Add TreeNode.tree

Currently, in the various TreeNode messages, and the handlers you'd write to
handle them, there's no way to easily know *which* tree sent the message and
so which tree the node belongs to.

This commit adds public access to the tree reference to the nodes, so that
in an event handler the developer can check the tree involved in the event.

See #2413.

tests/tree/test_tree_messages.py

@@ -16,18 +16,26 @@ class TreeApp(App[None]):
 
     def __init__(self, *args: Any, **kwargs: Any) -> None:
         super().__init__(*args, **kwargs)
-        self.messages: list[str] = []
+        self.messages: list[tuple[str, str]] = []
 
     def compose(self) -> ComposeResult:
         """Compose the child widgets."""
-        yield MyTree("Root")
+        yield MyTree("Root", id="test-tree")
 
     def on_mount(self) -> None:
         self.query_one(MyTree).root.add("Child")
         self.query_one(MyTree).focus()
 
-    def record(self, event: Message) -> None:
-        self.messages.append(event.__class__.__name__)
+    def record(
+        self,
+        event: Tree.NodeSelected[None]
+        | Tree.NodeExpanded[None]
+        | Tree.NodeCollapsed[None]
+        | Tree.NodeHighlighted[None],
+    ) -> None:
+        self.messages.append(
+            (event.__class__.__name__, event.node.tree.id or "Unknown")
+        )
 
     def on_tree_node_selected(self, event: Tree.NodeSelected[None]) -> None:
         self.record(event)
@@ -47,7 +55,10 @@ async def test_tree_node_selected_message() -> None:
     async with TreeApp().run_test() as pilot:
         await pilot.press("enter")
         await pilot.pause()
-        assert pilot.app.messages == ["NodeExpanded", "NodeSelected"]
+        assert pilot.app.messages == [
+            ("NodeExpanded", "test-tree"),
+            ("NodeSelected", "test-tree"),
+        ]
 
 
 async def test_tree_node_selected_message_no_auto() -> None:
@@ -56,7 +67,7 @@ async def test_tree_node_selected_message_no_auto() -> None:
         pilot.app.query_one(MyTree).auto_expand = False
         await pilot.press("enter")
         await pilot.pause()
-        assert pilot.app.messages == ["NodeSelected"]
+        assert pilot.app.messages == [("NodeSelected", "test-tree")]
 
 
 async def test_tree_node_expanded_message() -> None:
@@ -64,7 +75,7 @@ async def test_tree_node_expanded_message() -> None:
     async with TreeApp().run_test() as pilot:
         await pilot.press("space")
         await pilot.pause()
-        assert pilot.app.messages == ["NodeExpanded"]
+        assert pilot.app.messages == [("NodeExpanded", "test-tree")]
 
 
 async def test_tree_node_collapsed_message() -> None:
@@ -72,7 +83,10 @@ async def test_tree_node_collapsed_message() -> None:
     async with TreeApp().run_test() as pilot:
         await pilot.press("space", "space")
         await pilot.pause()
-        assert pilot.app.messages == ["NodeExpanded", "NodeCollapsed"]
+        assert pilot.app.messages == [
+            ("NodeExpanded", "test-tree"),
+            ("NodeCollapsed", "test-tree"),
+        ]
 
 
 async def test_tree_node_highlighted_message() -> None:
@@ -80,4 +94,8 @@ async def test_tree_node_highlighted_message() -> None:
     async with TreeApp().run_test() as pilot:
         await pilot.press("enter", "down")
         await pilot.pause()
-        assert pilot.app.messages == ["NodeExpanded", "NodeSelected", "NodeHighlighted"]
+        assert pilot.app.messages == [
+            ("NodeExpanded", "test-tree"),
+            ("NodeSelected", "test-tree"),
+            ("NodeHighlighted", "test-tree"),
+        ]