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

Arend v. Reinersdorff created VELOCITY-987:
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             Summary: 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 v. Reinersdorff


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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