Add BytesRefIterator to TermInSetQuery (#13806)

TermInSetQuery used to have an accessor to its terms that was removed in #12173
to protect leaking internal encoding details. This introduces an accessor to the
term data in the query that doesn't expose internals but merely allows iterating
over the decoded BytesRef, making inspection of the querys content possible again.

Closes #13804

lucene/CHANGES.txt

@@ -295,6 +295,8 @@ Build
 API Changes
 ---------------------
 
+* GITHUB#13806: Add TermInSetQuery#getBytesRefIterator to be able to iterate over query terms. (Christoph Büscher)
+
 * GITHUB#13469: Expose FlatVectorsFormat as a first-class format; can be configured using a custom Codec. (Michael Sokolov)
 
 * GITHUB#13612: Hunspell: add Suggester#proceedPastRep to avoid losing relevant suggestions. (Peter Gromov)

lucene/core/src/java/org/apache/lucene/search/TermInSetQuery.java

@@ -27,13 +27,7 @@
 import org.apache.lucene.index.Term;
 import org.apache.lucene.index.Terms;
 import org.apache.lucene.index.TermsEnum;
-import org.apache.lucene.util.Accountable;
-import org.apache.lucene.util.AttributeSource;
-import org.apache.lucene.util.BytesRef;
-import org.apache.lucene.util.BytesRefBuilder;
-import org.apache.lucene.util.BytesRefComparator;
-import org.apache.lucene.util.RamUsageEstimator;
-import org.apache.lucene.util.StringSorter;
+import org.apache.lucene.util.*;
 import org.apache.lucene.util.automaton.Automata;
 import org.apache.lucene.util.automaton.Automaton;
 import org.apache.lucene.util.automaton.ByteRunAutomaton;
@@ -141,6 +135,16 @@ public long getTermsCount() {
     return termData.size();
   }
 
+  /**
+   * Get an iterator over the encoded terms for query inspection.
+   *
+   * @lucene.experimental
+   */
+  public BytesRefIterator getBytesRefIterator() {
+    final TermIterator iterator = this.termData.iterator();
+    return () -> iterator.next();
+  }
+
   @Override
   public void visit(QueryVisitor visitor) {
     if (visitor.acceptField(field) == false) {

lucene/core/src/test/org/apache/lucene/search/TestTermInSetQuery.java

@@ -52,6 +52,7 @@
 import org.apache.lucene.tests.util.RamUsageTester;
 import org.apache.lucene.tests.util.TestUtil;
 import org.apache.lucene.util.BytesRef;
+import org.apache.lucene.util.BytesRefIterator;
 import org.apache.lucene.util.IOUtils;
 import org.apache.lucene.util.automaton.ByteRunAutomaton;
 
@@ -527,4 +528,19 @@ public void consumeTermsMatching(
           }
         });
   }
+
+  public void testTermsIterator() throws IOException {
+    TermInSetQuery empty = new TermInSetQuery("field", Collections.emptyList());
+    BytesRefIterator it = empty.getBytesRefIterator();
+    assertNull(it.next());
+
+    TermInSetQuery query =
+        new TermInSetQuery(
+            "field", List.of(newBytesRef("term1"), newBytesRef("term2"), newBytesRef("term3")));
+    it = query.getBytesRefIterator();
+    assertEquals(newBytesRef("term1"), it.next());
+    assertEquals(newBytesRef("term2"), it.next());
+    assertEquals(newBytesRef("term3"), it.next());
+    assertNull(it.next());
+  }
 }