On 17/10/2016 08:32, Peter Levart wrote:
The module declaration is intended to be authoritative and so we have to
trust module author when they declare that the module `requires M`. So
my view is that options such as --exclude-modules that would have the
effect of dropping requires puts us on the road to anarchy.
Do we need an --exclude-modules (in addition to --add-modules) option
on javac, java and jlink commands?
--exclude-modules would be different to --limit-modules. If some
module requires module M and there is no module M on the module path
or it is not observable because it was not mentioned in the
--limit-modules option, then an exception is raised. OTOH if some
module X requires module M and module M is mentioned in the
--exclude-modules option, then such requires is silently ignored in
hope that module X will not actually need types from module M.
That said, I do see Robert's concern that there might be orphaned
`requires` clauses in some modules. My module started using the
preferences API but later the implementation changed to use something
else. I neglected to remove the `requires java.prefs` from the module
declaration and the result is that my module cannot compile against or
run on a run-time image that doesn't include this module. Static
analysis tools might help here, as might the IDE. We are used to IDEs
highlighting unused `import` statements and in time then I expect they
will do the same for apparently unused `requires` clauses in
module-info.java. If the usage is purely reflective then the module
author might need to put a comment on the `requires` clause to avoid
other maintainers from removing it (a bit like "// used by javadoc" in
comments today when an import is for an unqualified reference in the
Another part to Robert's mail is the case where something is making use
of types in modules that it doesn't depend on. Assuming these are static
references then they will be caught at compile-time. This is big
improvement compared to today's class path.
A more general comment is that module authors will need to learn a few
new things about compatibility and refactoring. One example is changing
`requires transitive M` to `requires M` is an incompatible change.
Another is splitting a module (several sub-cases) where the module
author will need to add `requires transitive` to avoid breaking
consumers. There are lots of opportunities here for authoritative books
and documentation to help module authors do this right.