[GitHub] [incubator-daffodil] stevedlawrence commented on a change in pull request #414: Throw SDE in the case of inputValueCalc containing checkConstraints(.)

[GitBox <gi...@apache.org>]

stevedlawrence commented on a change in pull request #414:
URL: https://github.com/apache/incubator-daffodil/pull/414#discussion_r483685311



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File path: daffodil-core/src/main/scala/org/apache/daffodil/dsom/ElementBase.scala
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@@ -1114,4 +1115,10 @@ trait ElementBase
     case (_, _) => this.subset((floating eq YesNo.No), "Property value floating='yes' is not supported.")
   }
 
+  private lazy val checkInputValueCalcExpression: Boolean = {
+    if (this.inputValueCalcOption.toString.contains("checkConstraints(.)")) {
+      SDE("For inputValueCalc, you cannot use checkConstraints(.) because the inputValueCalc expression is computing that value.")
+    }
+    true
+  }

Review comment:
       This feels like too specific of a check, and it's going to fail in some edgecases. For example, what if the expression was ``checkConstraints(     .)`` with a bunch of spaces. That wouldn't cause an error.
   
   Really, we don't care about checkConstraints, we just want to error if a inputValueCalc references itself. I thought we already had checks for if a property references it self. This issue isn't specific to inputValueCalc. I can also imagine cases where it references itself not via just dot, for example:
   
   ``dfdl:inputValueCalc="{ ../../foo/bar/myself }``
   
   And this isn't a trival check. It's not always possible to statically check if an element is referencing itself. For example, it could reference itself but in a previous array element, which is allowed.
   
   All that to say, I'm not sure how we improve this. Maybe the existing error is sufficient? Or perhaps we do a runtime check that if an expression tries to get the value of the context element then we do a different error message?




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