Add support for missing value fetchers. (elastic#63515)

This PR implements value fetching for the following field types:
* `text` phrase and prefix subfields
* `search_as_you_type`, plus its subfields
* `token_count`, which is implemented by fetching doc values

Supporting these types helps ensure that retrieving all fields through
`"fields": ["*"]` doesn't fail because of unsupported value fetchers.

modules/mapper-extras/src/main/java/org/elasticsearch/index/mapper/SearchAsYouTypeFieldMapper.java

@@ -265,7 +265,7 @@ private ShingleFieldType shingleFieldForPositions(int positions) {
 
         @Override
         public ValueFetcher valueFetcher(MapperService mapperService, SearchLookup searchLookup, String format) {
-            throw new UnsupportedOperationException();
+            return SourceValueFetcher.toString(name(), mapperService, format);
         }
 
         @Override
@@ -376,7 +376,9 @@ public Query prefixQuery(String value, MultiTermQuery.RewriteMethod method, bool
 
         @Override
         public ValueFetcher valueFetcher(MapperService mapperService, SearchLookup searchLookup, String format) {
-            throw new UnsupportedOperationException();
+            // Because this internal field is modelled as a multi-field, SourceValueFetcher will look up its
+            // parent field in _source. So we don't need to use the parent field name here.
+            return SourceValueFetcher.toString(name(), mapperService, format);
         }
 
         @Override
@@ -480,7 +482,9 @@ void setPrefixFieldType(PrefixFieldType prefixFieldType) {
 
         @Override
         public ValueFetcher valueFetcher(MapperService mapperService, SearchLookup searchLookup, String format) {
-            throw new UnsupportedOperationException();
+            // Because this internal field is modelled as a multi-field, SourceValueFetcher will look up its
+            // parent field in _source. So we don't need to use the parent field name here.
+            return SourceValueFetcher.toString(name(), mapperService, format);
         }
 
         @Override

modules/mapper-extras/src/main/java/org/elasticsearch/index/mapper/TokenCountFieldMapper.java

@@ -23,6 +23,7 @@
 import org.apache.lucene.analysis.TokenStream;
 import org.apache.lucene.analysis.tokenattributes.PositionIncrementAttribute;
 import org.elasticsearch.index.analysis.NamedAnalyzer;
+import org.elasticsearch.search.lookup.SearchLookup;
 
 import java.io.IOException;
 import java.util.Arrays;
@@ -72,19 +73,33 @@ public TokenCountFieldMapper build(BuilderContext context) {
             if (analyzer.getValue() == null) {
                 throw new MapperParsingException("Analyzer must be set for field [" + name + "] but wasn't.");
             }
-            MappedFieldType ft = new NumberFieldMapper.NumberFieldType(
+            MappedFieldType ft = new TokenCountFieldType(
                 buildFullName(context),
-                NumberFieldMapper.NumberType.INTEGER,
                 index.getValue(),
                 store.getValue(),
                 hasDocValues.getValue(),
-                false,
                 nullValue.getValue(),
                 meta.getValue());
             return new TokenCountFieldMapper(name, ft, multiFieldsBuilder.build(this, context), copyTo.build(), this);
         }
     }
 
+    static class TokenCountFieldType extends NumberFieldMapper.NumberFieldType {
+
+        TokenCountFieldType(String name, boolean isSearchable, boolean isStored,
+                            boolean hasDocValues, Number nullValue, Map<String, String> meta) {
+            super(name, NumberFieldMapper.NumberType.INTEGER, isSearchable, isStored, hasDocValues, false, nullValue, meta);
+        }
+
+        @Override
+        public ValueFetcher valueFetcher(MapperService mapperService, SearchLookup searchLookup, String format) {
+            if (hasDocValues() == false) {
+                return lookup -> org.elasticsearch.common.collect.List.of();
+            }
+            return new DocValueFetcher(docValueFormat(format, null), searchLookup.doc().getForField(this));
+        }
+    }
+
     public static TypeParser PARSER = new TypeParser((n, c) -> new Builder(n));
 
     private final boolean index;

modules/mapper-extras/src/test/java/org/elasticsearch/index/mapper/SearchAsYouTypeFieldTypeTests.java

