Index: lucene/core/src/java/org/apache/lucene/index/BaseCompositeReader.java
===================================================================
--- lucene/core/src/java/org/apache/lucene/index/BaseCompositeReader.java	(revision 1662487)
+++ lucene/core/src/java/org/apache/lucene/index/BaseCompositeReader.java	(working copy)
@@ -64,24 +64,32 @@
    * cloned and not protected for modification, the subclass is responsible 
    * to do this.
    */
-  protected BaseCompositeReader(R[] subReaders) {
+  protected BaseCompositeReader(R[] subReaders) throws IOException {
     this.subReaders = subReaders;
     this.subReadersList = Collections.unmodifiableList(Arrays.asList(subReaders));
     starts = new int[subReaders.length + 1];    // build starts array
-    int maxDoc = 0, numDocs = 0;
+    long maxDoc = 0, numDocs = 0;
     for (int i = 0; i < subReaders.length; i++) {
-      starts[i] = maxDoc;
+      starts[i] = (int) maxDoc;
       final IndexReader r = subReaders[i];
       maxDoc += r.maxDoc();      // compute maxDocs
-      if (maxDoc < 0 /* overflow */ || maxDoc > IndexWriter.getActualMaxDocs()) {
-        throw new IllegalArgumentException("Too many documents, composite IndexReaders cannot exceed " + IndexWriter.getActualMaxDocs());
-      }
       numDocs += r.numDocs();    // compute numDocs
       r.registerParentReader(this);
     }
-    starts[subReaders.length] = maxDoc;
-    this.maxDoc = maxDoc;
-    this.numDocs = numDocs;
+
+    if (maxDoc > IndexWriter.getActualMaxDocs()) {
+      if (this instanceof DirectoryReader) {
+        // A single index has too many documents and it is corrupt (IndexWriter prevents this as of LUCENE-6299)
+        throw new CorruptIndexException("Too many documents: an index cannot exceed " + IndexWriter.getActualMaxDocs() + " but readers have total maxDoc=" + maxDoc, Arrays.toString(subReaders));
+      } else {
+        // Caller is building a MultiReader and it has too many documents; this case is just illegal arguments:
+        throw new IllegalArgumentException("Too many documents: composite IndexReaders cannot exceed " + IndexWriter.getActualMaxDocs() + " but readers have total maxDoc=" + maxDoc);
+      }
+    }
+
+    this.maxDoc = Math.toIntExact(maxDoc);
+    starts[subReaders.length] = this.maxDoc;
+    this.numDocs = Math.toIntExact(numDocs);
   }
 
   @Override
Index: lucene/core/src/java/org/apache/lucene/index/DirectoryReader.java
===================================================================
--- lucene/core/src/java/org/apache/lucene/index/DirectoryReader.java	(revision 1662487)
+++ lucene/core/src/java/org/apache/lucene/index/DirectoryReader.java	(working copy)
@@ -305,11 +305,11 @@
    * Subclasses of {@code DirectoryReader} should take care to not allow
    * modification of this internal array, e.g. {@link #doOpenIfChanged()}.
    */
-  protected DirectoryReader(Directory directory, LeafReader[] segmentReaders) {
+  protected DirectoryReader(Directory directory, LeafReader[] segmentReaders) throws IOException {
     super(segmentReaders);
     this.directory = directory;
   }
-  
+
   /** Returns the directory this index resides in. */
   public final Directory directory() {
     // Don't ensureOpen here -- in certain cases, when a
Index: lucene/core/src/java/org/apache/lucene/index/DocumentsWriterPerThread.java
===================================================================
--- lucene/core/src/java/org/apache/lucene/index/DocumentsWriterPerThread.java	(revision 1662487)
+++ lucene/core/src/java/org/apache/lucene/index/DocumentsWriterPerThread.java	(working copy)
@@ -205,7 +205,7 @@
     if (pendingNumDocs.incrementAndGet() > IndexWriter.getActualMaxDocs()) {
       // Reserve failed
       pendingNumDocs.decrementAndGet();
-      throw new IllegalStateException("number of documents in the index cannot exceed " + IndexWriter.getActualMaxDocs());
+      throw new IllegalArgumentException("number of documents in the index cannot exceed " + IndexWriter.getActualMaxDocs());
     }
   }
 
