[PR] [improve][build] Require Java 21 for servers while preserving Java 17 client compatibility [pulsar]

["lhotari (via GitHub)" <gi...@apache.org>]

lhotari opened a new pull request, #26769:
URL: https://github.com/apache/pulsar/pull/26769

   ### Motivation
   
   Pulsar 5 server components should require Java 21 while client libraries remain usable on Java 17, as discussed on the [dev mailing list](https://lists.apache.org/thread/3zclb8cq0dt95c8f1lh83qxyyj11m8pq). Users must also be able to compile Functions and IO implementations against the public interfaces with Java 17, even though Pulsar's Functions runtime requires Java 21.
   
   ### Modifications
   
   - Default main sources and server startup to Java 21. Keep an explicit Java 17 dependency closure covering both client generations, admin/auth/crypto clients, TLS/HTTP SPIs, shared APIs, and Functions/IO interfaces.
   - Publish matching Gradle JVM attributes and reject incompatible dependencies. Check Java 17 class-file versions in dependencies and final shaded jars, respecting multi-release jar selection.
   - Keep the fastutil minimizer's Java 21 reachability inputs separate from its Java 17 published artifact.
   - Compile ordinary tests for Java 21 so client tests can use server fixtures. Add a dedicated consumer test compiled with `--release 17` and executed with Gradle's Java 17 toolchain launcher, plus CI setup and documentation.
   
   ### Verifying this change
   
   - [ ] Make sure that the change passes the CI checks.
   
   Passed locally on Gradle 9.8.0:
   
   - `./gradlew help assemble sanityCheck :tests:pulsar-java17-compatibility:test generateMetadataFileForMavenPublication -PtestRetryCount=0 --configuration-cache --warning-mode all`
   - `./gradlew -p build-logic :conventions:test --tests VerifyJavaCompatibilityTest`
   - Two Java 17 consumer tests and four bytecode-checker tests passed. `sanityCheck` includes Spotless, Checkstyle, and main/test compilation.
   - Inspected generated client, minimized/shaded client, Functions API, and broker JVM metadata.
   
   Full broker and cross-JVM interoperability tests were not run. The bytecode checker does not prove all third-party JDK API or reflective compatibility. Gradle reports deprecations for `Configuration.setVisible` and publication dependencies on unpublished projects; these are outside this change.
   
   ### Does this pull request potentially affect one of the following parts:
   
   - [ ] Dependencies (add or upgrade a dependency)
   - [ ] The public API
   - [ ] The schema
   - [ ] The default values of configurations
   - [ ] The threading model
   - [ ] The binary protocol
   - [ ] The REST endpoints
   - [ ] The admin CLI options
   - [ ] The metrics
   - [x] Anything that affects deployment
   
   Server components, CLI tools, and Functions runtime implementations now require Java 21 or later. Client libraries and Functions/IO public interfaces retain Java 17 compatibility.
   
   


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Re: [PR] [improve][build] Require Java 21 for servers while preserving Java 17 client compatibility [pulsar]

["lhotari (via GitHub)" <gi...@apache.org>]

lhotari merged PR #26769:
URL: https://github.com/apache/pulsar/pull/26769


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