Upgrading a Vastly Outdated Plugin: Lessons Learned

[gounthar]

Background

Yesterday, I embarked on upgrading the Vagrant plugin, which had remained untouched for over 7 years. The plugin was still declaring Java 7 compatibility, causing our current Maven setup to reject it due to its inability to handle versions below Java 8.

Manual Upgrade Process

Unable to use our automated tools, I resorted to manual interventions:

1. Followed the "Improve a Plugin Tutorial"
2. Removed the java.level property
3. Upgraded the Jenkins version
4. Added the BOM (Bill of Materials)
5. Changed the parent POM
6. Changed the Jenkins version

These steps alone were insufficient. Further actions included:

• Adding missing dependencies (incorporating code previously extracted from core and now available as plugins) to the pom file to achieve compilation

Questions and Considerations

1. Should we create a recipe listing these dependencies and add them automatically?
2. The plugin dependencies page suggests potential beneficial dependencies. Are we already extracting this information from updates.jenkins.io?
3. Should we add dependencies incrementally to test the waters?

Final Resolution

Mark Waite identified an outdated test-harness specific version reference. Removing this allowed the tests to pass, as maintaining an old test harness version is inadvisable due to compatibility issues with recent Jenkins core versions.

Key Insights

1. Our tool reaches its limits when dealing with plugins untouched since Java 7.
2. Many steps (if not all) could potentially be automated, particularly for plugins still dependent on older Java versions. Automated does not mean "with this tool", as we're stuck with the Maven compatibility problem with older Java versions.
3. We should implement "recipes" already listed in the "Upgrade a Plugin" tutorial.

Future Steps

While this single plugin upgrade doesn't reveal all potential limitations, I plan to periodically attempt upgrades on seriously outdated plugins to gather more insights for our automation process.

Note: The Vagrant plugin now successfully compiles with JDK 21.