UFile (package = ) [public class MutableField {...]
    UClass (name = MutableField) [public class MutableField {...}]
        UField (name = mutable) [static var mutable: int = 0]
            ULiteralExpression (value = 0) [0] = 0
        UMethod (name = foo) [public static fun foo() : int {...}]
            UBlockExpression [{...}] = Nothing
                UBinaryExpression (operator = =) [mutable = 1] = 1
                    USimpleNameReferenceExpression (identifier = mutable) [mutable] = external mutable()
                    ULiteralExpression (value = 1) [1] = 1
                UCallExpression (kind = UastCallKind(name='method_call'), argCount = 0)) [bar()] = external bar()()
                    UIdentifier (Identifier (bar)) [UIdentifier (Identifier (bar))]
                UReturnExpression [return mutable] = Nothing
                    USimpleNameReferenceExpression (identifier = mutable) [mutable] = external mutable()
        UMethod (name = bar) [public static fun bar() : void {...}]
            UBlockExpression [{...}] = 2
                UBinaryExpression (operator = =) [mutable = 2] = 2
                    USimpleNameReferenceExpression (identifier = mutable) [mutable] = external mutable()
                    ULiteralExpression (value = 2) [2] = 2
