LUCENE-7623: Add FunctionMatchQuery and FunctionScoreQuery

lucene/CHANGES.txt

@@ -63,6 +63,11 @@ Other
 
 ======================= Lucene 6.5.0 =======================
 
+New Features
+
+* LUCENE-7623: Add FunctionScoreQuery and FunctionMatchQuery (Alan Woodward,
+  Adrien Grand, David Smiley)
+
 Bug Fixes
 
 * LUCENE-7630: Fix (Edge)NGramTokenFilter to no longer drop payloads

lucene/core/src/java/org/apache/lucene/search/DoubleValuesSource.java

@@ -20,7 +20,9 @@ package org.apache.lucene.search;
 import java.io.IOException;
 import java.util.Objects;
 import java.util.function.DoubleToLongFunction;
+import java.util.function.DoubleUnaryOperator;
 import java.util.function.LongToDoubleFunction;
+import java.util.function.ToDoubleBiFunction;
 
 import org.apache.lucene.index.DocValues;
 import org.apache.lucene.index.LeafReaderContext;
@@ -173,6 +175,69 @@ public abstract class DoubleValuesSource {
       public boolean needsScores() {
         return false;
       }
+
+      @Override
+      public String toString() {
+        return "constant(" + value + ")";
+      }
+    };
+  }
+
+  /**
+   * Creates a DoubleValuesSource that is a function of another DoubleValuesSource
+   */
+  public static DoubleValuesSource function(DoubleValuesSource in, DoubleUnaryOperator function) {
+    return new DoubleValuesSource() {
+      @Override
+      public DoubleValues getValues(LeafReaderContext ctx, DoubleValues scores) throws IOException {
+        DoubleValues inputs = in.getValues(ctx, scores);
+        return new DoubleValues() {
+          @Override
+          public double doubleValue() throws IOException {
+            return function.applyAsDouble(inputs.doubleValue());
+          }
+
+          @Override
+          public boolean advanceExact(int doc) throws IOException {
+            return inputs.advanceExact(doc);
+          }
+        };
+      }
+
+      @Override
+      public boolean needsScores() {
+        return in.needsScores();
+      }
+    };
+  }
+
+  /**
+   * Creates a DoubleValuesSource that is a function of another DoubleValuesSource and a score
+   * @param in        the DoubleValuesSource to use as an input
+   * @param function  a function of the form (source, score) == result
+   */
+  public static DoubleValuesSource scoringFunction(DoubleValuesSource in, ToDoubleBiFunction<Double, Double> function) {
+    return new DoubleValuesSource() {
+      @Override
+      public DoubleValues getValues(LeafReaderContext ctx, DoubleValues scores) throws IOException {
+        DoubleValues inputs = in.getValues(ctx, scores);
+        return new DoubleValues() {
+          @Override
+          public double doubleValue() throws IOException {
+            return function.applyAsDouble(inputs.doubleValue(), scores.doubleValue());
+          }
+
+          @Override
+          public boolean advanceExact(int doc) throws IOException {
+            return inputs.advanceExact(doc);
+          }
+        };
+      }
+
+      @Override
+      public boolean needsScores() {
+        return true;
+      }
     };
   }
 
@@ -221,7 +286,17 @@ public abstract class DoubleValuesSource {
     @Override
     public DoubleValues getValues(LeafReaderContext ctx, DoubleValues scores) throws IOException {
       final NumericDocValues values = DocValues.getNumeric(ctx.reader(), field);
-      return toDoubleValues(values, decoder::applyAsDouble);
+      return new DoubleValues() {
+        @Override
+        public double doubleValue() throws IOException {
+          return decoder.applyAsDouble(values.longValue());
+        }
+
+        @Override
+        public boolean advanceExact(int target) throws IOException {
+          return values.advanceExact(target);
+        }
+      };
     }
 
     @Override
@@ -288,21 +363,6 @@ public abstract class DoubleValuesSource {
     }
   }
 
-  private static DoubleValues toDoubleValues(NumericDocValues in, LongToDoubleFunction map) {
-    return new DoubleValues() {
-      @Override
-      public double doubleValue() throws IOException {
-        return map.applyAsDouble(in.longValue());
-      }
-
-      @Override
-      public boolean advanceExact(int target) throws IOException {
-        return in.advanceExact(target);
-      }
-
-    };
-  }
-
   private static NumericDocValues asNumericDocValues(DoubleValuesHolder in, DoubleToLongFunction converter) {
     return new NumericDocValues() {
       @Override

lucene/queries/src/java/org/apache/lucene/queries/function/FunctionMatchQuery.java

