Switched to try/except

src/travertino/node.py

@@ -1,6 +1,3 @@
-from inspect import signature
-
-
 class Node:
     def __init__(self, style, applicator=None, children=None):
         # Parent needs to be primed before style is (potentially) applied with
@@ -173,43 +170,29 @@ def refresh(self, viewport):
             self._root.refresh(viewport)
         else:
             if self.applicator:
+
                 ######################################################################
                 # 2024-12: Backwards compatibility for Toga <= 0.4.8
                 ######################################################################
-                # (See below)
-                if self._old_layout_args():
-                    self.style.layout(self, viewport)
-                else:
+                # Accommodate the earlier signature of layout(), which included the node
+                # as a parameter.
+                try:
                     self.style.layout(viewport)
+
+                except TypeError as error:
+                    if (
+                        ".layout() missing 1 required positional argument: 'viewport'"
+                        in str(error)
+                    ):
+                        self.style.layout(self, viewport)
+                    else:
+                        raise
                 ######################################################################
                 # End backwards compatibility
                 ######################################################################
 
                 self.applicator.set_bounds()
 
-    ######################################################################
-    # 2024-12: Backwards compatibility for Toga <= 0.4.8
-    ######################################################################
-
-    # Accommodate the earlier signature of layout(), which included the node as a
-    # parameter. This needs to be called on the *instance* -- to have access to the
-    # style -- but it needs to be cached on the *class*, so all instances have access
-    # to it.
-
-    def _old_layout_args(self):
-        try:
-            return self.__class__._cached_old_layout_args
-        except AttributeError:
-            self.__class__._cached_old_layout_args = (
-                "node" in signature(self.style.layout).parameters
-            )
-
-            return self.__class__._cached_old_layout_args
-
-    ######################################################################
-    # End backwards compatibility
-    ######################################################################
-
     def _set_root(self, node, root):
         # Propagate a root node change through a tree.
         node._root = root

tests/test_node.py

@@ -33,6 +33,18 @@ def layout(self, node, viewport):
         super().layout(viewport)
 
 
+class TypeErrorStyle(Style):
+    # Uses the correct signature, but raises an unrelated TypeError in layout
+    def layout(self, viewport):
+        raise TypeError("An unrelated TypeError has occurred somewhere in layout()")
+
+
+class OldTypeErrorStyle(Style):
+    # Just to be extra safe...
+    def layout(self, node, viewport):
+        raise TypeError("An unrelated TypeError has occurred somewhere in layout()")
+
+
 @prep_style_class
 class BrokenStyle(BaseStyle):
     def reapply(self):
@@ -136,39 +148,6 @@ def test_create_node():
     assert child3.root == new_node
 
 
-@pytest.mark.parametrize(
-    "StyleClass, cached_value",
-    [
-        (Style, False),
-        (OldStyle, True),
-    ],
-)
-def test_layout_signature_check(StyleClass, cached_value):
-    """After the first call to refresh(), node class should cache args version."""
-
-    class Applicator:
-        def set_bounds(self):
-            pass
-
-    class TestNode(Node):
-        # So we don't change the actual Node class
-        pass
-
-    # Before refresh() is called, the cached value isn't set.
-    assert not hasattr(TestNode, "_cached_old_layout_args")
-
-    # Check again, just to be sure nothing has changed from creating an instance.
-    node = TestNode(style=StyleClass(), applicator=Applicator())
-    assert not hasattr(TestNode, "_cached_old_layout_args")
-
-    # Refresh for the first time.
-    node.refresh(Viewport(width=10, height=20))
-
-    # After refreshing, which signature to use for layout() should be cached on the
-    # class, and thus accessible to both instances.
-    assert TestNode._cached_old_layout_args == cached_value
-
-
 @pytest.mark.parametrize("StyleClass", [Style, OldStyle])
 def test_refresh(StyleClass):
     """The layout can be refreshed, and the applicator invoked"""
@@ -224,6 +203,19 @@ def __init__(self, style, children=None):
     assert child3.applicator.tasks == []
 
 
+@pytest.mark.parametrize("StyleClass", [TypeErrorStyle, OldTypeErrorStyle])
+def test_type_error_in_layout(StyleClass):
+    """The shim shouldn't hide unrelated TypeErrors."""
+
+    class Applicator:
+        def set_bounds(self):
+            pass
+
+    node = Node(style=StyleClass(), applicator=Applicator())
+    with pytest.raises(TypeError, match=r"unrelated TypeError"):
+        node.refresh(Viewport(50, 50))
+
+
 def test_add():
     """Nodes can be added as children to another node"""