Handle other Tabs widgets as DOM descendants of a TabbedContent (#3602)

* Handle other Tabs widgets as DOM descendants of a TabbedContent

* Update CHANGELOG.md

* Ensure TabbedContent can identify messages from the associated Tabs so that it can ignore messages from other, irrelevant Tabs instances that may exist as descendants deeper in the DOM. Also adds some tests to ensure corresponding issues are fixed.

* Improve docstrings for Tabs.Cleared and corresponding handler inside TabbedContent - it now includes a note that the Cleared message is sent when all tabs are hidden.

CHANGELOG.md

@@ -20,6 +20,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 - Fix issue with chunky highlights on buttons https://github.com/Textualize/textual/pull/3571
 - Fixed `OptionList` event leakage from `CommandPalette` to `App`.
 - Fixed crash in `LoadingIndicator` https://github.com/Textualize/textual/pull/3498
+- Fixed crash when `Tabs` appeared as a descendant of `TabbedContent` in the DOM https://github.com/Textualize/textual/pull/3602
 
 ### Added
 

src/textual/widgets/_tabbed_content.py

@@ -37,6 +37,26 @@ def __init__(self, label: Text, content_id: str, disabled: bool = False):
         super().__init__(label, id=content_id, disabled=disabled)
 
 
+class ContentTabs(Tabs):
+    """A Tabs which is associated with a TabbedContent."""
+
+    def __init__(
+        self,
+        *tabs: Tab | TextType,
+        active: str | None = None,
+        tabbed_content: TabbedContent,
+    ):
+        """Initialize a ContentTabs.
+
+        Args:
+            *tabs: The child tabs.
+            active: ID of the tab which should be active on start.
+            tabbed_content: The associated TabbedContent instance.
+        """
+        super().__init__(*tabs, active=active)
+        self.tabbed_content = tabbed_content
+
+
 class TabPane(Widget):
     """A container for switchable content, with additional title.
 
@@ -245,11 +265,21 @@ def compose(self) -> ComposeResult:
         ]
         # Get a tab for each pane
         tabs = [
-            ContentTab(content._title, content.id or "", disabled=content.disabled)
+            ContentTab(
+                content._title,
+                content.id or "",
+                disabled=content.disabled,
+            )
             for content in pane_content
         ]
-        # Yield the tabs
-        yield Tabs(*tabs, active=self._initial or None)
+
+        # Yield the tabs, and ensure they're linked to this TabbedContent.
+        # It's important to associate the Tabs with the TabbedContent, so that this
+        # TabbedContent can determine whether a message received from a Tabs instance
+        # has been sent from this Tabs, or from a Tabs that may exist as a descendant
+        # deeper in the DOM.
+        yield ContentTabs(*tabs, active=self._initial or None, tabbed_content=self)
+
         # Yield the content switcher and panes
         with ContentSwitcher(initial=self._initial or None):
             yield from pane_content
@@ -282,7 +312,7 @@ def add_pane(
             before = before.id
         if isinstance(after, TabPane):
             after = after.id
-        tabs = self.get_child_by_type(Tabs)
+        tabs = self.get_child_by_type(ContentTabs)
         pane = self._set_id(pane, tabs.tab_count + 1)
         assert pane.id is not None
         pane.display = False
@@ -301,7 +331,7 @@ def remove_pane(self, pane_id: str) -> AwaitComplete:
             An optionally awaitable object that waits for the pane to be removed
                 and the Cleared message to be posted.
         """
-        removal_awaitables = [self.get_child_by_type(Tabs).remove_tab(pane_id)]
+        removal_awaitables = [self.get_child_by_type(ContentTabs).remove_tab(pane_id)]
         try:
             removal_awaitables.append(
                 self.get_child_by_type(ContentSwitcher)
@@ -332,7 +362,7 @@ def clear_panes(self) -> AwaitComplete:
                 and the Cleared message to be posted.
         """
         await_clear = gather(
-            self.get_child_by_type(Tabs).clear(),
+            self.get_child_by_type(ContentTabs).clear(),
             self.get_child_by_type(ContentSwitcher).remove_children(),
         )
 
