ability to generate META-INF/services/* from module-info

[hohwille]

I have alredy migrated my entire OSS project (https://github.com/m-m-m) to JPMS/jigsaw and it works great.
I am using service-loader for dynamic and flexible plugin/extensions mechanism and declare the implementations in my module-info.java files (see e.g. https://github.com/m-m-m/property/blob/master/core/src/main/java/module-info.java#L23).
However, when my modules are not loaded via module-path but via legacy classpath the module-info is not loaded and therefore services are not discovered.
To workaround this problem, one can manually add legacy META-INF/servicess/«api-fqn» files and list the implemenations there (see e.g. https://github.com/m-m-m/ui-tvm/blob/master/core/src/main/resources/META-INF/services/io.github.mmm.property.factory.PropertyFactory).
However, maintaining this manually as redundant files is kind of tedious. It would therefore be awesome to have some maven-plugin that could generate this automatically during the build from module-info.java. I searched if such solution is already available and stumbled over your plugin.

So with this issue I want to kindly ask if you would consider this as a suitable and valuable feature for your project (since you were asking for YOUR ideas :)).
If so please get in touch. If you want I could even contribute via PR.

[aalmiray]

IMHO a feature like this requires parsing the module information and determine the services exposed. As an alternative you may use an annotation processor to generate the required service files, albeit there will be some sort of duplication as you need both the module definition and the annotated service.

There are handful of annotation processors that can do the job:

• AutoService - https://github.com/google/auto/tree/master/service
• Jipsy - https://github.com/kordamp/jipsy

Personally I chose Jipsy (I'm the maintainer so I'm biased). Here's how I put it to work on the Ikonli build

https://github.com/kordamp/ikonli/blob/master/icon-packs/ikonli-fontawesome-pack/src/main/java/module-info.java
https://github.com/kordamp/ikonli/blob/master/icon-packs/ikonli-fontawesome-pack/src/main/java/org/kordamp/ikonli/fontawesome/FontAwesomeIkonProvider.java#L26

[hohwille]

Thanks for your hint. That is interesting. As I still have to maintain services in the module-info, I would like to generate the services file from that. I would like to avoid adding silly annotations to my code and therefore requiring further third-party dependencies to all my modules.
However, if this is not the right place, feel free to close this issue.
I might create a new maven plugin at mojohaus or somewhere else if I do not find anything else.

[gunnarmorling]

How are you defining your module-info descriptor? If you generate it via ModiTect, it will pick up all class service definitions and expose them as "provided" services. We could think of doing it the other way around too. Happy to accept a PR if you feel like giving it a try.

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