Do not require validate_assignment to use Field.frozen

docs/errors/validation_errors.md

@@ -606,18 +606,15 @@ except ValidationError as exc:
 
 ## `frozen_field`
 
-This error is raised when `model_config['validate_assignment'] == True` and you attempt to assign
-a value to a field with `frozen=True`:
+This error is raised when you attempt to assign a value to a field with `frozen=True`:
 
 ```py
-from pydantic import BaseModel, ConfigDict, Field, ValidationError
+from pydantic import BaseModel, Field, ValidationError
 
 
 class Model(BaseModel):
     x: str = Field('test', frozen=True)
 
-    model_config = ConfigDict(validate_assignment=True)
-
 
 model = Model()
 try:

docs/usage/fields.md

@@ -623,20 +623,18 @@ assigned a new value after the model is created (immutability).
 See the [frozen dataclass documentation] for more details.
 
 ```py
-from pydantic import BaseModel, ConfigDict, Field, ValidationError
+from pydantic import BaseModel, Field, ValidationError
 
 
 class User(BaseModel):
-    model_config = ConfigDict(validate_assignment=True)  # (1)!
-
     name: str = Field(frozen=True)
     age: int
 
 
 user = User(name='John', age=42)
 
 try:
-    user.name = 'Jane'  # (2)!
+    user.name = 'Jane'  # (1)!
 except ValidationError as e:
     print(e)
     """
@@ -646,11 +644,7 @@ except ValidationError as e:
     """
 ```
 
-1. The `model_config` field is used to enable the validation of assignments.
-
-    See the [Validate Assignment] section for more details.
-
-2. Since `validate_assignment` is enabled, and the `name` field is frozen, the assignment is not allowed.
+1. Since `name` field is frozen, the assignment is not allowed.
 
 ## Exclude
 

pydantic/main.py

@@ -748,6 +748,13 @@ def __setattr__(self, name: str, value: Any) -> None:
                 'input': value,
             }
             raise pydantic_core.ValidationError.from_exception_data(self.__class__.__name__, [error])
+        elif getattr(self.model_fields.get(name), 'frozen', False):
+            error: pydantic_core.InitErrorDetails = {
+                'type': 'frozen_field',
+                'loc': (name,),
+                'input': value,
+            }
+            raise pydantic_core.ValidationError.from_exception_data(self.__class__.__name__, [error])
 
         attr = getattr(self.__class__, name, None)
         if isinstance(attr, property):

tests/test_main.py

@@ -503,6 +503,19 @@ class FrozenModel(BaseModel):
     ]
 
 
+def test_frozen_field():
+    class FrozenModel(BaseModel):
+        a: int = Field(10, frozen=True)
+
+    m = FrozenModel()
+
+    with pytest.raises(ValidationError) as exc_info:
+        m.a = 11
+    assert exc_info.value.errors(include_url=False) == [
+        {'type': 'frozen_field', 'loc': ('a',), 'msg': 'Field is frozen', 'input': 11}
+    ]
+
+
 def test_not_frozen_are_not_hashable():
     class TestModel(BaseModel):
         a: int = 10
@@ -1660,7 +1673,7 @@ class M(BaseModel):
     get_type_hints(type(M.model_config))
 
 
-def test_frozen_field():
+def test_frozen_field_with_validate_assignment():
     """assigning a frozen=True field should raise a TypeError"""
 
     class Entry(BaseModel):