Fix for interaction between pseudoclasses and widget-level render caches (#2155)

* Using pseudoclass state in DataTable cache keys

* Use full pseudo-class state on tree cache key

* Adding tests for Widget.get_pseudo_class_state

* Test hiding hover cursor when mouse cursor leaves DataTable

* Update CHANGELOG.md

CHANGELOG.md

@@ -12,6 +12,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 - Issue with parsing action strings whose arguments contained quoted closing parenthesis https://github.com/Textualize/textual/pull/2112
 - Issues with parsing action strings with tuple arguments https://github.com/Textualize/textual/pull/2112
 - Fix for tabs not invalidating https://github.com/Textualize/textual/issues/2125
+- Fix for interaction between pseudo-classes and widget-level render caches https://github.com/Textualize/textual/pull/2155
 
 ### Changed
 
@@ -35,6 +36,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 
 - Added auto_scroll attribute to TextLog https://github.com/Textualize/textual/pull/2127
 - Added scroll_end switch to TextLog.write https://github.com/Textualize/textual/pull/2127
+- Added `Widget.get_pseudo_class_state` https://github.com/Textualize/textual/pull/2155
 - Added Screen.ModalScreen which prevents App from handling bindings. https://github.com/Textualize/textual/pull/2139
 - Added TEXTUAL_LOG env var which should be a path that Textual will write verbose logs to (textual devtools is generally preferred) https://github.com/Textualize/textual/pull/2148
 - Added textual.logging.TextualHandler logging handler

src/textual/widget.py

@@ -179,6 +179,15 @@ class MountError(WidgetError):
     """Error raised when there was a problem with the mount request."""
 
 
+class PseudoClasses(NamedTuple):
+    """Used for render/render_line based widgets that use caching. This structure can be used as a
+    cache-key."""
+
+    enabled: bool
+    focus: bool
+    hover: bool
+
+
 @rich.repr.auto
 class Widget(DOMNode):
     """
@@ -2357,6 +2366,27 @@ class Widget(DOMNode):
                         break
                     node = node._parent
 
+    def get_pseudo_class_state(self) -> PseudoClasses:
+        """Get an object describing whether each pseudo class is present on this object or not.
+
+        Returns:
+            A PseudoClasses object describing the pseudo classes that are present.
+        """
+        node: MessagePump | None = self
+        disabled = False
+        while isinstance(node, Widget):
+            if node.disabled:
+                disabled = True
+                break
+            node = node._parent
+
+        pseudo_classes = PseudoClasses(
+            enabled=not disabled,
+            hover=self.mouse_over,
+            focus=self.has_focus,
+        )
+        return pseudo_classes
+
     def post_render(self, renderable: RenderableType) -> ConsoleRenderable:
         """Applies style attributes to the default renderable.
 

src/textual/widgets/_data_table.py

@@ -29,14 +29,13 @@ from ..reactive import Reactive
 from ..render import measure
 from ..scroll_view import ScrollView
 from ..strip import Strip
+from ..widget import PseudoClasses
 
-CellCacheKey: TypeAlias = "tuple[RowKey, ColumnKey, Style, bool, bool, int]"
+CellCacheKey: TypeAlias = (
-LineCacheKey: TypeAlias = (
+    "tuple[RowKey, ColumnKey, Style, bool, bool, int, PseudoClasses]"
-    "tuple[int, int, int, int, Coordinate, Coordinate, Style, CursorType, bool, int]"
-)
-RowCacheKey: TypeAlias = (
-    "tuple[RowKey, int, Style, Coordinate, Coordinate, CursorType, bool, bool, int]"
 )
+LineCacheKey: TypeAlias = "tuple[int, int, int, int, Coordinate, Coordinate, Style, CursorType, bool, int, PseudoClasses]"
+RowCacheKey: TypeAlias = "tuple[RowKey, int, Style, Coordinate, Coordinate, CursorType, bool, bool, int, PseudoClasses]"
 CursorType = Literal["cell", "row", "column", "none"]
 CellType = TypeVar("CellType")
 
@@ -609,6 +608,11 @@ class DataTable(ScrollView, Generic[CellType], can_focus=True):
         self._ordered_row_cache: LRUCache[tuple[int, int], list[Row]] = LRUCache(1)
         """Caches row ordering - key is (num_rows, update_count)."""
 
+        self._pseudo_class_state = PseudoClasses(False, False, False)
+        """The pseudo-class state is used as part of cache keys to ensure that, for example,
+        when we lose focus on the DataTable, rules which apply to :focus are invalidated
+        and we prevent lingering styles."""
+
         self._require_update_dimensions: bool = False
         """Set to re-calculate dimensions on idle."""
         self._new_rows: set[RowKey] = set()
@@ -1558,7 +1562,15 @@ class DataTable(ScrollView, Generic[CellType], can_focus=True):
             row_key = self._row_locations.get_key(row_index)
 
         column_key = self._column_locations.get_key(column_index)
-        cell_cache_key = (row_key, column_key, style, cursor, hover, self._update_count)
+        cell_cache_key = (
+            row_key,
+            column_key,
+            style,
+            cursor,
+            hover,
+            self._update_count,
+            self._pseudo_class_state,
+        )
 
         if cell_cache_key not in self._cell_render_cache:
             style += Style.from_meta({"row": row_index, "column": column_index})
@@ -1614,6 +1626,7 @@ class DataTable(ScrollView, Generic[CellType], can_focus=True):
             show_cursor,
             self._show_hover_cursor,
             self._update_count,
+            self._pseudo_class_state,
         )
 
         if cache_key in self._row_render_cache:
@@ -1786,6 +1799,7 @@ class DataTable(ScrollView, Generic[CellType], can_focus=True):
             self.cursor_type,
             self._show_hover_cursor,
             self._update_count,
+            self._pseudo_class_state,
         )
         if cache_key in self._line_cache:
             return self._line_cache[cache_key]
@@ -1810,6 +1824,10 @@ class DataTable(ScrollView, Generic[CellType], can_focus=True):
         self._line_cache[cache_key] = strip
         return strip
 
