Add option to preserve service registry

[yuchangyuan]

Add preserveServiceRegistry, serviceRegistryInclude &
serviceRegistryExclude keys.

When preserveServiceRegistry is true, files in META-INF/services
will be merged, filtered and then insert into the final apk.

Any class name that match any regexp in serviceRegistryInclude and
not match any regexp in serviceRegistryExclude will be included.

[appamatto]

@yuchangyuan can you explain what the use case for this is?

[yuchangyuan]

Some library(for example, sesame, http://www.openrdf.org/), use java service registry(or service loader) to provide service(which is a part of android api: http://developer.android.com/reference/java/util/ServiceLoader.html), the usage of ServiceLoader depend on some files in META-INF/services. But these files in seperate jars are not merged into final jar, which cause ServiceLoader can not find any service, and make any code depend on these service not work.

[appamatto]

Thanks! This does seem interesting. Perhaps we could detect when the services directory is present and do the right thing in that case, with a single switch to turn it off. Is there any reason to exclude service definitions if they are present?

[yuchangyuan]

Yes, there some use case.

For example, the library jar contains 100 service definitions, and the jar is large. but my android app only need few of these, so I tell proguard to only preserve these I need. If there're more service definitions than actual implementation in classpath, and my code use iterator to find all implementations, maybe a class not found exception will rise(I am not sure about this, but sure that some exception will be thrown).