SOLR-17477: Support custom aggregates in plugin code

solr/core/src/java/org/apache/solr/search/facet/DocValuesAcc.java

@@ -37,7 +37,7 @@
  * org.apache.lucene.index.DocValues}
  */
 public abstract class DocValuesAcc extends SlotAcc {
-  SchemaField sf;
+  protected final SchemaField sf;
 
   public DocValuesAcc(FacetContext fcontext, SchemaField sf) throws IOException {
     super(fcontext);

solr/core/src/java/org/apache/solr/search/facet/FacetModule.java

@@ -370,7 +370,7 @@ static class FacetComponentState {
   }
 
   // base class for facet functions that can be used in a sort
-  abstract static class FacetSortableMerger extends FacetMerger {
+  public abstract static class FacetSortableMerger extends FacetMerger {
     public void prepareSort() {}
 
     @Override
@@ -386,7 +386,7 @@ public void finish(Context mcontext) {
     public abstract int compareTo(FacetSortableMerger other, FacetRequest.SortDirection direction);
   }
 
-  abstract static class FacetDoubleMerger extends FacetSortableMerger {
+  public abstract static class FacetDoubleMerger extends FacetSortableMerger {
     @Override
     public abstract void merge(Object facetResult, Context mcontext);
 
@@ -422,8 +422,8 @@ public static int compare(double a, double b, FacetRequest.SortDirection directi
     }
   }
 
-  static class FacetLongMerger extends FacetSortableMerger {
-    long val;
+  public static class FacetLongMerger extends FacetSortableMerger {
+    private long val;
 
     @Override
     public void merge(Object facetResult, Context mcontext) {
@@ -442,8 +442,9 @@ public int compareTo(FacetSortableMerger other, FacetRequest.SortDirection direc
   }
 
   // base class for facets that create buckets (and can hence have sub-facets)
-  abstract static class FacetBucketMerger<FacetRequestT extends FacetRequest> extends FacetMerger {
-    FacetRequestT freq;
+  public abstract static class FacetBucketMerger<FacetRequestT extends FacetRequest>
+      extends FacetMerger {
+    protected final FacetRequestT freq;
 
     public FacetBucketMerger(FacetRequestT freq) {
       this.freq = freq;
@@ -483,8 +484,8 @@ FacetMerger createFacetMerger(String key, Object val) {
     }
   }
 
-  static class FacetQueryMerger extends FacetBucketMerger<FacetQuery> {
-    FacetBucket bucket;
+  public static class FacetQueryMerger extends FacetBucketMerger<FacetQuery> {
+    private FacetBucket bucket;
 
     public FacetQueryMerger(FacetQuery freq) {
       super(freq);

solr/core/src/java/org/apache/solr/search/facet/FacetParser.java

@@ -33,7 +33,7 @@
 import org.apache.solr.search.QParser;
 import org.apache.solr.search.SyntaxError;
 
-abstract class FacetParser<T extends FacetRequest> {
+public abstract class FacetParser<T extends FacetRequest> {
   protected T facet;
   protected FacetParser<?> parent;
   protected String key;

solr/core/src/java/org/apache/solr/search/facet/UniqueMultiDvSlotAcc.java

@@ -28,7 +28,7 @@
 import org.apache.lucene.util.LongValues;
 import org.apache.solr.schema.SchemaField;
 
-class UniqueMultiDvSlotAcc extends UniqueSlotAcc {
+public class UniqueMultiDvSlotAcc extends UniqueSlotAcc {
   SortedSetDocValues topLevel;
   SortedSetDocValues[] subDvs;
   OrdinalMap ordMap;

solr/core/src/java/org/apache/solr/search/facet/UniqueMultivaluedSlotAcc.java

@@ -24,7 +24,7 @@
 import org.apache.solr.schema.SchemaField;
 import org.apache.solr.search.SolrIndexSearcher;
 
-class UniqueMultivaluedSlotAcc extends UniqueSlotAcc implements UnInvertedField.Callback {
+public class UniqueMultivaluedSlotAcc extends UniqueSlotAcc implements UnInvertedField.Callback {
   private UnInvertedField uif;
   private UnInvertedField.DocToTerm docToTerm;
 

solr/core/src/java/org/apache/solr/search/facet/UniqueSinglevaluedSlotAcc.java

@@ -28,7 +28,7 @@
 import org.apache.lucene.util.LongValues;
 import org.apache.solr.schema.SchemaField;
 
-class UniqueSinglevaluedSlotAcc extends UniqueSlotAcc {
+public class UniqueSinglevaluedSlotAcc extends UniqueSlotAcc {
   SortedDocValues topLevel;
   SortedDocValues[] subDvs;
   OrdinalMap ordMap;

solr/core/src/java/org/apache/solr/search/facet/UniqueSlotAcc.java

@@ -27,7 +27,7 @@
 import org.apache.solr.schema.SchemaField;
 import org.apache.solr.util.hll.HLL;
 
-abstract class UniqueSlotAcc extends SlotAcc {
+public abstract class UniqueSlotAcc extends SlotAcc {
   HLLAgg.HLLFactory factory;
   SchemaField field;
   FixedBitSet[] arr;

solr/core/src/test/org/apache/solr/search/function/AggValueSourceTest.java

@@ -23,6 +23,7 @@
 import org.apache.solr.SolrTestCase;
 import org.apache.solr.search.facet.FacetContext;
 import org.apache.solr.search.facet.FacetMerger;
+import org.apache.solr.search.facet.FacetModule;
 import org.apache.solr.search.facet.SimpleAggValueSource;
 import org.apache.solr.search.facet.SlotAcc;
 import org.junit.Test;
@@ -76,22 +77,22 @@ public Object getValue(int slot) {
 
     @Override
     public FacetMerger createFacetMerger(Object prototype) {
-      return new FacetMerger() {
-        double total = 0.0D;
-
-        @Override
-        public void merge(Object facetResult, Context mcontext) {
-          total += (Double) facetResult;
-        }
-
-        @Override
-        public void finish(Context mcontext) {}
-
-        @Override
-        public Object getMergedResult() {
-          return total;
-        }
-      };
+      // check these inner classes can be referenced by name
+      FacetModule.FacetSortableMerger merger =
+          new FacetModule.FacetDoubleMerger() {
+            double total = 0.0D;
+
+            @Override
+            public void merge(Object facetResult, Context mcontext) {
+              total += (Double) facetResult;
+            }
+
+            @Override
+            public double getDouble() {
+              return total;
+            }
+          };
+      return merger;
     }
 
     @Override