Repository: pydantic/pydantic

Issue:
Pydantic 1.8.0 raises Exception when overriding __eq__
### Checks

* [x] I added a descriptive title to this issue
* [x] I have searched (google, github) for similar issues and couldn't find anything
* [x] I have read and followed [the docs](https://pydantic-docs.helpmanual.io/) and still think this is a bug

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# Bug

<!-- or if you're using pydantic prior to v1.3, manually include: OS, python version and pydantic version -->

<!-- Please read the [docs](https://pydantic-docs.helpmanual.io/) and search through issues to
confirm your bug hasn't already been reported. -->

<!-- Where possible please include a self-contained code snippet describing your bug: -->

```py
from pydantic import BaseModel


class Foo(BaseModel):
    value: int

    def __eq__(self, other):
        return self.value == other.value


class Test(BaseModel):
    foo: Foo = Foo(value=10)
```
for pydantic 1.7.x it works.
when 1.8.1 it raises:
```
Traceback (most recent call last):
  File "main.py", line 11, in <module>
    class Test(BaseModel):
  File "pydantic/main.py", line 287, in pydantic.main.ModelMetaclass.__new__
  File "pydantic/fields.py", line 384, in pydantic.fields.ModelField.infer
  File "pydantic/fields.py", line 369, in pydantic.fields.ModelField._get_field_info
  File "pydantic/fields.py", line 157, in pydantic.fields.FieldInfo._validate
  File "main.py", line 8, in __eq__
    return self.value < other.value
AttributeError: 'UndefinedType' object has no attribute 'value'
```



Comments:

Patch:
diff --git a/pydantic/decorator.py b/pydantic/decorator.py
--- a/pydantic/decorator.py
+++ b/pydantic/decorator.py
@@ -1,23 +1,10 @@
 from functools import wraps
-from typing import (
-    TYPE_CHECKING,
-    Any,
-    Callable,
-    Dict,
-    List,
-    Mapping,
-    Optional,
-    Tuple,
-    Type,
-    TypeVar,
-    Union,
-    get_type_hints,
-    overload,
-)
+from typing import TYPE_CHECKING, Any, Callable, Dict, List, Mapping, Optional, Tuple, Type, TypeVar, Union, overload
 
 from . import validator
 from .errors import ConfigError
 from .main import BaseModel, Extra, create_model
+from .typing import get_all_type_hints
 from .utils import to_camel
 
 __all__ = ('validate_arguments',)
@@ -87,17 +74,17 @@ def __init__(self, function: 'AnyCallableT', config: 'ConfigType'):  # noqa C901
         self.v_args_name = 'args'
         self.v_kwargs_name = 'kwargs'
 
-        type_hints = get_type_hints(function)
+        type_hints = get_all_type_hints(function)
         takes_args = False
         takes_kwargs = False
         fields: Dict[str, Tuple[Any, Any]] = {}
         for i, (name, p) in enumerate(parameters.items()):
-            if p.annotation == p.empty:
+            if p.annotation is p.empty:
                 annotation = Any
             else:
                 annotation = type_hints[name]
 
-            default = ... if p.default == p.empty else p.default
+            default = ... if p.default is p.empty else p.default
             if p.kind == Parameter.POSITIONAL_ONLY:
                 self.arg_mapping[i] = name
                 fields[name] = annotation, default
diff --git a/pydantic/fields.py b/pydantic/fields.py
--- a/pydantic/fields.py
+++ b/pydantic/fields.py
@@ -169,7 +169,7 @@ def update_from_config(self, from_config: Dict[str, Any]) -> None:
                     setattr(self, attr_name, value)
 
     def _validate(self) -> None:
-        if self.default not in (Undefined, Ellipsis) and self.default_factory is not None:
+        if self.default is not Undefined and self.default_factory is not None:
             raise ValueError('cannot specify both default and default_factory')
 
