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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