Fix ByteKnnVectorFieldSource & FloatKnnVectorFieldSource to work correctly when a segment does not contain any docs with vectors (#13105)

lucene/CHANGES.txt

@@ -206,7 +206,9 @@ Optimizations
 
 Bug Fixes
 ---------------------
-(No changes)
+
+* GITHUB#13105: Fix ByteKnnVectorFieldSource & FloatKnnVectorFieldSource to work correctly when a segment does not contain
+  any docs with vectors (hossman)
 
 Other
 ---------------------

lucene/queries/src/java/org/apache/lucene/queries/function/valuesource/ByteKnnVectorFieldSource.java

@@ -20,7 +20,9 @@ import java.io.IOException;
 import java.util.Map;
 import java.util.Objects;
 import org.apache.lucene.index.ByteVectorValues;
+import org.apache.lucene.index.LeafReader;
 import org.apache.lucene.index.LeafReaderContext;
+import org.apache.lucene.index.VectorEncoding;
 import org.apache.lucene.queries.function.FunctionValues;
 import org.apache.lucene.queries.function.ValueSource;
 import org.apache.lucene.search.DocIdSetIterator;
@@ -39,11 +41,25 @@ public class ByteKnnVectorFieldSource extends ValueSource {
   public FunctionValues getValues(Map<Object, Object> context, LeafReaderContext readerContext)
       throws IOException {
 
-    final ByteVectorValues vectorValues = readerContext.reader().getByteVectorValues(fieldName);
+    final LeafReader reader = readerContext.reader();
+    final ByteVectorValues vectorValues = reader.getByteVectorValues(fieldName);
 
     if (vectorValues == null) {
-      throw new IllegalArgumentException(
-          "no byte vector value is indexed for field '" + fieldName + "'");
+      VectorFieldFunction.checkField(reader, fieldName, VectorEncoding.BYTE);
+
+      return new VectorFieldFunction(this) {
+        private final DocIdSetIterator empty = DocIdSetIterator.empty();
+
+        @Override
+        public byte[] byteVectorVal(int doc) throws IOException {
+          return null;
+        }
+
+        @Override
+        protected DocIdSetIterator getVectorIterator() {
+          return empty;
+        }
+      };
     }
 
     return new VectorFieldFunction(this) {

lucene/queries/src/java/org/apache/lucene/queries/function/valuesource/FloatKnnVectorFieldSource.java

@@ -20,7 +20,9 @@ import java.io.IOException;
 import java.util.Map;
 import java.util.Objects;
 import org.apache.lucene.index.FloatVectorValues;
+import org.apache.lucene.index.LeafReader;
 import org.apache.lucene.index.LeafReaderContext;
+import org.apache.lucene.index.VectorEncoding;
 import org.apache.lucene.queries.function.FunctionValues;
 import org.apache.lucene.queries.function.ValueSource;
 import org.apache.lucene.search.DocIdSetIterator;
@@ -39,12 +41,26 @@ public class FloatKnnVectorFieldSource extends ValueSource {
   public FunctionValues getValues(Map<Object, Object> context, LeafReaderContext readerContext)
       throws IOException {
 
-    final FloatVectorValues vectorValues = readerContext.reader().getFloatVectorValues(fieldName);
+    final LeafReader reader = readerContext.reader();
+    final FloatVectorValues vectorValues = reader.getFloatVectorValues(fieldName);
 
     if (vectorValues == null) {
-      throw new IllegalArgumentException(
-          "no float vector value is indexed for field '" + fieldName + "'");
+      VectorFieldFunction.checkField(reader, fieldName, VectorEncoding.FLOAT32);
+      return new VectorFieldFunction(this) {
+        private final DocIdSetIterator empty = DocIdSetIterator.empty();
+
+        @Override
+        public float[] floatVectorVal(int doc) throws IOException {
+          return null;
+        }
+
+        @Override
+        protected DocIdSetIterator getVectorIterator() {
+          return empty;
+        }
+      };
     }
+
     return new VectorFieldFunction(this) {
 
       @Override

lucene/queries/src/java/org/apache/lucene/queries/function/valuesource/VectorFieldFunction.java

@@ -17,6 +17,9 @@
 package org.apache.lucene.queries.function.valuesource;
 
 import java.io.IOException;
+import org.apache.lucene.index.FieldInfo;
+import org.apache.lucene.index.LeafReader;
+import org.apache.lucene.index.VectorEncoding;
 import org.apache.lucene.queries.function.FunctionValues;
 import org.apache.lucene.queries.function.ValueSource;
 import org.apache.lucene.search.DocIdSetIterator;
@@ -53,4 +56,29 @@ public abstract class VectorFieldFunction extends FunctionValues {
     }
     return doc == curDocID;
   }
+
+  /**
+   * Checks the Vector Encoding of a field
+   *
+   * @throws IllegalStateException if {@code field} exists, but was not indexed with vectors.
+   * @throws IllegalStateException if {@code field} has vectors, but using a different encoding
+   * @lucene.internal
+   * @lucene.experimental
+   */
+  static void checkField(LeafReader in, String field, VectorEncoding expectedEncoding) {
+    FieldInfo fi = in.getFieldInfos().fieldInfo(field);
+    if (fi != null) {
+      final VectorEncoding actual = fi.hasVectorValues() ? fi.getVectorEncoding() : null;
+      if (expectedEncoding != actual) {
+        throw new IllegalStateException(
+            "Unexpected vector encoding ("
+                + actual
+                + ") for field "
+                + field
+                + "(expected="
+                + expectedEncoding
+                + ")");
+      }
+    }
+  }
 }

lucene/queries/src/test/org/apache/lucene/queries/function/TestKnnVectorSimilarityFunctions.java

@@ -78,6 +78,10 @@ public class TestKnnVectorSimilarityFunctions extends LuceneTestCase {
     document.add(new KnnByteVectorField("knnByteField2", new byte[] {4, 2, 3}));
     iw.addDocument(document);
 
+    if (usually(random())) {
+      iw.commit();
+    }
+
     Document document2 = new Document();
     document2.add(new StringField("id", "2", Field.Store.NO));
     document2.add(new SortedDocValuesField("id", new BytesRef("2")));
@@ -232,7 +236,7 @@ public class TestKnnVectorSimilarityFunctions extends LuceneTestCase {
         new ByteVectorSimilarityFunction(VectorSimilarityFunction.EUCLIDEAN, v1, v2);
 
     assertThrows(
-        IllegalArgumentException.class,
+        IllegalStateException.class,
         () -> searcher.search(new FunctionQuery(byteDenseVectorSimilarityFunction), 10));
 
     v1 = new FloatKnnVectorFieldSource("knnByteField1");
@@ -241,8 +245,16 @@ public class TestKnnVectorSimilarityFunctions extends LuceneTestCase {
         new FloatVectorSimilarityFunction(VectorSimilarityFunction.EUCLIDEAN, v1, v2);
 
     assertThrows(
-        IllegalArgumentException.class,
+        IllegalStateException.class,
         () -> searcher.search(new FunctionQuery(floatVectorSimilarityFunction), 10));
+
+    v1 = new FloatKnnVectorFieldSource("id");
+    FloatVectorSimilarityFunction idVectorSimilarityFunction =
+        new FloatVectorSimilarityFunction(VectorSimilarityFunction.EUCLIDEAN, v1, v2);
+
+    assertThrows(
+        IllegalStateException.class,
+        () -> searcher.search(new FunctionQuery(idVectorSimilarityFunction), 10));
   }
 
   private static void assertHits(Query q, float[] scores) throws Exception {