Fix bug when mypy plugin fail on construct method call (pydantic#2767)

* Fix bug when mypy plugin fail on construct method call

* Update type annotation for __config__ field

* Remove type ignore

* Update changes/2753-uriyyo.md

Co-authored-by: Eric Jolibois <em.jolibois@gmail.com>

Co-authored-by: Eric Jolibois <em.jolibois@gmail.com>

changes/2753-uriyyo.md

@@ -0,0 +1 @@
+Fix bug when `mypy` plugin fails on `construct` method call for `BaseSettings` derived classes.

pydantic/env_settings.py

@@ -1,7 +1,7 @@
 import os
 import warnings
 from pathlib import Path
-from typing import AbstractSet, Any, Callable, Dict, List, Mapping, Optional, Tuple, Union
+from typing import AbstractSet, Any, Callable, ClassVar, Dict, List, Mapping, Optional, Tuple, Type, Union
 
 from .config import BaseConfig, Extra
 from .fields import ModelField
@@ -114,7 +114,7 @@ def customise_sources(
         ) -> Tuple[SettingsSourceCallable, ...]:
             return init_settings, env_settings, file_secret_settings
 
-    __config__: Config  # type: ignore
+    __config__: ClassVar[Type[Config]]  # type: ignore
 
 
 class InitSettingsSource:
@@ -170,7 +170,7 @@ def __call__(self, settings: BaseSettings) -> Dict[str, Any]:
 
             if field.is_complex():
                 try:
-                    env_val = settings.__config__.json_loads(env_val)  # type: ignore
+                    env_val = settings.__config__.json_loads(env_val)
                 except ValueError as e:
                     raise SettingsError(f'error parsing JSON for "{env_name}"') from e
             elif (
@@ -179,7 +179,7 @@ def __call__(self, settings: BaseSettings) -> Dict[str, Any]:
                 and any(f.is_complex() for f in field.sub_fields)
             ):
                 try:
-                    env_val = settings.__config__.json_loads(env_val)  # type: ignore
+                    env_val = settings.__config__.json_loads(env_val)
                 except ValueError:
                     pass
             d[field.alias] = env_val

tests/mypy/modules/plugin_success.py

@@ -1,6 +1,6 @@
 from typing import ClassVar, Optional, Union
 
-from pydantic import BaseModel, Field, create_model
+from pydantic import BaseModel, BaseSettings, Field, create_model
 from pydantic.dataclasses import dataclass
 
 
@@ -162,3 +162,10 @@ class Config:
 
 class ModelWithSelfField(BaseModel):
     self: str
+
+
+class SettingsModel(BaseSettings):
+    pass
+
+
+settings = SettingsModel.construct()