Fix InternalSearchHit#hasSource to return the proper boolean value (#21441)

The method used to be called `isSourceEmpty`, and was renamed to `hasSource`, but the return value never changed. Updated tests and users accordingly.

Closes #21419

Author: javanna

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

@@ -252,7 +252,7 @@ public byte[] source() {
 
     @Override
     public boolean hasSource() {
-        return source == null;
+        return source != null;
     }
 
     @Override

core/src/test/java/org/elasticsearch/search/fields/SearchFieldsIT.java

@@ -293,7 +293,7 @@ public void testScriptDocAndFields() throws Exception {
         assertNoFailures(response);
 
         assertThat(response.getHits().totalHits(), equalTo(3L));
-        assertThat(response.getHits().getAt(0).hasSource(), equalTo(true));
+        assertFalse(response.getHits().getAt(0).hasSource());
         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

core/src/test/java/org/elasticsearch/search/internal/InternalSearchHitTests.java

@@ -19,14 +19,14 @@
 
 package org.elasticsearch.search.internal;
 
+import org.elasticsearch.common.bytes.BytesArray;
 import org.elasticsearch.common.io.stream.BytesStreamOutput;
 import org.elasticsearch.common.io.stream.InputStreamStreamInput;
 import org.elasticsearch.common.text.Text;
 import org.elasticsearch.index.Index;
 import org.elasticsearch.search.SearchShardTarget;
 import org.elasticsearch.test.ESTestCase;
 
-import java.io.ByteArrayInputStream;
 import java.io.InputStream;
 import java.util.HashMap;
 import java.util.Map;
@@ -87,4 +87,11 @@ public void testNullSource() throws Exception {
         assertThat(searchHit.getSourceRef(), nullValue());
         assertThat(searchHit.getSourceAsString(), nullValue());
     }
+
+    public void testHasSource() {
+        InternalSearchHit searchHit = new InternalSearchHit(randomInt());
+        assertFalse(searchHit.hasSource());
+        searchHit.sourceRef(new BytesArray("{}"));
+        assertTrue(searchHit.hasSource());
+    }
 }

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

@@ -197,9 +197,9 @@ private static class ClientHit implements Hit {
         private final SearchHit delegate;
         private final BytesReference source;
 
-        public ClientHit(SearchHit delegate) {
+        ClientHit(SearchHit delegate) {
             this.delegate = delegate;
-            source = delegate.hasSource() ? null : delegate.getSourceRef();
+            source = delegate.hasSource() ? delegate.getSourceRef() : null;
         }
 
         @Override