Side note: I know issue #17954 is not approved yet, and thus the "Check PR Description / Analyze (pull_request)" CI will fail.

The goal of pushing this PR early is to have the rest of the CI run and assess whether this is a viable solution, or whether this change will break some other CI flow (e.g., if alternative JVMs are used, or if some test somehow depends on JVM behavior).

In the worst case, if the project maintainers aren't on board with this approach, both the issue and the PR shold be closed.

There are two CI failures.
Check PR Description / Analyze (pull_request) is expected to fail, as the issue is not approved (yet).
ci/semaphoreci/pr: Checkstyle CI pipeline on Semaphore fails in the job setup phase, and seems like an ephemeral environmental issue - the previous iteration of this PR did not fail that test, so I'm guessing rerunning this job should clear the error.

Both relaunched.

Please share knowledge or links to knowledge what such jvm parameters means and why we need two of them to fix issue

Is this different or same issue?
https://ci.appveyor.com/project/Checkstyle/checkstyle/builds/52930182/job/51iwjpcb4vln1oa9?fullLog=true#L118

Ok, I got it, we addressed only

[INFO] Running com.puppycrawl.tools.checkstyle.api.LineColumnTest
OpenJDK 64-Bit Server VM warning: Sharing is only supported for boot loader classes because bootstrap classpath has been appended
WARNING: A Java agent has been loaded dynamically (/home/vsts/work/1/.m2/repository/net/bytebuddy/byte-buddy-agent/1.14.11/byte-buddy-agent-1.14.11.jar)
WARNING: If a serviceability tool is in use, please run with -XX:+EnableDynamicAgentLoading to hide this warning
WARNING: If a serviceability tool is not in use, please run with -Djdk.instrument.traceUsage for more information
WARNING: Dynamic loading of agents will be disallowed by default in a future release

Ok, please share links to knowledge and we are merging this PR.

Thanks a lot for help.

Ok, please share links to knowledge and we are merging this PR.

WRT --xShrare:off:
Class Data Sharing (CDS) is a feature that can potentially speed up application startup by having a shared archive of system classes, which acts as a sort of a cache.
When using Mockito in test scenarios, some of these classes are loaded by a different classsloader than the one CDS expects, causing this warning message. As the performance gain is negligible anyway in this scenario, it's easier to just shut it off.
Relevant links:

• Mockito issue: VM warning: Sharing is only supported for boot loader classes mockito/mockito#3111
• CDS documentation: https://docs.oracle.com/en/java/javase/25/vm/class-data-sharing.html#GUID-2942983A-E83C-4DA3-A60C-60411D731D5A
• A good explanation on CDS internals, that also walks through this warning: https://nipafx.dev/java-application-class-data-sharing.

WRT -XX:+EnableDynamicAgentLoading:
Java has been preparing to get rid of dynamic agent loading since Java 21 (see JEP 451), and will issue a warning when you try to use this feature, as Mockito does internally.
At the time of writing (and note that Java 25 is now the latest!) there's no equivalent feature that provides similar functionality, so the common practice is just to allow this feature (or disable the warning) with that JVM flag.
Note that this isn't really an edge case - it's used by mocking libraries (like Mockito), APM tools and even IAST tools, so I don't think it will be going away any time soon.