@@ -0,0 +1,99 @@
+/*
+ * 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.queries.function;
+
+import java.io.IOException;
+import java.util.Objects;
+import java.util.function.DoublePredicate;
+
+import org.apache.lucene.index.LeafReaderContext;
+import org.apache.lucene.search.ConstantScoreScorer;
+import org.apache.lucene.search.ConstantScoreWeight;
+import org.apache.lucene.search.DocIdSetIterator;
+import org.apache.lucene.search.DoubleValues;
+import org.apache.lucene.search.DoubleValuesSource;
+import org.apache.lucene.search.IndexSearcher;
+import org.apache.lucene.search.Query;
+import org.apache.lucene.search.Scorer;
+import org.apache.lucene.search.TwoPhaseIterator;
+import org.apache.lucene.search.Weight;
+
+/**
+ * A query that retrieves all documents with a {@link DoubleValues} value matching a predicate
+ *
+ * This query works by a linear scan of the index, and is best used in
+ * conjunction with other queries that can restrict the number of
+ * documents visited
+ */
+public final class FunctionMatchQuery extends Query {
+
+  private final DoubleValuesSource source;
+  private final DoublePredicate filter;
+
+  /**
+   * Create a FunctionMatchQuery
+   * @param source  a {@link DoubleValuesSource} to use for values
+   * @param filter  the predicate to match against
+   */
+  public FunctionMatchQuery(DoubleValuesSource source, DoublePredicate filter) {
+    this.source = source;
+    this.filter = filter;
+  }
+
+  @Override
+  public String toString(String field) {
+    return "FunctionMatchQuery(" + source.toString() + ")";
+  }
+
+  @Override
+  public Weight createWeight(IndexSearcher searcher, boolean needsScores, float boost) throws IOException {
+    return new ConstantScoreWeight(this, boost) {
+      @Override
+      public Scorer scorer(LeafReaderContext context) throws IOException {
+        DoubleValues values = source.getValues(context, null);
+        DocIdSetIterator approximation = DocIdSetIterator.all(context.reader().maxDoc());
+        TwoPhaseIterator twoPhase = new TwoPhaseIterator(approximation) {
+          @Override
+          public boolean matches() throws IOException {
+            return values.advanceExact(approximation.docID()) && filter.test(values.doubleValue());
+          }
+
+          @Override
+          public float matchCost() {
+            return 100; // TODO maybe DoubleValuesSource should have a matchCost?
+          }
+        };
+        return new ConstantScoreScorer(this, score(), twoPhase);
+      }
+    };
+  }
+
+  @Override
+  public boolean equals(Object o) {
+    if (this == o) return true;
+    if (o == null || getClass() != o.getClass()) return false;
+    FunctionMatchQuery that = (FunctionMatchQuery) o;
+    return Objects.equals(source, that.source) && Objects.equals(filter, that.filter);
+  }
+
+  @Override
+  public int hashCode() {
+    return Objects.hash(source, filter);
+  }
+
+}

lucene/queries/src/java/org/apache/lucene/queries/function/FunctionScoreQuery.java