@@ -356,35 +386,52 @@ def compose_add_child(self, widget: Widget) -> None:
 
     def _on_tabs_tab_activated(self, event: Tabs.TabActivated) -> None:
         """User clicked a tab."""
-        assert isinstance(event.tab, ContentTab)
-        assert isinstance(event.tab.id, str)
-        event.stop()
-        switcher = self.get_child_by_type(ContentSwitcher)
-        switcher.current = event.tab.id
-        self.active = event.tab.id
-        self.post_message(
-            TabbedContent.TabActivated(
-                tabbed_content=self,
-                tab=event.tab,
+        if self._is_associated_tabs(event.tabs):
+            # The message is relevant, so consume it and update state accordingly.
+            event.stop()
+            switcher = self.get_child_by_type(ContentSwitcher)
+            switcher.current = event.tab.id
+            self.active = event.tab.id
+            self.post_message(
+                TabbedContent.TabActivated(
+                    tabbed_content=self,
+                    tab=event.tab,
+                )
             )
-        )
 
     def _on_tabs_cleared(self, event: Tabs.Cleared) -> None:
-        """All tabs were removed."""
-        event.stop()
-        self.get_child_by_type(ContentSwitcher).current = None
-        self.active = ""
+        """Called when there are no active tabs. The tabs may have been cleared,
+        or they may all be hidden."""
+        if self._is_associated_tabs(event.tabs):
+            event.stop()
+            self.get_child_by_type(ContentSwitcher).current = None
+            self.active = ""
+
+    def _is_associated_tabs(self, tabs: Tabs) -> bool:
+        """Determine whether a tab is associated with this TabbedContent or not.
+
+        A tab is "associated" with a `TabbedContent`, if it's one of the tabs that can
+        be used to control it. These have a special type: `ContentTab`, and are linked
+        back to this `TabbedContent` instance via a `tabbed_content` attribute.
+
+        Args:
+            tabs: The Tabs instance to check.
+
+        Returns:
+            True if the tab is associated with this `TabbedContent`.
+        """
+        return isinstance(tabs, ContentTabs) and tabs.tabbed_content is self
 
     def _watch_active(self, active: str) -> None:
         """Switch tabs when the active attributes changes."""
         with self.prevent(Tabs.TabActivated):
-            self.get_child_by_type(Tabs).active = active
+            self.get_child_by_type(ContentTabs).active = active
             self.get_child_by_type(ContentSwitcher).current = active
 
     @property
     def tab_count(self) -> int:
         """Total number of tabs."""
-        return self.get_child_by_type(Tabs).tab_count
+        return self.get_child_by_type(ContentTabs).tab_count
 
     def _on_tabs_tab_disabled(self, event: Tabs.TabDisabled) -> None:
         """Disable the corresponding tab pane."""
@@ -404,7 +451,7 @@ def _on_tab_pane_disabled(self, event: TabPane.Disabled) -> None:
         tab_pane_id = event.tab_pane.id or ""
         try:
             with self.prevent(Tab.Disabled):
-                self.get_child_by_type(Tabs).query_one(
+                self.get_child_by_type(ContentTabs).query_one(
                     f"Tab#{tab_pane_id}"
                 ).disabled = True
         except NoMatches:
@@ -428,7 +475,7 @@ def _on_tab_pane_enabled(self, event: TabPane.Enabled) -> None:
         tab_pane_id = event.tab_pane.id or ""
         try:
             with self.prevent(Tab.Enabled):
-                self.get_child_by_type(Tabs).query_one(
+                self.get_child_by_type(ContentTabs).query_one(
                     f"Tab#{tab_pane_id}"
                 ).disabled = False
         except NoMatches:
@@ -444,7 +491,7 @@ def disable_tab(self, tab_id: str) -> None:
             Tabs.TabError: If there are any issues with the request.
         """
 
