Clean up KNN related backward-codecs changes (#12019)

lucene/backward-codecs/src/java/org/apache/lucene/backward_codecs/lucene90/Lucene90HnswGraphBuilder.java

@@ -57,7 +57,7 @@ public final class Lucene90HnswGraphBuilder {
 
   // we need two sources of vectors in order to perform diversity check comparisons without
   // colliding
-  private RandomAccessVectorValues buildVectors;
+  private final RandomAccessVectorValues buildVectors;
 
   /**
    * Reads all the vectors from a VectorValues, builds a graph connecting them by their dense

lucene/backward-codecs/src/java/org/apache/lucene/backward_codecs/lucene90/Lucene90HnswVectorsReader.java

@@ -55,15 +55,12 @@ import org.apache.lucene.util.hnsw.RandomAccessVectorValues;
  */
 public final class Lucene90HnswVectorsReader extends KnnVectorsReader {
 
-  private final FieldInfos fieldInfos;
   private final Map<String, FieldEntry> fields = new HashMap<>();
   private final IndexInput vectorData;
   private final IndexInput vectorIndex;
   private final long checksumSeed;
 
   Lucene90HnswVectorsReader(SegmentReadState state) throws IOException {
-    this.fieldInfos = state.fieldInfos;
-
     int versionMeta = readMetadata(state);
     long[] checksumRef = new long[1];
     boolean success = false;
@@ -305,20 +302,6 @@ public final class Lucene90HnswVectorsReader extends KnnVectorsReader {
     };
   }
 
-  /** Get knn graph values; used for testing */
-  public HnswGraph getGraphValues(String field) throws IOException {
-    FieldInfo info = fieldInfos.fieldInfo(field);
-    if (info == null) {
-      throw new IllegalArgumentException("No such field '" + field + "'");
-    }
-    FieldEntry entry = fields.get(field);
-    if (entry != null && entry.indexDataLength > 0) {
-      return getGraphValues(entry);
-    } else {
-      return HnswGraph.EMPTY;
-    }
-  }
-
   private HnswGraph getGraphValues(FieldEntry entry) throws IOException {
     IndexInput bytesSlice =
         vectorIndex.slice("graph-data", entry.indexDataOffset, entry.indexDataLength);

lucene/backward-codecs/src/java/org/apache/lucene/backward_codecs/lucene91/Lucene91HnswVectorsReader.java

@@ -57,13 +57,11 @@ import org.apache.lucene.util.hnsw.RandomAccessVectorValues;
  */
 public final class Lucene91HnswVectorsReader extends KnnVectorsReader {
 
-  private final FieldInfos fieldInfos;
   private final Map<String, FieldEntry> fields = new HashMap<>();
   private final IndexInput vectorData;
   private final IndexInput vectorIndex;
 
   Lucene91HnswVectorsReader(SegmentReadState state) throws IOException {
-    this.fieldInfos = state.fieldInfos;
     int versionMeta = readMetadata(state);
     boolean success = false;
     try {
@@ -299,20 +297,6 @@ public final class Lucene91HnswVectorsReader extends KnnVectorsReader {
     };
   }
 
-  /** Get knn graph values; used for testing */
-  public HnswGraph getGraph(String field) throws IOException {
-    FieldInfo info = fieldInfos.fieldInfo(field);
-    if (info == null) {
-      throw new IllegalArgumentException("No such field '" + field + "'");
-    }
-    FieldEntry entry = fields.get(field);
-    if (entry != null && entry.vectorIndexLength > 0) {
-      return getGraph(entry);
-    } else {
-      return HnswGraph.EMPTY;
-    }
-  }
-
   private HnswGraph getGraph(FieldEntry entry) throws IOException {
     IndexInput bytesSlice =
         vectorIndex.slice("graph-data", entry.vectorIndexOffset, entry.vectorIndexLength);
@@ -581,12 +565,12 @@ public final class Lucene91HnswVectorsReader extends KnnVectorsReader {
     }
 
     @Override
-    public int numLevels() throws IOException {
+    public int numLevels() {
       return numLevels;
     }
 
     @Override
-    public int entryNode() throws IOException {
+    public int entryNode() {
       return entryNode;
     }
 

lucene/backward-codecs/src/java/org/apache/lucene/backward_codecs/lucene92/Lucene92HnswVectorsReader.java

@@ -440,12 +440,12 @@ public final class Lucene92HnswVectorsReader extends KnnVectorsReader {
     }
 
