Fix: if field has custom decoder, schema takes it into account

dataclasses_json/mm.py

@@ -1,5 +1,5 @@
 # flake8: noqa
-
+import dataclasses
 import typing
 import warnings
 import sys
@@ -116,6 +116,7 @@ class _TupleVarLen(fields.List):
     """
     variable-length homogeneous tuples
     """
+
     def _deserialize(self, value, attr, data, **kwargs):
         optional_list = super()._deserialize(value, attr, data, **kwargs)
         return None if optional_list is None else tuple(optional_list)
@@ -162,15 +163,16 @@ def __init__(self, *args, **kwargs):
             raise NotImplementedError()
 
         @typing.overload
-        def dump(self, obj: typing.List[A], many: typing.Optional[bool] = None) -> typing.List[TEncoded]:  # type: ignore
+        def dump(self, obj: typing.List[A],  # type: ignore
+                 many: typing.Optional[bool] = None) -> typing.List[TEncoded]:
             # mm has the wrong return type annotation (dict) so we can ignore the mypy error
             pass
 
         @typing.overload
         def dump(self, obj: A, many: typing.Optional[bool] = None) -> TEncoded:
             pass
 
-        def dump(self, obj: TOneOrMulti,    # type: ignore
+        def dump(self, obj: TOneOrMulti,  # type: ignore
                  many: typing.Optional[bool] = None) -> TOneOrMultiEncoded:
             pass
 
@@ -183,7 +185,7 @@ def dumps(self, obj: typing.List[A], many: typing.Optional[bool] = None, *args,
         def dumps(self, obj: A, many: typing.Optional[bool] = None, *args, **kwargs) -> str:
             pass
 
-        def dumps(self, obj: TOneOrMulti, many: typing.Optional[bool] = None, *args,   # type: ignore
+        def dumps(self, obj: TOneOrMulti, many: typing.Optional[bool] = None, *args,  # type: ignore
                   **kwargs) -> str:
             pass
 
@@ -208,16 +210,16 @@ def load(self, data: TOneOrMultiEncoded,
 
         @typing.overload  # type: ignore
         def loads(self, json_data: JsonData,  # type: ignore
-                  many: typing.Optional[bool] = True, partial: typing.Optional[bool] = None, unknown: typing.Optional[str] = None,
-                  **kwargs) -> typing.List[A]:
+                  many: typing.Optional[bool] = True, partial: typing.Optional[bool] = None,
+                  unknown: typing.Optional[str] = None, **kwargs) -> typing.List[A]:
             # ignore the mypy error of the decorator because mm does not define bytes as correct input data
             # mm has the wrong return type annotation (dict) so we can ignore the mypy error
             # for the return type overlap
             pass
 
         def loads(self, json_data: JsonData,
-                  many: typing.Optional[bool] = None, partial: typing.Optional[bool] = None, unknown: typing.Optional[str] = None,
-                  **kwargs) -> TOneOrMulti:
+                  many: typing.Optional[bool] = None, partial: typing.Optional[bool] = None,
+                  unknown: typing.Optional[str] = None, **kwargs) -> TOneOrMulti:
             pass
 
 
@@ -253,10 +255,10 @@ def inner(type_, options):
         origin = getattr(type_, '__origin__', type_)
         args = [inner(a, {}) for a in getattr(type_, '__args__', []) if
                 a is not type(None)]
-        
+
         if type_ == Ellipsis:
             return type_
-        
+
         if _is_optional(type_):
             options["allow_none"] = True
         if origin is tuple:
@@ -318,13 +320,26 @@ def schema(cls, mixin, infer_missing):
                 options['data_key'] = metadata.letter_case(field.name)
 
             t = build_type(type_, options, mixin, field, cls)
+            _account_for_decoder_if_necessary(field, t)
+
             # if type(t) is not fields.Field:  # If we use `isinstance` we would return nothing.
             if field.type != typing.Optional[CatchAllVar]:
                 schema[field.name] = t
 
     return schema
 
 
+def _account_for_decoder_if_necessary(field: dataclasses.Field, t: fields.Field):
+    decoder = field.metadata.get('dataclasses_json', {}).get('decoder')
+    if decoder:
+        # Used in order to avoid mypy error. See https://github.com/python/mypy/issues/2427 for more details
+        t._deserialize = _dummy_deserialize  # type: ignore
+
+
+def _dummy_deserialize(value: typing.Any, *_args, **_kwargs):
+    return value
+
+
 def build_schema(cls: typing.Type[A],
                  mixin,
                  infer_missing,

tests/entities.py

@@ -271,6 +271,16 @@ class DataClassWithErroneousDecode:
     id: float = field(metadata=config(decoder=lambda: None))
 
 
+def split_str(data: str, *_args, **_kwargs):
+    return data.split(',')
+
+
+@dataclass_json
+@dataclass
+class DataClassDifferentTypeDecode:
+    lst: List[str] = field(default=None, metadata=config(decoder=split_str))
+
+
 @dataclass_json
 @dataclass
 class DataClassMappingBadDecode:

tests/test_schema.py

@@ -2,7 +2,8 @@
 import pytest
 
 from .entities import (DataClassDefaultListStr, DataClassDefaultOptionalList, DataClassList, DataClassOptional,
-                       DataClassWithNestedOptional, DataClassWithNestedOptionalAny, DataClassWithNestedAny)
+                       DataClassWithNestedOptional, DataClassWithNestedOptionalAny, DataClassWithNestedAny,
+                       DataClassDifferentTypeDecode)
 from .test_letter_case import CamelCasePerson, KebabCasePerson, SnakeCasePerson, FieldNamePerson
 
 test_do_list = """[{}, {"children": [{"name": "a"}, {"name": "b"}]}]"""
@@ -47,3 +48,7 @@ def test_nested_optional_any(self):
     def test_nested_any_accepts_optional(self):
         DataClassWithNestedAny.schema().loads(nested_optional_data)
         assert True
+
+    def test_accounts_for_decode(self):
+        assert DataClassDifferentTypeDecode.schema().load({'lst': '1,2,3'}) == \
+               DataClassDifferentTypeDecode(lst=['1', '2', '3'])