FastVectorHighlighter should use ValueFetchers to load source data (#85815)

FVH was relying on `SourceLookup.extractRawValues()` to load its data, but this no
longer works for multifields. It should instead use value fetchers which will correctly
locate the input for multifields and/or copy fields.

Fixes #84690
Fixes #82458
Fixes #80895
Fixes #75011

Author: romseygeek

docs/changelog/85815.yaml

@@ -0,0 +1,9 @@
+pr: 85815
+summary: '`FastVectorHighlighter` should use `ValueFetchers` to load source data'
+area: Highlighting
+type: bug
+issues:
+ - 75011
+ - 84690
+ - 82458
+ - 80895

server/src/main/java/org/elasticsearch/search/fetch/subphase/highlight/FastVectorHighlighter.java

@@ -26,6 +26,7 @@
 import org.elasticsearch.common.util.CollectionUtils;
 import org.elasticsearch.index.mapper.MappedFieldType;
 import org.elasticsearch.index.mapper.TextSearchInfo;
+import org.elasticsearch.index.query.SearchExecutionContext;
 import org.elasticsearch.lucene.search.vectorhighlight.CustomFieldQuery;
 import org.elasticsearch.search.fetch.FetchSubPhase;
 import org.elasticsearch.search.fetch.subphase.highlight.SearchHighlightContext.Field;
@@ -98,6 +99,7 @@ public HighlightField highlight(FieldHighlightContext fieldContext) throws IOExc
             Function<SourceLookup, FragmentsBuilder> fragmentsBuilderSupplier = fragmentsBuilderSupplier(
                 field,
                 fieldType,
+                fieldContext.context.getSearchExecutionContext(),
                 forceSource,
                 fixBrokenAnalysis
             );
@@ -217,6 +219,7 @@ public HighlightField highlight(FieldHighlightContext fieldContext) throws IOExc
     private Function<SourceLookup, FragmentsBuilder> fragmentsBuilderSupplier(
         SearchHighlightContext.Field field,
         MappedFieldType fieldType,
+        SearchExecutionContext context,
         boolean forceSource,
         boolean fixBrokenAnalysis
     ) {
@@ -239,6 +242,7 @@ private Function<SourceLookup, FragmentsBuilder> fragmentsBuilderSupplier(
             if (options.numberOfFragments() != 0 && options.scoreOrdered()) {
                 supplier = lookup -> new SourceScoreOrderFragmentsBuilder(
                     fieldType,
+                    context,
                     fixBrokenAnalysis,
                     lookup,
                     options.preTags(),
@@ -248,6 +252,7 @@ private Function<SourceLookup, FragmentsBuilder> fragmentsBuilderSupplier(
             } else {
                 supplier = lookup -> new SourceSimpleFragmentsBuilder(
                     fieldType,
+                    context,
                     fixBrokenAnalysis,
                     lookup,
                     options.preTags(),

server/src/main/java/org/elasticsearch/search/fetch/subphase/highlight/SourceScoreOrderFragmentsBuilder.java

@@ -15,19 +15,24 @@
 import org.apache.lucene.search.vectorhighlight.FieldFragList.WeightedFragInfo;
 import org.apache.lucene.search.vectorhighlight.ScoreOrderFragmentsBuilder;
 import org.elasticsearch.index.mapper.MappedFieldType;
+import org.elasticsearch.index.mapper.ValueFetcher;
+import org.elasticsearch.index.query.SearchExecutionContext;
 import org.elasticsearch.search.lookup.SourceLookup;
 
 import java.io.IOException;
+import java.util.ArrayList;
 import java.util.List;
 
 public class SourceScoreOrderFragmentsBuilder extends ScoreOrderFragmentsBuilder {
 
     private final MappedFieldType fieldType;
     private final SourceLookup sourceLookup;
+    private final ValueFetcher valueFetcher;
     private final boolean fixBrokenAnalysis;
 
     public SourceScoreOrderFragmentsBuilder(
         MappedFieldType fieldType,
+        SearchExecutionContext context,
         boolean fixBrokenAnalysis,
         SourceLookup sourceLookup,
         String[] preTags,
@@ -37,13 +42,14 @@ public SourceScoreOrderFragmentsBuilder(
         super(preTags, postTags, boundaryScanner);
         this.fieldType = fieldType;
         this.sourceLookup = sourceLookup;
+        this.valueFetcher = fieldType.valueFetcher(context, null);
         this.fixBrokenAnalysis = fixBrokenAnalysis;
     }
 
     @Override
     protected Field[] getFields(IndexReader reader, int docId, String fieldName) throws IOException {
         // we know its low level reader, and matching docId, since that's how we call the highlighter with
-        List<Object> values = sourceLookup.extractRawValues(fieldType.name());
+        List<Object> values = valueFetcher.fetchValues(sourceLookup, new ArrayList<>());
         Field[] fields = new Field[values.size()];
         for (int i = 0; i < values.size(); i++) {
             fields[i] = new Field(fieldType.name(), values.get(i).toString(), TextField.TYPE_NOT_STORED);

server/src/main/java/org/elasticsearch/search/fetch/subphase/highlight/SourceSimpleFragmentsBuilder.java