@@ -212,6 +212,7 @@
   public void updateDocument(IndexDocument doc, Analyzer analyzer, Term delTerm) throws IOException, AbortingException {
     testPoint("DocumentsWriterPerThread addDocument start");
     assert deleteQueue != null;
+    reserveDoc();
     docState.doc = doc;
     docState.analyzer = analyzer;
     docState.docID = numDocsInRAM;
@@ -224,7 +225,6 @@
     // document, so the counter will be "wrong" in that case, but
     // it's very hard to fix (we can't easily distinguish aborting
     // vs non-aborting exceptions):
-    reserveDoc();
     boolean success = false;
     try {
       try {
Index: lucene/core/src/java/org/apache/lucene/index/ExitableDirectoryReader.java
===================================================================
--- lucene/core/src/java/org/apache/lucene/index/ExitableDirectoryReader.java	(revision 1662487)
+++ lucene/core/src/java/org/apache/lucene/index/ExitableDirectoryReader.java	(working copy)
@@ -185,13 +185,13 @@
    * @param in DirectoryReader that this ExitableDirectoryReader wraps around to make it Exitable.
    * @param queryTimeout The object to periodically check if the query should time out.
    */
-  public ExitableDirectoryReader(DirectoryReader in, QueryTimeout queryTimeout) {
+  public ExitableDirectoryReader(DirectoryReader in, QueryTimeout queryTimeout) throws IOException {
     super(in, new ExitableSubReaderWrapper(queryTimeout));
     this.queryTimeout = queryTimeout;
   }
 
   @Override
-  protected DirectoryReader doWrapDirectoryReader(DirectoryReader in) {
+  protected DirectoryReader doWrapDirectoryReader(DirectoryReader in) throws IOException {
     return new ExitableDirectoryReader(in, queryTimeout);
   }
 
@@ -200,7 +200,7 @@
    * can be used normally (e.g. passed to {@link DirectoryReader#openIfChanged(DirectoryReader)})
    * and so on.
    */
-  public static DirectoryReader wrap(DirectoryReader in, QueryTimeout queryTimeout) {
+  public static DirectoryReader wrap(DirectoryReader in, QueryTimeout queryTimeout) throws IOException {
     return new ExitableDirectoryReader(in, queryTimeout);
   }
 
Index: lucene/core/src/java/org/apache/lucene/index/FilterDirectoryReader.java
===================================================================
--- lucene/core/src/java/org/apache/lucene/index/FilterDirectoryReader.java	(revision 1662487)
+++ lucene/core/src/java/org/apache/lucene/index/FilterDirectoryReader.java	(working copy)
@@ -79,7 +79,7 @@
    * @param in the DirectoryReader to filter
    * @param wrapper the SubReaderWrapper to use to wrap subreaders
    */
-  public FilterDirectoryReader(DirectoryReader in, SubReaderWrapper wrapper) {
+  public FilterDirectoryReader(DirectoryReader in, SubReaderWrapper wrapper) throws IOException {
     super(in.directory(), wrapper.wrap(in.getSequentialSubReaders()));
     this.in = in;
   }
@@ -93,9 +93,9 @@
    * @param in the DirectoryReader to wrap
    * @return the wrapped DirectoryReader
    */
-  protected abstract DirectoryReader doWrapDirectoryReader(DirectoryReader in);
+  protected abstract DirectoryReader doWrapDirectoryReader(DirectoryReader in) throws IOException;
 
-  private final DirectoryReader wrapDirectoryReader(DirectoryReader in) {
+  private final DirectoryReader wrapDirectoryReader(DirectoryReader in) throws IOException {
     return in == null ? null : doWrapDirectoryReader(in);
   }
 
