Add test cases to handle nested classes

Author: MichaelLeeDBX

mypy/checkexpr.py

@@ -55,13 +55,17 @@ def extract_refexpr_names(expr: RefExpr) -> Set[str]:
     while expr.kind == MODULE_REF or expr.fullname is not None:
         if expr.kind == MODULE_REF:
             output.add(expr.fullname)
-        elif expr.fullname is not None and '.' in expr.fullname:
-            if not (isinstance(expr.node, Var) and expr.node.is_import):
-                output.add(expr.fullname.rsplit('.', 1)[0])
 
         if isinstance(expr, NameExpr):
+            is_silenced_import = isinstance(expr.node, Var) and expr.node.is_import
             if expr.info is not None:
+                # Reference to regular type
                 output.update(split_module_names(expr.info.module_name))
+            elif isinstance(expr.node, TypeInfo):
+                # Nested class
+                output.update(split_module_names(expr.node.module_name))
+            elif expr.fullname is not None and '.' in expr.fullname and not is_silenced_import:
+                output.add(expr.fullname.rsplit('.', 1)[0])
             break
         elif isinstance(expr, MemberExpr):
             if isinstance(expr.expr, RefExpr):

test-data/unit/check-incremental.test

@@ -1178,3 +1178,17 @@ def test() -> str: return "foo"
 [stale foo, unrelated]
 [out]
 tmp/main.py:3: error: Revealed type is 'builtins.str'
+
+[case testIncrementalWorksWithNestedClasses]
+import foo
+
+[file foo.py]
+class MyClass:
+    class NestedClass:
+        pass
+
+    class_attr = NestedClass()
+
+[rechecked]
+[stale]
+[out]