garantee order

src/textual/css/stylesheet.py

@@ -406,7 +406,7 @@ class Stylesheet:
         )
         self.replace_rules(node, node_rules, animate=animate)
 
-        component_classes = node._get_component_classes()
+        component_classes = DOMNode._get_component_classes(type(node))
         if component_classes:
             old_component_styles = node._component_styles.copy()
             node._component_styles.clear()

src/textual/dom.py

@@ -229,8 +229,8 @@ class DOMNode(MessagePump):
         # Node bases are in reversed order so that the base class is lower priority
         return self._css_bases(self.__class__)
 
-    @classmethod
-    def _css_bases(cls, base: Type[DOMNode]) -> Iterable[Type[DOMNode]]:
+    @staticmethod
+    def _css_bases(base: Type[DOMNode]) -> Iterable[Type[DOMNode]]:
         """Get the DOMNode base classes, which inherit CSS.
 
         Args:
@@ -317,8 +317,8 @@ class DOMNode(MessagePump):
 
         return css_stack
 
-    @classmethod
-    def _get_component_classes(cls) -> frozenset[str]:
+    @staticmethod
+    def _get_component_classes(node_type: type[DOMNode]) -> Iterable[str]:
         """Gets the component classes for this class and inherited from bases.
 
         Component classes are inherited from base classes, unless
@@ -327,13 +327,13 @@ class DOMNode(MessagePump):
         Returns:
             A set with all the component classes available.
         """
-        component_classes: set[str] = set()
-        for base in cls._css_bases(cls):
-            component_classes.update(base.__dict__.get("COMPONENT_CLASSES", set()))
+        component_classes: list[str] = []
+        for base in DOMNode._css_bases(node_type):
+            component_classes.extend(base.__dict__.get("COMPONENT_CLASSES", ()))
             if not base.__dict__.get("_inherit_component_classes", True):
                 break
 
-        return frozenset(component_classes)
+        return sorted(component_classes)
 
     @property
     def parent(self) -> DOMNode | None:

tests/snapshot_tests/test_snapshots.py

@@ -238,4 +238,6 @@ def test_disabled_widgets(snap_compare):
 
 
 def test_focus_component_class(snap_compare):
-    assert snap_compare(SNAPSHOT_APPS_DIR / "focus_component_class.py", press=["tab"])
+    assert snap_compare(
+        SNAPSHOT_APPS_DIR / "focus_component_class.py", press=["tab", "_"]
+    )

tests/test_dom.py

@@ -143,27 +143,27 @@ def test_component_classes_inheritance():
         COMPONENT_CLASSES = {"f-1"}
 
     node = DOMNode()
-    node_cc = node._get_component_classes()
+    node_cc = DOMNode._get_component_classes(type(node))
     a = A()
-    a_cc = a._get_component_classes()
+    a_cc = DOMNode._get_component_classes(type(a))
     b = B()
-    b_cc = b._get_component_classes()
+    b_cc = DOMNode._get_component_classes(type(b))
     c = C()
-    c_cc = c._get_component_classes()
+    c_cc = DOMNode._get_component_classes(type(c))
     d = D()
-    d_cc = d._get_component_classes()
+    d_cc = DOMNode._get_component_classes(type(d))
     e = E()
-    e_cc = e._get_component_classes()
+    e_cc = DOMNode._get_component_classes(type(e))
     f = F()
-    f_cc = f._get_component_classes()
+    f_cc = DOMNode._get_component_classes(type(f))
 
-    assert node_cc == set()
-    assert a_cc == {"a-1", "a-2"}
-    assert b_cc == {"b-1"}
-    assert c_cc == {"b-1", "c-1", "c-2"}
+    assert node_cc == []
+    assert a_cc == ["a-1", "a-2"]
+    assert b_cc == ["b-1"]
+    assert c_cc == ["b-1", "c-1", "c-2"]
     assert d_cc == c_cc
-    assert e_cc == {"b-1", "c-1", "c-2", "e-1"}
-    assert f_cc == {"f-1"}
+    assert e_cc == ["b-1", "c-1", "c-2", "e-1"]
+    assert f_cc == ["f-1"]
 
 
 @pytest.fixture