Index: lucene/core/src/java/org/apache/lucene/index/IndexWriter.java
===================================================================
--- lucene/core/src/java/org/apache/lucene/index/IndexWriter.java	(revision 1662487)
+++ lucene/core/src/java/org/apache/lucene/index/IndexWriter.java	(working copy)
@@ -196,7 +196,7 @@
 public class IndexWriter implements Closeable, TwoPhaseCommit, Accountable {
 
   /** Hard limit on maximum number of documents that may be added to the
-   *  index.  If you try to add more than this you'll hit {@code IllegalStateException}. */
+   *  index.  If you try to add more than this you'll hit {@code IllegalArgumentException}. */
   // We defensively subtract 128 to be well below the lowest
   // ArrayUtil.MAX_ARRAY_LENGTH on "typical" JVMs.  We don't just use
   // ArrayUtil.MAX_ARRAY_LENGTH here because this can vary across JVMs:
@@ -839,6 +839,7 @@
       }
 
       rollbackSegments = segmentInfos.createBackupSegmentInfos();
+      pendingNumDocs.set(segmentInfos.totalDocCount());
 
       // start with previous field numbers, but new FieldInfos
       globalFieldNumberMap = getFieldNumberMap();
@@ -2077,6 +2078,7 @@
             ++changeCount;
             segmentInfos.changed();
             globalFieldNumberMap.clear();
+            pendingNumDocs.set(0);
             success = true;
           } finally {
             docWriter.unlockAllAfterAbortAll(this);
@@ -2317,6 +2319,8 @@
    * @throws IOException if there is a low-level IO error
    * @throws LockObtainFailedException if we were unable to
    *   acquire the write lock in at least one directory
+   * @throws IllegalArgumentException if addIndexes would cause
+   *   the index to exceed {@link #MAX_DOCS}
    */
   public void addIndexes(Directory... dirs) throws IOException {
     ensureOpen();
@@ -2335,16 +2339,26 @@
       flush(false, true);
 
       List<SegmentCommitInfo> infos = new ArrayList<>();
-      int totalDocCount = 0;
+
+      // long so we can detect int overflow:
+      long totalDocCount = 0;
+      List<SegmentInfos> commits = new ArrayList<>(dirs.length);
+      for (Directory dir : dirs) {
+        if (infoStream.isEnabled("IW")) {
+          infoStream.message("IW", "addIndexes: process directory " + dir);
+        }
+        SegmentInfos sis = SegmentInfos.readLatestCommit(dir); // read infos from dir
+        totalDocCount += sis.totalDocCount();
+        commits.add(sis);
+      }
+        
+      // Make sure adding the new documents to this index won't
+      // exceed the limit:
+      reserveDocs(totalDocCount);
+
       boolean success = false;
       try {
-        for (Directory dir : dirs) {
-          if (infoStream.isEnabled("IW")) {
-            infoStream.message("IW", "addIndexes: process directory " + dir);
-          }
-          SegmentInfos sis = SegmentInfos.readLatestCommit(dir); // read infos from dir
-          totalDocCount += sis.totalDocCount();
-
+        for (SegmentInfos sis : commits) {
           for (SegmentCommitInfo info : sis) {
             assert !infos.contains(info): "dup info dir=" + info.info.dir + " name=" + info.info.name;
 
@@ -2367,12 +2381,7 @@
       } finally {
         if (!success) {
           for(SegmentCommitInfo sipc : infos) {
-            for(String file : sipc.files()) {
-              try {
-                directory.deleteFile(file);
-              } catch (Throwable t) {
-              }
-            }
+            IOUtils.deleteFilesIgnoringExceptions(directory, sipc.files().toArray(new String[0]));
           }
         }
       }
@@ -2381,9 +2390,6 @@
         success = false;
         try {
           ensureOpen();
-          // Make sure adding the new documents to this index won't
-          // exceed the limit:
-          reserveDocs(totalDocCount);
           success = true;
         } finally {
           if (!success) {
@@ -2441,11 +2447,15 @@
    *           if the index is corrupt
    * @throws IOException
    *           if there is a low-level IO error
+   * @throws IllegalArgumentException
+   *           if addIndexes would cause the index to exceed {@link #MAX_DOCS}
    */
   public void addIndexes(CodecReader... readers) throws IOException {
     ensureOpen();
-    int numDocs = 0;
 
