[Java SDK] use CustomResource by default to rehydrate a resource

[EronWright]

When a Java SDK program applies a manifest containing a custom resource (e.g. using ConfigGroup v2), the resultant resources output should contain an instance of com.pulumi.kubernetes.apiextensions.CustomResource, but doesn't. Well-known kinds like ConfigMap work as expected, but it appears that the SDK is unaware of the possibility of using CustomResource as a fallback. As a result, the resources array has incomplete information.

Example program snippet:

            var issuer = new ConfigGroup("example", ConfigGroupArgs.builder()
                .objs(Map.ofEntries(
                    Map.entry("apiVersion", "cert-manager.io/v1"),
                    Map.entry("kind", "Issuer"),
                    Map.entry("metadata", Map.ofEntries(
                        Map.entry("name", "my-issuer")
                    )),
                    Map.entry("spec", Map.ofEntries(
                        Map.entry("selfSigned", Map.ofEntries())
                    ))
                ))
                .build());

Debug logs show:

I0722 18:15:15.359646   88274 eventsink.go:59] Deserialize/ResourcePackages: can't find a resource: 'kubernetes:cert-manager.io/v1:Issuer'; version= urn=urn:pulumi:dev::issue-3057::kubernetes:yaml/v2:ConfigGroup$kubernetes:cert-manager.io/v1:Issuer::example:default/my-issuer

The relevant code snippet in pulumi-java is here. The code appears to scan the classpath for resource classes marked with the @ResourceType annotation.

Observe that com.pulumi.kubernetes.apiextensions.CustomResource does have a @ResourceType annotation, with an apparently useless value, given that no actual resource is of type kubernetes:apiextensions:CustomResource. When I authored CustomResource, I didn't know enough about the purpose of ResourceType.

@ResourceType(type="kubernetes:apiextensions:CustomResource")
public class CustomResource extends com.pulumi.resources.CustomResource {
}

I would suggest as a possible fix that the Java SDK allow for a given resource to be marked as the default, e.g.

@ResourceType(type="*")
@ResourceType(typeExpression="kubernetes:.+")
public class CustomResource extends com.pulumi.resources.CustomResource {
}

[EronWright]

This issue is about how resource references are hydrated by the Pulumi Java SDK. Basically the SDK expects to find (on the classpath) a resource class for the given type token. But is that a reasonable expectation (that you have an SDK type for all resource types that you may encounter), especially when crossing a component boundary?

In this example, a program is basically applying a Kubernetes manifest, and this causes a sub-graph of resources from the Kubernetes provider, but the provider doesn't provide an SDK type for all possible kinds.