[invalid-class-object] Fix crash when __class__ is defined with a tuple

doc/whatsnew/fragments/7467.bugfix

@@ -0,0 +1,3 @@
+``invalid-class-object`` does not crash anymore when ``__class__`` is assigned alongside another variable.
+
+Closes #7467

pylint/checkers/classes/class_checker.py

@@ -684,7 +684,7 @@ def _has_same_layout_slots(
         "Used when a value in __slots__ conflicts with a class variable, property or method.",
     ),
     "E0243": (
-        "Invalid __class__ object",
+        "Invalid assignment to '__class__'. Should be a class definition but got a '%s'",
         "invalid-class-object",
         "Used when an invalid object is assigned to a __class__ property. "
         "Only a class is permitted.",
@@ -1560,15 +1560,31 @@ def visit_assignattr(self, node: nodes.AssignAttr) -> None:
     def _check_invalid_class_object(self, node: nodes.AssignAttr) -> None:
         if not node.attrname == "__class__":
             return
-        inferred = safe_infer(node.parent.value)
+        if isinstance(node.parent, nodes.Tuple):
+            class_index = -1
+            for i, elt in enumerate(node.parent.elts):
+                if hasattr(elt, "attrname") and elt.attrname == "__class__":
+                    class_index = i
+            if class_index == -1:
+                # This should not happen because we checked that the node name
+                # is '__class__' earlier, but let's not be too confident here
+                return  # pragma: no cover
+            inferred = safe_infer(node.parent.parent.value.elts[class_index])
+        else:
+            inferred = safe_infer(node.parent.value)
         if (
             isinstance(inferred, nodes.ClassDef)
             or inferred is astroid.Uninferable
             or inferred is None
         ):
             # If is uninferable, we allow it to prevent false positives
             return
-        self.add_message("invalid-class-object", node=node)
+        self.add_message(
+            "invalid-class-object",
+            node=node,
+            args=inferred.__class__.__name__,
+            confidence=INFERENCE,
+        )
 
     def _check_in_slots(self, node: nodes.AssignAttr) -> None:
         """Check that the given AssignAttr node

tests/functional/i/invalid/invalid_class_object.py

@@ -1,12 +1,15 @@
 # pylint: disable=missing-docstring,too-few-public-methods,invalid-name
 from collections import defaultdict
 
+
 class A:
     pass
 
+
 class B:
     pass
 
+
 A.__class__ = B
 A.__class__ = str
 A.__class__ = float
@@ -30,3 +33,43 @@ def __deepcopy__(self, memo):
         obj = C()
         obj.__class__ = self.__class__
         return obj
+
+
+class AnotherClass:
+    ...
+
+
+class Pylint7429Good:
+    """See https://github.com/PyCQA/pylint/issues/7467"""
+
+    def class_defining_function_good(self):
+        self.__class__, myvar = AnotherClass, "myvalue"
+        print(myvar)
+
+    def class_defining_function_bad(self):
+        self.__class__, myvar = 1, "myvalue"  # [invalid-class-object]
+        print(myvar)
+
+    def class_defining_function_good_inverted(self):
+        myvar, self.__class__ = "myvalue", AnotherClass
+        print(myvar)
+
+    def class_defining_function_bad_inverted(self):
+        myvar, self.__class__ = "myvalue", 1  # [invalid-class-object]
+        print(myvar)
+
+    def class_defining_function_complex_bad(self):
+        myvar, self.__class__, other = (  # [invalid-class-object]
+            "myvalue",
+            1,
+            "othervalue",
+        )
+        print(myvar, other)
+
+    def class_defining_function_complex_good(self):
+        myvar, self.__class__, other = (
+            "myvalue",
+            str,
+            "othervalue",
+        )
+        print(myvar, other)

tests/functional/i/invalid/invalid_class_object.txt

@@ -1,2 +1,5 @@
-invalid-class-object:17:0:17:11::Invalid __class__ object:UNDEFINED
-invalid-class-object:18:0:18:11::Invalid __class__ object:UNDEFINED
+invalid-class-object:20:0:20:11::Invalid assignment to '__class__'. Should be a class definition but got a 'Instance':INFERENCE
+invalid-class-object:21:0:21:11::Invalid assignment to '__class__'. Should be a class definition but got a 'Const':INFERENCE
+invalid-class-object:50:8:50:22:Pylint7429Good.class_defining_function_bad:Invalid assignment to '__class__'. Should be a class definition but got a 'Const':INFERENCE
+invalid-class-object:58:15:58:29:Pylint7429Good.class_defining_function_bad_inverted:Invalid assignment to '__class__'. Should be a class definition but got a 'Const':INFERENCE
+invalid-class-object:62:15:62:29:Pylint7429Good.class_defining_function_complex_bad:Invalid assignment to '__class__'. Should be a class definition but got a 'Const':INFERENCE