 
@@ -370,9 +370,10 @@ def _get_field_info(
             field_info = next(iter(field_infos), None)
             if field_info is not None:
                 field_info.update_from_config(field_info_from_config)
-                if field_info.default not in (Undefined, Ellipsis):
+                if field_info.default is not Undefined:
                     raise ValueError(f'`Field` default cannot be set in `Annotated` for {field_name!r}')
-                if value not in (Undefined, Ellipsis):
+                if value is not Undefined and value is not Required:
+                    # check also `Required` because of `validate_arguments` that sets `...` as default value
                     field_info.default = value
 
         if isinstance(value, FieldInfo):
@@ -450,7 +451,6 @@ def prepare(self) -> None:
         self._type_analysis()
         if self.required is Undefined:
             self.required = True
-            self.field_info.default = Required
         if self.default is Undefined and self.default_factory is None:
             self.default = None
         self.populate_validators()
diff --git a/pydantic/generics.py b/pydantic/generics.py
--- a/pydantic/generics.py
+++ b/pydantic/generics.py
@@ -15,13 +15,14 @@
     TypeVar,
     Union,
     cast,
-    get_type_hints,
 )
 
+from typing_extensions import Annotated
+
 from .class_validators import gather_all_validators
 from .fields import DeferredType
 from .main import BaseModel, create_model
-from .typing import display_as_type, get_args, get_origin, typing_base
+from .typing import display_as_type, get_all_type_hints, get_args, get_origin, typing_base
 from .utils import all_identical, lenient_issubclass
 
 _generic_types_cache: Dict[Tuple[Type[Any], Union[Any, Tuple[Any, ...]]], Type[BaseModel]] = {}
@@ -73,7 +74,7 @@ def __class_getitem__(cls: Type[GenericModelT], params: Union[Type[Any], Tuple[T
         model_name = cls.__concrete_name__(params)
         validators = gather_all_validators(cls)
 
-        type_hints = get_type_hints(cls).items()
+        type_hints = get_all_type_hints(cls).items()
         instance_type_hints = {k: v for k, v in type_hints if get_origin(v) is not ClassVar}
 
         fields = {k: (DeferredType(), cls.__fields__[k].field_info) for k in instance_type_hints if k in cls.__fields__}
@@ -159,6 +160,10 @@ def replace_types(type_: Any, type_map: Mapping[Any, Any]) -> Any:
     type_args = get_args(type_)
     origin_type = get_origin(type_)
 
+    if origin_type is Annotated:
+        annotated_type, *annotations = type_args
+        return Annotated[replace_types(annotated_type, type_map), tuple(annotations)]
+
     # Having type args is a good indicator that this is a typing module
     # class instantiation or a generic alias of some sort.
     if type_args:
diff --git a/pydantic/typing.py b/pydantic/typing.py
--- a/pydantic/typing.py
+++ b/pydantic/typing.py
@@ -18,6 +18,7 @@
     Union,
     _eval_type,
     cast,
+    get_type_hints,
 )
 
 from typing_extensions import Annotated, Literal
@@ -70,6 +71,18 @@ def evaluate_forwardref(type_: ForwardRef, globalns: Any, localns: Any) -> Any:
         return cast(Any, type_)._evaluate(globalns, localns, set())
 
 
+if sys.version_info < (3, 9):
+    # Ensure we always get all the whole `Annotated` hint, not just the annotated type.
+    # For 3.6 to 3.8, `get_type_hints` doesn't recognize `typing_extensions.Annotated`,
+    # so it already returns the full annotation
+    get_all_type_hints = get_type_hints
+
+else:
+
+    def get_all_type_hints(obj: Any, globalns: Any = None, localns: Any = None) -> Any:
+        return get_type_hints(obj, globalns, localns, include_extras=True)
+
+
 if sys.version_info < (3, 7):
     from typing import Callable as Callable
 
@@ -225,6 +238,7 @@ def get_args(tp: Type[Any]) -> Tuple[Any, ...]:
     'get_args',
     'get_origin',
     'typing_base',
+    'get_all_type_hints',
 )
 
 


Test patch:
diff --git a/tests/test_annotated.py b/tests/test_annotated.py
--- a/tests/test_annotated.py
+++ b/tests/test_annotated.py
@@ -1,11 +1,9 @@
-import sys
-from typing import get_type_hints
-
 import pytest
 from typing_extensions import Annotated
 
 from pydantic import BaseModel, Field
 from pydantic.fields import Undefined
+from pydantic.typing import get_all_type_hints
 
