[GitHub] [netbeans-mavenutils-nbm-maven-plugin] ahauschulte commented on pull request #28: [NETBEANSINFRA-264] Include runtime module libraries

[GitBox <gi...@apache.org>]

ahauschulte commented on pull request #28:
URL: https://github.com/apache/netbeans-mavenutils-nbm-maven-plugin/pull/28#issuecomment-1081030849


   I think there are three different cases regarding dependency scopes in maven (https://maven.apache.org/guides/introduction/introduction-to-dependency-mechanism.html#Dependency_Scope) that need to be taken into account here:
   
   - Dependencies with scope "compile" are necessary to compile and run the module. Those dependencies need to be put on the compile and runtime classpaths and they need to be bundled. The current implementation of the nbm maven plugin handles this correctly.
   - Dependencies with scope "provided" are necessary to run the module and might also be necessary to compile it. However, they are indeed supplied by the runtime environment. Thus, there is no need to include them in the module’s nbm file. The current implementation of the nbm maven plugin handles this correctly as well.
   - Dependencies with scope "runtime" need to be on the runtime classpath for the module to work properly but they are not required to compile the module. This might be the case for one reason or another. For example, classes could be loaded manually, which is commonly done for JDBC drivers. (Something like `Class.forName("com.mysql.cj.jdbc.Driver")`) This is where the current implementation of the nbm maven plugin causes me some trouble, since those runtime dependencies are not bundled with the module’s nbm file. If, in this example, the dependency for the MySQL driver has the scope "runtime", and is not, by chance, provided by the runtime environment, the JDBC driver will just be missing, which will cause trouble at runtime.
   
   While the problem described in the simplistic example above could be easily resolved by just changing the scope of the MySQL driver dependency from "runtime" to "compile", there are other constellations where this causes much more trouble. Consider large third-party libraries that make extensive use of scope "runtime" for their own dependencies. This is often the case when these libraries are built using gradle because gradle provides finer-grained control whether a library should "leak" its own dependencies to its client. This is done by making liberate use of the scope "runtime". (https://docs.gradle.org/current/userguide/java_library_plugin.html#sec:java_library_separation)
   
   An example is the kafka library (https://github.com/apache/kafka; https://repo1.maven.org/maven2/org/apache/kafka/kafka_2.13/3.1.0/kafka_2.13-3.1.0.pom), which has quite a lot of runtime dependencies. If such a library is a dependency of your Netbeans module, a huge number of libs will be missing in the nbm file. In this case, though, you’ll get warnings from the nbm maven plugin if the verifyRuntime option hasn’t been deactivated. Anyway, with the current implementation, you’ll need to manually add all the missing transitive dependencies to your module’s pom file. 
   


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