mypy plugin support for dataclasses (#966)

* mypy plugin support for dataclassesv

* fix styles and types

* - change type-hint for `Config`
- change name of an expected file
- update documents

* fix broken a reference of a document.

* - update unittest
- update documents

* fix a document link

* Update docs/mypy_plugin.md

Co-Authored-By: Samuel Colvin <samcolvin@gmail.com>

* Update docs/mypy_plugin.md

Co-Authored-By: Samuel Colvin <samcolvin@gmail.com>

* Update docs/mypy_plugin.md

Co-Authored-By: Samuel Colvin <samcolvin@gmail.com>

* remove extra whitespaces on mypy test results

* fix output file name of mypy test

* Update docs/usage/dataclasses.md

Co-Authored-By: Samuel Colvin <samcolvin@gmail.com>

* use TypeVar for DataclassType

changes/966-koxudaxi.md

@@ -0,0 +1 @@
+Mypy plugin support for dataclasses

docs/mypy_plugin.md

@@ -53,7 +53,11 @@ There are other benefits too! See below for more details.
 #### Respect `Config.orm_mode`
 * If `Config.orm_mode` is `False`, you'll get a mypy error if you try to call `.from_orm()`;
   cf. [ORM mode](usage/models.md#orm-mode-aka-arbitrary-class-instances)
-
+
+#### Generate a signature for `dataclasses`
+* classes decorated with [`@pydantic.dataclasess.dataclass`](usage/dataclasses.md) are type checked the same as standard python dataclasses
+* The `@pydantic.dataclasess.dataclass` decorator accepts a `config` keyword argument which has the same meaning as [the `Config` sub-class](usage/model_config.md).
+
 ### Optional Capabilites:
 #### Prevent the use of required dynamic aliases
 * If the [`warn_required_dynamic_aliases` **plugin setting**](#plugin-settings) is set to `True`, you'll get a mypy

docs/usage/dataclasses.md

@@ -30,11 +30,8 @@ _(This script is complete, it should run "as is")_
 `pydantic.dataclasses.dataclass`'s arguments are the same as the standard decorator, except one extra
 keyword argument `config` which has the same meaning as [Config](model_config.md).
 
-!!! note
-    As a side effect of getting pydantic dataclasses to play nicely with mypy, the `config` argument will show
-    as invalid in IDEs and mypy. Use `@dataclass(..., config=Config) # type: ignore` as a workaround. 
-
-    See [python/mypy#6239](https://github.com/python/mypy/issues/6239) for an explanation of this issue.
+!!! warning
+    After v1.2, [The Mypy plugin](/mypy_plugin.md) must be installed to type check pydantic dataclasses.
 
 For more information about combining validators with dataclasses, see 
 [dataclass validators](validators.md#dataclass-validators).

pydantic/dataclasses.py

@@ -1,5 +1,5 @@
 import dataclasses
-from typing import TYPE_CHECKING, Any, Callable, Dict, Generator, Optional, Type, Union
+from typing import TYPE_CHECKING, Any, Callable, Dict, Generator, Optional, Type, TypeVar, Union
 
 from .class_validators import gather_all_validators
 from .error_wrappers import ValidationError
@@ -9,7 +9,9 @@
 from .typing import AnyType
 
 if TYPE_CHECKING:
-    from .main import BaseConfig, BaseModel  # noqa: F401
+    from .main import BaseModel  # noqa: F401
+
+    DataclassT = TypeVar('DataclassT', bound='DataclassType')
 
     class DataclassType:
         __pydantic_model__: Type[BaseModel]
@@ -19,11 +21,14 @@ def __init__(self, *args: Any, **kwargs: Any) -> None:
             pass
 
         @classmethod
-        def __validate__(cls, v: Any) -> 'DataclassType':
+        def __validate__(cls: Type['DataclassT'], v: Any) -> 'DataclassT':
+            pass
+
+        def __call__(self: 'DataclassT', *args: Any, **kwargs: Any) -> 'DataclassT':
             pass
 
 
-def _validate_dataclass(cls: Type['DataclassType'], v: Any) -> 'DataclassType':
+def _validate_dataclass(cls: Type['DataclassT'], v: Any) -> 'DataclassT':
     if isinstance(v, cls):
         return v
     elif isinstance(v, (list, tuple)):
@@ -34,7 +39,7 @@ def _validate_dataclass(cls: Type['DataclassType'], v: Any) -> 'DataclassType':
         raise DataclassTypeError(class_name=cls.__name__)
 
