Decorate Pack as dataclass (#3215)

Decorated Pack as dataclass, and tweaked error messages to preserve detailed reporting.

Author: HalfWhitt

changes/3215.feature.rst

@@ -0,0 +1 @@
+Pack is now a dataclass. This should allow most IDEs to infer the names and types of properties and suggest them in creating a Pack instance.

core/src/toga/style/pack.py

@@ -1,6 +1,8 @@
 from __future__ import annotations
 
+import sys
 import warnings
+from dataclasses import dataclass
 from typing import TYPE_CHECKING, Any
 
 if TYPE_CHECKING:
@@ -132,8 +134,7 @@ def __get__(self, obj, objtype=None):
         return super().__get__(obj)
 
     def __set__(self, obj, value):
-        # This won't be executed until @dataclass is added
-        if value is self:  # pragma: no cover
+        if value is self:
             # This happens during autogenerated dataclass __init__ when no value is
             # supplied.
             return
@@ -176,7 +177,13 @@ def warn_if_deprecated(self):
 # End backwards compatibility
 ######################################################################
 
+if sys.version_info < (3, 10):
+    _DATACLASS_KWARGS = {"init": False, "repr": False}
+else:
+    _DATACLASS_KWARGS = {"kw_only": True, "repr": False}
 
+
+@dataclass(**_DATACLASS_KWARGS)
 class Pack(BaseStyle):
     _doc_link = ":doc:`style properties </reference/style/pack>`"
 

core/tests/style/test_mixin.py

@@ -27,7 +27,10 @@ def test_constructor(name, value, default):
     assert getattr(widget.style, name) == value
     assert widget.style.display == "none"
 
-    with raises(NameError, match="Unknown style 'nonexistent'"):
+    with raises(
+        TypeError,
+        match=r"Pack\.__init__\(\) got an unexpected keyword argument 'nonexistent'",
+    ):
         ExampleWidget(nonexistent=None)
 
 

travertino/src/travertino/style.py

@@ -13,9 +13,13 @@ class BaseStyle:
     """A base class for style declarations.
 
     Exposes a dict-like interface. Designed for subclasses to be decorated
-    with @dataclass(kw_only=True), which most IDEs should be able to interpret and
-    provide autocompletion of argument names. On Python < 3.10, init=False can be used
-    to still get the keyword-only behavior from the included __init__.
+    with @dataclass(kw_only=True, repr=False).
+
+    The kw_only parameter was added in Python 3.10; for 3.9, init=False can be used
+    instead to still get the keyword-only behavior from the included __init__.
+
+    Most IDEs should see the dataclass decorator and provide autocompletion / type hints
+    for parameters to the constructor.
     """
 
     _BASE_PROPERTIES = defaultdict(set)
@@ -26,10 +30,35 @@ def __init_subclass__(cls):
         cls._PROPERTIES = cls._BASE_PROPERTIES[cls]
         cls._ALL_PROPERTIES = cls._BASE_ALL_PROPERTIES[cls]
 
+    ########################################################################
+    # 03-2025: Backwards compatibility for Toga < 0.5.0 *and* for Python 3.9
+    ########################################################################
+
     # Fallback in case subclass isn't decorated as dataclass (probably from using
     # previous API) or for pre-3.10, before kw_only argument existed.
     def __init__(self, **properties):
-        self.update(**properties)
+        try:
+            self.update(**properties)
+        except NameError:
+            # It still makes sense for update() to raise a NameError. However, here we
+            # simulate the behavior of the dataclass-generated __init__() for
+            # consistency.
+            for name in properties:
+                # This is redoing work, but it should only ever happen when a property
+                # name is invalid, and only in outdated Python or Toga, and only once.
+                if name not in self._ALL_PROPERTIES:
+                    raise TypeError(
+                        f"{type(self).__name__}.__init__() got an unexpected keyword "
+                        f"argument '{name}'"
+                    )
+            # The above for loop should never run to completion, so that needs to be
+            # excluded from coverage.
+            else:  # pragma: no cover
+                pass
+
+    ######################################################################
+    # End backwards compatibility
+    ######################################################################
 
     @property
     def _applicator(self):
@@ -197,6 +226,12 @@ def __str__(self):
             f"{name.replace('_', '-')}: {value}" for name, value in sorted(self.items())
         )
 
+    def __repr__(self):
+        properties = ", ".join(
+            f"{name}={repr(value)}" for name, value in sorted(self.items())
+        )
+        return f"{type(self).__name__}({properties})"
+
     ######################################################################
     # Backwards compatibility
     ######################################################################

travertino/tests/test_style.py

@@ -150,6 +150,16 @@ def test_positional_argument(StyleClass):
         StyleClass(5)
 
 
+@pytest.mark.parametrize("StyleClass", [Style, DeprecatedStyle])
+def test_constructor_invalid_property(StyleClass):
+    """Whether dataclass or not, the error should be the same."""
+    with pytest.raises(
+        TypeError,
+        match=r"Style\.__init__\(\) got an unexpected keyword argument 'bogus'",
+    ):
+        StyleClass(explicit_const=5, bogus=None)
+
+
 @pytest.mark.parametrize("StyleClass", [Style, DeprecatedStyle])
 def test_create_and_copy(StyleClass):
     style = StyleClass(explicit_const=VALUE2, implicit=VALUE3)
@@ -704,6 +714,22 @@ def test_str(StyleClass):
     )
 
 
+def test_repr():
+    # Doesn't need to be tested with deprecated API.
+    style = Style(explicit_const=VALUE2, explicit_value=20, thing=(30, 40, 50, 60))
+
+    assert repr(style) == (
+        "Style("
+        "explicit_const='value2', "
+        "explicit_value=20, "
+        "thing_bottom=50, "
+        "thing_left=60, "
+        "thing_right=40, "
+        "thing_top=30"
+        ")"
+    )
+
+
 @pytest.mark.parametrize("StyleClass", [Style, DeprecatedStyle])
 def test_dict(StyleClass):
     "Style declarations expose a dict-like interface"

travertino/tests/utils.py

@@ -7,9 +7,9 @@
 from travertino.colors import hsl, hsla, rgb, rgba
 
 if sys.version_info < (3, 10):
-    _DATACLASS_KWARGS = {"init": False}
+    _DATACLASS_KWARGS = {"init": False, "repr": False}
 else:
-    _DATACLASS_KWARGS = {"kw_only": True}
+    _DATACLASS_KWARGS = {"kw_only": True, "repr": False}
 
 
 def apply_dataclass(cls):