[jira] [Updated] (CALCITE-4387) Document that RexSimplify.simplifyUnknownAs could narrow or widen nullness of the given expression

["Vladimir Sitnikov (Jira)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/CALCITE-4387?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Vladimir Sitnikov updated CALCITE-4387:
---------------------------------------
    Issue Type: Improvement  (was: Bug)

> Document that RexSimplify.simplifyUnknownAs could narrow or widen nullness of the given expression
> --------------------------------------------------------------------------------------------------
>
>                 Key: CALCITE-4387
>                 URL: https://issues.apache.org/jira/browse/CALCITE-4387
>             Project: Calcite
>          Issue Type: Improvement
>          Components: core
>    Affects Versions: 1.26.0
>         Environment: It is expected that {{RexSimplify.simplifyUnknownAs}} would make the expression "simpler" (e.g. less RexNodes or something like that), however, there's no explicit contract on the resulting expression.
> For instance the following expression has non-nullable type
> {noformat}
> case_(isUnknown(vBool(1)), trueLiteral, vBool(1), falseLiteral, trueLiteral)
> {noformat}
> however, it might be simplified to the following **nullable** expression:
> {noformat}
> or(isUnknown(vBool(1)), not(vBool(1)))
> {noformat}
> Note: the expression never returns null, however, it might be not that obvious that the simplified expression never returns null.
> I suggest we add explicit note to {{simplifyUnknownAs}} method that says the method is allowed to narrow or widen the nullness of the given expression type
> {{simplifyPreservingType(RexNode, RexUnknownAs, boolean matchNullability)}} could be used to keep nullness intact.
> PS. It woud be nice to simplify {{or(isUnknown(vBool(1)), not(vBool(1)))}} to {{isNotTrue(vBool(1))}}, however, that is another story. I guess there might be different cases (e.g. involving more complicated cases) that would result in nullability "widening".
>            Reporter: Vladimir Sitnikov
>            Priority: Major
>




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