 
-def _get_validators(cls: Type['DataclassType']) -> Generator[Any, None, None]:
+def _get_validators(cls: Type['DataclassT']) -> Generator[Any, None, None]:
     yield cls.__validate__
 
 
@@ -59,7 +64,7 @@ def _process_class(
     order: bool,
     unsafe_hash: bool,
     frozen: bool,
-    config: Type['BaseConfig'],
+    config: Optional[Type[Any]],
 ) -> 'DataclassType':
     post_init_original = getattr(_cls, '__post_init__', None)
     if post_init_original and post_init_original.__name__ == '_pydantic_post_init':
@@ -113,33 +118,28 @@ def _pydantic_post_init(self: 'DataclassType', *initvars: Any) -> None:
     return cls
 
 
-if TYPE_CHECKING:
-    # see https://github.com/python/mypy/issues/6239 for explanation of why we do this
-    from dataclasses import dataclass as dataclass
-else:
-
-    def dataclass(
-        _cls: Optional[AnyType] = None,
-        *,
-        init: bool = True,
-        repr: bool = True,
-        eq: bool = True,
-        order: bool = False,
-        unsafe_hash: bool = False,
-        frozen: bool = False,
-        config: Type['BaseConfig'] = None,
-    ) -> Union[Callable[[AnyType], 'DataclassType'], 'DataclassType']:
-        """
-        Like the python standard lib dataclasses but with type validation.
-
-        Arguments are the same as for standard dataclasses, except for validate_assignment which has the same meaning
-        as Config.validate_assignment.
-        """
-
-        def wrap(cls: AnyType) -> 'DataclassType':
-            return _process_class(cls, init, repr, eq, order, unsafe_hash, frozen, config)
-
-        if _cls is None:
-            return wrap
-
-        return wrap(_cls)
+def dataclass(
+    _cls: Optional[AnyType] = None,
+    *,
+    init: bool = True,
+    repr: bool = True,
+    eq: bool = True,
+    order: bool = False,
+    unsafe_hash: bool = False,
+    frozen: bool = False,
+    config: Type[Any] = None,
+) -> Union[Callable[[AnyType], 'DataclassType'], 'DataclassType']:
+    """
+    Like the python standard lib dataclasses but with type validation.
+
+    Arguments are the same as for standard dataclasses, except for validate_assignment which has the same meaning
+    as Config.validate_assignment.
+    """
+
+    def wrap(cls: AnyType) -> 'DataclassType':
+        return _process_class(cls, init, repr, eq, order, unsafe_hash, frozen, config)
+
+    if _cls is None:
+        return wrap
+
+    return wrap(_cls)

pydantic/mypy.py

@@ -33,6 +33,7 @@
 )
 from mypy.options import Options
 from mypy.plugin import CheckerPluginInterface, ClassDefContext, MethodContext, Plugin, SemanticAnalyzerPluginInterface
+from mypy.plugins import dataclasses
 from mypy.semanal import set_callable_name  # type: ignore
 from mypy.server.trigger import make_wildcard_trigger
 from mypy.types import (
@@ -55,6 +56,7 @@
 BASEMODEL_FULLNAME = 'pydantic.main.BaseModel'
 BASESETTINGS_FULLNAME = 'pydantic.env_settings.BaseSettings'
 FIELD_FULLNAME = 'pydantic.fields.Field'
+DATACLASS_FULLNAME = 'pydantic.dataclasses.dataclass'
 
 
 def plugin(version: str) -> 'TypingType[Plugin]':
@@ -85,6 +87,11 @@ def get_method_hook(self, fullname: str) -> Optional[Callable[[MethodContext], T
             return from_orm_callback
         return None
 
+    def get_class_decorator_hook(self, fullname: str) -> Optional[Callable[[ClassDefContext], None]]:
+        if fullname == DATACLASS_FULLNAME:
+            return dataclasses.dataclass_class_maker_callback
+        return None
+
     def _pydantic_model_class_maker_callback(self, ctx: ClassDefContext) -> None:
         transformer = PydanticModelTransformer(ctx, self.plugin_config)
         transformer.transform()

tests/mypy/modules/plugin_fail.py

@@ -1,6 +1,7 @@
 from typing import Any, Generic, Optional, Set, TypeVar, Union
 
 from pydantic import BaseModel, BaseSettings, Extra, Field
+from pydantic.dataclasses import dataclass
 from pydantic.generics import GenericModel
 
