Interoperability with Ivy and Maven dependency resolvers

[ckulenkampff]

This enhancement would allow to create a flat classpath of Ceylon CARs for Java projects using Maven, Ivy or Gradle. This is possible by offering appropriate repository "facades" through the Herd repository server.

Maven repository structure Maven expects the following layout (see Maven Repository Layout - Final) for primary artifacts: /$groupId[0]/../${groupId[n]/$artifactId/$version/$artifactId-$version.$extension and for secondary artifacts: /$groupId[0]/../$groupId[n]/$artifactId/$version/$artifactId-$version-$classifier.$extension

Ivy repository structure Ivy is more flexible and allows to specify custom patterns for artifact resolution (see Ivy Documentation - Main Concepts). The default patten that is used by Gradle is the following (see Gradle DSL Reference - IvyArtifactRepository): Artifacts: $baseUri/[organisation]/[module]/[revision]/[type]s/[artifact](.[ext]) Ivy module descriptors: $baseUri/[organisation]/[module]/[revision]/[type]s/[artifact](.[ext])

Meta information To resolve transitive dependencies both repository types require meta information. Maven uses pom.xmls. Ivy uses ivy.xmls, but can also process pom.xmls. Those files must be accessible via HTTP requests.

Meta information augmentation When the repository server responds to a "foreign" meta data request for a Ceylon module, it should automatically add all implicit dependencies of the Ceylon language to the response. For interoperability these Ceylon language modules should be published to the Herd repository so that Java projects that depend on a Ceylon library do not have to provide them by themselves.

Artifact aliases For interoperability it would be very useful when CAR files are also available under the same name but with JAR file extension when accessed through a facade.

Many IDEs automatically link source and javadoc JARs to the downloaded artifacts by searching in the module cache for files like $artifactId-$version-$classifier-sources.$extension (IDE dependent see NetBeans DependencyNode). Ceylon source artifacts should be made available in a way that this resolution works out of the box. This means that the artifacts are made available under another name than they are normally accessible in Herd.