real breadth first, and tests

src/textual/app.py

@@ -37,7 +37,7 @@ from .css.stylesheet import Stylesheet
 from .design import ColorSystem
 from .devtools.client import DevtoolsClient, DevtoolsConnectionError, DevtoolsLog
 from .devtools.redirect_output import StdoutRedirector
-from .dom import DOMNode
+from .dom import DOMNode, NoScreen
 from .driver import Driver
 from .drivers.headless_driver import HeadlessDriver
 from .features import FeatureFlag, parse_features
@@ -1142,7 +1142,10 @@ class App(Generic[ReturnType], DOMNode):
         Args:
             widget (Widget): A Widget to unregister
         """
-        widget.screen._reset_focus(widget)
+        try:
+            widget.screen._reset_focus(widget)
+        except NoScreen:
+            pass
 
         if isinstance(widget._parent, Widget):
             widget._parent.children._remove(widget)
@@ -1394,8 +1397,8 @@ class App(Generic[ReturnType], DOMNode):
         if parent is not None:
             parent.refresh(layout=True)
 
-        remove_widgets = list(
-            widget.walk_children(Widget, with_self=True, method="depth")
+        remove_widgets = widget.walk_children(
+            Widget, with_self=True, method="depth", reverse=True
         )
         for child in remove_widgets:
             self._unregister(child)

src/textual/css/styles.py

@@ -573,7 +573,7 @@ class Styles(StylesBase):
         if self.node is not None:
             self.node.refresh(layout=layout)
             if children:
-                for child in self.node.walk_children(with_self=False):
+                for child in self.node.walk_children(with_self=False, reverse=True):
                     child.refresh(layout=layout)
 
     def reset(self) -> None:

src/textual/dom.py

@@ -632,13 +632,18 @@ class DOMNode(MessagePump):
         filter_type: type[WalkType],
         *,
         with_self: bool = True,
-        method: WalkMethod = "breadth",
+        method: WalkMethod = "depth",
+        reverse: bool = False,
     ) -> Iterable[WalkType]:
         ...
 
     @overload
     def walk_children(
-        self, *, with_self: bool = True, method: WalkMethod = "breadth"
+        self,
+        *,
+        with_self: bool = True,
+        method: WalkMethod = "depth",
+        reverse: bool = False,
     ) -> Iterable[DOMNode]:
         ...
 
@@ -647,7 +652,8 @@ class DOMNode(MessagePump):
         filter_type: type[WalkType] | None = None,
         *,
         with_self: bool = True,
-        method: WalkMethod = "breadth",
+        method: WalkMethod = "depth",
+        reverse: bool = False,
     ) -> Iterable[DOMNode | WalkType]:
         """Generate descendant nodes.
 
@@ -655,14 +661,15 @@ class DOMNode(MessagePump):
             filter_type (type[WalkType] | None, optional): Filter only this type, or None for no filter.
                 Defaults to None.
             with_self (bool, optional): Also yield self in addition to descendants. Defaults to True.
-            method (Literal["breadth", "depth"], optional): One of "depth" or "breadth". Defaults to "breadth".
+            method (Literal["breadth", "depth"], optional): One of "depth" or "breadth". Defaults to "depth".
+            reverse (bool, optional): Reverse the order (bottom up). Defaults to False
 
         Returns:
             Iterable[DOMNode | WalkType]: An iterable of nodes.
 