     @Override
-    public int numLevels() throws IOException {
+    public int numLevels() {
       return numLevels;
     }
 
     @Override
-    public int entryNode() throws IOException {
+    public int entryNode() {
       return entryNode;
     }
 

lucene/backward-codecs/src/java/org/apache/lucene/backward_codecs/lucene94/Lucene94Codec.java

@@ -63,7 +63,7 @@ public class Lucene94Codec extends Codec {
 
     private final Lucene90StoredFieldsFormat.Mode storedMode;
 
-    private Mode(Lucene90StoredFieldsFormat.Mode storedMode) {
+    Mode(Lucene90StoredFieldsFormat.Mode storedMode) {
       this.storedMode = Objects.requireNonNull(storedMode);
     }
   }
@@ -164,7 +164,7 @@ public class Lucene94Codec extends Codec {
   }
 
   @Override
-  public final KnnVectorsFormat knnVectorsFormat() {
+  public KnnVectorsFormat knnVectorsFormat() {
     return knnVectorsFormat;
   }
 

lucene/backward-codecs/src/java/org/apache/lucene/backward_codecs/lucene94/Lucene94HnswVectorsFormat.java

@@ -96,7 +96,7 @@ import org.apache.lucene.util.hnsw.HnswGraph;
  *
  * @lucene.experimental
  */
-public final class Lucene94HnswVectorsFormat extends KnnVectorsFormat {
+public class Lucene94HnswVectorsFormat extends KnnVectorsFormat {
 
   static final String META_CODEC_NAME = "lucene94HnswVectorsFormatMeta";
   static final String VECTOR_DATA_CODEC_NAME = "lucene94HnswVectorsFormatData";
@@ -115,20 +115,18 @@ public final class Lucene94HnswVectorsFormat extends KnnVectorsFormat {
    */
   public static final int DEFAULT_BEAM_WIDTH = 100;
 
-  static final int DIRECT_MONOTONIC_BLOCK_SHIFT = 16;
-
   /**
    * Controls how many of the nearest neighbor candidates are connected to the new node. Defaults to
    * {@link Lucene94HnswVectorsFormat#DEFAULT_MAX_CONN}. See {@link HnswGraph} for more details.
    */
-  private final int maxConn;
+  final int maxConn;
 
   /**
    * The number of candidate neighbors to track while searching the graph for each newly inserted
    * node. Defaults to to {@link Lucene94HnswVectorsFormat#DEFAULT_BEAM_WIDTH}. See {@link
    * HnswGraph} for details.
    */
-  private final int beamWidth;
+  final int beamWidth;
 
   /** Constructs a format using default graph construction parameters */
   public Lucene94HnswVectorsFormat() {
@@ -149,7 +147,7 @@ public final class Lucene94HnswVectorsFormat extends KnnVectorsFormat {
 
   @Override
   public KnnVectorsWriter fieldsWriter(SegmentWriteState state) throws IOException {
-    return new Lucene94HnswVectorsWriter(state, maxConn, beamWidth);
+    throw new UnsupportedOperationException("Old codecs may only be used for reading");
   }
 
   @Override

lucene/backward-codecs/src/java/org/apache/lucene/backward_codecs/lucene94/Lucene94HnswVectorsReader.java

@@ -504,12 +504,12 @@ public final class Lucene94HnswVectorsReader extends KnnVectorsReader {
     }
 
     @Override
-    public int numLevels() throws IOException {
+    public int numLevels() {
       return numLevels;
     }
 
     @Override
-    public int entryNode() throws IOException {
+    public int entryNode() {
       return entryNode;
     }
 

lucene/backward-codecs/src/test/org/apache/lucene/backward_codecs/lucene94/Lucene94HnswVectorsWriter.java

@@ -17,7 +17,7 @@
 
 package org.apache.lucene.backward_codecs.lucene94;
 
-import static org.apache.lucene.backward_codecs.lucene94.Lucene94HnswVectorsFormat.DIRECT_MONOTONIC_BLOCK_SHIFT;
+import static org.apache.lucene.backward_codecs.lucene94.Lucene94RWHnswVectorsFormat.DIRECT_MONOTONIC_BLOCK_SHIFT;
 import static org.apache.lucene.search.DocIdSetIterator.NO_MORE_DOCS;
 
 import java.io.IOException;

lucene/backward-codecs/src/test/org/apache/lucene/backward_codecs/lucene94/Lucene94RWCodec.java