+    // long so we can detect int overflow:
+    long numDocs = 0;
+
     try {
       if (infoStream.isEnabled("IW")) {
         infoStream.message("IW", "flush at addIndexes(CodecReader...)");
@@ -2461,7 +2471,7 @@
       // exceed the limit:
       reserveDocs(numDocs);
       
-      final IOContext context = new IOContext(new MergeInfo(numDocs, -1, false, -1));
+      final IOContext context = new IOContext(new MergeInfo(Math.toIntExact(numDocs), -1, false, -1));
 
       // TODO: somehow we should fix this merge so it's
       // abortable so that IW.close(false) is able to stop it
@@ -2557,7 +2567,7 @@
         checkpoint();
       }
     } catch (OutOfMemoryError oom) {
-      tragicEvent(oom, "addIndexes(IndexReader...)");
+      tragicEvent(oom, "addIndexes(CodecReader...)");
     }
     maybeMerge();
   }
@@ -4616,12 +4626,12 @@
 
   /** Anything that will add N docs to the index should reserve first to
    *  make sure it's allowed.  This will throw {@code
-   *  IllegalStateException} if it's not allowed. */ 
-  private void reserveDocs(int numDocs) {
+   *  IllegalArgumentException} if it's not allowed. */ 
+  private void reserveDocs(long numDocs) {
     if (pendingNumDocs.addAndGet(numDocs) > actualMaxDocs) {
       // Reserve failed
       pendingNumDocs.addAndGet(-numDocs);
-      throw new IllegalStateException("number of documents in the index cannot exceed " + actualMaxDocs);
+      throw new IllegalArgumentException("number of documents in the index cannot exceed " + actualMaxDocs + " (current document count is " + pendingNumDocs.get() + "; added numDocs is " + numDocs + ")");
     }
   }
 
Index: lucene/core/src/java/org/apache/lucene/index/MultiReader.java
===================================================================
--- lucene/core/src/java/org/apache/lucene/index/MultiReader.java	(revision 1662487)
+++ lucene/core/src/java/org/apache/lucene/index/MultiReader.java	(working copy)
@@ -45,7 +45,7 @@
   * <p>Note that all subreaders are closed if this Multireader is closed.</p>
   * @param subReaders set of (sub)readers
   */
-  public MultiReader(IndexReader... subReaders) {
+  public MultiReader(IndexReader... subReaders) throws IOException {
     this(subReaders, true);
   }
 
@@ -55,7 +55,7 @@
    * @param closeSubReaders indicates whether the subreaders should be closed
    * when this MultiReader is closed
    */
-  public MultiReader(IndexReader[] subReaders, boolean closeSubReaders) {
+  public MultiReader(IndexReader[] subReaders, boolean closeSubReaders) throws IOException {
     super(subReaders.clone());
     this.closeSubReaders = closeSubReaders;
     if (!closeSubReaders) {
Index: lucene/core/src/java/org/apache/lucene/index/SegmentInfos.java
===================================================================
--- lucene/core/src/java/org/apache/lucene/index/SegmentInfos.java	(revision 1662487)
+++ lucene/core/src/java/org/apache/lucene/index/SegmentInfos.java	(working copy)
@@ -284,6 +284,7 @@
       if (numSegments < 0) {
         throw new CorruptIndexException("invalid segment count: " + numSegments, input);
       }
+      long totalDocs = 0;
       for (int seg = 0; seg < numSegments; seg++) {
         String segName = input.readString();
         final byte segmentID[];
@@ -297,6 +298,7 @@
         Codec codec = Codec.forName(input.readString());
         SegmentInfo info = codec.segmentInfoFormat().read(directory, segName, segmentID, IOContext.READ);
         info.setCodec(codec);
+        totalDocs += info.getDocCount();
         long delGen = input.readLong();
         int delCount = input.readInt();
         if (delCount < 0 || delCount > info.getDocCount()) {
@@ -323,6 +325,11 @@
 