 
 @pytest.mark.parametrize(
@@ -43,15 +41,7 @@ class M(BaseModel):
 
     assert M().x == 5
     assert M(x=10).x == 10
-
-    # get_type_hints doesn't recognize typing_extensions.Annotated, so will return the full
-    # annotation. 3.9 w/ stock Annotated will return the wrapped type by default, but return the
-    # full thing with the new include_extras flag.
-    if sys.version_info >= (3, 9):
-        assert get_type_hints(M)['x'] is int
-        assert get_type_hints(M, include_extras=True)['x'] == hint
-    else:
-        assert get_type_hints(M)['x'] == hint
+    assert get_all_type_hints(M)['x'] == hint
 
 
 @pytest.mark.parametrize(
diff --git a/tests/test_decorator.py b/tests/test_decorator.py
--- a/tests/test_decorator.py
+++ b/tests/test_decorator.py
@@ -3,14 +3,13 @@
 import sys
 from pathlib import Path
 from typing import List
-from unittest.mock import ANY
 
 import pytest
+from typing_extensions import Annotated
 
 from pydantic import BaseModel, Field, ValidationError, validate_arguments
 from pydantic.decorator import ValidatedFunction
 from pydantic.errors import ConfigError
-from pydantic.typing import Annotated
 
 skip_pre_38 = pytest.mark.skipif(sys.version_info < (3, 8), reason='testing >= 3.8 behaviour only')
 
@@ -154,13 +153,14 @@ def foo(a: int, b: int = Field(default_factory=lambda: 99), *args: int) -> int:
     assert foo(1, 2, 3) == 6
 
 
-@pytest.mark.skipif(not Annotated, reason='typing_extensions not installed')
 def test_annotated_field_can_provide_factory() -> None:
     @validate_arguments
-    def foo2(a: int, b: Annotated[int, Field(default_factory=lambda: 99)] = ANY, *args: int) -> int:
+    def foo2(a: int, b: Annotated[int, Field(default_factory=lambda: 99)], *args: int) -> int:
         """mypy reports Incompatible default for argument "b" if we don't supply ANY as default"""
         return a + b + sum(args)
 
+    assert foo2(1) == 100
+
 
 @skip_pre_38
 def test_positional_only(create_module):
diff --git a/tests/test_edge_cases.py b/tests/test_edge_cases.py
--- a/tests/test_edge_cases.py
+++ b/tests/test_edge_cases.py
@@ -1839,3 +1839,19 @@ class Config:
     with pytest.raises(TypeError):
         b.a = 'y'
     assert b.dict() == {'a': 'x'}
+
+
+def test_arbitrary_types_allowed_custom_eq():
+    class Foo:
+        def __eq__(self, other):
+            if other.__class__ is not Foo:
+                raise TypeError(f'Cannot interpret {other.__class__.__name__!r} as a valid type')
+            return True
+
+    class Model(BaseModel):
+        x: Foo = Foo()
+
+        class Config:
+            arbitrary_types_allowed = True
+
+    assert Model().x == Foo()
diff --git a/tests/test_generics.py b/tests/test_generics.py
--- a/tests/test_generics.py
+++ b/tests/test_generics.py
@@ -3,7 +3,7 @@
 from typing import Any, Callable, ClassVar, Dict, Generic, List, Optional, Sequence, Tuple, Type, TypeVar, Union
 
 import pytest
-from typing_extensions import Literal
+from typing_extensions import Annotated, Literal
 
 from pydantic import BaseModel, Field, ValidationError, root_validator, validator
 from pydantic.generics import GenericModel, _generic_types_cache, iter_contained_typevars, replace_types
@@ -1071,3 +1071,13 @@ class GModel(GenericModel, Generic[FieldType, ValueType]):
     Fields = Literal['foo', 'bar']
     m = GModel[Fields, str](field={'foo': 'x'})
     assert m.dict() == {'field': {'foo': 'x'}}
+
+
+@skip_36
+def test_generic_annotated():
+    T = TypeVar('T')
+
+    class SomeGenericModel(GenericModel, Generic[T]):
+        some_field: Annotated[T, Field(alias='the_alias')]
+
+    SomeGenericModel[str](the_alias='qwe')