[Backport 2.x] Add positive_score_impact support for rank_features

modules/mapper-extras/src/main/java/org/opensearch/index/mapper/RankFeaturesFieldMapper.java

@@ -42,7 +42,6 @@
 import org.opensearch.search.lookup.SearchLookup;
 
 import java.io.IOException;
-import java.util.Collections;
 import java.util.List;
 import java.util.Map;
 import java.util.function.Supplier;
@@ -55,8 +54,18 @@ public class RankFeaturesFieldMapper extends ParametrizedFieldMapper {
 
     public static final String CONTENT_TYPE = "rank_features";
 
+    private static RankFeaturesFieldType ft(FieldMapper in) {
+        return ((RankFeaturesFieldMapper) in).fieldType();
+    }
+
     public static class Builder extends ParametrizedFieldMapper.Builder {
 
+        private final Parameter<Boolean> positiveScoreImpact = Parameter.boolParam(
+            "positive_score_impact",
+            false,
+            m -> ft(m).positiveScoreImpact,
+            true
+        );
         private final Parameter<Map<String, String>> meta = Parameter.metaParam();
 
         public Builder(String name) {
@@ -66,16 +75,17 @@ public Builder(String name) {
 
         @Override
         protected List<Parameter<?>> getParameters() {
-            return Collections.singletonList(meta);
+            return List.of(meta, positiveScoreImpact);
         }
 
         @Override
         public RankFeaturesFieldMapper build(BuilderContext context) {
             return new RankFeaturesFieldMapper(
                 name,
-                new RankFeaturesFieldType(buildFullName(context), meta.getValue()),
+                new RankFeaturesFieldType(buildFullName(context), meta.getValue(), positiveScoreImpact.getValue()),
                 multiFieldsBuilder.build(this, context),
-                copyTo.build()
+                copyTo.build(),
+                positiveScoreImpact.getValue()
             );
         }
     }
@@ -84,16 +94,23 @@ public RankFeaturesFieldMapper build(BuilderContext context) {
 
     public static final class RankFeaturesFieldType extends MappedFieldType {
 
-        public RankFeaturesFieldType(String name, Map<String, String> meta) {
+        private final boolean positiveScoreImpact;
+
+        public RankFeaturesFieldType(String name, Map<String, String> meta, boolean positiveScoreImpact) {
             super(name, false, false, false, TextSearchInfo.NONE, meta);
             setIndexAnalyzer(Lucene.KEYWORD_ANALYZER);
+            this.positiveScoreImpact = positiveScoreImpact;
         }
 
         @Override
         public String typeName() {
             return CONTENT_TYPE;
         }
 
+        public boolean positiveScoreImpact() {
+            return positiveScoreImpact;
+        }
+
         @Override
         public Query existsQuery(QueryShardContext context) {
             throw new IllegalArgumentException("[rank_features] fields do not support [exists] queries");
@@ -115,9 +132,18 @@ public Query termQuery(Object value, QueryShardContext context) {
         }
     }
 
-    private RankFeaturesFieldMapper(String simpleName, MappedFieldType mappedFieldType, MultiFields multiFields, CopyTo copyTo) {
+    private final boolean positiveScoreImpact;
+
+    private RankFeaturesFieldMapper(
+        String simpleName,
+        MappedFieldType mappedFieldType,
+        MultiFields multiFields,
+        CopyTo copyTo,
+        boolean positiveScoreImpact
+    ) {
         super(simpleName, mappedFieldType, multiFields, copyTo);
         assert fieldType.indexOptions().compareTo(IndexOptions.DOCS_AND_FREQS) <= 0;
+        this.positiveScoreImpact = positiveScoreImpact;
     }
 
     @Override
@@ -164,6 +190,9 @@ public void parse(ParseContext context) throws IOException {
                             + "] in the same document"
                     );
                 }
+                if (positiveScoreImpact == false) {
+                    value = 1 / value;
+                }
                 context.doc().addWithKey(key, new FeatureField(name(), feature, value));
             } else {
                 throw new IllegalArgumentException(

modules/mapper-extras/src/test/java/org/opensearch/index/mapper/RankFeaturesFieldMapperTests.java

@@ -67,8 +67,8 @@ protected void minimalMapping(XContentBuilder b) throws IOException {
     }
 
