Aggs fix- don't error if significant text ago run on non-existent fie…

…ld. (#70778) (#71066)

Now returns empty results rather than errors when fields don't exist.

Closes #69809

server/src/main/java/org/elasticsearch/search/aggregations/bucket/terms/SignificantTextAggregatorFactory.java

@@ -29,8 +29,10 @@
 import org.elasticsearch.search.aggregations.AggregatorFactories;
 import org.elasticsearch.search.aggregations.AggregatorFactory;
 import org.elasticsearch.search.aggregations.CardinalityUpperBound;
+import org.elasticsearch.search.aggregations.InternalAggregation;
 import org.elasticsearch.search.aggregations.LeafBucketCollector;
 import org.elasticsearch.search.aggregations.LeafBucketCollectorBase;
+import org.elasticsearch.search.aggregations.NonCollectingAggregator;
 import org.elasticsearch.search.aggregations.bucket.BucketUtils;
 import org.elasticsearch.search.aggregations.bucket.terms.IncludeExclude.StringFilter;
 import org.elasticsearch.search.aggregations.bucket.terms.MapStringTermsAggregator.CollectConsumer;
@@ -70,23 +72,34 @@ public SignificantTextAggregatorFactory(String name,
         super(name, context, parent, subFactoriesBuilder, metadata);
 
         this.fieldType = context.getFieldType(fieldName);
-        if (fieldType == null) {
-            throw new IllegalArgumentException("Field [" + fieldName + "] does not exist, SignificantText " +
-                "requires an analyzed field");
-        }
-        if (supportsAgg(fieldType) == false) {
-            throw new IllegalArgumentException("Field [" + fieldType.name() + "] has no analyzer, but SignificantText " +
-                "requires an analyzed field");
+        if (fieldType != null) {
+            if (supportsAgg(fieldType) == false) {
+                throw new IllegalArgumentException("Field [" + fieldType.name() + "] has no analyzer, but SignificantText " +
+                    "requires an analyzed field");
+            }            
+            String indexedFieldName = fieldType.name();
+            this.sourceFieldNames = sourceFieldNames == null ? new String[] {indexedFieldName} : sourceFieldNames;
+        } else {
+            this.sourceFieldNames = new String[0];
         }
-        String indexedFieldName = fieldType.name();
-        this.sourceFieldNames = sourceFieldNames == null ? new String[] {indexedFieldName} : sourceFieldNames;
 
         this.includeExclude = includeExclude;
         this.backgroundFilter = backgroundFilter;
         this.filterDuplicateText = filterDuplicateText;
         this.bucketCountThresholds = bucketCountThresholds;
         this.significanceHeuristic = significanceHeuristic;
     }
+
+    protected Aggregator createUnmapped(Aggregator parent, Map<String, Object> metadata) throws IOException {
+        final InternalAggregation aggregation = new UnmappedSignificantTerms(name, bucketCountThresholds.getRequiredSize(),
+                bucketCountThresholds.getMinDocCount(), metadata);
+        return new NonCollectingAggregator(name, context, parent, factories, metadata) {
+            @Override
+            public InternalAggregation buildEmptyAggregation() {
+                return aggregation;
+            }
+        };
+    }    
 
     private static boolean supportsAgg(MappedFieldType ft) {
         return ft.getTextSearchInfo() != TextSearchInfo.NONE
@@ -96,6 +109,11 @@ private static boolean supportsAgg(MappedFieldType ft) {
     @Override
     protected Aggregator createInternal(Aggregator parent, CardinalityUpperBound cardinality, Map<String, Object> metadata)
         throws IOException {
+
+        if (fieldType == null) {
+            return createUnmapped(parent, metadata);
+        }
+
         BucketCountThresholds bucketCountThresholds = new BucketCountThresholds(this.bucketCountThresholds);
         if (bucketCountThresholds.getShardSize() == SignificantTextAggregationBuilder.DEFAULT_BUCKET_COUNT_THRESHOLDS.getShardSize()) {
             // The user has not made a shardSize selection.

server/src/test/java/org/elasticsearch/search/aggregations/bucket/terms/SignificantTextAggregatorTests.java

@@ -45,7 +45,6 @@
 
 import static org.elasticsearch.search.aggregations.AggregationBuilders.sampler;
 import static org.elasticsearch.search.aggregations.AggregationBuilders.significantText;
-import static org.hamcrest.Matchers.equalTo;
 
 public class SignificantTextAggregatorTests extends AggregatorTestCase {
     @Override
@@ -194,12 +193,9 @@ public void testMissingField() throws IOException {
 
             try (IndexReader reader = DirectoryReader.open(w)) {
                 IndexSearcher searcher = new IndexSearcher(reader);
-
-
-                IllegalArgumentException e = expectThrows(IllegalArgumentException.class,
-                    () ->  searchAndReduce(searcher, new TermQuery(new Term("text", "odd")), aggBuilder, textFieldType));
-                assertThat(e.getMessage(), equalTo("Field [this_field_does_not_exist] does not exist, SignificantText "
-                    + "requires an analyzed field"));
+                InternalSampler sampler = searchAndReduce(searcher, new TermQuery(new Term("text", "odd")), aggBuilder, textFieldType);
+                SignificantTerms terms = sampler.getAggregations().get("sig_text");
+                assertTrue(terms.getBuckets().isEmpty()); 
             }
         }
     }