Stop evolve dunders from being modified

changelog.d/1606.change.md

@@ -0,0 +1 @@
+The dunder methods of `attrs.evolve()` aren't mangled anymore.

src/attr/_make.py

@@ -1108,7 +1108,11 @@ def _attach_init(cls_dict, globs):
         return self
 
     def add_replace(self):
-        self._cls_dict["__replace__"] = self._add_method_dunders(evolve)
+        # We create a local `evolve` proxy because it gets modified in place.
+        def __replace__(*args, **changes):
+            return evolve(*args, **changes)
+
+        self._cls_dict["__replace__"] = self._add_method_dunders(__replace__)
         return self
 
     def add_match_args(self):

tests/test_functional.py

@@ -816,3 +816,16 @@ def test_invalid_field_name(self):
 
         with pytest.raises(TypeError):
             copy.replace(inst, z=42)
+
+    def test_is_not_evolve(self):
+        """
+        __replace__ is not the same as attrs.evolve.
+
+        Regression test for #1606.
+        """
+        inst = C1(1, 2)
+
+        assert "<bound method C1.__replace__ of C1(x=1, y=2)>" == str(
+            inst.__replace__
+        )
+        assert str(attr.evolve).startswith("<function evolve at")