Array length: store the result of the constant folding in a separate variable to keep origin expression

slither/core/solidity_types/array_type.py

@@ -12,13 +12,18 @@ class ArrayType(Type):
             if isinstance(length, int):
                 length = Literal(length)
             assert isinstance(length, Expression)
-            if not isinstance(length, Literal):
-                cf = ConstantFolding(length)
-                length = cf.result()
         super(ArrayType, self).__init__()
         self._type = t
         self._length = length
 
+        if length:
+            if not isinstance(length, Literal):
+                cf = ConstantFolding(length)
+                length = cf.result()
+            self._length_value = length
+        else:
+            self._length_value = None
+
     @property
     def type(self):
         return self._type
@@ -29,9 +34,7 @@ class ArrayType(Type):
 
     def __str__(self):
         if self._length:
-            if isinstance(self._length.value, Variable) and self._length.value.is_constant:
-                return str(self._type)+'[{}]'.format(str(self._length.value.expression))
-            return str(self._type)+'[{}]'.format(str(self._length))
+            return str(self._type)+'[{}]'.format(str(self._length_value))
         return str(self._type)+'[]'