@@ -34,6 +34,7 @@
 import org.elasticsearch.index.mapper.SearchAsYouTypeFieldMapper.SearchAsYouTypeFieldType;
 import org.elasticsearch.index.mapper.SearchAsYouTypeFieldMapper.ShingleFieldType;
 
+import java.io.IOException;
 import java.util.Collections;
 
 import static java.util.Arrays.asList;
@@ -109,4 +110,25 @@ public void testPrefixQuery() {
         assertEquals("[prefix] queries cannot be executed when 'search.allow_expensive_queries' is set to false. " +
                 "For optimised prefix queries on text fields please enable [index_prefixes].", ee.getMessage());
     }
+
+    public void testFetchSourceValue() throws IOException {
+        SearchAsYouTypeFieldType fieldType = createFieldType();
+        fieldType.setIndexAnalyzer(Lucene.STANDARD_ANALYZER);
+
+        assertEquals(org.elasticsearch.common.collect.List.of("value"), fetchSourceValue(fieldType, "value"));
+        assertEquals(org.elasticsearch.common.collect.List.of("42"), fetchSourceValue(fieldType, 42L));
+        assertEquals(org.elasticsearch.common.collect.List.of("true"), fetchSourceValue(fieldType, true));
+
+        SearchAsYouTypeFieldMapper.PrefixFieldType prefixFieldType = new SearchAsYouTypeFieldMapper.PrefixFieldType(
+            fieldType.name(), fieldType.getTextSearchInfo(), 2, 10);
+        assertEquals(org.elasticsearch.common.collect.List.of("value"), fetchSourceValue(prefixFieldType, "value"));
+        assertEquals(org.elasticsearch.common.collect.List.of("42"), fetchSourceValue(prefixFieldType, 42L));
+        assertEquals(org.elasticsearch.common.collect.List.of("true"), fetchSourceValue(prefixFieldType, true));
+
+        SearchAsYouTypeFieldMapper.ShingleFieldType shingleFieldType = new SearchAsYouTypeFieldMapper.ShingleFieldType(
+            fieldType.name(), 5, fieldType.getTextSearchInfo());
+        assertEquals(org.elasticsearch.common.collect.List.of("value"), fetchSourceValue(shingleFieldType, "value"));
+        assertEquals(org.elasticsearch.common.collect.List.of("42"), fetchSourceValue(shingleFieldType, 42L));
+        assertEquals(org.elasticsearch.common.collect.List.of("true"), fetchSourceValue(shingleFieldType, true));
+    }
 }

rest-api-spec/build.gradle

@@ -15,5 +15,9 @@ artifacts {
   restTests(new File(projectDir, "src/main/resources/rest-api-spec/test"))
 }
 
+testClusters.all {
+  module ':modules:mapper-extras'
+}
+
 test.enabled = false
 jarHell.enabled = false

rest-api-spec/src/main/resources/rest-api-spec/test/search/330_fetch_fields.yml

@@ -259,3 +259,39 @@ setup:
   - is_true: hits.hits.0._id
   - is_true: hits.hits.0._source
   - match: { hits.hits.0.fields.date.0: "1990/12/29" }
+
+---
+"Test token count":
+  - skip:
+      version: " - 7.99.99"
+      reason: "support for token_count isn't yet backported"
+  - do:
+      indices.create:
+        index:  test
+        body:
+          mappings:
+            properties:
+              count:
+                type: token_count
+                analyzer: standard
+              count_without_dv:
+                type: token_count
+                analyzer: standard
+                doc_values: false
+
+  - do:
+      index:
+        index:  test
+        id:     1
+        refresh: true
+        body:
+          count: "some text"
+  - do:
+      search:
+        index: test
+        body:
+          fields: [count, count_without_dv]
+
+  - is_true: hits.hits.0._id
+  - match: { hits.hits.0.fields.count: [2] }
+  - is_false: hits.hits.0.fields.count_without_dv

server/src/main/java/org/elasticsearch/index/mapper/MappedFieldType.java

@@ -102,6 +102,10 @@ public IndexFieldData.Builder fielddataBuilder(String fullyQualifiedIndexName, S
 
