Allow access to field_name and data in all validators if there is…

… data and a field name (#7542)

Co-authored-by: Adrian Garcia Badaracco <1755071+adriangb@users.noreply.github.com>

docs/migration.md

@@ -280,14 +280,14 @@ being validated. Some of these arguments have been removed from `@field_validato
     to index into `cls.model_fields`
 
 ```python
-from pydantic import BaseModel, FieldValidationInfo, field_validator
+from pydantic import BaseModel, ValidationInfo, field_validator
 
 
 class Model(BaseModel):
     x: int
 
     @field_validator('x')
-    def val_x(cls, v: int, info: FieldValidationInfo) -> int:
+    def val_x(cls, v: int, info: ValidationInfo) -> int:
         assert info.config is not None
         print(info.config.get('title'))
         #> Model

docs/usage/serialization.md

@@ -365,14 +365,14 @@ class DayThisYear(date):
     def __get_pydantic_core_schema__(
         cls, source: Type[Any], handler: GetCoreSchemaHandler
     ) -> core_schema.CoreSchema:
-        return core_schema.general_after_validator_function(
+        return core_schema.no_info_after_validator_function(
             cls.validate,
             core_schema.int_schema(),
             serialization=core_schema.format_ser_schema('%Y-%m-%d'),
         )
 
     @classmethod
-    def validate(cls, v: int, _info):
+    def validate(cls, v: int):
         return date.today().replace(month=1, day=1) + timedelta(days=v)
 
 

docs/usage/types/custom.md

@@ -1,5 +1,3 @@
-
-
 You can also define your own custom data types. There are several ways to achieve it.
 
 ## Composing types via `Annotated`
@@ -775,8 +773,8 @@ class MySequence(Sequence[T]):
         else:
             sequence_t_schema = handler.generate_schema(Sequence)
 
-        non_instance_schema = core_schema.general_after_validator_function(
-            lambda v, i: MySequence(v), sequence_t_schema
+        non_instance_schema = core_schema.no_info_after_validator_function(
+            MySequence, sequence_t_schema
         )
         return core_schema.union_schema([instance_schema, non_instance_schema])
 
@@ -807,11 +805,80 @@ except ValidationError as exc:
     2 validation errors for M
     s1.is-instance[MySequence]
       Input should be an instance of MySequence [type=is_instance_of, input_value=['a'], input_type=list]
-    s1.function-after[<lambda>(), json-or-python[json=list[int],python=chain[is-instance[Sequence],function-wrap[sequence_validator()]]]].0
+    s1.function-after[MySequence(), json-or-python[json=list[int],python=chain[is-instance[Sequence],function-wrap[sequence_validator()]]]].0
       Input should be a valid integer, unable to parse string as an integer [type=int_parsing, input_value='a', input_type=str]
     """
 ```
 
+### Access to field name
+
+!!!note
+    This was not possible with Pydantic V2 to V2.3, it was [re-added](https://github.com/pydantic/pydantic/pull/7542) in Pydantic V2.4.
+
+As of Pydantic V2.4, you can access the field name via the `handler.field_name` within `__get_pydantic_core_schema__`
+and thereby set the field name which will be available from `info.field_name`.
+
+```python
+from typing import Any
+
+from pydantic_core import core_schema
+
+from pydantic import BaseModel, GetCoreSchemaHandler, ValidationInfo
+
+
+class CustomType:
+    """Custom type that stores the field it was used in."""
+
+    def __init__(self, value: int, field_name: str):
+        self.value = value
+        self.field_name = field_name
+
+    def __repr__(self):
+        return f'CustomType<{self.value} {self.field_name!r}>'
+
+    @classmethod
+    def validate(cls, value: int, info: ValidationInfo):
+        return cls(value, info.field_name)
+
+    @classmethod
+    def __get_pydantic_core_schema__(
+        cls, source_type: Any, handler: GetCoreSchemaHandler
+    ) -> core_schema.CoreSchema:
+        return core_schema.with_info_after_validator_function(
+            cls.validate, handler(int), field_name=handler.field_name
+        )
+
+
+class MyModel(BaseModel):
+    my_field: CustomType
+
+
+m = MyModel(my_field=1)
+print(m.my_field)
+#> CustomType<1 'my_field'>
+```
+
+You can also access `field_name` from the markers used with `Annotated`, like [`AfterValidator`][pydantic.functional_validators.AfterValidator].
+
+```python
+from typing_extensions import Annotated
+
+from pydantic import AfterValidator, BaseModel, ValidationInfo
+
+
+def my_validators(value: int, info: ValidationInfo):
+    return f'<{value} {info.field_name!r}>'
+
+
+class MyModel(BaseModel):
+    my_field: Annotated[int, AfterValidator(my_validators)]
+
+
+m = MyModel(my_field=1)
+print(m.my_field)
+#> <1 'my_field'>
+```
+
 [PEP 593]: https://peps.python.org/pep-0593/
 [PEP 695]: https://peps.python.org/pep-0695/
 [typing-extensions]: https://github.com/python/typing_extensions