 
@@ -191,3 +192,13 @@ def from_orm(self) -> None:
 
 
 CoverageTester().from_orm()
+
+
+@dataclass(config={})
+class AddProject:
+    name: str
+    slug: Optional[str]
+    description: Optional[str]
+
+
+p = AddProject(name='x', slug='y', description='z')

tests/mypy/modules/plugin_success.py

@@ -1,6 +1,7 @@
 from typing import ClassVar, Optional
 
 from pydantic import BaseModel, Field
+from pydantic.dataclasses import dataclass
 
 
 class Model(BaseModel):
@@ -104,3 +105,17 @@ class ClassVarModel(BaseModel):
 
 
 ClassVarModel(x=1)
+
+
+class Config:
+    validate_assignment = True
+
+
+@dataclass(config=Config)
+class AddProject:
+    name: str
+    slug: Optional[str]
+    description: Optional[str]
+
+
+p = AddProject(name='x', slug='y', description='z')

tests/mypy/modules/success.py

@@ -9,7 +9,6 @@
 from typing import Any, Dict, Generic, List, Optional, TypeVar
 
 from pydantic import BaseModel, NoneStr, StrictBool, root_validator, validator
-from pydantic.dataclasses import dataclass
 from pydantic.fields import Field
 from pydantic.generics import GenericModel
 
@@ -94,16 +93,6 @@ def day_of_week(dt: datetime) -> int:
 assert m_copy.list_of_ints == m_from_obj.list_of_ints
 
 
-@dataclass
-class AddProject:
-    name: str
-    slug: Optional[str]
-    description: Optional[str]
-
-
-p = AddProject(name='x', slug='y', description='z')
-
-
 if sys.version_info >= (3, 7):
     T = TypeVar('T')
 

tests/mypy/outputs/fail4.txt

@@ -0,0 +1,3 @@
+121: error: Unexpected keyword argument "name" for "AddProject"  [call-arg]
+121: error: Unexpected keyword argument "slug" for "AddProject"  [call-arg]
+121: error: Unexpected keyword argument "description" for "AddProject"  [call-arg]

