Fix a regresion in parsing env value for nested dict (#301)

Author: hramezani

pydantic_settings/sources.py

@@ -683,7 +683,7 @@ def explode_env_vars(self, field_name: str, field: FieldInfo, env_vars: Mapping[
                     is_complex, allow_json_failure = self._field_is_complex(target_field)
                 else:
                     # nested field type is dict
-                    is_complex, allow_json_failure = True, False
+                    is_complex, allow_json_failure = True, True
                 if is_complex:
                     try:
                         env_val = self.decode_complex_value(last_key, target_field, env_val)  # type: ignore

tests/test_settings.py

@@ -3789,6 +3789,17 @@ class Settings(BaseSettings):
     assert s.model_dump() == {'nested': {'foo': {'a': 1}}, 'sub_dict': {'bar': {'foo': {'b': 2}}}}
 
 
+def test_env_nested_dict_value(env):
+    class Settings(BaseSettings):
+        nested: Dict[str, Dict[str, Dict[str, str]]]
+
+        model_config = SettingsConfigDict(env_nested_delimiter='__')
+
+    env.set('nested__foo__a__b', 'bar')
+    s = Settings()
+    assert s.model_dump() == {'nested': {'foo': {'a': {'b': 'bar'}}}}
+
+
 def test_nested_models_leaf_vs_deeper_env_dict_assumed(env):
     class NestedSettings(BaseModel):
         foo: str