_terminal    | True                |
| encoding       | utf-8               |
| max_height     | 24                  |
| justify        | None                |
| overflow       | None                |
| no_wrap        | False               |
| highlight      | None                |
| markup         | None                |
| height         | None                |

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[darrenburns]

Good catch - thanks. I've opened a PR for this.

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