Added schema generation for Generic fields (#2262)

* Added schema generation for Generic fields with tests.
Fixed test_assert_raises_validation_error.

* Added schema generation for Generic fields with tests.
Fixed test_assert_raises_validation_error.

* tested on python 3.6, 3.7, 3.8, 3.9

* tested on python 3.6, 3.7, 3.8, 3.9

* restore formatting

* fix mistakes

* formatting

* formatting

* formatting

* fixed coverage

* changes file

* changes file

* remove redundant len

* Update pydantic/schema.py

Co-authored-by: Maz Jaleel <mazjaleel@gmail.com>

Co-authored-by: Maxim Berg <berg@petrostyle.com>
Co-authored-by: Maz Jaleel <mazjaleel@gmail.com>

changes/2262-maximberg.md

@@ -0,0 +1 @@
+Support generating schema for Generic fields. 

pydantic/schema.py

@@ -11,6 +11,7 @@
     Callable,
     Dict,
     FrozenSet,
+    Generic,
     Iterable,
     List,
     Optional,
@@ -27,6 +28,7 @@
 
 from .fields import (
     SHAPE_FROZENSET,
+    SHAPE_GENERIC,
     SHAPE_ITERABLE,
     SHAPE_LIST,
     SHAPE_MAPPING,
@@ -488,7 +490,7 @@ def field_type_schema(
             sub_schema = sub_schema[0]  # type: ignore
         f_schema = {'type': 'array', 'items': sub_schema}
     else:
-        assert field.shape == SHAPE_SINGLETON, field.shape
+        assert field.shape in {SHAPE_SINGLETON, SHAPE_GENERIC}, field.shape
         f_schema, f_definitions, f_nested_models = field_singleton_schema(
             field,
             by_alias=by_alias,
@@ -503,7 +505,11 @@ def field_type_schema(
 
     # check field type to avoid repeated calls to the same __modify_schema__ method
     if field.type_ != field.outer_type_:
-        modify_schema = getattr(field.outer_type_, '__modify_schema__', None)
+        if field.shape == SHAPE_GENERIC:
+            field_type = field.type_
+        else:
+            field_type = field.outer_type_
+        modify_schema = getattr(field_type, '__modify_schema__', None)
         if modify_schema:
             modify_schema(f_schema)
     return f_schema, definitions, nested_models
@@ -845,6 +851,11 @@ def field_singleton_schema(  # noqa: C901 (ignore complexity)
         schema_ref = get_schema_ref(model_name, ref_prefix, ref_template, schema_overrides)
         return schema_ref, definitions, nested_models
 
+    # For generics with no args
+    args = get_args(field_type)
+    if args is not None and not args and Generic in field_type.__bases__:
+        return f_schema, definitions, nested_models
+
     raise ValueError(f'Value not declarable with JSON Schema, field: {field}')
 
 

pydantic/typing.py

@@ -124,7 +124,7 @@ class Annotated(metaclass=_FalseMeta):
     if sys.version_info < (3, 7):
 
         def get_args(t: Type[Any]) -> Tuple[Any, ...]:
-            """Simplest get_args compatability layer possible.
+            """Simplest get_args compatibility layer possible.
 
             The Python 3.6 typing module does not have `_GenericAlias` so
             this won't work for everything. In particular this will not
@@ -140,7 +140,7 @@ def get_args(t: Type[Any]) -> Tuple[Any, ...]:
         from typing import _GenericAlias
 
         def get_args(t: Type[Any]) -> Tuple[Any, ...]:
-            """Compatability version of get_args for python 3.7.
+            """Compatibility version of get_args for python 3.7.
 
             Mostly compatible with the python 3.8 `typing` module version
             and able to handle almost all use cases.

tests/test_schema.py

@@ -7,7 +7,21 @@
 from enum import Enum, IntEnum
 from ipaddress import IPv4Address, IPv4Interface, IPv4Network, IPv6Address, IPv6Interface, IPv6Network
 from pathlib import Path
-from typing import Any, Callable, Dict, FrozenSet, Iterable, List, NewType, Optional, Set, Tuple, Union
+from typing import (
+    Any,
+    Callable,
+    Dict,
+    FrozenSet,
+    Generic,
+    Iterable,
+    List,
+    NewType,
+    Optional,
+    Set,
+    Tuple,
+    TypeVar,
+    Union,
+)
 from uuid import UUID
 
 import pytest
@@ -2195,3 +2209,58 @@ class Model(BaseModel):
         f'{module_2.__name__}__MyEnum',
         f'{module_2.__name__}__MyModel',
     }
+
+
+@pytest.mark.skipif(
+    sys.version_info < (3, 7), reason='schema generation for generic fields is not available in python < 3.7'
+)
+def test_schema_for_generic_field():
+    T = TypeVar('T')
+
+    class GenModel(Generic[T]):
+        def __init__(self, data: Any):
+            self.data = data
+
+        @classmethod
+        def __get_validators__(cls):
+            yield cls.validate
+
+        @classmethod
+        def validate(cls, v: Any):
+            return v
+
+    class Model(BaseModel):
+        data: GenModel[str]
+        data1: GenModel
+
+    assert Model.schema() == {
+        'title': 'Model',
+        'type': 'object',
+        'properties': {
+            'data': {'title': 'Data', 'type': 'string'},
+            'data1': {
+                'title': 'Data1',
+            },
+        },
+        'required': ['data', 'data1'],
+    }
+
+    class GenModelModified(GenModel, Generic[T]):
+        @classmethod
+        def __modify_schema__(cls, field_schema):
+            field_schema.pop('type', None)
+            field_schema.update(anyOf=[{'type': 'string'}, {'type': 'array', 'items': {'type': 'string'}}])
+
+    class ModelModified(BaseModel):
+        data: GenModelModified[str]
+        data1: GenModelModified
+
+    assert ModelModified.schema() == {
+        'title': 'ModelModified',
+        'type': 'object',
+        'properties': {
+            'data': {'title': 'Data', 'anyOf': [{'type': 'string'}, {'type': 'array', 'items': {'type': 'string'}}]},
+            'data1': {'title': 'Data1', 'anyOf': [{'type': 'string'}, {'type': 'array', 'items': {'type': 'string'}}]},
+        },
+        'required': ['data', 'data1'],
+    }