Fix PEP487 __set_name__ protocol in BaseModel (#4407)

* fix: fix __set_name__ protocol in BaseModel

* undo changes

* add comment

* fix lint

* fix lint

* add change file

* remove mock, move imports

changes/4407-tlambert03.md

@@ -0,0 +1 @@
+Fix PEP487 protocol in `BaseModel`: call `__set_name__` on namespace values that implement the method.

pydantic/main.py

@@ -286,6 +286,12 @@ def is_untouched(v: Any) -> bool:
         if resolve_forward_refs:
             cls.__try_update_forward_refs__()
 
+        # preserve `__set_name__` protocol defined in https://peps.python.org/pep-0487
+        for name, obj in namespace.items():
+            set_name = getattr(obj, '__set_name__', None)
+            if callable(set_name):
+                set_name(cls, name)
+
         return cls
 
     def __instancecheck__(self, instance: Any) -> bool:

tests/test_create_model.py

@@ -3,6 +3,7 @@
 import pytest
 
 from pydantic import BaseModel, Extra, Field, ValidationError, create_model, errors, validator
+from pydantic.fields import ModelPrivateAttr
 from pydantic.generics import GenericModel
 
 
@@ -222,3 +223,22 @@ class TestGenericModel(GenericModel):
     result = AAModel[int](aa=1)
     assert result.aa == 1
     assert result.__config__.orm_mode is True
+
+
+def test_set_name():
+    calls = []
+
+    class class_deco(ModelPrivateAttr):
+        def __init__(self, fn):
+            super().__init__()
+            self.fn = fn
+
+        def __set_name__(self, owner, name):
+            calls.append((owner, name))
+
+    class A(BaseModel):
+        @class_deco
+        def _some_func(self):
+            return self
+
+    assert calls == [(A, '_some_func')]