Hi, Unfortunately Maven 3 didn’t define a proper API. In effect everything somehow exposed through class loaders was considered API by plugin/extension developers. For Maven 4 a completely separate API was established in package “org.apache.maven.api”, but what about the old packages used and exported in Maven 3?
For example in the context of https://issues.apache.org/jira/browse/MNG-7588 <https://issues.apache.org/jira/browse/MNG-7588> I want to evolve the package “org.apache.maven.plugin.descriptor”. We already figured out that this particular package (although not part of the Maven 4 API) is used from both Maven Core as well as Maven Plugin Tools, therefore this probably needs to stay backwards compatible. What about others like https://github.com/apache/maven/blob/master/maven-core/src/main/java/org/apache/maven/plugin/MavenPluginManager.java? <https://github.com/apache/maven/blob/master/maven-core/src/main/java/org/apache/maven/plugin/MavenPluginManager.java?> This interface should IMHO never been implemented outside Maven Core but in fact it was exposed to all plugins/extensions (via https://github.com/apache/maven/blob/a6b1ebb1cd40ca4b288fdeb30c6d2460323aa25b/maven-core/src/main/resources/META-INF/maven/extension.xml#L40 <https://github.com/apache/maven/blob/a6b1ebb1cd40ca4b288fdeb30c6d2460323aa25b/maven-core/src/main/resources/META-INF/maven/extension.xml#L40>). There are three options coming to my mind: 1. Deprecate the interfaces we don’t consider API and create new ones for Maven 4 which are not exported! 2. Modify the existing interfaces in a backwards compatible way (but somehow add a marker that they should not be implemented outside core) 3. Modify the existing interfaces in a backwards compatible way (but somehow add a marker that they should not be implemented outside core) For all three options we somehow need to come up with a list of classes/interfaces currently being exported through the API class loader, which should be considered private and agree on an Annotation/Javadoc for that (something like https://github.com/mulesoft/api-annotations/blob/40b258afeff6560241dee5001ed00f1deb392e47/src/main/java/org/mule/api/annotation/NoImplement.java#L29 <https://github.com/mulesoft/api-annotations/blob/40b258afeff6560241dee5001ed00f1deb392e47/src/main/java/org/mule/api/annotation/NoImplement.java#L29> or https://wiki.eclipse.org/API_Javadoc_tags#The_New_Solution <https://wiki.eclipse.org/API_Javadoc_tags#The_New_Solution> WDYT? Konrad
