private ResolveResult resolveClusterSearchChain(String cluster,
                                                    ComponentSpecification sourceRef,
                                                    Properties sourceToProviderMap) {
        var resolveResult = searchChainResolver.resolve(new ComponentSpecification(cluster), sourceToProviderMap);
        if (resolveResult.invocationSpec() == null) {
            return new ResolveResult("Failed to resolve cluster search chain '" + cluster +
                                     "' when using source ref '" + sourceRef + "' as a document name.");
        }
        return resolveResult;
    }
Maps a source reference to search chain invocation specs.

@author Tony Vaagenes
container-search/src/main/java/com/yahoo/search/federation/sourceref/SourceRefResolver.java