Fix ForwardRef collection bug (#450)

* fix ForwardRef collection bug, fix #439

* reformat codes

* minor document error

* add HISTORY.rst and simplified unit test

* restore the original example for ForwardRef

HISTORY.rst

@@ -8,6 +8,7 @@ v0.23 (unreleased)
 * improve documentation for contributing section, # 441 @pilosus
 * improve README.rst to include essential information about the package, #446 by @pilosus
 * ``IntEnum`` support, #444 by @potykion
+* fix ``ForwardRef`` collection bug, #450 by @tigerwings
 
 v0.22 (2019-03-29)
 ....................

pydantic/validators.py

@@ -10,7 +10,7 @@ from uuid import UUID
 
 from . import errors
 from .datetime_parse import parse_date, parse_datetime, parse_duration, parse_time
-from .utils import AnyCallable, AnyType, change_exception, display_as_type, is_callable_type, sequence_like
+from .utils import AnyCallable, AnyType, ForwardRef, change_exception, display_as_type, is_callable_type, sequence_like
 
 if TYPE_CHECKING:  # pragma: no cover
     from .fields import Field
@@ -357,7 +357,7 @@ _VALIDATORS: List[Tuple[AnyType, List[AnyCallable]]] = [
 
 
 def find_validators(type_: AnyType, arbitrary_types_allowed: bool = False) -> List[AnyCallable]:
-    if type_ is Any:
+    if type_ is Any or type(type_) == ForwardRef:
         return []
     if type_ is Pattern:
         return pattern_validators

tests/test_py37.py

@@ -5,7 +5,7 @@ import sys
 
 import pytest
 
-from pydantic import ConfigError
+from pydantic import ConfigError, ValidationError
 
 skip_not_37 = pytest.mark.skipif(sys.version_info < (3, 7), reason='testing >= 3.7 behaviour only')
 
@@ -83,6 +83,40 @@ Foo.update_forward_refs()
     assert module.Foo(b={'a': '321'}).dict() == {'a': 123, 'b': {'a': 321, 'b': None}}
 
 
+@skip_not_37
+def test_self_forward_ref_collection(create_module):
+    module = create_module(
+        """
+from typing import ForwardRef, List, Dict
+from pydantic import BaseModel
+
+Foo = ForwardRef('Foo')
+
+class Foo(BaseModel):
+    a: int = 123
+    b: Foo = None
+    c: List[Foo] = []
+    d: Dict[str, Foo] = {}
+
+Foo.update_forward_refs()
+    """
+    )
+
+    assert module.Foo().dict() == {'a': 123, 'b': None, 'c': [], 'd': {}}
+    assert module.Foo(b={'a': '321'}, c=[{'a': 234}], d={'bar': {'a': 345}}).dict() == {
+        'a': 123,
+        'b': {'a': 321, 'b': None, 'c': [], 'd': {}},
+        'c': [{'a': 234, 'b': None, 'c': [], 'd': {}}],
+        'd': {'bar': {'a': 345, 'b': None, 'c': [], 'd': {}}},
+    }
+
+    with pytest.raises(ValidationError) as exc_info:
+        module.Foo(b={'a': '321'}, c=[{'b': 234}], d={'bar': {'a': 345}})
+    assert exc_info.value.errors() == [
+        {'loc': ('c', 0, 'b'), 'msg': 'value is not a valid dict', 'type': 'type_error.dict'}
+    ]
+
+
 @skip_not_37
 def test_self_forward_ref_local(create_module):
     module = create_module(