Hi! This is a discussion about altering the way we handle dependencies and shading in Flink. I ran into quite a view problems trying to adjust / fix some shading issues during release validation.
The issue is tracked under: https://issues.apache.org/jira/browse/FLINK-6529 Bring this discussion thread up because it is a bigger issue *Problem* Currently, Flink shades dependencies like ASM and Guava into all jars of projects that reference it and relocate the classes. There are some drawbacks to that approach, let's discuss them at the example of ASM: - The ASM classes are for example in flink-core, flink-java, flink-scala, flink-runtime, etc. - Users that reference these dependencies have the classes multiple times in the classpath. That is unclean (works, through, because the classes are identical). The same happens when building the final dist. jar. - Some of these dependencies require to include license files in the shaded jar. It is hard to impossible to build a good automatic solution for that, partly due to Maven's very poor cross-project path support - Most importantly: Scala does not support shading really well. Scala classes have references to classes in more places than just the class names (apparently for Scala reflect support). Referencing a Scala project with shaded ASM still requires to add a reference to unshaded ASM (at least as a compile dependency). *Proposal* I propose that we build and deploy a asm-flink-shaded version of ASM and directly program against the relocated namespaces. Since we never use classes that we relocate in public interfaces, Flink users will never see the relocated class names. Internally, it does not hurt to use them. - Proper maven dependency management, no hidden (shaded) dependencies - One copy of each class for shaded dependencies - Proper Scala interoperability - Natural License management (license is part of deployed asm-flink-shaded jar) Happy to hear thoughts! Stephan
