Merge pull request #1627 from Textualize/fix-1616

Changing overflow programmatically updates layout

CHANGELOG.md

@@ -11,6 +11,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 
 - Fixed stuck screen  https://github.com/Textualize/textual/issues/1632
 - Fixed relative units in `grid-rows` and `grid-columns` being computed with respect to the wrong dimension https://github.com/Textualize/textual/issues/1406
+- Programmatically setting `overflow_x`/`overflow_y` refreshes the layout correctly https://github.com/Textualize/textual/issues/1616
 - Fixed double-paste into `Input` https://github.com/Textualize/textual/issues/1657
 
 ## [0.10.1] - 2023-01-20

src/textual/css/_style_properties.py

@@ -704,6 +704,9 @@ def __get__(self, obj: StylesBase, objtype: type[StylesBase] | None = None) -> s
         """
         return obj.get_rule(self.name, self._default)
 
+    def _before_refresh(self, obj: StylesBase, value: str | None) -> None:
+        """Do any housekeeping before asking for a layout refresh after a value change."""
+
     def __set__(self, obj: StylesBase, value: str | None = None):
         """Set the string property and ensure it is in the set of allowed values.
 
@@ -717,6 +720,7 @@ def __set__(self, obj: StylesBase, value: str | None = None):
         _rich_traceback_omit = True
         if value is None:
             if obj.clear_rule(self.name):
+                self._before_refresh(obj, value)
                 obj.refresh(layout=self._layout)
         else:
             if value not in self._valid_values:
@@ -729,9 +733,20 @@ def __set__(self, obj: StylesBase, value: str | None = None):
                     ),
                 )
             if obj.set_rule(self.name, value):
+                self._before_refresh(obj, value)
                 obj.refresh(layout=self._layout)
 
 
+class OverflowProperty(StringEnumProperty):
+    """Descriptor for overflow styles that forces widgets to refresh scrollbars."""
+
+    def _before_refresh(self, obj: StylesBase, value: str | None) -> None:
+        from ..widget import Widget  # Avoid circular import
+
+        if isinstance(obj.node, Widget):
+            obj.node._refresh_scrollbars()
+
+
 class NameProperty:
     """Descriptor for getting and setting name properties."""
 

src/textual/css/styles.py

@@ -26,6 +26,7 @@
     NameListProperty,
     NameProperty,
     OffsetProperty,
+    OverflowProperty,
     ScalarListProperty,
     ScalarProperty,
     SpacingProperty,
@@ -246,8 +247,8 @@ class StylesBase(ABC):
 
     dock = DockProperty()
 
-    overflow_x = StringEnumProperty(VALID_OVERFLOW, "hidden")
-    overflow_y = StringEnumProperty(VALID_OVERFLOW, "hidden")
+    overflow_x = OverflowProperty(VALID_OVERFLOW, "hidden")
+    overflow_y = OverflowProperty(VALID_OVERFLOW, "hidden")
 
     layer = NameProperty()
     layers = NameListProperty()

src/textual/widget.py

@@ -1,7 +1,6 @@
 from __future__ import annotations
 
 from asyncio import Lock, wait
-from asyncio import Lock, create_task, wait
 from collections import Counter
 from fractions import Fraction
 from itertools import islice
@@ -922,7 +921,7 @@ def _refresh_scrollbars(self) -> None:
         show_horizontal = self.show_horizontal_scrollbar
         if overflow_x == "hidden":
             show_horizontal = False
-        if overflow_x == "scroll":
+        elif overflow_x == "scroll":
             show_horizontal = True
         elif overflow_x == "auto":
             show_horizontal = self.virtual_size.width > width
@@ -1974,13 +1973,14 @@ def _get_scrollable_region(self, region: Region) -> Region:
         """
         show_vertical_scrollbar, show_horizontal_scrollbar = self.scrollbars_enabled
 
-        scrollbar_size_horizontal = self.styles.scrollbar_size_horizontal
-        scrollbar_size_vertical = self.styles.scrollbar_size_vertical
+        styles = self.styles
+        scrollbar_size_horizontal = styles.scrollbar_size_horizontal
+        scrollbar_size_vertical = styles.scrollbar_size_vertical
 
-        if self.styles.scrollbar_gutter == "stable":
+        if styles.scrollbar_gutter == "stable":
             # Let's _always_ reserve some space, whether the scrollbar is actually displayed or not:
             show_vertical_scrollbar = True
-            scrollbar_size_vertical = self.styles.scrollbar_size_vertical
+            scrollbar_size_vertical = styles.scrollbar_size_vertical
 
         if show_horizontal_scrollbar and show_vertical_scrollbar:
             (region, _, _, _) = region.split(

tests/test_overflow_change.py

@@ -0,0 +1,37 @@
+"""Regression test for #1616 https://github.com/Textualize/textual/issues/1616"""
+import pytest
+
+
+from textual.app import App
+from textual.containers import Vertical
+
+
+async def test_overflow_change_updates_virtual_size_appropriately():
+    class MyApp(App):
+        def compose(self):
+            yield Vertical()
+
+    app = MyApp()
+
+    async with app.run_test() as pilot:
+        vertical = app.query_one(Vertical)
+
+        height = vertical.virtual_size.height
+
+        vertical.styles.overflow_x = "scroll"
+        await pilot.pause()  # Let changes propagate.
+        assert vertical.virtual_size.height < height
+
+        vertical.styles.overflow_x = "hidden"
+        await pilot.pause()
+        assert vertical.virtual_size.height == height
+
+        width = vertical.virtual_size.width
+
+        vertical.styles.overflow_y = "scroll"
+        await pilot.pause()
+        assert vertical.virtual_size.width < width
+
+        vertical.styles.overflow_y = "hidden"
+        await pilot.pause()
+        assert vertical.virtual_size.width == width