interactive: fix dark mode (#3582)

Fixes crash when switching theme caused by a textual update. Also adds a
test to catch this in the future.

tests/interactive/test_app.py

@@ -519,3 +519,21 @@ async def test_argument_pass_screen():
 
         arg_screen_str: type[Screen[Any]] = AddArguments
         assert isinstance(app.screen, arg_screen_str)
+
+
+@pytest.mark.asyncio
+async def test_dark_mode():
+    """Tests that 'd' switches between dark and light mode"""
+
+    async with InputApp(tuple(), tuple()).run_test() as pilot:
+        app = cast(InputApp, pilot.app)
+
+        assert app.theme == "textual-dark"
+
+        await pilot.press("d")
+
+        assert app.theme == "textual-light"
+
+        await pilot.press("d")
+
+        assert app.theme == "textual-dark"

xdsl/interactive/app.py

@@ -635,7 +635,9 @@ def watch_diff_operation_count_tuple(self) -> None:
 
     def action_toggle_dark(self) -> None:
         """An action to toggle dark mode."""
-        self.dark = not self.dark
+        self.theme = (
+            "textual-dark" if self.theme == "textual-light" else "textual-light"
+        )
 
     def action_quit_app(self) -> None:
         """An action to quit the app."""