         """
 
-        def walk_breadth_first() -> Iterable[DOMNode]:
+        def walk_depth_first() -> Iterable[DOMNode]:
             """Walk the tree breadth first (parent's first)."""
             stack: list[Iterator[DOMNode]] = [iter(self.children)]
             pop = stack.pop
@@ -682,31 +689,29 @@ class DOMNode(MessagePump):
                     if node.children:
                         push(iter(node.children))
 
-        def walk_depth_first() -> Iterable[DOMNode]:
+        def walk_breadth_first() -> Iterable[DOMNode]:
             """Walk the tree depth first (children first)."""
-            depth_stack: list[tuple[DOMNode, Iterator[DOMNode]]] = (
-                [(self, iter(self.children))]
-                if with_self
-                else [(node, iter(node.children)) for node in reversed(self.children)]
-            )
-            pop = depth_stack.pop
-            push = depth_stack.append
-            check_type = filter_type or DOMNode
+            queue: deque[DOMNode] = deque()
+            popleft = queue.popleft
+            extend = queue.extend
 
-            while depth_stack:
-                node, iter_nodes = pop()
-                child_widget = next(iter_nodes, None)
-                if child_widget is None:
-                    if isinstance(node, check_type):
-                        yield node
-                else:
-                    push((node, iter_nodes))
-                    push((child_widget, iter(child_widget.children)))
+            if with_self:
+                yield self
+            queue.extend(self.children)
 
-        if method == "depth":
-            yield from walk_depth_first()
+            while queue:
+                node = popleft()
+                yield node
+                extend(node.children)
+
+        node_generator = (
+            walk_depth_first() if method == "depth" else walk_breadth_first()
+        )
+
+        if reverse:
+            yield from reversed(list(node_generator))
         else:
-            yield from walk_breadth_first()
+            yield from node_generator
 
     def get_child(self, id: str) -> DOMNode:
         """Return the first child (immediate descendent) of this node with the given ID.

tests/test_dom.py

@@ -77,27 +77,63 @@ def test_validate():
         node.toggle_class("1")
 
 
-def test_walk_children(parent):
-    children = [node.id for node in parent.walk_children(with_self=False)]
-    assert children == ["child1", "grandchild1", "child2"]
+@pytest.fixture
+def search():
+    """
+        a
+       / \
+      b   c
+     /   / \
+    d   e   f
+    """
+    a = DOMNode(id="a")
+    b = DOMNode(id="b")
+    c = DOMNode(id="c")
+    d = DOMNode(id="d")
+    e = DOMNode(id="e")
+    f = DOMNode(id="f")
+
+    a._add_child(b)
+    a._add_child(c)
+    b._add_child(d)
+    c._add_child(e)
+    c._add_child(f)
+
+    yield a
 
 
-def test_walk_children_with_self(parent):
-    children = [node.id for node in parent.walk_children(with_self=True)]
-    assert children == ["parent", "child1", "grandchild1", "child2"]
-
-
-def test_walk_children_depth(parent):
+def test_walk_children_depth(search):
     children = [
-        node.id for node in parent.walk_children(with_self=False, method="depth")
+        node.id for node in search.walk_children(method="depth", with_self=False)
+    ]
+    assert children == ["b", "d", "c", "e", "f"]
+
+
+def test_walk_children_with_self_depth(search):
+    children = [
+        node.id for node in search.walk_children(method="depth", with_self=True)
+    ]
+    assert children == ["a", "b", "d", "c", "e", "f"]
+
+
+def test_walk_children_breadth(search):
+    children = [
+        node.id for node in search.walk_children(with_self=False, method="breadth")
     ]
     print(children)
-    assert children == ["grandchild1", "child1", "child2"]
+    assert children == ["b", "c", "d", "e", "f"]
 
 
-def test_walk_children_with_self_depth(parent):
+def test_walk_children_with_self_breadth(search):
     children = [
-        node.id for node in parent.walk_children(with_self=True, method="depth")
+        node.id for node in search.walk_children(with_self=True, method="breadth")
     ]
     print(children)
-    assert children == ["grandchild1", "child1", "child2", "parent"]
+    assert children == ["a", "b", "c", "d", "e", "f"]
+
+    children = [
+        node.id
+        for node in search.walk_children(with_self=True, method="breadth", reverse=True)
+    ]
+
+    assert children == ["f", "e", "d", "c", "b", "a"]