Fix simple literal inference in class bodies in import cycle (#13552)

This fixes a little regression caused by #13494

Author: ilevkivskyi

mypy/semanal.py

@@ -3007,11 +3007,14 @@ def process_type_annotation(self, s: AssignmentStmt) -> None:
             ):
                 self.fail("All protocol members must have explicitly declared types", s)
             # Set the type if the rvalue is a simple literal (even if the above error occurred).
-            # We skip this step for type scope because it messes up with class attribute
-            # inference for literal types (also annotated and non-annotated variables at class
-            # scope are semantically different, so we should not souch statement type).
-            if len(s.lvalues) == 1 and isinstance(s.lvalues[0], RefExpr) and not self.type:
-                if s.lvalues[0].is_inferred_def:
+            if len(s.lvalues) == 1 and isinstance(s.lvalues[0], RefExpr):
+                ref_expr = s.lvalues[0]
+                safe_literal_inference = True
+                if self.type and isinstance(ref_expr, NameExpr) and len(self.type.mro) > 1:
+                    # Check if there is a definition in supertype. If yes, we can't safely
+                    # decide here what to infer: int or Literal[42].
+                    safe_literal_inference = self.type.mro[1].get(ref_expr.name) is None
+                if safe_literal_inference and ref_expr.is_inferred_def:
                     s.type = self.analyze_simple_literal_type(s.rvalue, s.is_final_def)
         if s.type:
             # Store type into nodes.

test-data/unit/check-inference.test

@@ -3337,3 +3337,19 @@ class A:
         class B(A):
             args = value
 [builtins fixtures/dict.pyi]
+
+[case testInferSimpleLiteralInClassBodyCycle]
+import a
+[file a.py]
+import b
+reveal_type(b.B.x)
+class A:
+    x = 42
+[file b.py]
+import a
+reveal_type(a.A.x)
+class B:
+    x = 42
+[out]
+tmp/b.py:2: note: Revealed type is "builtins.int"
+tmp/a.py:2: note: Revealed type is "builtins.int"