     /**
      * Create a helper class to fetch field values during the {@link FetchFieldsPhase}.
+     *
+     * New field types must implement this method in order to support the search 'fields' option. Except
+     * for metadata fields, field types should not throw {@link UnsupportedOperationException} since this
+     * could cause a search retrieving multiple fields (like "fields": ["*"]) to fail.
      */
     public abstract ValueFetcher valueFetcher(MapperService mapperService, SearchLookup searchLookup, @Nullable String format);
 

server/src/main/java/org/elasticsearch/index/mapper/NumberFieldMapper.java

@@ -889,7 +889,7 @@ public static Query longRangeQuery(
         }
     }
 
-    public static final class NumberFieldType extends SimpleMappedFieldType {
+    public static class NumberFieldType extends SimpleMappedFieldType {
 
         private final NumberType type;
         private final boolean coerce;

server/src/main/java/org/elasticsearch/index/mapper/TextFieldMapper.java

@@ -447,11 +447,11 @@ protected TokenStreamComponents wrapComponents(String fieldName, TokenStreamComp
         }
     }
 
-    private static final class PhraseFieldType extends StringFieldType {
+    static final class PhraseFieldType extends StringFieldType {
 
         final TextFieldType parent;
 
-        private PhraseFieldType(TextFieldType parent) {
+        PhraseFieldType(TextFieldType parent) {
             super(parent.name() + FAST_PHRASE_SUFFIX, true, false, false, parent.getTextSearchInfo(), Collections.emptyMap());
             setAnalyzer(parent.indexAnalyzer().name(), parent.indexAnalyzer().analyzer());
             this.parent = parent;
@@ -468,7 +468,9 @@ public String typeName() {
 
         @Override
         public ValueFetcher valueFetcher(MapperService mapperService, SearchLookup searchLookup, String format) {
-            throw new UnsupportedOperationException();
+            // Because this internal field is modelled as a multi-field, SourceValueFetcher will look up its
+            // parent field in _source. So we don't need to use the parent field name here.
+            return SourceValueFetcher.toString(name(), mapperService, format);
         }
 
         @Override
@@ -496,7 +498,9 @@ static final class PrefixFieldType extends StringFieldType {
 
         @Override
         public ValueFetcher valueFetcher(MapperService mapperService, SearchLookup searchLookup, String format) {
-            throw new UnsupportedOperationException();
+            // Because this internal field is modelled as a multi-field, SourceValueFetcher will look up its
+            // parent field in _source. So we don't need to use the parent field name here.
+            return SourceValueFetcher.toString(name(), mapperService, format);
         }
 
         void setAnalyzer(NamedAnalyzer delegate) {

server/src/test/java/org/elasticsearch/index/mapper/TextFieldTypeTests.java

@@ -35,12 +35,9 @@
 import org.apache.lucene.util.automaton.Automaton;
 import org.apache.lucene.util.automaton.Operations;
 import org.elasticsearch.ElasticsearchException;
-import org.elasticsearch.Version;
-import org.elasticsearch.cluster.metadata.IndexMetadata;
 import org.elasticsearch.common.lucene.BytesRefs;
 import org.elasticsearch.common.lucene.Lucene;
 import org.elasticsearch.common.lucene.search.AutomatonQueries;
-import org.elasticsearch.common.settings.Settings;
 import org.elasticsearch.common.unit.Fuzziness;
 import org.elasticsearch.index.mapper.TextFieldMapper.TextFieldType;
 
