[JEXL-384] Improve control over JexlArithmetic null argument handling

• Type: Task
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 3.3
• Fix Version/s: 3.3
• Assignee: Henri Biestro
• Reporter: Hussachai Puripunpinyo
• Created: 04/Nov/22 05:59
• Updated: 27/Mar/23 10:59
• Resolved: 17/Feb/23 14:35

Description

https://issues.apache.org/jira/browse/JEXL-359 

A typical case is '+' for string and null where one would like to consider null as a valid argument even if arithmetic is strict. 

While the above reason is valid, the code introduced in JEXL-359 causes more confusion, and the behavior is now inconsistent.
Also, I'd like to give some counter arguments about not supporting null + string in the strict mode. If we want to make null + string works even if arithmetic is strict, there will be no difference between "" + "ABC" and null + "ABC" because both cases yield "ABC" in both strict and non-strict mode. In our code base, we set the engine to be strict, so users have to be careful about null since it can give an undesirable result. In a non-strict mode, we don't have a way to distinguish whether the result is the combination of null or empty string and a string. Users need to explicitly check for null, but there will be no enforcement
which means nobody will do that check. That's why we prefer it to be strict and a user has to check null before using or use some namespace functions that we provide where null will be explicitly handled. Otherwise, the exception will be thrown.

Let me elaborate why some part of JEXL-359 causes the behavior to be inconsistent.

Strict Mode

var i = null;
i + 'ABC'; // This will throw an exception.
null + 'ABC'; // This yields 'ABC' - the same as non-strict mode.

 

Non Strict Mode

var i = null;
i + 'ABC'; // This yields 'ABC';
null + 'ABC'; // This also yields 'ABC';

 

You can see that the behavior of null + 'ABC' in the strict mode is not consistent with the null variable.

Also, there is a way to allow string concatenation with null using a namespace function in a strict mode, and I think JEXL shouldn't make an exception for this one particular case.

I'd like to propose the PR with some regression tests that applies to only null (literal) + string case.

https://github.com/apache/commons-jexl/pull/136

Note: I ignored one test testNullArgs because the feature doesn't seem to be defined well. It won't work with numeric types.
I can pass around the JexlOperator to isStrict function everywhere to address that, but I'm trying to refrain from changing things too much since you may have some ideas and my code might get in the way. 

Please let me know if I can help with that, or you can merge my PR, take part of it or ignore it completely  

My idea about fixing testNullArgs properly is that all toString, toDouble, toBigDecimal functions should take an additional argument which is JexlOperator where a user can override for specific operator as stated in testNullArgs test. If that sounds right to you, I can help creating another Jira and PR to tackle this. Thank you.

Issue Links

• is related to: JEXL-359 Allow per-operator arithmetic handling of null arguments
• links to: GitHub Pull Request #136
• links to: GitHub Pull Request #138