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Drop Mandatory Requires on JRE

This is a proposed Change for Fedora Linux.
This document represents a proposed Change. As part of the Changes process, proposals are publicly announced in order to receive community feedback. This proposal will only be implemented if approved by the Fedora Engineering Steering Committee.

Summary

Drop the requirement of Java libraries to have Requires on JREs.

Owner

Current status

  • Targeted release: Fedora Linux 41
  • Last updated: 2024-04-18
  • [<will be assigned by the Wrangler> devel thread]
  • FESCo issue: <will be assigned by the Wrangler>
  • Tracker bug: <will be assigned by the Wrangler>
  • Release notes tracker: <will be assigned by the Wrangler>

Detailed Description

Current guidelines require all Java packages to Require: java-headless or java-headless >= 1:minimal_required_version.

Our aim is to drop this explicit requirement on Java library packages. The requirement should stay for Java applications.

Context

Java packages are compiled using javac into .class files and composed into .jar archives. Jar archives can be used as compile or runtime dependencies for other packages or can be directly executed with the java command provided by a JRE.

Jar archives can be executed using the command: java -jar ${FILE}. This command executes the main method either specified via CLI or specified within the Jar manifest file.

Java packages, which serve as libraries only, lack the main method and are not executable. Therefore, there is no requirement on any specific JRE imposed by the library implicitly.

Different JDKs

This proposal is also related to the topic of different JDKs. Developers may want to use or build packages which use a JDK different than the one provided by the java-<N>-openjdk package. After this proposal was implemented, they would be able to depend on Java library packages with no introduction of the OpenJDK package.

Rationale

Java libraries are more similar to native libraries than to libraries written in dynamic scripting languages. They are compiled to a bytecode and are not executable. Java libraries can be used as dependencies for any Java application and there is no implicit dependency on the system default JDK.

Java applications, on the other hand, are expected to be tested and to work with the system JDK and from the user's perspective: after installing an application they must be able to simply run the binary. Therefore the Requires on the system JDK is kept for Java applications.

Feedback

Benefit to Fedora

  • Very little user-visible benefit.
  • Reduced dependencies of Java packages.
  • Simplified maintenance of Java packages.
    • Smaller impact of JDK major updates (e.g. 1.8.0 -> 11 -> 17 -> 21). Introducing a new system version of JDK requires the rebuild of each Java package in order to have updated Requires to contain the newest version.

Scope

  • Proposal owners:
    • Find all Java applications in Fedora, i.e. packages which BuildRequire java-devel / maven-local / ant and at the same time install files into /bin or /sbin or /usr/bin or /usr/sbin.
    • Open pull requests adding Requires: java-headless into their .spec file.
    • Remove Requires generator from javapackages-tools
    • Wait for a mass rebuild.
  • Other developers:
    • Maintainers of Java applications will need to add an explicit Requires: java-headless field into their .spec file or a specific version of thereof (such as java-17-openjdk-headless).
  • Release engineering: #Releng issue number
    • Mass rebuild is not required, this change can propagate via natural rebuilds.
  • Trademark approval: N/A (not needed for this Change)
  • Alignment with Community Initiatives: N/A

Upgrade/compatibility impact

  • For Java libraries:
    • This change is removing Requires and therefore users manually installing a Java library will not additionally install the JVM.
  • For Java applications:
    • After fully implemented, applications will no longer be installable along with any JVM but rather only the system one (unless the package maintainer decides otherwise)

How To Test

  • Installing a Java library should not typically install JVM (but can if the library depends on a Java application)
  • Installing a Java application MUST cause the installation of the system-wide JVM (or a different version thereof)
  • Executing a binary installed in typical locations (such as /usr/bin) MUST NOT cause an error related to the JVM not being installed.

User Experience

Users with no Java application installed, but some Java libraries installed: the JVM may be automatically uninstalled as it is possibly not required by anything.

It is possible that there are users with only some older JVM installed. The following depends on the decision of each Java application package maintainer, but the general expectation is that the system-wide JVM will be installed and the older JVM will no longer be required by other packages.

Users who explicitly installed JVMs of various versions: no change.

Dependencies

  • javapackages-tools
    • This change allows the removal of the Requires generator.

Contingency Plan

  • Contingency mechanism:
    • In case of unexpected problems, the Requires generators can be reintroduced into javapackages-tools and packages can be rebuilt.
  • Contingency deadline: Branch Fedora Linux 41 from Rawhide Tue 2024-08-06
  • Blocks release? No

Documentation

No documentation outside of this document.

Release Notes

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