fix: collect only valid fields in mypy plugin (#3247)

* fix: collect only valid fields in mypy plugin

* Fix flake8 C901 in `PydanticModelTransformer.collect_fields`

changes/3146-hi-ogawa.md

@@ -0,0 +1 @@
+Fix mypy plugin to collect fields based on `pydantic.utils.is_valid_field` so that it ignores untyped private variables

pydantic/mypy.py

@@ -1,6 +1,8 @@
 from configparser import ConfigParser
 from typing import Any, Callable, Dict, List, Optional, Set, Tuple, Type as TypingType, Union
 
+from pydantic.utils import is_valid_field
+
 try:
     import toml
 except ImportError:  # pragma: no cover
@@ -247,7 +249,7 @@ class PydanticModelTransformer:
                 continue
 
             lhs = stmt.lvalues[0]
-            if not isinstance(lhs, NameExpr):
+            if not isinstance(lhs, NameExpr) or not is_valid_field(lhs.name):
                 continue
 
             if not stmt.new_syntax and self.plugin_config.warn_untyped_fields:

tests/mypy/modules/plugin_success.py

@@ -1,6 +1,6 @@
 from typing import ClassVar, Optional, Union
 
-from pydantic import BaseModel, BaseSettings, Field, create_model
+from pydantic import BaseModel, BaseSettings, Field, create_model, validator
 from pydantic.dataclasses import dataclass
 
 
@@ -169,3 +169,15 @@ class SettingsModel(BaseSettings):
 
 
 settings = SettingsModel.construct()
+
+
+def f(name: str) -> str:
+    return name
+
+
+class ModelWithAllowReuseValidator(BaseModel):
+    name: str
+    _normalize_name = validator('name', allow_reuse=True)(f)
+
+
+model_with_allow_reuse_validator = ModelWithAllowReuseValidator(name='xyz')

tests/mypy/outputs/plugin-success-strict.txt

@@ -1,4 +1,3 @@
 29: error: Unexpected keyword argument "z" for "Model"  [call-arg]
 64: error: Untyped fields disallowed  [pydantic-field]
-79: error: Argument "x" to "OverrideModel" has incompatible type "float"; expected "int"  [arg-type]
-125: error: Untyped fields disallowed  [pydantic-field]
+79: error: Argument "x" to "OverrideModel" has incompatible type "float"; expected "int"  [arg-type]