@@ -0,0 +1,46 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.lucene.backward_codecs.lucene94;
+
+import org.apache.lucene.codecs.KnnVectorsFormat;
+import org.apache.lucene.codecs.perfield.PerFieldKnnVectorsFormat;
+
+/** Implements the Lucene 9.4 index format for backwards compat testing */
+public class Lucene94RWCodec extends Lucene94Codec {
+
+  private final KnnVectorsFormat defaultKnnVectorsFormat;
+  private final KnnVectorsFormat knnVectorsFormat =
+      new PerFieldKnnVectorsFormat() {
+        @Override
+        public KnnVectorsFormat getKnnVectorsFormatForField(String field) {
+          return defaultKnnVectorsFormat;
+        }
+      };
+
+  /** Instantiates a new codec. */
+  public Lucene94RWCodec() {
+    defaultKnnVectorsFormat =
+        new Lucene94RWHnswVectorsFormat(
+            Lucene94HnswVectorsFormat.DEFAULT_MAX_CONN,
+            Lucene94HnswVectorsFormat.DEFAULT_BEAM_WIDTH);
+  }
+
+  @Override
+  public final KnnVectorsFormat knnVectorsFormat() {
+    return knnVectorsFormat;
+  }
+}

lucene/backward-codecs/src/test/org/apache/lucene/backward_codecs/lucene94/Lucene94RWHnswVectorsFormat.java

@@ -0,0 +1,51 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.lucene.backward_codecs.lucene94;
+
+import java.io.IOException;
+import org.apache.lucene.codecs.KnnVectorsReader;
+import org.apache.lucene.codecs.KnnVectorsWriter;
+import org.apache.lucene.index.SegmentReadState;
+import org.apache.lucene.index.SegmentWriteState;
+
+public final class Lucene94RWHnswVectorsFormat extends Lucene94HnswVectorsFormat {
+  static final int DIRECT_MONOTONIC_BLOCK_SHIFT = 16;
+
+  public Lucene94RWHnswVectorsFormat(int maxConn, int beamWidth) {
+    super(maxConn, beamWidth);
+  }
+
+  @Override
+  public KnnVectorsWriter fieldsWriter(SegmentWriteState state) throws IOException {
+    return new Lucene94HnswVectorsWriter(state, DEFAULT_MAX_CONN, DEFAULT_BEAM_WIDTH);
+  }
+
+  @Override
+  public KnnVectorsReader fieldsReader(SegmentReadState state) throws IOException {
+    return new Lucene94HnswVectorsReader(state);
+  }
+
+  @Override
+  public String toString() {
+    return "Lucene94RWHnswVectorsFormat(name=Lucene94RWHnswVectorsFormat, maxConn="
+        + maxConn
+        + ", beamWidth="
+        + beamWidth
+        + ")";
+  }
+}

lucene/backward-codecs/src/test/org/apache/lucene/backward_codecs/lucene94/TestLucene94HnswVectorsFormat.java

@@ -19,24 +19,23 @@ package org.apache.lucene.backward_codecs.lucene94;
 import org.apache.lucene.codecs.Codec;
 import org.apache.lucene.codecs.KnnVectorsFormat;
 import org.apache.lucene.tests.index.BaseKnnVectorsFormatTestCase;
-import org.apache.lucene.tests.util.TestUtil;
 
 public class TestLucene94HnswVectorsFormat extends BaseKnnVectorsFormatTestCase {
   @Override
   protected Codec getCodec() {
-    return TestUtil.getDefaultCodec();
+    return new Lucene94RWCodec();
   }
 
   public void testToString() {
-    Lucene94Codec customCodec =
+    Lucene94RWCodec customCodec =
-        new Lucene94Codec() {
+        new Lucene94RWCodec() {
           @Override
           public KnnVectorsFormat getKnnVectorsFormatForField(String field) {
-            return new Lucene94HnswVectorsFormat(10, 20);
+            return new Lucene94RWHnswVectorsFormat(10, 20);
           }
         };
     String expectedString =
-        "Lucene94HnswVectorsFormat(name=Lucene94HnswVectorsFormat, maxConn=10, beamWidth=20)";
+        "Lucene94RWHnswVectorsFormat(name=Lucene94RWHnswVectorsFormat, maxConn=10, beamWidth=20)";
     assertEquals(expectedString, customCodec.getKnnVectorsFormatForField("bogus_field").toString());
   }
 }