Checkstyle 13.3.0 requires Java 21

[Mark Waite]

I've reported a checkstyle issue that the 13.3.0 release requires Java 21 without mentioning it in the release notes.  Jenkins plugins that use checkstyle 13.3.0 cannot be compiled with Java 17.

I think it is time to revisit my decision to remove Java 17 from the Jenkinsfile while performing the Java 25 upgrade.  We've had several cases where we lost the ability to build with Java 17.

Mark Waite

[Ullrich Hafner]

Actually Java 21 is required since the breaking change 13.0.0, see https://checkstyle.org/releasenotes.html#Release_13.0.0

Plugins can change the CheckStyle version that is used in their pom.xml if they need to.

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[Verachten Bruno]

That's what I discovered this morning: https://github.com/jenkinsci/gitlab-oauth-plugin/pull/218#issuecomment-3995690311 .

[Ullrich Hafner]

As a side note: when are we planning to switch the BOM builds from Java 17 to Java 21? When I understand correctly, as soon as we have Java 21 plugins, these will break the BOM because they cannot be built with Java 17 anymore.

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[Adrien Lecharpentier]

bom-weekly is already on java 21: https://github.com/jenkinsci/bom/blob/25cf5802d5d7726372034971a88cd40d51edb48a/Jenkinsfile#L115.

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[Mark Waite]

On Wed, Mar 4, 2026 at 2:20 PM Ullrich Hafner <ullrich...@gmail.com> wrote:

As a side note: when are we planning to switch the BOM builds from Java 17 to Java 21? When I understand correctly, as soon as we have Java 21 plugins, these will break the BOM because they cannot be built with Java 17 anymore.

I think that BOM builds will switch from Java 17 to Java 21 in a series of steps, with the final step occurring around September 30, 2026.

Jenkins plugins should not require Java 21 until they require Jenkins 2.545 or newer because Jenkins core does not require Java 21 until version 2.545.  The next LTS baseline has been proposed as 2.553.  Jenkins 2.553.1 is scheduled for release on April 15, 2026.  When the plugin BOM adds the Jenkins 2.553.x line, that line of the plugin BOM will need to use Java 21.  However, the preceding lines of the plugin BOM do not need to use Java 21 and should not use it, lest they fail to detect incompatibilities in a plugin.

I think that we should allow the usual process to work in this case.  We will release Jenkins 2.553.1 April 15, 2026 and it will require Java 21 for the 2.553.x line in the plugin BOM.  We will drop the 2.516.x at that time, but the 2.528.x line and the 2.541.x line will continue to compile and test with Java 17.  July 8, 2026 we will release ".1" of the next LTS baseline and will drop the 2.528.x line.  Sep 30, 2026 we will release the ".1" of the "next-next" LTS baseline and will drop the 2.541.x line.  At that point, the plugin BOM will build entirely with Java 21.

Mark Waite