Add a dedicated field data type for the _index field mapper.

src/main/java/org/elasticsearch/index/fielddata/IndexFieldDataService.java

@@ -35,6 +35,7 @@
 import org.elasticsearch.index.fielddata.ordinals.InternalGlobalOrdinalsBuilder;
 import org.elasticsearch.index.fielddata.plain.*;
 import org.elasticsearch.index.mapper.FieldMapper;
+import org.elasticsearch.index.mapper.internal.IndexFieldMapper;
 import org.elasticsearch.index.mapper.internal.ParentFieldMapper;
 import org.elasticsearch.index.service.IndexService;
 import org.elasticsearch.index.settings.IndexSettings;
@@ -73,6 +74,7 @@ public class IndexFieldDataService extends AbstractIndexComponent {
                 .put("long", new PackedArrayIndexFieldData.Builder().setNumericType(IndexNumericFieldData.NumericType.LONG))
                 .put("geo_point", new GeoPointDoubleArrayIndexFieldData.Builder())
                 .put(ParentFieldMapper.NAME, new ParentChildIndexFieldData.Builder())
+                .put(IndexFieldMapper.NAME, new IndexIndexFieldData.Builder())
                 .put("binary", new DisabledIndexFieldData.Builder())
                 .immutableMap();
 

src/main/java/org/elasticsearch/index/fielddata/plain/IndexIndexFieldData.java

@@ -0,0 +1,211 @@
+/*
+ * Licensed to Elasticsearch under one or more contributor
+ * license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright
+ * ownership. Elasticsearch 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.elasticsearch.index.fielddata.plain;
+
+import org.apache.lucene.index.AtomicReaderContext;
+import org.apache.lucene.index.IndexReader;
+import org.apache.lucene.index.TermsEnum;
+import org.apache.lucene.util.BytesRef;
+import org.elasticsearch.common.settings.Settings;
+import org.elasticsearch.index.Index;
+import org.elasticsearch.index.fielddata.*;
+import org.elasticsearch.index.fielddata.fieldcomparator.BytesRefFieldComparatorSource;
+import org.elasticsearch.index.fielddata.ordinals.GlobalOrdinalsBuilder;
+import org.elasticsearch.index.fielddata.ordinals.Ordinals;
+import org.elasticsearch.index.mapper.FieldMapper;
+import org.elasticsearch.index.mapper.MapperService;
+import org.elasticsearch.indices.fielddata.breaker.CircuitBreakerService;
+import org.elasticsearch.search.MultiValueMode;
+
+public class IndexIndexFieldData implements IndexFieldData.WithOrdinals<AtomicFieldData.WithOrdinals<ScriptDocValues>> {
+
+    public static class Builder implements IndexFieldData.Builder {
+
+        @Override
+        public IndexFieldData<?> build(Index index, Settings indexSettings, FieldMapper<?> mapper, IndexFieldDataCache cache,
+                CircuitBreakerService breakerService, MapperService mapperService, GlobalOrdinalsBuilder globalOrdinalBuilder) {
+            return new IndexIndexFieldData(index, mapper.names());
+        }
+
+    }
+
+    private static final Ordinals.Docs INDEX_ORDINALS = new Ordinals.Docs() {
+
+        @Override
+        public int setDocument(int docId) {
+            return 1;
+        }
+
+        @Override
+        public long nextOrd() {
+            return Ordinals.MIN_ORDINAL;
+        }
+
+        @Override
+        public boolean isMultiValued() {
+            return false;
+        }
+
+        @Override
+        public long getOrd(int docId) {
+            return Ordinals.MIN_ORDINAL;
+        }
+
+        @Override
+        public long getMaxOrd() {
+            return 1;
+        }
+
+        @Override
+        public long currentOrd() {
+            return Ordinals.MIN_ORDINAL;
+        }
+    };
+
+    private static class IndexBytesValues extends BytesValues.WithOrdinals {
+
+        final int hash;
+
+        protected IndexBytesValues(String index) {
+            super(INDEX_ORDINALS);
+            scratch.copyChars(index);
+            hash = scratch.hashCode();
+        }
+
+        @Override
+        public int currentValueHash() {
+            return hash;
+        }
+
+        @Override
+        public BytesRef getValueByOrd(long ord) {
+            return scratch;
+        }
+
+    }
+
+    private static class IndexAtomicFieldData implements AtomicFieldData.WithOrdinals<ScriptDocValues> {
+
+        private final String index;
+
+        IndexAtomicFieldData(String index) {
+            this.index = index;
+        }
+
+        @Override
+        public long getMemorySizeInBytes() {
+            return 0;
+        }
+
+        @Override
+        public boolean isMultiValued() {
+            return false;
+        }
+
+        @Override
+        public long getNumberUniqueValues() {
+            return 1;
+        }
+
+        @Override
+        public BytesValues.WithOrdinals getBytesValues(boolean needsHashes) {
+            return new IndexBytesValues(index);
+        }
+
+        @Override
+        public ScriptDocValues getScriptValues() {
+            return new ScriptDocValues.Strings(getBytesValues(false));
+        }
+
+        @Override
+        public void close() {
+        }
+
+        @Override
+        public TermsEnum getTermsEnum() {
+            return new AtomicFieldDataWithOrdinalsTermsEnum(this);
+        }
+
+    }
+
+    private final FieldMapper.Names names;
+    private final Index index;
+
+    private IndexIndexFieldData(Index index, FieldMapper.Names names) {
+        this.index = index;
+        this.names = names;
+    }
+
+    @Override
+    public Index index() {
+        return index;
+    }
+
+    @Override
+    public org.elasticsearch.index.mapper.FieldMapper.Names getFieldNames() {
+        return names;
+    }
+
+    @Override
+    public FieldDataType getFieldDataType() {
+        return new FieldDataType("string");
+    }
+
+    @Override
+    public boolean valuesOrdered() {
+        return true;
+    }
+
+    @Override
+    public org.elasticsearch.index.fielddata.IndexFieldData.XFieldComparatorSource comparatorSource(Object missingValue,
+            MultiValueMode sortMode) {
+        return new BytesRefFieldComparatorSource(this, missingValue, sortMode);
+    }
+
+    @Override
+    public void clear() {
+    }
+
+    @Override
+    public void clear(IndexReader reader) {
+    }
+
+    @Override
+    public AtomicFieldData.WithOrdinals<ScriptDocValues> load(AtomicReaderContext context) {
+        return new IndexAtomicFieldData(index().name());
+    }
+
+    @Override
+    public AtomicFieldData.WithOrdinals<ScriptDocValues> loadDirect(AtomicReaderContext context)
+            throws Exception {
+        return load(context);
+    }
+
+    @Override
+    public IndexFieldData.WithOrdinals<?> loadGlobal(IndexReader indexReader) {
+        return this;
+    }
+
+    @Override
+    public IndexFieldData.WithOrdinals<?> localGlobalDirect(IndexReader indexReader) throws Exception {
+        return loadGlobal(indexReader);
+    }
+
+}