       CodecUtil.checkFooter(input);
 
+      // LUCENE-6299: check we are in bounds
+      if (totalDocs > IndexWriter.getActualMaxDocs()) {
+        throw new CorruptIndexException("Too many documents: an index cannot exceed " + IndexWriter.getActualMaxDocs() + " but readers have total maxDoc=" + totalDocs, input);
+      }
+      
       return infos;
     }
   }
@@ -722,11 +729,13 @@
   /** Returns sum of all segment's docCounts.  Note that
    *  this does not include deletions */
   public int totalDocCount() {
-    int count = 0;
+    long count = 0;
     for(SegmentCommitInfo info : this) {
       count += info.info.getDocCount();
     }
-    return count;
+    // we should never hit this, checks should happen elsewhere...
+    assert count <= IndexWriter.getActualMaxDocs();
+    return Math.toIntExact(count);
   }
 
   /** Call this before committing if changes have been made to the
Index: lucene/core/src/java/org/apache/lucene/index/StandardDirectoryReader.java
===================================================================
--- lucene/core/src/java/org/apache/lucene/index/StandardDirectoryReader.java	(revision 1662487)
+++ lucene/core/src/java/org/apache/lucene/index/StandardDirectoryReader.java	(working copy)
@@ -38,7 +38,7 @@
   
   /** called only from static open() methods */
   StandardDirectoryReader(Directory directory, LeafReader[] readers, IndexWriter writer,
-    SegmentInfos sis, boolean applyAllDeletes) {
+    SegmentInfos sis, boolean applyAllDeletes) throws IOException {
     super(directory, readers);
     this.writer = writer;
     this.segmentInfos = sis;
@@ -52,18 +52,23 @@
       protected DirectoryReader doBody(String segmentFileName) throws IOException {
         SegmentInfos sis = SegmentInfos.readCommit(directory, segmentFileName);
         final SegmentReader[] readers = new SegmentReader[sis.size()];
-        for (int i = sis.size()-1; i >= 0; i--) {
-          boolean success = false;
-          try {
+        boolean success = false;
+        try {
+          for (int i = sis.size()-1; i >= 0; i--) {
             readers[i] = new SegmentReader(sis.info(i), IOContext.READ);
-            success = true;
-          } finally {
-            if (!success) {
-              IOUtils.closeWhileHandlingException(readers);
-            }
           }
+
+          // This may throw CorruptIndexException if there are too many docs, so
+          // it must be inside try clause so we close readers in that case:
+          DirectoryReader reader = new StandardDirectoryReader(directory, readers, null, sis, false);
+          success = true;
+
+          return reader;
+        } finally {
+          if (success == false) {
+            IOUtils.closeWhileHandlingException(readers);
+          }
         }
-        return new StandardDirectoryReader(directory, readers, null, sis, false);
       }
     }.run(commit);
   }
Index: lucene/core/src/test/org/apache/lucene/index/TestDemoParallelLeafReader.java
===================================================================
--- lucene/core/src/test/org/apache/lucene/index/TestDemoParallelLeafReader.java	(revision 1662487)
+++ lucene/core/src/test/org/apache/lucene/index/TestDemoParallelLeafReader.java	(working copy)
@@ -191,7 +191,7 @@
     }
 
     private class ParallelLeafDirectoryReader extends FilterDirectoryReader {
-      public ParallelLeafDirectoryReader(DirectoryReader in) {
+      public ParallelLeafDirectoryReader(DirectoryReader in) throws IOException {
         super(in, new FilterDirectoryReader.SubReaderWrapper() {
             final long currentSchemaGen = getCurrentSchemaGen();
             @Override
@@ -207,7 +207,7 @@
       }
 
       @Override
-      protected DirectoryReader doWrapDirectoryReader(DirectoryReader in) {
+      protected DirectoryReader doWrapDirectoryReader(DirectoryReader in) throws IOException {
         return new ParallelLeafDirectoryReader(in);
       }
 
