[jira] [Commented] (VELOCITY-987) Directive to fail execution of the current template with an error message

    [ https://issues.apache.org/jira/browse/VELOCITY-987?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=18034766#comment-18034766 ] 

Claude Brisson commented on VELOCITY-987:
-----------------------------------------

The user did solve his problem. See:

* [the stackoverflow thread|https://stackoverflow.com/a/79333428/710286]
* [the corresponding Maven Doxia Sitetool issue|https://issues.apache.org/jira/browse/DOXIASITETOOLS-179]


> Directive to fail execution of the current template with an error message
> -------------------------------------------------------------------------
>
>                 Key: VELOCITY-987
>                 URL: https://issues.apache.org/jira/browse/VELOCITY-987
>             Project: Velocity
>          Issue Type: New Feature
>            Reporter: Arend von Reinersdorff
>            Priority: Major
>
> My current use case is generating a Dockerfile and setting the base image according to a Java version parameter. Accepted values for Java versions are limited (17, 11, 8). Problem was when 21 was added as a new Java version, the if-block was not updated. Template generation succeeded using a fallback image and an error appeared later.
> If the fallback could have failed the template generation, the error would have been discovered sooner.
> *Requirements*
>  * Directive to fail the template generation
>  * Ability to add an error message
>  * Error should lead to the place of failure (template file, line number)
> *Example usage*
> {code:java}
> #if (${javaVersion} == '21')
>     FROM icr.io/appcafe/open-liberty:full-java21-openj9-ubi-minimal
> #elseif (${javaVersion} == '17')
>     FROM icr.io/appcafe/open-liberty:full-java17-openj9-ubi
> #else
>     #fail("Unsupported Java version: ${javaVersion}")
> #end{code}
> Error  message might loook like this:
> Template execution failed for example.vm line 6: Unsupported Java version: 11
> *Difference to stop*
> I am aware of the #stop directive. But as it doesn't fail the template generation. So it is not visible that an error occured.
> *See also*
> https://stackoverflow.com/questions/46587599/how-to-fail-velocity-template-processing-with-tracable-message



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