Index: lucene/CHANGES.txt
===================================================================
--- lucene/CHANGES.txt	(revision 1173280)
+++ lucene/CHANGES.txt	(working copy)
@@ -20,6 +20,10 @@
   should ignore the maxMergedSegmentMB setting (v.sevel via Mike
   McCandless)
 
+* LUCENE-3442: TermQuery.TermWeight.scorer() returns null for non-atomic
+  IndexReaders (optimization bug), preventing QueryWrapperFilter and similar
+  classes to get a top-level DocIdSet. (Dan C., Uwe Schindler)
+
 New Features
 
 Optimizations
Index: lucene/src/java/org/apache/lucene/search/TermQuery.java
===================================================================
--- lucene/src/java/org/apache/lucene/search/TermQuery.java	(revision 1173280)
+++ lucene/src/java/org/apache/lucene/search/TermQuery.java	(working copy)
@@ -94,7 +94,8 @@
 
     @Override
     public Scorer scorer(IndexReader reader, boolean scoreDocsInOrder, boolean topScorer) throws IOException {
-      if (hash != null && !hash.contains(reader.hashCode())) {
+      // only use the early exit condition if we have an atomic reader, because Lucene 3.x still supports non-atomic readers here:
+      if (hash != null && reader.getSequentialSubReaders() == null && !hash.contains(reader.hashCode())) {
         return null;
       }
       
Index: lucene/src/test/org/apache/lucene/search/TestQueryWrapperFilter.java
===================================================================
--- lucene/src/test/org/apache/lucene/search/TestQueryWrapperFilter.java	(revision 1173280)
+++ lucene/src/test/org/apache/lucene/search/TestQueryWrapperFilter.java	(working copy)
@@ -81,4 +81,37 @@
     reader.close();
     dir.close();
   }
+
+  // this test is for 3.x only, in 4.x we no longer support non-atomic readers passed to getDocIdSet():
+  public void test_LUCENE3442() throws Exception {
+    Directory dir = newDirectory();
+    RandomIndexWriter writer = new RandomIndexWriter(random, dir);
+    Document doc = new Document();
+    doc.add(newField("id", "1001", Store.YES, Index.NOT_ANALYZED));
+    doc.add(newField("text", "headline one group one", Store.YES, Index.ANALYZED));
+    writer.addDocument(doc);
+    IndexReader rdr = writer.getReader();
+    writer.close();
+    IndexSearcher searcher = new IndexSearcher(rdr);
+    TermQuery tq = new TermQuery(new Term("text", "headline"));
+    TopDocs results = searcher.search(tq, 5);
+    assertEquals(1, results.totalHits);
+    
+    Filter f = new QueryWrapperFilter(tq);
+    // rdr may not be atomic (it isn't in most cases), TermQuery inside QWF should still work!
+    DocIdSet dis = f.getDocIdSet(rdr);
+    assertNotNull(dis);
+    DocIdSetIterator it = dis.iterator();
+    assertNotNull(it);
+    int docId, count = 0;
+    while ((docId = it.nextDoc()) != DocIdSetIterator.NO_MORE_DOCS) {
+      assertEquals("1001", rdr.document(docId).get("id"));
+      count++;
+    }
+    assertEquals(1, count);
+    searcher.close();
+    rdr.close();
+    dir.close();
+  }
+
 }