-        self.get_child_by_type(Tabs).disable(tab_id)
+        self.get_child_by_type(ContentTabs).disable(tab_id)
 
     def enable_tab(self, tab_id: str) -> None:
         """Enables the tab with the given ID.
@@ -456,7 +503,7 @@ def enable_tab(self, tab_id: str) -> None:
             Tabs.TabError: If there are any issues with the request.
         """
 
-        self.get_child_by_type(Tabs).enable(tab_id)
+        self.get_child_by_type(ContentTabs).enable(tab_id)
 
     def hide_tab(self, tab_id: str) -> None:
         """Hides the tab with the given ID.
@@ -468,7 +515,7 @@ def hide_tab(self, tab_id: str) -> None:
             Tabs.TabError: If there are any issues with the request.
         """
 
-        self.get_child_by_type(Tabs).hide(tab_id)
+        self.get_child_by_type(ContentTabs).hide(tab_id)
 
     def show_tab(self, tab_id: str) -> None:
         """Shows the tab with the given ID.
@@ -480,4 +527,4 @@ def show_tab(self, tab_id: str) -> None:
             Tabs.TabError: If there are any issues with the request.
         """
 
-        self.get_child_by_type(Tabs).show(tab_id)
+        self.get_child_by_type(ContentTabs).show(tab_id)

src/textual/widgets/_tabs.py

@@ -266,7 +266,10 @@ class TabShown(TabMessage):
         """Sent when a tab is shown."""
 
     class Cleared(Message):
-        """Sent when there are no active tabs."""
+        """Sent when there are no active tabs.
+
+        This can occur when Tabs are cleared, or if all tabs are hidden.
+        """
 
         def __init__(self, tabs: Tabs) -> None:
             """Initialize the event.

tests/test_tabbed_content.py

@@ -796,3 +796,49 @@ def compose(self) -> ComposeResult:
         await pilot.pause()
         tabber.show_tab("tab-1")
         await pilot.pause()
+
+
+async def test_tabs_nested_in_tabbed_content_doesnt_crash():
+    """Regression test for https://github.com/Textualize/textual/issues/3412"""
+
+    class TabsNestedInTabbedContent(App):
+        def compose(self) -> ComposeResult:
+            with TabbedContent():
+                with TabPane("Outer TabPane"):
+                    yield Tabs("Inner Tab")
+
+    app = TabsNestedInTabbedContent()
+    async with app.run_test() as pilot:
+        await pilot.pause()
+
+
+async def test_tabs_nested_doesnt_interfere_with_ancestor_tabbed_content():
+    """When a Tabs is nested as a descendant in the DOM of a TabbedContent,
+    the messages posted from that Tabs should not interfere with the TabbedContent.
+    A TabbedContent should only handle messages from Tabs which are direct children.
+
+    Relates to https://github.com/Textualize/textual/issues/3412
+    """
+
+    class TabsNestedInTabbedContent(App):
+        def compose(self) -> ComposeResult:
+            with TabbedContent():
+                with TabPane("OuterTab", id="outer1"):
+                    yield Tabs(
+                        Tab("Tab1", id="tab1"),
+                        Tab("Tab2", id="tab2"),
+                        id="inner-tabs",
+                    )
+
+    app = TabsNestedInTabbedContent()
+    async with app.run_test():
+        inner_tabs = app.query_one("#inner-tabs", Tabs)
+        tabbed_content = app.query_one(TabbedContent)
+
+        assert inner_tabs.active_tab.id == "tab1"
+        assert tabbed_content.active == "outer1"
+
+        await inner_tabs.clear()
+
+        assert inner_tabs.active_tab is None
+        assert tabbed_content.active == "outer1"