Fix the drawing of Tree lines in respect to things being selected

CHANGELOG.md

@@ -10,11 +10,14 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 ### Fixed
 
 - Fixed crash when creating a `DirectoryTree` starting anywhere other than `.`
+- Fixed line drawing in `Tree` when `Tree.show_root` is `True` https://github.com/Textualize/textual/issues/2397
+- Fixed line drawing in `Tree` not marking branches as selected when first getting focus https://github.com/Textualize/textual/issues/2397
 
 ### Changed
 
 - The DataTable cursor is now scrolled into view when the cursor coordinate is changed programmatically https://github.com/Textualize/textual/issues/2459
 - run_worker exclusive parameter is now `False` by default https://github.com/Textualize/textual/pull/2470
+- Added `always_update` as an optional argument for `reactive.var`
 
 ## [0.23.0] - 2023-05-03
 

src/textual/reactive.py

@@ -76,11 +76,13 @@ def __rich_repr__(self) -> rich.repr.Result:
     def var(
         cls,
         default: ReactiveType | Callable[[], ReactiveType],
+        always_update: bool = False,
     ) -> Reactive:
         """A reactive variable that doesn't update or layout.
 
         Args:
             default: A default value or callable that returns a default.
+            always_update: Call watchers even when the new value equals the old value.
 
         Returns:
             A Reactive descriptor.
@@ -326,18 +328,21 @@ class var(Reactive[ReactiveType]):
     Args:
         default: A default value or callable that returns a default.
         init: Call watchers on initialize (post mount).
+        always_update: Call watchers even when the new value equals the old value.
     """
 
     def __init__(
         self,
         default: ReactiveType | Callable[[], ReactiveType],
         init: bool = True,
+        always_update: bool = False,
     ) -> None:
         super().__init__(
             default,
             layout=False,
             repaint=False,
             init=init,
+            always_update=always_update,
         )
 
 

src/textual/widgets/_tree.py

@@ -429,7 +429,7 @@ class Tree(Generic[TreeDataType], ScrollView, can_focus=True):
     """Show the root of the tree."""
     hover_line = var(-1)
     """The line number under the mouse pointer, or -1 if not under the mouse pointer."""
-    cursor_line = var(-1)
+    cursor_line = var(-1, always_update=True)
     """The line with the cursor, or -1 if no cursor."""
     show_guides = reactive(True)
     """Enable display of tree guide lines."""
@@ -976,8 +976,8 @@ def _render_line(self, y: int, x1: int, x2: int, base_style: Style) -> Strip:
                 "tree--guides-selected", partial=True
             )
 
-            hover = self.root._hover
-            selected = self.root._selected and self.has_focus
+            hover = line.path[0]._hover
+            selected = line.path[0]._selected and self.has_focus
 
             def get_guides(style: Style) -> tuple[str, str, str, str]:
                 """Get the guide strings for a given style.