docs/usage/validators.md

@@ -305,8 +305,8 @@ If you want to attach a validator to a specific field of a model you can use the
 ```py
 from pydantic import (
     BaseModel,
-    FieldValidationInfo,
     ValidationError,
+    ValidationInfo,
     field_validator,
 )
 
@@ -325,7 +325,7 @@ class UserModel(BaseModel):
     # you can select multiple fields, or use '*' to select all fields
     @field_validator('id', 'name')
     @classmethod
-    def check_alphanumeric(cls, v: str, info: FieldValidationInfo) -> str:
+    def check_alphanumeric(cls, v: str, info: ValidationInfo) -> str:
         if isinstance(v, str):
             # info.field_name is the name of the field being validated
             is_alphanumeric = v.replace(' ', '').isalnum()
@@ -372,7 +372,7 @@ A few things to note on validators:
 
 * `@field_validator`s are "class methods", so the first argument value they receive is the `UserModel` class, not an instance of `UserModel`. We recommend you use the `@classmethod` decorator on them below the `@field_validator` decorator to get proper type checking.
 * the second argument is the field value to validate; it can be named as you please
-* the third argument, if present, is an instance of `pydantic.FieldValidationInfo`
+* the third argument, if present, is an instance of `pydantic.ValidationInfo`
 * validators should either return the parsed value or raise a `ValueError` or `AssertionError` (``assert`` statements may be used).
 * A single validator can be applied to multiple fields by passing it multiple field names.
 * A single validator can also be called on *all* fields by passing the special value `'*'`.
@@ -382,8 +382,8 @@ A few things to note on validators:
     Python with the [`-O` optimization flag](https://docs.python.org/3/using/cmdline.html#cmdoption-o)
     disables `assert` statements, and **validators will stop working**.
 
-If you want to access values from another field inside a `@field_validator`, this may be possible using `FieldValidationInfo.data`, which is a dict of field name to field value.
-Validation is done in the order fields are defined, so you have to be careful when using `FieldValidationInfo.data` to not access a field that has not yet been validated/populated — in the code above, for example, you would not be able to access `info.data['id']` from within `name_must_contain_space`.
+If you want to access values from another field inside a `@field_validator`, this may be possible using `ValidationInfo.data`, which is a dict of field name to field value.
+Validation is done in the order fields are defined, so you have to be careful when using `ValidationInfo.data` to not access a field that has not yet been validated/populated — in the code above, for example, you would not be able to access `info.data['id']` from within `name_must_contain_space`.
 However, in most cases where you want to perform validation using multiple field values, it is better to use `@model_validator` which is discussed in the section below.
 
 ## Model validators
@@ -604,15 +604,15 @@ You can pass a context object to the validation methods which can be accessed fr
 argument to decorated validator functions:
 
 ```python
-from pydantic import BaseModel, FieldValidationInfo, field_validator
+from pydantic import BaseModel, ValidationInfo, field_validator
 
 
 class Model(BaseModel):
     text: str
 
     @field_validator('text')
     @classmethod
-    def remove_stopwords(cls, v: str, info: FieldValidationInfo):
+    def remove_stopwords(cls, v: str, info: ValidationInfo):
         context = info.context
         if context:
             stopwords = context.get('stopwords', set())
@@ -638,8 +638,8 @@ from typing import Any, Dict, List
 
 from pydantic import (
     BaseModel,
-    FieldValidationInfo,
     ValidationError,
+    ValidationInfo,
     field_validator,
 )
 
@@ -660,7 +660,7 @@ class Model(BaseModel):
 
     @field_validator('choice')
     @classmethod
-    def validate_choice(cls, v: str, info: FieldValidationInfo):
+    def validate_choice(cls, v: str, info: ValidationInfo):
         allowed_choices = info.context.get('allowed_choices')
         if allowed_choices and v not in allowed_choices:
             raise ValueError(f'choice must be one of {allowed_choices}')
@@ -702,7 +702,7 @@ from contextlib import contextmanager
 from contextvars import ContextVar
 from typing import Any, Dict, Iterator
 
-from pydantic import BaseModel, FieldValidationInfo, field_validator
+from pydantic import BaseModel, ValidationInfo, field_validator
 
 _init_context_var = ContextVar('_init_context_var', default=None)
 
@@ -728,9 +728,7 @@ class Model(BaseModel):
 
     @field_validator('my_number')
     @classmethod
-    def multiply_with_context(
-        cls, value: int, info: FieldValidationInfo
-    ) -> int:
+    def multiply_with_context(cls, value: int, info: ValidationInfo) -> int:
         if info.context:
             multiplier = info.context.get('multiplier', 1)
             value = value * multiplier