fix for focus reset edge case

src/textual/demo.css

@@ -196,6 +196,7 @@ DataTable {
     height: 16;
 }
 
+
 LoginForm {
     height: auto;
     margin: 1 0;

src/textual/demo.py

@@ -1,5 +1,7 @@
 from __future__ import annotations
 
+from pathlib import Path
+
 from rich import box
 from rich.console import RenderableType
 from rich.markdown import Markdown
@@ -303,6 +305,7 @@ class DemoApp(App):
         self.query_one(TextLog).write(renderable)
 
     def compose(self) -> ComposeResult:
+        example_css = "\n".join(Path(self.css_path).read_text().splitlines()[:50])
         yield Container(
             Sidebar(classes="-hidden"),
             Header(show_clock=True),
@@ -341,9 +344,15 @@ class DemoApp(App):
                     Section(
                         SectionTitle("CSS"),
                         Text(Markdown(CSS_MD)),
-                        Static(
-                            Syntax(
-                                EXAMPLE_CSS, "css", theme="material", line_numbers=True
+                        Window(
+                            Static(
+                                Syntax(
+                                    example_css,
+                                    "css",
+                                    theme="material",
+                                    line_numbers=True,
+                                ),
+                                expand=True,
                             )
                         ),
                     ),

src/textual/dom.py

@@ -278,7 +278,7 @@ class DOMNode(MessagePump):
         while node and not isinstance(node, Screen):
             node = node._parent
         if not isinstance(node, Screen):
-            raise NoScreen(f"{self} has no screen")
+            raise NoScreen(f"node has no screen")
         return node
 
     @property

src/textual/screen.py

@@ -225,7 +225,7 @@ class Screen(Widget):
         return self._move_focus(-1)
 
     def _reset_focus(
-        self, widget: Widget, avoiding: list[DOMNode] | None = None
+        self, widget: Widget, avoiding: list[Widget] | None = None
     ) -> None:
         """Reset the focus when a widget is removed
 
@@ -252,14 +252,20 @@ class Screen(Widget):
             # the focus chain.
             widget_index = focusable_widgets.index(widget)
         except ValueError:
-            # Seems we can't find it. There's no good reason this should
-            # happen but, on the off-chance, let's go into a "no focus" state.
-            self.set_focus(None)
+            # widget is not in focusable widgets
+            # It may have been made invisible
+            # Move to a sibling if possible
+            for sibling in widget.visible_siblings:
+                if sibling not in avoiding and sibling.can_focus:
+                    self.set_focus(sibling)
+                    break
+            else:
+                self.set_focus(None)
             return
 
         # Now go looking for something before it, that isn't about to be
         # removed, and which can receive focus, and go focus that.
-        chosen: DOMNode | None = None
+        chosen: Widget | None = None
         for candidate in reversed(
             focusable_widgets[widget_index + 1 :] + focusable_widgets[:widget_index]
         ):
@@ -368,6 +374,7 @@ class Screen(Widget):
             hidden, shown, resized = self._compositor.reflow(self, size)
             Hide = events.Hide
             Show = events.Show
+
             for widget in hidden:
                 widget.post_message_no_wait(Hide(self))
             for widget in shown:

src/textual/widget.py

@@ -261,6 +261,18 @@ class Widget(DOMNode):
         else:
             return []
 
+    @property
+    def visible_siblings(self) -> list[Widget]:
+        """A list of siblings which will be shown.
+
+        Returns:
+            list[Widget]: List of siblings.
+        """
+        siblings = [
+            widget for widget in self.siblings if widget.visible and widget.display
+        ]
+        return siblings
+
     @property
     def allow_vertical_scroll(self) -> bool:
         """Check if vertical scroll is permitted.
@@ -1576,9 +1588,12 @@ class Widget(DOMNode):
             yield "hover"
         if self.has_focus:
             yield "focus"
-        focused = self.screen.focused
-        if focused and self in focused.ancestors:
-            yield "focus-within"
+        try:
+            focused = self.screen.focused
+            if focused and self in focused.ancestors:
+                yield "focus-within"
+        except NoScreen:
+            pass
 
     def post_render(self, renderable: RenderableType) -> ConsoleRenderable:
         """Applies style attributes to the default renderable.