@@ -12,17 +12,22 @@
 import org.apache.lucene.index.IndexReader;
 import org.apache.lucene.search.vectorhighlight.BoundaryScanner;
 import org.elasticsearch.index.mapper.MappedFieldType;
+import org.elasticsearch.index.mapper.ValueFetcher;
+import org.elasticsearch.index.query.SearchExecutionContext;
 import org.elasticsearch.search.lookup.SourceLookup;
 
 import java.io.IOException;
+import java.util.ArrayList;
 import java.util.List;
 
 public class SourceSimpleFragmentsBuilder extends SimpleFragmentsBuilder {
 
     private final SourceLookup sourceLookup;
+    private final ValueFetcher valueFetcher;
 
     public SourceSimpleFragmentsBuilder(
         MappedFieldType fieldType,
+        SearchExecutionContext context,
         boolean fixBrokenAnalysis,
         SourceLookup sourceLookup,
         String[] preTags,
@@ -31,14 +36,15 @@ public SourceSimpleFragmentsBuilder(
     ) {
         super(fieldType, fixBrokenAnalysis, preTags, postTags, boundaryScanner);
         this.sourceLookup = sourceLookup;
+        this.valueFetcher = fieldType.valueFetcher(context, null);
     }
 
     public static final Field[] EMPTY_FIELDS = new Field[0];
 
     @Override
     protected Field[] getFields(IndexReader reader, int docId, String fieldName) throws IOException {
         // we know its low level reader, and matching docId, since that's how we call the highlighter with
-        List<Object> values = sourceLookup.extractRawValues(fieldType.name());
+        List<Object> values = valueFetcher.fetchValues(sourceLookup, new ArrayList<>());
         if (values.isEmpty()) {
             return EMPTY_FIELDS;
         }

server/src/main/java/org/elasticsearch/search/lookup/SourceLookup.java

@@ -159,19 +159,11 @@ public boolean hasSourceAsMap() {
         return source != null;
     }
 
-    /**
-     * Returns the values associated with the path. Those are "low" level values, and it can
-     * handle path expression where an array/list is navigated within.
-     */
-    public List<Object> extractRawValues(String path) {
-        return XContentMapValues.extractRawValues(path, source());
-    }
-
     /**
      * Returns the values associated with the path. Those are "low" level values, and it can
      * handle path expression where an array/list is navigated within.
      *
-     * The major difference with {@link SourceLookup#extractRawValues(String)} is that this version will:
+     * This method will:
      *
      *  - not cache source if it's not already parsed
      *  - will only extract the desired values from the compressed source instead of deserializing the whole object
@@ -204,8 +196,7 @@ public List<Object> extractRawValuesWithoutCaching(String path) {
     /**
      * For the provided path, return its value in the source.
      *
-     * Note that in contrast with {@link SourceLookup#extractRawValues}, array and object values
-     * can be returned.
+     * Both array and object values can be returned.
      *
      * @param path the value's path in the source.
      * @param nullValue a value to return if the path exists, but the value is 'null'. This helps

server/src/test/java/org/elasticsearch/search/fetch/subphase/highlight/FastVectorHighlighterTests.java

@@ -0,0 +1,68 @@
+/*
+ * Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
+ * or more contributor license agreements. Licensed under the Elastic License
+ * 2.0 and the Server Side Public License, v 1; you may not use this file except
+ * in compliance with, at your election, the Elastic License 2.0 or the Server
+ * Side Public License, v 1.
+ */
+
+package org.elasticsearch.search.fetch.subphase.highlight;
+
+import org.elasticsearch.index.mapper.MapperService;
+import org.elasticsearch.index.mapper.ParsedDocument;
+import org.elasticsearch.index.query.QueryBuilders;
+import org.elasticsearch.search.builder.SearchSourceBuilder;
+import org.elasticsearch.search.fetch.HighlighterTestCase;
+
+import java.io.IOException;
+
+public class FastVectorHighlighterTests extends HighlighterTestCase {
+
+    public void testHighlightingMultiFields() throws IOException {
+
+        MapperService mapperService = createMapperService("""
+            { "_doc" : { "properties" : {
+                "field" : {
+                    "type" : "text",
+                    "fields" : {
+                        "stemmed" : {
+                            "type" : "text",
+                            "term_vector" : "with_positions_offsets"
+                        }
+                    }
+                }
+            }}}
+            """);
+
+        ParsedDocument doc = mapperService.documentMapper().parse(source("""
+            { "field" : "here is some text, which is followed by some more text" }
+            """));
+
+        {
+            // test SimpleFragmentsBuilder case
+            SearchSourceBuilder search = new SearchSourceBuilder().query(QueryBuilders.termQuery("field.stemmed", "some"))
+                .highlighter(new HighlightBuilder().field("field.stemmed").highlighterType("fvh"));
+
+            assertHighlights(
+                highlight(mapperService, doc, search),
+                "field.stemmed",
+                "here is <em>some</em> text, which is followed by <em>some</em> more text"
+            );
+        }
+
+        {
+            // test ScoreOrderFragmentsBuilder case
+            SearchSourceBuilder search = new SearchSourceBuilder().query(QueryBuilders.termQuery("field.stemmed", "some"))
+                .highlighter(new HighlightBuilder().field("field.stemmed").highlighterType("fvh").numOfFragments(2).fragmentSize(18));
+
+            assertHighlights(
+                highlight(mapperService, doc, search),
+                "field.stemmed",
+                "here is <em>some</em> text, which",
+                "followed by <em>some</em> more text"
+            );
+        }
+
+    }
+
+}

test/framework/src/main/java/org/elasticsearch/search/fetch/HighlighterTestCase.java

@@ -71,7 +71,7 @@ protected final Map<String, HighlightField> highlight(MapperService mapperServic
      * Given a set of highlights, assert that any particular field has the expected fragments
      */
     protected static void assertHighlights(Map<String, HighlightField> highlights, String field, String... fragments) {
-        assertNotNull(highlights.get(field));
+        assertNotNull("No highlights reported for field [" + field + "]", highlights.get(field));
         Set<String> actualFragments = Arrays.stream(highlights.get(field).getFragments()).map(Text::toString).collect(Collectors.toSet());
         Set<String> expectedFragments = Set.of(fragments);
         assertEquals(expectedFragments, actualFragments);