with the introduction of the module-info something interesting is
happening. Up until now the scope of a Java project was limited to the
compilation of the classes. In case of Maven the end-user was in full
control regarding the classpath and the order of entries. With the order
of the dependencies you can control the order of classpath entries. You
could add your own dependencies but could also exclude them. The exclude
is especially powerful in those cases where library builders have made
mistakes (e.g. junit without test-scope) or simply forgot to remove
dependencies when refactoring code.
The first project poms are often quite clean, but it requires discipline
to keep cleaning up your pom, e.g. removing unused dependencies. However,
you're not really punished if you don't do this.
With the shift to module-info, suddenly every library-builder gets
control. If the module-info of that library "requires A.B", it means that
every project using this library MUST have A.B on its module-path. As
end-user you cannot exclude A.B, nor can you say "B.A replaces A.B for
x.y.z" in case of duplicate classes as allowed on the classpath. In short:
the end-users must rely on the discipline of library builders.
This loss of control for the end-user will have huge impact. Maven has a
analyze-goal in the maven-dependency-plugin which show both unused
declared dependencies and used undeclared dependencies (which means pulled
in as transitive dependency, even though the code directly uses it).
Almost every time I run this goal on any project it detects dependencies
in one of both groups.
To enforce the discipline, the java compiler should IMHO at least check if
all required modules are indeed required and if the transitive required
modules are indeed transitive. The role of the module-info is way too
important to simply allow all content. The scope is not just about the
classes anymore; the complete module tree is now locked into the jar. Any
mis-configured module-info down the tree can never be fixed by the
end-user, which could block the end-user to use the modulepath.
just sharing my concerns,
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