Rename isSourceEmpty to hasSource

And add a test case for {} to reindex.

core/src/main/java/org/elasticsearch/search/SearchHit.java

@@ -108,9 +108,10 @@ public interface SearchHit extends Streamable, ToXContent, Iterable<SearchHitFie
     byte[] source();
 
     /**
-     * Is the source empty (not available) or not.
+     * Is the source available or not. A source with no fields will return true. This will return false if {@code fields} doesn't contain
+     * {@code _source} or if source is disabled in the mapping.
      */
-    boolean isSourceEmpty();
+    boolean hasSource();
 
     /**
      * The source of the document as a map (can be <tt>null</tt>).

core/src/main/java/org/elasticsearch/search/internal/InternalSearchHit.java

@@ -240,7 +240,7 @@ public class InternalSearchHit implements SearchHit {
     }
 
     @Override
-    public boolean isSourceEmpty() {
+    public boolean hasSource() {
         return source == null;
     }
 

modules/lang-groovy/src/test/java/org/elasticsearch/messy/tests/SearchFieldsTests.java

@@ -201,7 +201,7 @@ public class SearchFieldsTests extends ESIntegTestCase {
         assertNoFailures(response);
 
         assertThat(response.getHits().totalHits(), equalTo(3L));
-        assertThat(response.getHits().getAt(0).isSourceEmpty(), equalTo(true));
+        assertThat(response.getHits().getAt(0).hasSource(), equalTo(true));
         assertThat(response.getHits().getAt(0).id(), equalTo("1"));
         Set<String> fields = new HashSet<>(response.getHits().getAt(0).fields().keySet());
         fields.remove(TimestampFieldMapper.NAME); // randomly enabled via templates

modules/reindex/src/main/java/org/elasticsearch/index/reindex/AbstractAsyncBulkIndexByScrollAction.java

@@ -86,7 +86,7 @@ public abstract class AbstractAsyncBulkIndexByScrollAction<
         Map<String, Object> scriptCtx = null;
 
         for (SearchHit doc : docs) {
-            if (doc.isSourceEmpty()) {
+            if (doc.hasSource()) {
                 /*
                  * Either the document didn't store _source or we didn't fetch it for some reason. Since we don't allow the user to
                  * change the "fields" part of the search request it is unlikely that we got here because we didn't fetch _source.

modules/reindex/src/test/resources/rest-api-spec/test/reindex/10_basic.yaml

@@ -374,3 +374,30 @@
         index: new_twitter
         type: tweet
   - match: { hits.total: 1 }
+
+---
+"Source document without any fields works":
+  - do:
+      index:
+        index:   source
+        type:    foo
+        id:      1
+        body:    {}
+  - do:
+      indices.refresh: {}
+
+  - do:
+      reindex:
+        body:
+          source:
+            index: source
+          dest:
+            index: dest
+  - match: {created: 1}
+
+  - do:
+      get:
+        index:   dest
+        type:    foo
+        id:      1
+  - match: { _source: {} }

modules/reindex/src/test/resources/rest-api-spec/test/update_by_query/10_basic.yaml

@@ -226,3 +226,27 @@
         index: test
         scroll_size: 1
   - match: {batches: 3}
+
+---
+"Source document without any fields works":
+  - do:
+      index:
+        index:   test
+        type:    foo
+        id:      1
+        body:    {}
+  - do:
+      indices.refresh: {}
+
+  - do:
+      update_by_query:
+        index: test
+  - match: {updated: 1}
+
+  - do:
+      get:
+        index:   test
+        type:    foo
+        id:      1
+  - match: { _source: {} }
+  - match: { _version: 2 }