Make flatVectorsFormat injectable in Lucene99HnswVectorsFormat to allow custom format and scorers

lucene/core/src/java/org/apache/lucene/codecs/lucene99/Lucene99HnswVectorsFormat.java

@@ -18,6 +18,7 @@
 package org.apache.lucene.codecs.lucene99;
 
 import java.io.IOException;
+import java.util.Objects;
 import java.util.concurrent.ExecutorService;
 import org.apache.lucene.codecs.KnnVectorsFormat;
 import org.apache.lucene.codecs.KnnVectorsReader;
@@ -132,8 +133,7 @@ public final class Lucene99HnswVectorsFormat extends KnnVectorsFormat {
   private final int beamWidth;
 
   /** The format for storing, reading, and merging vectors on disk. */
-  private static final FlatVectorsFormat flatVectorsFormat =
-      new Lucene99FlatVectorsFormat(FlatVectorScorerUtil.getLucene99FlatVectorsScorer());
+  private final FlatVectorsFormat flatVectorsFormat;
 
   private final int numMergeWorkers;
   private final TaskExecutor mergeExec;
@@ -168,7 +168,13 @@ public Lucene99HnswVectorsFormat(int maxConn, int beamWidth) {
    */
   public Lucene99HnswVectorsFormat(
       int maxConn, int beamWidth, int numMergeWorkers, ExecutorService mergeExec) {
-    this(maxConn, beamWidth, numMergeWorkers, mergeExec, VERSION_CURRENT);
+    this(
+        maxConn,
+        beamWidth,
+        numMergeWorkers,
+        mergeExec,
+        VERSION_CURRENT,
+        new Lucene99FlatVectorsFormat(FlatVectorScorerUtil.getLucene99FlatVectorsScorer()));
   }
 
   /**
@@ -190,6 +196,56 @@ public Lucene99HnswVectorsFormat(
       int numMergeWorkers,
       ExecutorService mergeExec,
       int writeVersion) {
+    this(
+        maxConn,
+        beamWidth,
+        numMergeWorkers,
+        mergeExec,
+        writeVersion,
+        new Lucene99FlatVectorsFormat(FlatVectorScorerUtil.getLucene99FlatVectorsScorer()));
+  }
+
+  /**
+   * Constructs a format using the given graph construction parameters.
+   *
+   * @param maxConn the maximum number of connections to a node in the HNSW graph
+   * @param beamWidth the size of the queue maintained during graph construction.
+   * @param numMergeWorkers number of workers (threads) that will be used when doing merge. If
+   *     larger than 1, a non-null {@link ExecutorService} must be passed as mergeExec
+   * @param mergeExec the {@link ExecutorService} that will be used by ALL vector writers that are
+   *     generated by this format to do the merge. If null, the configured {@link
+   *     MergeScheduler#getIntraMergeExecutor(MergePolicy.OneMerge)} is used.
+   * @param flatVectorsFormat the format used to store vectors on disk
+   */
+  public Lucene99HnswVectorsFormat(
+      int maxConn,
+      int beamWidth,
+      int numMergeWorkers,
+      ExecutorService mergeExec,
+      FlatVectorsFormat flatVectorsFormat) {
+    this(maxConn, beamWidth, numMergeWorkers, mergeExec, VERSION_CURRENT, flatVectorsFormat);
+  }
+
+  /**
+   * Constructs a format using the given graph construction parameters.
+   *
+   * @param maxConn the maximum number of connections to a node in the HNSW graph
+   * @param beamWidth the size of the queue maintained during graph construction.
+   * @param numMergeWorkers number of workers (threads) that will be used when doing merge. If
+   *     larger than 1, a non-null {@link ExecutorService} must be passed as mergeExec
+   * @param mergeExec the {@link ExecutorService} that will be used by ALL vector writers that are
+   *     generated by this format to do the merge. If null, the configured {@link
+   *     MergeScheduler#getIntraMergeExecutor(MergePolicy.OneMerge)} is used.
+   * @param writeVersion the version used for the writer to encode docID's (VarInt=0, GroupVarInt=1)
+   * @param flatVectorsFormat the format used to store vectors on disk
+   */
+  Lucene99HnswVectorsFormat(
+      int maxConn,
+      int beamWidth,
+      int numMergeWorkers,
+      ExecutorService mergeExec,
+      int writeVersion,
+      FlatVectorsFormat flatVectorsFormat) {
     super("Lucene99HnswVectorsFormat");
     if (maxConn <= 0 || maxConn > MAXIMUM_MAX_CONN) {
       throw new IllegalArgumentException(
@@ -218,6 +274,8 @@ public Lucene99HnswVectorsFormat(
     } else {
       this.mergeExec = null;
     }
+    // fail fast if caller forgot to supply a FlatVectorsFormat
+    this.flatVectorsFormat = Objects.requireNonNull(flatVectorsFormat, "flatVectorsFormat");
   }
 
   @Override