Index: lucene/core/src/test/org/apache/lucene/index/TestIndexWriterMaxDocs.java
===================================================================
--- lucene/core/src/test/org/apache/lucene/index/TestIndexWriterMaxDocs.java	(revision 1662487)
+++ lucene/core/src/test/org/apache/lucene/index/TestIndexWriterMaxDocs.java	(working copy)
@@ -17,6 +17,7 @@
  * limitations under the License.
  */
 
+import java.io.IOException;
 import java.util.Arrays;
 import java.util.Collections;
 
@@ -28,6 +29,9 @@
 import org.apache.lucene.search.TermQuery;
 import org.apache.lucene.search.TopDocs;
 import org.apache.lucene.store.Directory;
+import org.apache.lucene.store.FilterDirectory;
+import org.apache.lucene.store.MockDirectoryWrapper;
+import org.apache.lucene.store.NoLockFactory;
 import org.apache.lucene.util.LuceneTestCase.SuppressCodecs;
 import org.apache.lucene.util.LuceneTestCase;
 import org.apache.lucene.util.TestUtil;
@@ -93,7 +97,7 @@
       try {
         w.addDocument(new Document());
         fail("didn't hit exception");
-      } catch (IllegalStateException ise) {
+      } catch (IllegalArgumentException iae) {
         // expected
       }
       w.close();
@@ -116,7 +120,7 @@
       try {
         w.addDocuments(Collections.singletonList(new Document()));
         fail("didn't hit exception");
-      } catch (IllegalStateException ise) {
+      } catch (IllegalArgumentException iae) {
         // expected
       }
       w.close();
@@ -139,7 +143,7 @@
       try {
         w.updateDocument(new Term("field", "foo"), new Document());
         fail("didn't hit exception");
-      } catch (IllegalStateException ise) {
+      } catch (IllegalArgumentException iae) {
         // expected
       }
       w.close();
@@ -162,7 +166,7 @@
       try {
         w.updateDocuments(new Term("field", "foo"), Collections.singletonList(new Document()));
         fail("didn't hit exception");
-      } catch (IllegalStateException ise) {
+      } catch (IllegalArgumentException iae) {
         // expected
       }
       w.close();
@@ -201,7 +205,7 @@
       try {
         w.addDocument(new Document());
         fail("didn't hit exception");
-      } catch (IllegalStateException ise) {
+      } catch (IllegalArgumentException iae) {
         // expected
       }
       w.close();
@@ -247,7 +251,7 @@
       try {
         w.addDocument(new Document());
         fail("didn't hit exception");
-      } catch (IllegalStateException ise) {
+      } catch (IllegalArgumentException iae) {
         // expected
       }
       w.close();
@@ -273,7 +277,7 @@
       try {
         w2.addIndexes(new Directory[] {dir});
         fail("didn't hit exception");
-      } catch (IllegalStateException ise) {
+      } catch (IllegalArgumentException iae) {
         // expected
       }
       assertEquals(1, w2.maxDoc());
@@ -281,7 +285,7 @@
       try {
         TestUtil.addIndexesSlowly(w2, ir);
         fail("didn't hit exception");
-      } catch (IllegalStateException ise) {
+      } catch (IllegalArgumentException iae) {
         // expected
       }
       w2.close();
@@ -369,7 +373,104 @@
     dir.close();
     dir2.close();
   }
+  
+  /** 
+   * LUCENE-6299: Test if addindexes(Dir[]) prevents exceeding max docs.
+   */
+  public void testAddTooManyIndexesDir() throws Exception {
+    // we cheat and add the same one over again... IW wants a write lock on each
+    Directory dir = newDirectory(random(), NoLockFactory.INSTANCE);
+    Document doc = new Document();
+    IndexWriter w = new IndexWriter(dir, new IndexWriterConfig(null));
+    for (int i = 0; i < 100000; i++) {
+      w.addDocument(doc);
+    }
+    w.forceMerge(1);
+    w.commit();
+    w.close();
+    
+    // wrap this with disk full, so test fails faster and doesn't fill up real disks.
+    MockDirectoryWrapper dir2 = newMockDirectory();
+    w = new IndexWriter(dir2, new IndexWriterConfig(null));
+    w.commit(); // don't confuse checkindex
+    dir2.setMaxSizeInBytes(dir2.sizeInBytes() + 65536); // 64KB
+    Directory dirs[] = new Directory[1 + (IndexWriter.MAX_DOCS / 100000)];
+    for (int i = 0; i < dirs.length; i++) {
+      // bypass iw check for duplicate dirs
+      dirs[i] = new FilterDirectory(dir) {};
+    }
 
