Updating styles on demand instead of on_idle (#2304)

* Updating styles on demand instead of on_idle

* Tidy up update_styles

* Fix LRU cache tests

* Remove some debugging code

* Adding test for pseudoclass style update

* Update changelog

CHANGELOG.md

@@ -12,6 +12,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 - Changed signature of Driver. Technically a breaking change, but unlikely to affect anyone.
 - Breaking change: Timer.start is now private, and returns No
 - A clicked tab will now be scrolled to the center of its tab container https://github.com/Textualize/textual/pull/2276
+- Style updates are now done immediately rather than on_idle https://github.com/Textualize/textual/pull/2304
 - `ButtonVariant` is now exported from `textual.widgets.button` https://github.com/Textualize/textual/issues/2264
 
 ### Added
@@ -28,9 +29,9 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 
 - Fixed order styles are applied in DataTable - allows combining of renderable styles and component classes https://github.com/Textualize/textual/pull/2272
 - Fix empty ListView preventing bindings from firing https://github.com/Textualize/textual/pull/2281
+- Fix `get_component_styles` returning incorrect values on first call when combined with pseudoclasses https://github.com/Textualize/textual/pull/2304
 - Fixed `active_message_pump.get` sometimes resulting in a `LookupError` https://github.com/Textualize/textual/issues/2301
 
-
 ## [0.19.1] - 2023-04-10
 
 ### Fixed

src/textual/_cache.py

@@ -72,9 +72,7 @@ class LRUCache(Generic[CacheKey, CacheValue]):
         return len(self._cache)
 
     def __repr__(self) -> str:
-        return (
-            f"<LRUCache maxsize={self._maxsize} hits={self.hits} misses={self.misses}>"
-        )
+        return f"<LRUCache size={len(self)} maxsize={self._maxsize} hits={self.hits} misses={self.misses}>"
 
     def grow(self, maxsize: int) -> None:
         """Grow the maximum size to at least `maxsize` elements.

src/textual/app.py

@@ -322,7 +322,6 @@ class App(Generic[ReturnType], DOMNode):
         self.design = DEFAULT_COLORS
 
         self.stylesheet = Stylesheet(variables=self.get_css_variables())
-        self._require_stylesheet_update: set[DOMNode] = set()
 
         css_path = css_path or self.CSS_PATH
         if css_path is not None:
@@ -1229,13 +1228,15 @@ class App(Generic[ReturnType], DOMNode):
         return self.screen.get_child_by_type(expect_type)
 
     def update_styles(self, node: DOMNode | None = None) -> None:
-        """Request update of styles.
+        """Immediately update the styles of this node and all descendant nodes.
 
         Should be called whenever CSS classes / pseudo classes change.
-
+        For example, when you hover over a button, the :hover pseudo class
+        will be added, and this method is called to apply the corresponding
+        :hover styles.
         """
-        self._require_stylesheet_update.add(self.screen if node is None else node)
-        self.check_idle()
+        descendants = node.walk_children(with_self=True)
+        self.stylesheet.update_nodes(descendants, animate=True)
 
     def mount(
         self,
@@ -1773,14 +1774,6 @@ class App(Generic[ReturnType], DOMNode):
 
     def _on_idle(self) -> None:
         """Perform actions when there are no messages in the queue."""
-        if self._require_stylesheet_update and not self._batch_count:
-            nodes: set[DOMNode] = {
-                child
-                for node in self._require_stylesheet_update
-                for child in node.walk_children(with_self=True)
-            }
-            self._require_stylesheet_update.clear()
-            self.stylesheet.update_nodes(nodes, animate=True)
 
     def _register_child(
         self, parent: DOMNode, child: Widget, before: int | None, after: int | None

src/textual/css/stylesheet.py

@@ -530,7 +530,6 @@ class Stylesheet:
             nodes: Nodes to update.
             animate: Enable CSS animation.
         """
-
         rules_map = self.rules_map
         apply = self.apply
 

src/textual/devtools/service.py

@@ -252,6 +252,7 @@ class ClientHandler:
                     ):
                         await self.incoming_queue.put(message)
                 elif websocket_message.type == WSMsgType.ERROR:
+                    self.service.console.print(websocket_message.data)
                     self.service.console.print(
                         DevConsoleNotice("Websocket error occurred", level="error")
                     )

src/textual/widgets/_data_table.py

@@ -269,7 +269,7 @@ class DataTable(ScrollView, Generic[CellType], can_focus=True):
         background: $primary 10%;
     }
 
-    DataTable >  .datatable--cursor {
+    DataTable > .datatable--cursor {
         background: $secondary;
         color: $text;
     }

tests/test_app.py

@@ -1,4 +1,5 @@
-from textual.app import App
+from textual.app import App, ComposeResult
+from textual.widgets import Button
 
 
 def test_batch_update():
@@ -15,3 +16,23 @@ def test_batch_update():
         assert app._batch_count == 1  # Exiting decrements
 
     assert app._batch_count == 0  # Back to zero
+
+
+class MyApp(App):
+    def compose(self) -> ComposeResult:
+        yield Button("Click me!")
+
+
+async def test_hover_update_styles():
+    app = MyApp()
+    async with app.run_test() as pilot:
+        button = app.query_one(Button)
+        assert button.pseudo_classes == {"enabled"}
+
+        # Take note of the initial background colour
+        initial_background = button.styles.background
+        await pilot.hover(Button)
+
+        # We've hovered, so ensure the pseudoclass is present and background changed
+        assert button.pseudo_classes == {"enabled", "hover"}
+        assert button.styles.background != initial_background

tests/test_cache.py

@@ -8,7 +8,7 @@ from textual._cache import FIFOCache, LRUCache
 def test_lru_cache():
     cache = LRUCache(3)
 
-    assert str(cache) == "<LRUCache maxsize=3 hits=0 misses=0>"
+    assert str(cache) == "<LRUCache size=0 maxsize=3 hits=0 misses=0>"
 
     # insert some values
     cache["foo"] = 1
@@ -65,7 +65,7 @@ def test_lru_cache_hits():
     assert cache.hits == 3
     assert cache.misses == 2
 
-    assert str(cache) == "<LRUCache maxsize=4 hits=3 misses=2>"
+    assert str(cache) == "<LRUCache size=1 maxsize=4 hits=3 misses=2>"
 
 
 def test_lru_cache_get():