LUCENE-5690: MultiTerms should expose sub-Terms

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/trunk@1597079 13f79535-47bb-0310-9956-ffa450edef68

lucene/core/src/java/org/apache/lucene/index/MultiTerms.java

@@ -68,6 +68,16 @@ public final class MultiTerms extends Terms {
     hasPayloads = hasPositions && _hasPayloads; // if all subs have pos, and at least one has payloads.
   }
 
+  /** Expert: returns the Terms being merged. */
+  public Terms[] getSubTerms() {
+    return subs;
+  }
+
+  /** Expert: returns  pointers to the sub-readers corresponding to the Terms being merged. */
+  public ReaderSlice[] getSubSlices() {
+    return subSlices;
+  }
+
   @Override
   public TermsEnum intersect(CompiledAutomaton compiled, BytesRef startTerm) throws IOException {
     final List<MultiTermsEnum.TermsEnumIndex> termsEnums = new ArrayList<>();