SlowCompositeReaderWrapper: fix index sort and hasBlocks

changelog/unreleased/SlowCompositeReaderWrapper-sort-hasblocks-fix.yml

@@ -0,0 +1,6 @@
+# See https://github.com/apache/solr/blob/main/dev-docs/changelog.adoc
+title: SlowCompositeReaderWrapper no longer misreports the index sort and hasBlocks of a multi-segment composite view; both were previously taken from the first segment only, which is wrong whenever there is more than one segment.
+type: fixed # added, changed, fixed, deprecated, removed, dependency_update, security, other
+authors:
+  - name: David Smiley
+links:

solr/core/src/java/org/apache/solr/index/SlowCompositeReaderWrapper.java

@@ -51,6 +51,7 @@
 import org.apache.lucene.index.Terms;
 import org.apache.lucene.search.AcceptDocs;
 import org.apache.lucene.search.KnnCollector;
+import org.apache.lucene.search.Sort;
 import org.apache.lucene.util.Bits;
 import org.apache.lucene.util.Version;
 import org.apache.lucene.util.packed.PackedInts;
@@ -84,38 +85,44 @@ public final class SlowCompositeReaderWrapper extends LeafReader {
    * This method is sugar for getting an {@link LeafReader} from an {@link IndexReader} of any kind.
    * If the reader is already atomic, it is returned unchanged, otherwise wrapped by this class.
    */
-  public static LeafReader wrap(IndexReader reader) throws IOException {
-    if (reader instanceof CompositeReader) {
-      return new SlowCompositeReaderWrapper((CompositeReader) reader);
+  public static LeafReader wrap(IndexReader reader) {
+    if (reader instanceof CompositeReader compositeReader) {
+      return new SlowCompositeReaderWrapper(compositeReader);
     } else {
       assert reader instanceof LeafReader;
       return (LeafReader) reader;
     }
   }
 
-  SlowCompositeReaderWrapper(CompositeReader reader) throws IOException {
+  SlowCompositeReaderWrapper(CompositeReader reader) {
     in = reader;
     in.registerParentReader(this);
-    if (reader.leaves().isEmpty()) {
+    List<LeafReaderContext> leaves = reader.leaves();
+    if (leaves.isEmpty()) {
       metaData = new LeafMetaData(Version.LATEST.major, Version.LATEST, null, false);
     } else {
       Version minVersion = Version.LATEST;
-      for (LeafReaderContext leafReaderContext : reader.leaves()) {
-        Version leafVersion = leafReaderContext.reader().getMetaData().minVersion();
-        if (leafVersion == null) {
-          minVersion = null;
-          break;
-        } else if (minVersion.onOrAfter(leafVersion)) {
-          minVersion = leafVersion;
+      boolean hasBlocks = false;
+      for (LeafReaderContext leafReaderContext : leaves) {
+        LeafMetaData leafMetaData = leafReaderContext.reader().getMetaData();
+        if (minVersion != null) {
+          Version leafVersion = leafMetaData.minVersion();
+          if (leafVersion == null) {
+            minVersion = null;
+          } else if (minVersion.onOrAfter(leafVersion)) {
+            minVersion = leafVersion;
+          }
         }
+        // A block (child/nested docs), once written, is never split across segments, so the
+        // composite view has blocks as soon as any one of its segments does.
+        hasBlocks |= leafMetaData.hasBlocks();
       }
-      LeafMetaData leafMetaData = reader.leaves().get(0).reader().getMetaData();
+      LeafMetaData firstLeafMetaData = leaves.getFirst().reader().getMetaData();
+      // The composite view is only actually sorted in the trivial single-leaf case: concatenating
+      // multiple segments does not preserve their shared per-segment sort as a sort of the whole.
+      Sort sort = leaves.size() == 1 ? firstLeafMetaData.sort() : null;
       metaData =
-          new LeafMetaData(
-              leafMetaData.createdVersionMajor(),
-              minVersion,
-              leafMetaData.sort(),
-              leafMetaData.hasBlocks());
+          new LeafMetaData(firstLeafMetaData.createdVersionMajor(), minVersion, sort, hasBlocks);
     }
     fieldInfos = FieldInfos.getMergedFieldInfos(in);
   }