@@ -167,13 +164,21 @@ public void testIndexPrefixes() {
     }
 
     public void testFetchSourceValue() throws IOException {
-        Settings settings = Settings.builder().put(IndexMetadata.SETTING_VERSION_CREATED, Version.CURRENT.id).build();
-        Mapper.BuilderContext context = new Mapper.BuilderContext(settings, new ContentPath());
-
-        MappedFieldType mapper = new TextFieldMapper.Builder("field", () -> Lucene.STANDARD_ANALYZER).build(context).fieldType();
-
-        assertEquals(Collections.singletonList("value"), fetchSourceValue(mapper, "value"));
-        assertEquals(Collections.singletonList("42"), fetchSourceValue(mapper, 42L));
-        assertEquals(Collections.singletonList("true"), fetchSourceValue(mapper, true));
+        TextFieldType fieldType = createFieldType();
+        fieldType.setIndexAnalyzer(Lucene.STANDARD_ANALYZER);
+
+        assertEquals(org.elasticsearch.common.collect.List.of("value"), fetchSourceValue(fieldType, "value"));
+        assertEquals(org.elasticsearch.common.collect.List.of("42"), fetchSourceValue(fieldType, 42L));
+        assertEquals(org.elasticsearch.common.collect.List.of("true"), fetchSourceValue(fieldType, true));
+
+        TextFieldMapper.PrefixFieldType prefixFieldType = new TextFieldMapper.PrefixFieldType(fieldType, "field._index_prefix", 2, 10);
+        assertEquals(org.elasticsearch.common.collect.List.of("value"), fetchSourceValue(prefixFieldType, "value"));
+        assertEquals(org.elasticsearch.common.collect.List.of("42"), fetchSourceValue(prefixFieldType, 42L));
+        assertEquals(org.elasticsearch.common.collect.List.of("true"), fetchSourceValue(prefixFieldType, true));
+
+        TextFieldMapper.PhraseFieldType phraseFieldType = new TextFieldMapper.PhraseFieldType(fieldType);
+        assertEquals(org.elasticsearch.common.collect.List.of("value"), fetchSourceValue(phraseFieldType, "value"));
+        assertEquals(org.elasticsearch.common.collect.List.of("42"), fetchSourceValue(phraseFieldType, 42L));
+        assertEquals(org.elasticsearch.common.collect.List.of("true"), fetchSourceValue(phraseFieldType, true));
     }
 }

server/src/test/java/org/elasticsearch/search/fetch/subphase/FieldFetcherTests.java

@@ -33,6 +33,7 @@
 import java.util.List;
 import java.util.Map;
 
+import static org.hamcrest.Matchers.containsInAnyOrder;
 import static org.hamcrest.Matchers.equalTo;
 import static org.hamcrest.Matchers.hasItems;
 
@@ -359,6 +360,34 @@ public void testObjectFields() throws IOException {
         assertFalse(fields.containsKey("object"));
     }
 
+    public void testTextSubFields() throws IOException {
+        XContentBuilder mapping = XContentFactory.jsonBuilder().startObject()
+            .startObject("properties")
+                .startObject("field")
+                    .field("type", "text")
+                    .startObject("index_prefixes").endObject()
+                    .field("index_phrases", true)
+                .endObject()
+            .endObject()
+        .endObject();
+
+        IndexService indexService = createIndex("index", Settings.EMPTY, MapperService.SINGLE_MAPPING_NAME, mapping);
+        MapperService mapperService = indexService.mapperService();
+
+        XContentBuilder source = XContentFactory.jsonBuilder().startObject()
+            .array("field", "some text")
+            .endObject();
+
+        Map<String, DocumentField> fields = fetchFields(mapperService, source, "*");
+        assertThat(fields.size(), equalTo(3));
+        assertThat(fields.keySet(), containsInAnyOrder("field", "field._index_prefix", "field._index_phrase"));
+
+        for (DocumentField field : fields.values()) {
+            assertThat(field.getValues().size(), equalTo(1));
+            assertThat(field.getValue(), equalTo("some text"));
+        }
+    }
+
     private Map<String, DocumentField> fetchFields(MapperService mapperService, XContentBuilder source, String fieldPattern)
         throws IOException {
 

test/framework/src/main/java/org/elasticsearch/index/mapper/FieldTypeTestCase.java

@@ -51,7 +51,6 @@ public static List<?> fetchSourceValue(MappedFieldType fieldType, Object sourceV
 
     public static List<?> fetchSourceValue(MappedFieldType fieldType, Object sourceValue, String format) throws IOException {
         String field = fieldType.name();
-
         MapperService mapperService = mock(MapperService.class);
         when(mapperService.sourcePath(field)).thenReturn(org.elasticsearch.common.collect.Set.of(field));
 
@@ -60,5 +59,4 @@ public static List<?> fetchSourceValue(MappedFieldType fieldType, Object sourceV
         lookup.setSource(Collections.singletonMap(field, sourceValue));
         return fetcher.fetchValues(lookup);
     }
-
 }