Requires runtime considered?

[Alan Bateman]

On 28/06/2021 09:49, Christian Beikov wrote:
> Hello experts,
>
> I am in the process of modularizing one of my projects and hit some 
> rather annoying limitations that requires me to change parts of my 
> build and dependencies due to the way the Java module system works.
>
> I usually have modules like x-api, x-impl and x-testsuite where I have 
> a compile time dependency from x-impl to x-api. In x-testsuite I only 
> code against x-api, so I define a Maven runtime dependency on x-impl 
> in order for my CDI container to pick up the implementations. The 
> annoying part is that with modularization I now need to declare my 
> dependency in x-testsuite on x-impl as compile time dependency, 
> because otherwise I can't list the module in the module-info. If I 
> don't list the module, then it is not "visible" to the CDI container, 
> which I guess is on purpose, even though it probably ends up in the 
> module path.
>
> Is that by design that classes are not visible if no module depends on 
> a module like x-impl in such a scenario, or is that maybe something 
> that could work and should be improved in the CDI implementation? I 
> was thinking that if "requires runtime ..." were allowed without 
> checking that the module is available during compilation, this would 
> work fine. Did this idea come up before already?

The module system supports services. x-api uses a service, x-impl 
provides an implementation of the service. If x-api is resolved then all 
observable modules that provide an implementation of the services used 
by x-api will be resolved too. In this scenario, x-impl requires x-api, 
x-api does not require x-impl. You used the phrase "compile time 
dependency" but it's more than that, it's all phases as there will be 
references in x-impl to x-api's exported API.

I don't know if you control the CDI implementation or not but if you 
aren't using services then you'll need to help the module system with 
"--add-modules x-impl". This is because no other module requires x-impl 
and it's not providing an implementation of a service. It may be 
observable but it's the same directory as 99,999 other modules that you 
don't care about.

-Alan