src/main/java/org/elasticsearch/index/mapper/FieldMapper.java

@@ -290,4 +290,5 @@ public static Loading parse(String loading, Loading defaultValue) {
     boolean hasDocValues();
 
     Loading normsLoading(Loading defaultLoading);
+
 }

src/main/java/org/elasticsearch/index/mapper/internal/IndexFieldMapper.java

@@ -136,7 +136,7 @@ public FieldType defaultFieldType() {
 
     @Override
     public FieldDataType defaultFieldDataType() {
-        return new FieldDataType("string");
+        return new FieldDataType(IndexFieldMapper.NAME);
     }
 
     @Override
@@ -225,4 +225,5 @@ public void merge(Mapper mergeWith, MergeContext mergeContext) throws MergeMappi
             }
         }
     }
+
 }

src/main/java/org/elasticsearch/search/facet/terms/TermsFacetParser.java

@@ -34,7 +34,6 @@
 import org.elasticsearch.search.facet.FacetExecutor;
 import org.elasticsearch.search.facet.FacetParser;
 import org.elasticsearch.search.facet.terms.doubles.TermsDoubleFacetExecutor;
-import org.elasticsearch.search.facet.terms.index.IndexNameFacetExecutor;
 import org.elasticsearch.search.facet.terms.longs.TermsLongFacetExecutor;
 import org.elasticsearch.search.facet.terms.strings.FieldsTermsStringFacetExecutor;
 import org.elasticsearch.search.facet.terms.strings.ScriptTermsStringFieldFacetExecutor;
@@ -151,10 +150,6 @@ public FacetExecutor parse(String facetName, XContentParser parser, SearchContex
             }
         }
 
-        if ("_index".equals(field)) {
-            return new IndexNameFacetExecutor(context.shardTarget().index(), comparatorType, size);
-        }
-
         if (fieldsNames != null && fieldsNames.length == 1) {
             field = fieldsNames[0];
             fieldsNames = null;

src/test/java/org/elasticsearch/search/aggregations/bucket/StringTermsTests.java

@@ -22,6 +22,7 @@
 import org.elasticsearch.ElasticsearchException;
 import org.elasticsearch.action.index.IndexRequestBuilder;
 import org.elasticsearch.action.search.SearchResponse;
+import org.elasticsearch.index.mapper.internal.IndexFieldMapper;
 import org.elasticsearch.index.query.FilterBuilders;
 import org.elasticsearch.search.aggregations.bucket.filter.Filter;
 import org.elasticsearch.search.aggregations.bucket.histogram.Histogram;
@@ -1154,4 +1155,27 @@ public void singleValuedField_OrderedByMultiValueExtendedStatsAsc() throws Excep
         }
 
     }
+
+    @Test
+    public void indexMetaField() throws Exception {
+        SearchResponse response = client().prepareSearch("idx", "empty_bucket_idx").setTypes("type")
+                .addAggregation(terms("terms")
+                        .executionHint(randomExecutionHint())
+                        .field(IndexFieldMapper.NAME)
+                ).execute().actionGet();
+
+        assertSearchResponse(response);
+        Terms terms = response.getAggregations().get("terms");
+        assertThat(terms, notNullValue());
+        assertThat(terms.getName(), equalTo("terms"));
+        assertThat(terms.getBuckets().size(), equalTo(2));
+
+        int i = 0;
+        for (Terms.Bucket bucket : terms.getBuckets()) {
+            assertThat(bucket, notNullValue());
+            assertThat(key(bucket), equalTo(i == 0 ? "idx" : "empty_bucket_idx"));
+            assertThat(bucket.getDocCount(), equalTo(i == 0 ? 5L : 2L));
+            i++;
+        }
+    }
 }