fix: add dataclass_transform to maintain IDE typing support for Event…

…edModel.__init__ (#154)

* fix: fix static init typing on eventedmodel

* undo typing changes

* class var

* style(pre-commit.ci): auto fixes [...]

* fix: ignore error

* fix: fix annotation

* style(pre-commit.ci): auto fixes [...]

* fix: fix coverage

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

src/psygnal/_evented_model.py

@@ -1,5 +1,3 @@
-from __future__ import annotations
-
 import sys
 import warnings
 from contextlib import contextmanager
@@ -19,20 +17,29 @@
 
 import pydantic.main
 from pydantic import BaseModel, PrivateAttr, utils
+from pydantic.fields import Field, FieldInfo
 
 from ._evented_decorator import _check_field_equality, _pick_equality_operator
 from ._group import SignalGroup
 from ._signal import Signal, SignalInstance
 
 if TYPE_CHECKING:
-    import inspect
+    from inspect import Signature
 
-    from pydantic import BaseConfig
     from pydantic.fields import ModelField
+    from typing_extensions import dataclass_transform
 
-    ConfigType = Type[BaseConfig]
     EqOperator = Callable[[Any, Any], bool]
 
+else:
+    try:
+        from typing_extensions import dataclass_transform
+    except ImportError:  # pragma: no cover
+
+        def dataclass_transform(*args, **kwargs):
+            return lambda a: a
+
+
 _NULL = object()
 ALLOW_PROPERTY_SETTERS = "allow_property_setters"
 PROPERTY_DEPENDENCIES = "property_dependencies"
@@ -73,7 +80,7 @@ def no_class_attributes() -> Iterator[None]:  # pragma: no cover
 
     # monkey patch the pydantic ClassAttribute object
     # the second argument to ClassAttribute is the inspect.Signature object
-    def _return2(x: str, y: inspect.Signature) -> inspect.Signature:
+    def _return2(x: str, y: "Signature") -> "Signature":
         return y
 
     pydantic.main.ClassAttribute = _return2  # type: ignore
@@ -84,6 +91,7 @@ def _return2(x: str, y: inspect.Signature) -> inspect.Signature:
         pydantic.main.ClassAttribute = utils.ClassAttribute  # type: ignore
 
 
+@dataclass_transform(kw_only_default=True, field_specifiers=(Field, FieldInfo))
 class EventedMetaclass(pydantic.main.ModelMetaclass):
     """pydantic ModelMetaclass that preps "equality checking" operations.
 
@@ -101,14 +109,14 @@ class EventedMetaclass(pydantic.main.ModelMetaclass):
     @no_type_check
     def __new__(  # noqa: C901
         mcs: type, name: str, bases: tuple, namespace: dict, **kwargs: Any
-    ) -> EventedMetaclass:
+    ) -> "EventedMetaclass":
         """Create new EventedModel class."""
         with no_class_attributes():
             cls = super().__new__(mcs, name, bases, namespace, **kwargs)
 
         cls.__eq_operators__ = {}
         signals = {}
-        fields: Dict[str, ModelField] = cls.__fields__
+        fields: Dict[str, "ModelField"] = cls.__fields__
         for n, f in fields.items():
             cls.__eq_operators__[n] = _pick_equality_operator(f.type_)
             if f.field_info.allow_mutation:
@@ -153,7 +161,7 @@ def __new__(  # noqa: C901
         return cls
 
 
-def _get_field_dependents(cls: EventedModel) -> Dict[str, Set[str]]:  # noqa: C901
+def _get_field_dependents(cls: "EventedModel") -> Dict[str, Set[str]]:  # noqa: C901
     """Return mapping of field name -> dependent set of property names.
 
     Dependencies may be declared in the Model Config to emit an event
@@ -288,14 +296,14 @@ class Config:
     """
 
     # add private attributes for event emission
-    _events: SignalGroup = PrivateAttr()
+    _events: ClassVar[SignalGroup] = PrivateAttr()
 
     # mapping of name -> property obj for methods that are property setters
     __property_setters__: ClassVar[Dict[str, property]]
     # mapping of field name -> dependent set of property names
     # when field is changed, an event for dependent properties will be emitted.
     __field_dependents__: ClassVar[Dict[str, Set[str]]]
-    __eq_operators__: ClassVar[Dict[str, EqOperator]]
+    __eq_operators__: ClassVar[Dict[str, "EqOperator"]]
     __slots__ = {"__weakref__"}
     __signal_group__: ClassVar[Type[SignalGroup]]
     # pydantic BaseModel configuration.  see:
@@ -307,7 +315,11 @@ class Config:
 
     def __init__(_model_self_, **data: Any) -> None:
         super().__init__(**data)
-        _model_self_._events = _model_self_.__signal_group__(_model_self_)
+        Group = _model_self_.__signal_group__
+        # the type error is "cannot assign to a class variable" ...
+        # but if we don't use `ClassVar`, then the `dataclass_transform` decorator
+        # will add _events: SignalGroup to the __init__ signature, for *all* user models
+        _model_self_._events = Group(_model_self_)  # type: ignore [misc]
 
     def _super_setattr_(self, name: str, value: Any) -> None:
         # pydantic will raise a ValueError if extra fields are not allowed
@@ -365,7 +377,7 @@ def reset(self) -> None:
             ):
                 setattr(self, name, value)
 
-    def update(self, values: Union[EventedModel, dict], recurse: bool = True) -> None:
+    def update(self, values: Union["EventedModel", dict], recurse: bool = True) -> None:
         """Update a model in place.
 
         Parameters