WORK IN PROGRESS msimacek, 2015-04-09

Describe RPM Provides and Requires, their interactions especially with relation to JAR file identification, explain mvn(gId:aId…​) strings.

RPM has multiple types of metadata to describe dependency relationships between packages. The two basic types are Requires and Provides. Requires denote that a package needs something to be present at runtime to work correctly and the package manager is supposed to ensure that requires are met. A single Requires item can specify a package or a virtual provide. RPM Provides are a way to express that a package provides certain capability that other packages might need. In case of Maven packages, the Provides are used to denote that a package contains certain Maven artifact. They add more flexibility to the dependency management as single package can have any number of provides, and they can be moved across different packages without breaking other packages' requires. Provides are usually generated by automatic tools based on the information from the built binaries or package source.

The Java packaging tooling on Fedora provides automatic Requires and Provides generation for packages built using XMvn. The Provides are based on Maven artifact coordinates of artifacts that were installed by the currenlty being built. They are generated for each subpackage separately. They follow a general format mvn(groupId:artifactId:extension:classifier:version), where the extension is omitted if it’s jar and classifier is omitted if empty. Version is present only for compat artifacts, but the trailing colon has to be present unless it’s a Jar artifact with no classifier.

The generated Requires are based on dependencies specified in Maven POMs in the project. Only dependencies with scope set to either compile, runtime or not set at all are used for Requires generation. Requires don’t rely on package names and instead always use virtual provides that were described above, in exactly the same format, in order to be satisfieable by the already existing provides. For packages consisting of multiple subpackages, Requires are generated separately for each subpackage. Additionally, Requires that point to an artifact in a different subpackage of the same source package are generated with exact versions to prevent version mismatches between artifacts belonging to the same project.

The requires generator also always generates Requires on java-headless and javapackages-tools.

If the package is built built using different tool than Apache Maven, but still ships Maven POM(s), the you will still get automatic provides generation if you install the POM using %mvn_artifact and %mvn_install. The requires generation will also be executed but the outcome largely depends on whether the POM contains accurate dependency insformation. If it contains dependency information, you should double check that it’s correct and up-to-date. Otherwise you need to add Requires tags manually as described in the next section.

For packages without POMs it’s necessary to specify Requires tags manually. In order to build the package you needed to specify BuildRequires tags. You Requires tags will therefore likely be a subset of your BuildRequires, excluding build tools and test only dependencies.

The generated Requires and Provides of built packages can be queried using rpm:

While Requires and Provides are automated for Maven projects, BuildRequires still remain a manual task. However, it can be at least a bit simplified. XMvn ships a script xmvn-builddep that takes a build.log output from mock and prints maven-style BuildRequires on artifacts that were actually used during the build. It doesn’t help you to figure out what the BuildRequires are before you actually build it, but it may help you to have a minimal set of BuildRequires that are less likely to break, as they don’t rely on transitive dependencies.