[SLING-8269] Generics in ResourceProvider SPI don't resolve

• Type: Improvement
• Status: Resolved
• Priority: Minor
• Resolution: Won't Fix
• Affects Version/s: API 2.11.0
• Component/s: API
• Assignee: Unassigned
• Reporter: Julian Sedding
• Created: 08/Feb/19 11:37
• Updated: 12/Apr/23 05:42
• Resolved: 12/Apr/23 05:42

Description

In the "new" ResourceProvider SPI a resource provider always "owns" its root. This means that below that path no other RP is asked for resources (unless it's registered on a more specific root path). In order to allow for the scenario where a RP falls back to {{Resource}}s provided by other RPs, an API was added, that I gather should be used as follows:

public Iterator<Resource> listChildren(ResolveContext<Whatever> ctx, Resource parent) {
    Iterator<Resource> ownChildren = ... // compute child resource
    ResolveContext<?> parentCtx = ctx.getParentResolveContext();
    ResourceProvider<?> parentProvider = ctx.getParentResourceProvider();
    if (parentCtx == null || parentProvider == null) {
        return null;
    }
    return merge(ownChildren, parentProvider.listChildren(parentCtx, parent));
}

 
However, the parentCtx on the last line does not match the signature of listChildren(ResourceContext<T>, Resource), because the generic type of both ResolveContext<?> and ResourceContext<T> (from the listChildren method signature) do not match, leading to the following compile-time error:

incompatible types: org.apache.sling.spi.resource.provider.ResolveContext<capture#1 of ?> cannot be converted to org.apache.sling.spi.resource.provider.ResolveContext<capture#2 of ?>

This can be worked around by dropping generic types of the local variables and accepting an "unchecked type" warning, i.e.:

ResolveContext parentCtx = ctx.getParentResolveContext();
ResourceProvider parentProvider = ctx.getParentResourceProvider();

cc cziegeler