tests/mypy/outputs/plugin-fail-strict.txt

@@ -1,34 +1,35 @@
-23: error: Unexpected keyword argument "z" for "Model"  [call-arg]
-24: error: Missing named argument "y" for "Model"  [call-arg]
-25: error: Property "y" defined in "Model" is read-only  [misc]
-26: error: "Model" does not have orm_mode=True  [pydantic-orm]
-35: error: Unexpected keyword argument "x" for "ForbidExtraModel"  [call-arg]
-46: error: Unexpected keyword argument "x" for "ForbidExtraModel2"  [call-arg]
-52: error: Invalid value for "Config.extra"  [pydantic-config]
-57: error: Invalid value for "Config.orm_mode"  [pydantic-config]
-62: error: Invalid value for "Config.orm_mode"  [pydantic-config]
-73: error: Incompatible types in assignment (expression has type "ellipsis", variable has type "int")  [assignment]
-76: error: Untyped fields disallowed  [pydantic-field]
-83: error: Untyped fields disallowed  [pydantic-field]
-86: error: Missing named argument "a" for "DefaultTestingModel"  [call-arg]
-86: error: Missing named argument "b" for "DefaultTestingModel"  [call-arg]
-86: error: Missing named argument "c" for "DefaultTestingModel"  [call-arg]
-86: error: Missing named argument "d" for "DefaultTestingModel"  [call-arg]
-86: error: Missing named argument "e" for "DefaultTestingModel"  [call-arg]
-90: error: Name 'Undefined' is not defined  [name-defined]
-93: error: Missing named argument "undefined" for "UndefinedAnnotationModel"  [call-arg]
-100: error: Missing named argument "y" for "construct" of "Model"  [call-arg]
-102: error: Argument "x" to "construct" of "Model" has incompatible type "str"; expected "int"  [arg-type]
-107: error: Argument "x" to "InheritingModel" has incompatible type "str"; expected "int"  [arg-type]
-108: error: Argument "x" to "Settings" has incompatible type "str"; expected "int"  [arg-type]
-109: error: Argument "x" to "Model" has incompatible type "str"; expected "int"  [arg-type]
-126: error: Argument "data" to "Response" has incompatible type "int"; expected "Model"  [arg-type]
-134: error: Argument "y" to "AliasModel" has incompatible type "int"; expected "str"  [arg-type]
-140: error: Required dynamic aliases disallowed  [pydantic-alias]
-144: error: Argument "z" to "DynamicAliasModel" has incompatible type "str"; expected "int"  [arg-type]
-155: error: Unexpected keyword argument "y" for "DynamicAliasModel2"  [call-arg]
-162: error: Required dynamic aliases disallowed  [pydantic-alias]
-180: error: Untyped fields disallowed  [pydantic-field]
-184: error: Unexpected keyword argument "x" for "AliasGeneratorModel2"  [call-arg]
-185: error: Unexpected keyword argument "z" for "AliasGeneratorModel2"  [call-arg]
-188: error: Name 'Missing' is not defined  [name-defined]
+24: error: Unexpected keyword argument "z" for "Model"  [call-arg]
+25: error: Missing named argument "y" for "Model"  [call-arg]
+26: error: Property "y" defined in "Model" is read-only  [misc]
+27: error: "Model" does not have orm_mode=True  [pydantic-orm]
+36: error: Unexpected keyword argument "x" for "ForbidExtraModel"  [call-arg]
+47: error: Unexpected keyword argument "x" for "ForbidExtraModel2"  [call-arg]
+53: error: Invalid value for "Config.extra"  [pydantic-config]
+58: error: Invalid value for "Config.orm_mode"  [pydantic-config]
+63: error: Invalid value for "Config.orm_mode"  [pydantic-config]
+74: error: Incompatible types in assignment (expression has type "ellipsis", variable has type "int")  [assignment]
+77: error: Untyped fields disallowed  [pydantic-field]
+84: error: Untyped fields disallowed  [pydantic-field]
+87: error: Missing named argument "a" for "DefaultTestingModel"  [call-arg]
+87: error: Missing named argument "b" for "DefaultTestingModel"  [call-arg]
+87: error: Missing named argument "c" for "DefaultTestingModel"  [call-arg]
+87: error: Missing named argument "d" for "DefaultTestingModel"  [call-arg]
+87: error: Missing named argument "e" for "DefaultTestingModel"  [call-arg]
+91: error: Name 'Undefined' is not defined  [name-defined]
+94: error: Missing named argument "undefined" for "UndefinedAnnotationModel"  [call-arg]
+101: error: Missing named argument "y" for "construct" of "Model"  [call-arg]
+103: error: Argument "x" to "construct" of "Model" has incompatible type "str"; expected "int"  [arg-type]
+108: error: Argument "x" to "InheritingModel" has incompatible type "str"; expected "int"  [arg-type]
+109: error: Argument "x" to "Settings" has incompatible type "str"; expected "int"  [arg-type]
+110: error: Argument "x" to "Model" has incompatible type "str"; expected "int"  [arg-type]
+127: error: Argument "data" to "Response" has incompatible type "int"; expected "Model"  [arg-type]
+135: error: Argument "y" to "AliasModel" has incompatible type "int"; expected "str"  [arg-type]
+141: error: Required dynamic aliases disallowed  [pydantic-alias]
+145: error: Argument "z" to "DynamicAliasModel" has incompatible type "str"; expected "int"  [arg-type]
+156: error: Unexpected keyword argument "y" for "DynamicAliasModel2"  [call-arg]
+163: error: Required dynamic aliases disallowed  [pydantic-alias]
+181: error: Untyped fields disallowed  [pydantic-field]
+185: error: Unexpected keyword argument "x" for "AliasGeneratorModel2"  [call-arg]
+186: error: Unexpected keyword argument "z" for "AliasGeneratorModel2"  [call-arg]
+189: error: Name 'Missing' is not defined  [name-defined]
+197: error: Argument "config" to "dataclass" has incompatible type "Dict[<nothing>, <nothing>]"; expected "Optional[Type[Any]]"  [arg-type]

