Some Collection and Map fallbacks don't work in GraalVM native image

[edudar]

Is your feature request related to a problem? Please describe.

I'm trying to run a service compiled with GraalVM into a native image. The service does not reference or create HashSet explicitly and uses Set in all DTOs instead. Upon deserialization, an exception happens that says that "java.util.HashSet can't be created because no creator, like default constructor, exists". Those are removed by dead code elimination as none are registered for reflection or used explicitly, and ContainerDefaultMappings provides just a class reference that is used later to create a given set via newInstance.

Describe the solution you'd like

My current solution using Spring Boot is to simply register these classes for reflection:

hints.reflection()
        .registerTypes(TypeReference.listOf(
                        ArrayList.class,
                        LinkedList.class,
                        HashSet.class,
                        TreeSet.class,
                        ConcurrentHashMap.class,
                        LinkedHashMap.class,
                        TreeMap.class),
                TypeHint.builtWith(INVOKE_PUBLIC_CONSTRUCTORS, INVOKE_PUBLIC_METHODS));

This is not perfect, though.

Another approach might be to create appropriate value instantiators in JDKValueInstantiators for every fallback collection as they specifically tell what constructor will be used.

Usage example

No response

Additional context

No response

[cowtowncoder]

Interesting. I would have thought dependency via JDKValueInstantiators would be enough to pull in dependencies....
I wonder if a small change would force GraalVM compiler to add dependencies?

I am open to suggestions for solution here.

[edudar]

It helps with classes it creates, but these are only ArrayList and LinkedHashMap/HashMap. Other lists, sets, and maps get nuked. Expanding JDKValueInstantiators to cover more common creators would probably help.

[cowtowncoder]

Ok. So those types are found at least. And due to defaulting, I guess adding support for others seems sensible too.

[edudar]

BTW, I added a simple but close-to-real reproducer for this issue at https://github.com/edudar/feign-native. It fails with the default Jackson version (2.15.3) and succeeds with a locally built 2.17.0 snapshot.

[cowtowncoder]

Thanks @edudar that is a good validation; important to know fix actually works for intended problem.

Aside from CLA for PR, the only thing I really was hoping to clarify was whether eager construction of ValueInstantiators was required for fix to work. Ideally it'd be nice to only eager instantiate ones that are very likely to be used (which is for types that are default mappings), and defer others to as-needed basis.
It may seem silly but I have tried to limit default set of eager static initializations to try to reduce startup overhead (granted these are very small portion of everything).

[edudar]

Eager instantiation is not required for the fix. The main difference is explicit instantiation vs. reflection via default constructor.

[cowtowncoder]

Thank you @edudar ! If possible, could you check that the resulting version (2.17.0-SNAPSHOT) works as expected? (if you haven't already done so). I assume it does, just want to make sure.