+    def render_lines(self, crop: Region) -> list[Strip]:
+        self._pseudo_class_state = self.get_pseudo_class_state()
+        return super().render_lines(crop)
+
     def render_line(self, y: int) -> Strip:
         width, height = self.size
         scroll_x, scroll_y = self.scroll_offset
@@ -1842,6 +1860,9 @@ class DataTable(ScrollView, Generic[CellType], can_focus=True):
             except KeyError:
                 pass
 
+    def on_leave(self, event: events.Leave) -> None:
+        self._set_hover_cursor(False)
+
     def _get_fixed_offset(self) -> Spacing:
         """Calculate the "fixed offset", that is the space to the top and left
         that is occupied by fixed rows and columns respectively. Fixed rows and columns

src/textual/widgets/_tree.py

@@ -925,6 +925,10 @@ class Tree(Generic[TreeDataType], ScrollView, can_focus=True):
                 self.cursor_line = -1
         self.refresh()
 
+    def render_lines(self, crop: Region) -> list[Strip]:
+        self._pseudo_class_state = self.get_pseudo_class_state()
+        return super().render_lines(crop)
+
     def render_line(self, y: int) -> Strip:
         width = self.size.width
         scroll_x, scroll_y = self.scroll_offset
@@ -952,7 +956,7 @@ class Tree(Generic[TreeDataType], ScrollView, can_focus=True):
             is_hover,
             width,
             self._updates,
-            self.has_focus,
+            self._pseudo_class_state,
             tuple(node._updates for node in line.path),
         )
         if cache_key in self._line_cache:

tests/test_data_table.py

@@ -652,6 +652,23 @@ async def test_hover_coordinate():
         assert table.hover_coordinate == Coordinate(1, 0)
 
 
+async def test_hover_mouse_leave():
+    """When the mouse cursor leaves the DataTable, there should be no hover highlighting."""
+    app = DataTableApp()
+    async with app.run_test() as pilot:
+        table = app.query_one(DataTable)
+        table.add_column("ABC")
+        table.add_row("123")
+        await pilot.pause()
+        assert table.hover_coordinate == Coordinate(0, 0)
+        # Hover over a cell, and the hover cursor is visible
+        await pilot.hover(DataTable, offset=Offset(1, 1))
+        assert table._show_hover_cursor
+        # Move our cursor away from the DataTable, and the hover cursor is hidden
+        await pilot.hover(DataTable, offset=Offset(-1, -1))
+        assert not table._show_hover_cursor
+
+
 async def test_header_selected():
     """Ensure that a HeaderSelected event gets posted when we click
     on the header in the DataTable."""

tests/test_widget.py

@@ -7,7 +7,7 @@ from textual.containers import Container
 from textual.css.errors import StyleValueError
 from textual.css.query import NoMatches
 from textual.geometry import Size
-from textual.widget import MountError, Widget
+from textual.widget import MountError, PseudoClasses, Widget
 from textual.widgets import Label
 
 
@@ -178,6 +178,39 @@ def test_widget_mount_ids_must_be_unique_mounting_multiple_calls(parent):
         parent.mount(widget2)
 
 
+def test_get_pseudo_class_state():
+    widget = Widget()
+    pseudo_classes = widget.get_pseudo_class_state()
+    assert pseudo_classes == PseudoClasses(enabled=True, focus=False, hover=False)
+
+
+def test_get_pseudo_class_state_disabled():
+    widget = Widget(disabled=True)
+    pseudo_classes = widget.get_pseudo_class_state()
+    assert pseudo_classes == PseudoClasses(enabled=False, focus=False, hover=False)
+
+
+def test_get_pseudo_class_state_parent_disabled():
+    child = Widget()
+    _parent = Widget(child, disabled=True)
+    pseudo_classes = child.get_pseudo_class_state()
+    assert pseudo_classes == PseudoClasses(enabled=False, focus=False, hover=False)
+
+
+def test_get_pseudo_class_state_hover():
+    widget = Widget()
+    widget.mouse_over = True
+    pseudo_classes = widget.get_pseudo_class_state()
+    assert pseudo_classes == PseudoClasses(enabled=True, focus=False, hover=True)
+
+
+def test_get_pseudo_class_state_focus():
+    widget = Widget()
+    widget.has_focus = True
+    pseudo_classes = widget.get_pseudo_class_state()
+    assert pseudo_classes == PseudoClasses(enabled=True, focus=True, hover=False)
+
+
 # Regression test for https://github.com/Textualize/textual/issues/1634
 async def test_remove():
     class RemoveMeLabel(Label):