@@ -0,0 +1,151 @@
+/*
+ * 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.queries.function;
+
+import java.io.IOException;
+import java.util.Objects;
+import java.util.Set;
+
+import org.apache.lucene.index.IndexReader;
+import org.apache.lucene.index.LeafReaderContext;
+import org.apache.lucene.index.Term;
+import org.apache.lucene.search.DoubleValues;
+import org.apache.lucene.search.DoubleValuesSource;
+import org.apache.lucene.search.Explanation;
+import org.apache.lucene.search.FilterScorer;
+import org.apache.lucene.search.IndexSearcher;
+import org.apache.lucene.search.Query;
+import org.apache.lucene.search.Scorer;
+import org.apache.lucene.search.Weight;
+
+/**
+ * A query that wraps another query, and uses a DoubleValuesSource to
+ * replace or modify the wrapped query's score
+ *
+ * If the DoubleValuesSource doesn't return a value for a particular document,
+ * then that document will be given a score of 0.
+ */
+public final class FunctionScoreQuery extends Query {
+
+  private final Query in;
+  private final DoubleValuesSource source;
+
+  /**
+   * Create a new FunctionScoreQuery
+   * @param in      the query to wrap
+   * @param source  a source of scores
+   */
+  public FunctionScoreQuery(Query in, DoubleValuesSource source) {
+    this.in = in;
+    this.source = source;
+  }
+
+  @Override
+  public Weight createWeight(IndexSearcher searcher, boolean needsScores, float boost) throws IOException {
+    Weight inner = in.createWeight(searcher, needsScores && source.needsScores(), 1f);
+    if (needsScores == false)
+      return inner;
+    return new FunctionScoreWeight(this, inner, source, boost);
+  }
+
+  @Override
+  public Query rewrite(IndexReader reader) throws IOException {
+    Query rewritten = in.rewrite(reader);
+    if (rewritten == in)
+      return this;
+    return new FunctionScoreQuery(rewritten, source);
+  }
+
+  @Override
+  public String toString(String field) {
+    return "FunctionScoreQuery(" + in.toString(field) + ", scored by " + source.toString() + ")";
+  }
+
+  @Override
+  public boolean equals(Object o) {
+    if (this == o) return true;
+    if (o == null || getClass() != o.getClass()) return false;
+    FunctionScoreQuery that = (FunctionScoreQuery) o;
+    return Objects.equals(in, that.in) &&
+        Objects.equals(source, that.source);
+  }
+
+  @Override
+  public int hashCode() {
+    return Objects.hash(in, source);
+  }
+
+  private static class FunctionScoreWeight extends Weight {
+
+    final Weight inner;
+    final DoubleValuesSource valueSource;
+    final float boost;
+
+    FunctionScoreWeight(Query query, Weight inner, DoubleValuesSource valueSource, float boost) {
+      super(query);
+      this.inner = inner;
+      this.valueSource = valueSource;
+      this.boost = boost;
+    }
+
+    @Override
+    public void extractTerms(Set<Term> terms) {
+      this.inner.extractTerms(terms);
+    }
+
+    @Override
+    public Explanation explain(LeafReaderContext context, int doc) throws IOException {
+      Scorer scorer = inner.scorer(context);
+      if (scorer.iterator().advance(doc) != doc)
+        return Explanation.noMatch("No match");
+      DoubleValues scores = valueSource.getValues(context, DoubleValuesSource.fromScorer(scorer));
+      scores.advanceExact(doc);
+      Explanation scoreExpl = scoreExplanation(context, doc, scores);
+      if (boost == 1f)
+        return scoreExpl;
+      return Explanation.match(scoreExpl.getValue() * boost, "product of:",
+          Explanation.match(boost, "boost"), scoreExpl);
+    }
+
+    private Explanation scoreExplanation(LeafReaderContext context, int doc, DoubleValues scores) throws IOException {
+      if (valueSource.needsScores() == false)
+        return Explanation.match((float) scores.doubleValue(), valueSource.toString());
+      float score = (float) scores.doubleValue();
+      return Explanation.match(score, "computed from:",
+          Explanation.match(score, valueSource.toString()),
+          inner.explain(context, doc));
+    }
+
+    @Override
+    public Scorer scorer(LeafReaderContext context) throws IOException {
+      Scorer in = inner.scorer(context);
+      if (in == null)
+        return null;
+      DoubleValues scores = valueSource.getValues(context, DoubleValuesSource.fromScorer(in));
+      return new FilterScorer(in) {
+        @Override
+        public float score() throws IOException {
+          if (scores.advanceExact(docID()))
+            return (float) (scores.doubleValue() * boost);
+          else
+            return 0;
+        }
+      };
+    }
+  }
+}

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

@@ -0,0 +1,61 @@
+/*
+ * 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.queries.function;
+
+import java.io.IOException;
+
+import org.apache.lucene.index.DirectoryReader;
+import org.apache.lucene.index.IndexReader;
+import org.apache.lucene.search.DoubleValuesSource;
+import org.apache.lucene.search.IndexSearcher;
+import org.apache.lucene.search.QueryUtils;
+import org.apache.lucene.search.TopDocs;
+import org.junit.AfterClass;
+import org.junit.BeforeClass;
+
+public class TestFunctionMatchQuery extends FunctionTestSetup {
+
+  static IndexReader reader;
+  static IndexSearcher searcher;
+
+  @BeforeClass
+  public static void beforeClass() throws Exception {
+    createIndex(true);
+    reader = DirectoryReader.open(dir);
+    searcher = new IndexSearcher(reader);
+  }
+
+  @AfterClass
+  public static void afterClass() throws Exception {
+    reader.close();
+  }
+
+  public void testRangeMatching() throws IOException {
+    DoubleValuesSource in = DoubleValuesSource.fromFloatField(FLOAT_FIELD);
+    FunctionMatchQuery fmq = new FunctionMatchQuery(in, d -> d >= 2 && d < 4);
+    TopDocs docs = searcher.search(fmq, 10);
+
+    assertEquals(2, docs.totalHits);
+    assertEquals(9, docs.scoreDocs[0].doc);
+    assertEquals(13, docs.scoreDocs[1].doc);
+
+    QueryUtils.check(random(), fmq, searcher, rarely());
+
+  }
+
+}

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

@@ -0,0 +1,105 @@
+/*
+ * 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.queries.function;
+
+import java.io.IOException;
+
+import org.apache.lucene.index.Term;
+import org.apache.lucene.search.BaseExplanationTestCase;
+import org.apache.lucene.search.BooleanClause;
+import org.apache.lucene.search.BooleanQuery;
+import org.apache.lucene.search.BoostQuery;
+import org.apache.lucene.search.DoubleValuesSource;
+import org.apache.lucene.search.Explanation;
+import org.apache.lucene.search.IndexSearcher;
+import org.apache.lucene.search.MatchAllDocsQuery;
+import org.apache.lucene.search.Query;
+import org.apache.lucene.search.TermQuery;
+import org.apache.lucene.search.similarities.BM25Similarity;
+import org.apache.lucene.search.similarities.ClassicSimilarity;
+
+public class TestFunctionScoreExplanations extends BaseExplanationTestCase {
+
+  public void testOneTerm() throws Exception {
+    Query q = new TermQuery(new Term(FIELD, "w1"));
+    FunctionScoreQuery fsq = new FunctionScoreQuery(q, DoubleValuesSource.constant(5));
+    qtest(fsq, new int[] { 0,1,2,3 });
+  }
+
+  public void testBoost() throws Exception {
+    Query q = new TermQuery(new Term(FIELD, "w1"));
+    FunctionScoreQuery csq = new FunctionScoreQuery(q, DoubleValuesSource.constant(5));
+    qtest(new BoostQuery(csq, 4), new int[] { 0,1,2,3 });
+  }
+
+  public void testTopLevelBoost() throws Exception {
+    Query q = new TermQuery(new Term(FIELD, "w1"));
+    FunctionScoreQuery csq = new FunctionScoreQuery(q, DoubleValuesSource.constant(5));
+    BooleanQuery.Builder bqB = new BooleanQuery.Builder();
+    bqB.add(new MatchAllDocsQuery(), BooleanClause.Occur.MUST);
+    bqB.add(csq, BooleanClause.Occur.MUST);
+    BooleanQuery bq = bqB.build();
+    qtest(new BoostQuery(bq, 6), new int[] { 0,1,2,3 });
+  }
+
+  public void testExplanationsIncludingScore() throws Exception {
+
+    DoubleValuesSource scores = DoubleValuesSource.function(DoubleValuesSource.SCORES, v -> v * 2);
+
+    Query q = new TermQuery(new Term(FIELD, "w1"));
+    FunctionScoreQuery csq = new FunctionScoreQuery(q, scores);
+
+    qtest(csq, new int[] { 0, 1, 2, 3 });
+
+    Explanation e1 = searcher.explain(q, 0);
+    Explanation e = searcher.explain(csq, 0);
+
+    assertEquals(e.getDetails().length, 2);
+
+    assertEquals(e1.getValue() * 2, e.getValue(), 0.00001);
+  }
+
+  public void testSubExplanations() throws IOException {
+    Query query = new FunctionScoreQuery(new MatchAllDocsQuery(), DoubleValuesSource.constant(5));
+    IndexSearcher searcher = newSearcher(BaseExplanationTestCase.searcher.getIndexReader());
+    searcher.setSimilarity(new BM25Similarity());
+
+    Explanation expl = searcher.explain(query, 0);
+    assertEquals("constant(5.0)", expl.getDescription());
+    assertEquals(0, expl.getDetails().length);
+
+    query = new BoostQuery(query, 2);
+    expl = searcher.explain(query, 0);
+    assertEquals(2, expl.getDetails().length);
+    // function
+    assertEquals(5f, expl.getDetails()[1].getValue(), 0f);
+    // boost
+    assertEquals("boost", expl.getDetails()[0].getDescription());
+    assertEquals(2f, expl.getDetails()[0].getValue(), 0f);
+
+    searcher.setSimilarity(new ClassicSimilarity()); // in order to have a queryNorm != 1
+    expl = searcher.explain(query, 0);
+    assertEquals(2, expl.getDetails().length);
+    // function
+    assertEquals(5f, expl.getDetails()[1].getValue(), 0f);
+    // boost
+    assertEquals("boost", expl.getDetails()[0].getDescription());
+    assertEquals(2f, expl.getDetails()[0].getValue(), 0f);
+  }
+
+}

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

@@ -0,0 +1,114 @@
+/*
+ * 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.queries.function;
+
+import org.apache.lucene.index.DirectoryReader;
+import org.apache.lucene.index.IndexReader;
+import org.apache.lucene.index.Term;
+import org.apache.lucene.search.BooleanClause;
+import org.apache.lucene.search.BooleanQuery;
+import org.apache.lucene.search.BoostQuery;
+import org.apache.lucene.search.DoubleValuesSource;
+import org.apache.lucene.search.IndexSearcher;
+import org.apache.lucene.search.Query;
+import org.apache.lucene.search.QueryUtils;
+import org.apache.lucene.search.TermQuery;
+import org.apache.lucene.search.TopDocs;
+import org.junit.AfterClass;
+import org.junit.BeforeClass;
+
+public class TestFunctionScoreQuery extends FunctionTestSetup {
+
+  static IndexReader reader;
+  static IndexSearcher searcher;
+
+  @BeforeClass
+  public static void beforeClass() throws Exception {
+    createIndex(true);
+    reader = DirectoryReader.open(dir);
+    searcher = new IndexSearcher(reader);
+  }
+
+  @AfterClass
+  public static void afterClass() throws Exception {
+    reader.close();
+  }
+
+  // FunctionQuery equivalent
+  public void testSimpleSourceScore() throws Exception {
+
+    FunctionScoreQuery q = new FunctionScoreQuery(new TermQuery(new Term(TEXT_FIELD, "first")),
+        DoubleValuesSource.fromIntField(INT_FIELD));
+
+    QueryUtils.check(random(), q, searcher, rarely());
+
+    int expectedDocs[] = new int[]{ 4, 7, 9 };
+    TopDocs docs = searcher.search(q, 4);
+    assertEquals(expectedDocs.length, docs.totalHits);
+    for (int i = 0; i < expectedDocs.length; i++) {
+      assertEquals(docs.scoreDocs[i].doc, expectedDocs[i]);
+    }
+
+  }
+
+  // CustomScoreQuery and BoostedQuery equivalent
+  public void testScoreModifyingSource() throws Exception {
+
+    DoubleValuesSource iii = DoubleValuesSource.fromIntField("iii");
+    DoubleValuesSource score = DoubleValuesSource.scoringFunction(iii, (v, s) -> v * s);
+
+    BooleanQuery bq = new BooleanQuery.Builder()
+        .add(new TermQuery(new Term(TEXT_FIELD, "first")), BooleanClause.Occur.SHOULD)
+        .add(new TermQuery(new Term(TEXT_FIELD, "text")), BooleanClause.Occur.SHOULD)
+        .build();
+    TopDocs plain = searcher.search(bq, 1);
+
+    FunctionScoreQuery fq = new FunctionScoreQuery(bq, score);
+
+    QueryUtils.check(random(), fq, searcher, rarely());
+
+    int[] expectedDocs = new int[]{ 4, 7, 9, 8, 12 };
+    TopDocs docs = searcher.search(fq, 5);
+    assertEquals(plain.totalHits, docs.totalHits);
+    for (int i = 0; i < expectedDocs.length; i++) {
+      assertEquals(expectedDocs[i], docs.scoreDocs[i].doc);
+
+    }
+
+  }
+
+  // check boosts with non-distributive score source
+  public void testBoostsAreAppliedLast() throws Exception {
+
+    DoubleValuesSource scores
+        = DoubleValuesSource.function(DoubleValuesSource.SCORES, v -> Math.log(v + 4));
+
+    Query q1 = new FunctionScoreQuery(new TermQuery(new Term(TEXT_FIELD, "text")), scores);
+    TopDocs plain = searcher.search(q1, 5);
+
+    Query boosted = new BoostQuery(q1, 2);
+    TopDocs afterboost = searcher.search(boosted, 5);
+    assertEquals(plain.totalHits, afterboost.totalHits);
+    for (int i = 0; i < 5; i++) {
+      assertEquals(plain.scoreDocs[i].doc, afterboost.scoreDocs[i].doc);
+      assertEquals(plain.scoreDocs[i].score, afterboost.scoreDocs[i].score / 2, 0.0001);
+    }
+
+  }
+
+}