     @Override
-    protected void registerParameters(ParameterChecker checker) {
-        // no parameters to configure
+    protected void registerParameters(ParameterChecker checker) throws IOException {
+        checker.registerConflictCheck("positive_score_impact", b -> b.field("positive_score_impact", false));
     }
 
     @Override
@@ -95,6 +95,33 @@ public void testDefaults() throws Exception {
         assertTrue(freq1 < freq2);
     }
 
+    public void testNegativeScoreImpact() throws Exception {
+        DocumentMapper mapper = createDocumentMapper(
+            fieldMapping(b -> b.field("type", "rank_features").field("positive_score_impact", false))
+        );
+
+        ParsedDocument doc1 = mapper.parse(source(this::writeField));
+
+        IndexableField[] fields = doc1.rootDoc().getFields("field");
+        assertEquals(2, fields.length);
+        assertThat(fields[0], Matchers.instanceOf(FeatureField.class));
+        FeatureField featureField1 = null;
+        FeatureField featureField2 = null;
+        for (IndexableField field : fields) {
+            if (field.stringValue().equals("foo")) {
+                featureField1 = (FeatureField) field;
+            } else if (field.stringValue().equals("bar")) {
+                featureField2 = (FeatureField) field;
+            } else {
+                throw new UnsupportedOperationException();
+            }
+        }
+
+        int freq1 = RankFeatureFieldMapperTests.getFrequency(featureField1.tokenStream(null, null));
+        int freq2 = RankFeatureFieldMapperTests.getFrequency(featureField2.tokenStream(null, null));
+        assertTrue(freq1 > freq2);
+    }
+
     public void testRejectMultiValuedFields() throws MapperParsingException, IOException {
         DocumentMapper mapper = createDocumentMapper(mapping(b -> {
             b.startObject("field").field("type", "rank_features").endObject();

modules/mapper-extras/src/test/java/org/opensearch/index/mapper/RankFeaturesFieldTypeTests.java

@@ -37,7 +37,7 @@
 public class RankFeaturesFieldTypeTests extends FieldTypeTestCase {
 
     public void testIsNotAggregatable() {
-        MappedFieldType fieldType = new RankFeaturesFieldMapper.RankFeaturesFieldType("field", Collections.emptyMap());
+        MappedFieldType fieldType = new RankFeaturesFieldMapper.RankFeaturesFieldType("field", Collections.emptyMap(), true);
         assertFalse(fieldType.isAggregatable());
     }
 }

modules/mapper-extras/src/yamlRestTest/resources/rest-api-spec/test/rank_feature/10_basic.yml

@@ -157,3 +157,24 @@ setup:
 
   - match:
       hits.hits.1._id: "1"
+
+---
+"Negative linear":
+
+  - do:
+      search:
+        index: test
+        body:
+          query:
+            rank_feature:
+              field: url_length
+              linear: {}
+
+  - match:
+      hits.total.value: 2
+
+  - match:
+      hits.hits.0._id: "2"
+
+  - match:
+      hits.hits.1._id: "1"

modules/mapper-extras/src/yamlRestTest/resources/rest-api-spec/test/rank_features/10_basic.yml

@@ -9,6 +9,9 @@ setup:
               properties:
                 tags:
                    type: rank_features
+                negative_reviews:
+                   type: rank_features
+                   positive_score_impact: false
 
   - do:
       index:
@@ -18,6 +21,9 @@ setup:
           tags:
             foo: 3
             bar: 5
+          negative_reviews:
+            1star: 10
+            2star: 1
 
   - do:
       index:
@@ -27,6 +33,9 @@ setup:
           tags:
             bar: 6
             quux: 10
+          negative_reviews:
+            1star: 1
+            2star: 10
 
   - do:
       indices.refresh: {}
@@ -97,3 +106,34 @@ setup:
 
   - match:
       hits.hits.1._id: "1"
+
+---
+"Linear negative impact":
+
+  - do:
+      search:
+        index: test
+        body:
+          query:
+            rank_feature:
+              field: negative_reviews.1star
+              linear: {}
+
+  - match:
+      hits.hits.0._id: "2"
+  - match:
+      hits.hits.1._id: "1"
+
+  - do:
+      search:
+        index: test
+        body:
+          query:
+            rank_feature:
+              field: negative_reviews.2star
+              linear: {}
+
+  - match:
+      hits.hits.0._id: "1"
+  - match:
+      hits.hits.1._id: "2"