tests/mypy/outputs/plugin-fail.txt

@@ -1,23 +1,24 @@
-23: error: Unexpected keyword argument "z" for "Model"  [call-arg]
-24: error: Missing named argument "y" for "Model"  [call-arg]
-25: error: Property "y" defined in "Model" is read-only  [misc]
-26: error: "Model" does not have orm_mode=True  [pydantic-orm]
-35: error: Unexpected keyword argument "x" for "ForbidExtraModel"  [call-arg]
-46: error: Unexpected keyword argument "x" for "ForbidExtraModel2"  [call-arg]
-52: error: Invalid value for "Config.extra"  [pydantic-config]
-57: error: Invalid value for "Config.orm_mode"  [pydantic-config]
-62: error: Invalid value for "Config.orm_mode"  [pydantic-config]
-73: error: Incompatible types in assignment (expression has type "ellipsis", variable has type "int")  [assignment]
-86: error: Missing named argument "a" for "DefaultTestingModel"  [call-arg]
-86: error: Missing named argument "b" for "DefaultTestingModel"  [call-arg]
-86: error: Missing named argument "c" for "DefaultTestingModel"  [call-arg]
-86: error: Missing named argument "d" for "DefaultTestingModel"  [call-arg]
-86: error: Missing named argument "e" for "DefaultTestingModel"  [call-arg]
-90: error: Name 'Undefined' is not defined  [name-defined]
-93: error: Missing named argument "undefined" for "UndefinedAnnotationModel"  [call-arg]
-100: error: Missing named argument "y" for "construct" of "Model"  [call-arg]
-102: error: Argument "x" to "construct" of "Model" has incompatible type "str"; expected "int"  [arg-type]
-155: error: Missing named argument "x" for "DynamicAliasModel2"  [call-arg]
-174: error: unused 'type: ignore' comment
-181: error: unused 'type: ignore' comment
-188: error: Name 'Missing' is not defined  [name-defined]
+24: error: Unexpected keyword argument "z" for "Model"  [call-arg]
+25: error: Missing named argument "y" for "Model"  [call-arg]
+26: error: Property "y" defined in "Model" is read-only  [misc]
+27: error: "Model" does not have orm_mode=True  [pydantic-orm]
+36: error: Unexpected keyword argument "x" for "ForbidExtraModel"  [call-arg]
+47: error: Unexpected keyword argument "x" for "ForbidExtraModel2"  [call-arg]
+53: error: Invalid value for "Config.extra"  [pydantic-config]
+58: error: Invalid value for "Config.orm_mode"  [pydantic-config]
+63: error: Invalid value for "Config.orm_mode"  [pydantic-config]
+74: error: Incompatible types in assignment (expression has type "ellipsis", variable has type "int")  [assignment]
+87: error: Missing named argument "a" for "DefaultTestingModel"  [call-arg]
+87: error: Missing named argument "b" for "DefaultTestingModel"  [call-arg]
+87: error: Missing named argument "c" for "DefaultTestingModel"  [call-arg]
+87: error: Missing named argument "d" for "DefaultTestingModel"  [call-arg]
+87: error: Missing named argument "e" for "DefaultTestingModel"  [call-arg]
+91: error: Name 'Undefined' is not defined  [name-defined]
+94: error: Missing named argument "undefined" for "UndefinedAnnotationModel"  [call-arg]
+101: error: Missing named argument "y" for "construct" of "Model"  [call-arg]
+103: error: Argument "x" to "construct" of "Model" has incompatible type "str"; expected "int"  [arg-type]
+156: error: Missing named argument "x" for "DynamicAliasModel2"  [call-arg]
+175: error: unused 'type: ignore' comment
+182: error: unused 'type: ignore' comment
+189: error: Name 'Missing' is not defined  [name-defined]
+197: error: Argument "config" to "dataclass" has incompatible type "Dict[<nothing>, <nothing>]"; expected "Optional[Type[Any]]"  [arg-type]

tests/mypy/outputs/plugin-success-strict.txt

@@ -1,3 +1,3 @@
-28: error: Unexpected keyword argument "z" for "Model"  [call-arg]
-63: error: Untyped fields disallowed  [pydantic-field]
-78: error: Argument "x" to "OverrideModel" has incompatible type "float"; expected "int"  [arg-type]
+29: error: Unexpected keyword argument "z" for "Model"  [call-arg]
+64: error: Untyped fields disallowed  [pydantic-field]
+79: error: Argument "x" to "OverrideModel" has incompatible type "float"; expected "int"  [arg-type]