Roll back ALLOW_CHILDREN and max height fix (#3814)

* max height

* changelog

* snapshot

* unused exception

CHANGELOG.md

@@ -17,6 +17,11 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 
 - Removed renderables/align.py which was no longer used
 
+### Changed
+
+- Dropped ALLOW_CHILDREN flag introduced in 0.43.0 https://github.com/Textualize/textual/pull/3814
+- Widgets with an auto height in an auto height container will now expand if they have no siblings https://github.com/Textualize/textual/pull/3814
+
 ### Added
 
 - Added `get_loading_widget` to Widget and App customize the loading widget. https://github.com/Textualize/textual/pull/3816

src/textual/_layout.py

@@ -183,7 +183,17 @@ def get_content_height(
             height = 0
         else:
             # Use a height of zero to ignore relative heights
-            arrangement = widget._arrange(Size(width, 0))
+            styles_height = widget.styles.height
+            if widget._parent and len(widget._nodes) == 1:
+                # If it is an only child with height auto we want it to expand
+                height = (
+                    container.height
+                    if styles_height is not None and styles_height.is_auto
+                    else 0
+                )
+            else:
+                height = 0
+            arrangement = widget._arrange(Size(width, height))
             height = arrangement.total_region.bottom
 
         return height

src/textual/scroll_view.py

@@ -18,8 +18,6 @@ class ScrollView(ScrollableContainer):
     on the compositor to render children).
     """
 
-    ALLOW_CHILDREN = False
-
     DEFAULT_CSS = """
     ScrollView {
         overflow-y: auto;

src/textual/widget.py

@@ -86,10 +86,6 @@
 }
 
 
-class NotAContainer(Exception):
-    """Exception raised if you attempt to add a child to a widget which doesn't permit child nodes."""
-
-
 _NULL_STYLE = Style()
 
 
@@ -267,9 +263,6 @@ class Widget(DOMNode):
     BORDER_SUBTITLE: ClassVar[str] = ""
     """Initial value for border_subtitle attribute."""
 
-    ALLOW_CHILDREN: ClassVar[bool] = True
-    """Set to `False` to prevent adding children to this widget."""
-
     can_focus: bool = False
     """Widget may receive focus."""
     can_focus_children: bool = True
@@ -518,8 +511,6 @@ def compose_add_child(self, widget: Widget) -> None:
             widget: A Widget to add.
         """
         _rich_traceback_omit = True
-        if not self.ALLOW_CHILDREN:
-            raise NotAContainer(f"Can't add children to {type(widget)} widgets")
         self._nodes._append(widget)
 
     def __enter__(self) -> Self:

src/textual/widgets/_button.py

@@ -153,8 +153,6 @@ class Button(Widget, can_focus=True):
 
     BINDINGS = [Binding("enter", "press", "Press Button", show=False)]
 
-    ALLOW_CHILDREN = False
-
     label: reactive[TextType] = reactive[TextType]("")
     """The text label that appears within the button."""
 

src/textual/widgets/_static.py

@@ -44,8 +44,6 @@ class Static(Widget, inherit_bindings=False):
     }
     """
 
-    ALLOW_CHILDREN = False
-
     _renderable: RenderableType
 
     def __init__(

src/textual/widgets/_toggle_button.py

@@ -51,8 +51,6 @@ class ToggleButton(Static, can_focus=True):
     | `toggle--label` | Targets the text label of the toggle button. |
     """
 
-    ALLOW_CHILDREN = False
-
     DEFAULT_CSS = """
     ToggleButton {
         width: auto;

tests/snapshot_tests/snapshot_apps/max_height_100.py

@@ -0,0 +1,27 @@
+from textual.app import App, ComposeResult
+from textual.widgets import DataTable, Static
+
+
+class HappyDataTableFunApp(App[None]):
+    """The DataTable should expand as if it has height 1fr."""
+
+    CSS = """
+    DataTable {
+        max-height: 100%;        
+    }
+    """
+
+    def populate(self, table: DataTable) -> DataTable:
+        for n in range(20):
+            table.add_column(f"Column {n}")
+        for row in range(100):
+            table.add_row(*[str(row * n) for n in range(20)])
+        return table
+
+    def compose(self) -> ComposeResult:
+        with Static(id="s"):
+            yield self.populate(DataTable())
+
+
+if __name__ == "__main__":
+    HappyDataTableFunApp().run()

tests/snapshot_tests/test_snapshots.py

@@ -937,6 +937,10 @@ def test_vertical_max_height(snap_compare):
     assert snap_compare(SNAPSHOT_APPS_DIR / "vertical_max_height.py")
 
 
+def test_max_height_100(snap_compare):
+    """Test vertical max height takes border in to account."""
+    assert snap_compare(SNAPSHOT_APPS_DIR / "max_height_100.py")
+
 def test_loading_indicator(snap_compare):
     """Test loading indicator."""
     # https://github.com/Textualize/textual/pull/3816
@@ -949,3 +953,4 @@ def test_loading_indicator_disables_widget(snap_compare):
     assert snap_compare(
         SNAPSHOT_APPS_DIR / "loading.py", press=["space", "down", "down", "space"]
     )
+

tests/test_widget.py

@@ -9,8 +9,8 @@
 from textual.css.query import NoMatches
 from textual.geometry import Offset, Size
 from textual.message import Message
-from textual.widget import MountError, NotAContainer, PseudoClasses, Widget
-from textual.widgets import Label, LoadingIndicator, Static
+from textual.widget import MountError, PseudoClasses, Widget
+from textual.widgets import Label, LoadingIndicator
 
 
 @pytest.mark.parametrize(
@@ -396,22 +396,6 @@ class TestWidgetIsMountedApp(App):
         assert widget.is_mounted is True
 
 
-async def test_not_allow_children():
-    """Regression test for https://github.com/Textualize/textual/pull/3758"""
-
-    class TestAppExpectFail(App):
-        def compose(self) -> ComposeResult:
-            # Statics don't have children, so this should error
-            with Static():
-                yield Label("foo")
-
-    app = TestAppExpectFail()
-
-    with pytest.raises(NotAContainer):
-        async with app.run_test():
-            pass
-
-
 async def test_mount_error_not_widget():
     class NotWidgetApp(App):
         def compose(self) -> ComposeResult: