SOLR-10321: highlighting (unified): Don't return fields with no highlights

solr/CHANGES.txt

@@ -217,6 +217,9 @@ when told to. The admin UI now tells it to. (Nazerke Seidan, David Smiley)
 * SOLR-15213: Atomic updates: "add" now uses add-or-replace logic for child documents.  They can
   also themselves be atomic updates.  (James Ashbourne, Endika Posadas via David Smiley)
 
+* SOLR-10321: highlighting (hl.method=unified): When there are no highlights for a field, don't
+  return the field in the response at all.  (David Smiley)
+
 * SOLR-15890: Add a limit to the Admin SQL panel if one is not included in the stmt (Joel Bernstein)
 
 * SOLR-15887: Remove <jmx/> from shipped solrconfig.xm. (Eric Pugh)

solr/core/src/java/org/apache/solr/highlight/UnifiedSolrHighlighter.java

@@ -118,7 +118,6 @@
 public class UnifiedSolrHighlighter extends SolrHighlighter implements PluginInfoInitialized {
 
   protected static final String SNIPPET_SEPARATOR = "\u0000";
-  private static final String[] ZERO_LEN_STR_ARRAY = new String[0];
 
   @Override
   public void init(PluginInfo info) {
@@ -174,7 +173,6 @@ protected NamedList<Object> encodeSnippets(String[] keys, String[] fieldNames, M
         String snippet = snippets.get(field)[i];
         if (snippet == null) {
           //TODO reuse logic of DefaultSolrHighlighter.alternateField
-          summary.add(field, ZERO_LEN_STR_ARRAY);
         } else {
           // we used a special snippet separator char and we can now split on it.
           summary.add(field, snippet.split(SNIPPET_SEPARATOR));

solr/core/src/test/org/apache/solr/highlight/TestUnifiedSolrHighlighter.java

@@ -331,4 +331,23 @@ public void testComplexPhraseQParser() {
         "count(//lst[@name='highlighting']/lst[@name='102']/arr[@name='text']/*)=1");
   }
 
+  // SOLR-10321
+  public void testDontReturnEmptyHighlights() throws Exception {
+    clearIndex();
+    // this doc has no value for field text2
+    assertU(adoc("text", "third document", "id", "103"));
+    assertU(commit());
+    // query on text & text2.  Assert we only highlight text; text2 shouldn't be present at all
+    assertJQ(
+        req(
+            "q", "text:document OR text2:document",
+            "hl", "true",
+            "hl.fl", "text, text2",
+            "sort", "id asc",
+            "hl", "true"),
+        "highlighting=={\n"
+            + "    '103':{\n"
+            + "      'text':['third <em>document</em>']}}}");
+  }
+
 }