+    try {
+      w.addIndexes(dirs);
+      fail("didn't get expected exception");
+    } catch (IllegalArgumentException expected) {
+      // pass
+    } catch (IOException fakeDiskFull) {
+      final Exception e;
+      if (fakeDiskFull.getMessage() != null && fakeDiskFull.getMessage().startsWith("fake disk full")) {
+        e = new RuntimeException("test failed: IW checks aren't working and we are executing addIndexes");
+        e.addSuppressed(fakeDiskFull);
+      } else {
+        e = fakeDiskFull;
+      }
+      throw e;
+    }
+    
+    w.close();
+    dir.close();
+    dir2.close();
+  }
+
+  /** 
+   * LUCENE-6299: Test if addindexes(CodecReader[]) prevents exceeding max docs.
+   */
+  public void testAddTooManyIndexesCodecReader() throws Exception {
+    // we cheat and add the same one over again... IW wants a write lock on each
+    Directory dir = newDirectory(random(), NoLockFactory.INSTANCE);
+    Document doc = new Document();
+    IndexWriter w = new IndexWriter(dir, new IndexWriterConfig(null));
+    for (int i = 0; i < 100000; i++) {
+      w.addDocument(doc);
+    }
+    w.forceMerge(1);
+    w.commit();
+    w.close();
+    
+    // wrap this with disk full, so test fails faster and doesn't fill up real disks.
+    MockDirectoryWrapper dir2 = newMockDirectory();
+    w = new IndexWriter(dir2, new IndexWriterConfig(null));
+    w.commit(); // don't confuse checkindex
+    dir2.setMaxSizeInBytes(dir2.sizeInBytes() + 65536); // 64KB
+    IndexReader r = DirectoryReader.open(dir);
+    CodecReader segReader = (CodecReader) r.leaves().get(0).reader();
+
+    CodecReader readers[] = new CodecReader[1 + (IndexWriter.MAX_DOCS / 100000)];
+    for (int i = 0; i < readers.length; i++) {
+      readers[i] = segReader;
+    }
+
+    try {
+      w.addIndexes(readers);
+      fail("didn't get expected exception");
+    } catch (IllegalArgumentException expected) {
+      // pass
+    } catch (IOException fakeDiskFull) {
+      final Exception e;
+      if (fakeDiskFull.getMessage() != null && fakeDiskFull.getMessage().startsWith("fake disk full")) {
+        e = new RuntimeException("test failed: IW checks aren't working and we are executing addIndexes");
+        e.addSuppressed(fakeDiskFull);
+      } else {
+        e = fakeDiskFull;
+      }
+      throw e;
+    }
+
+    r.close();
+    w.close();
+    dir.close();
+    dir2.close();
+  }
+
   public void testTooLargeMaxDocs() throws Exception {
     try {
       IndexWriter.setMaxDocs(Integer.MAX_VALUE);
@@ -378,4 +479,90 @@
       // expected
     }
   }
+
+  // LUCENE-6299
+  public void testDeleteAll() throws Exception {
+    setIndexWriterMaxDocs(1);
+    try {
+      Directory dir = newDirectory();
+      IndexWriter w = new IndexWriter(dir, new IndexWriterConfig(null));
+      w.addDocument(new Document());
+      try {
+        w.addDocument(new Document());
+        fail("didn't hit exception");
+      } catch (IllegalArgumentException iae) {
+        // expected
+      }
+      w.deleteAll();
+      w.addDocument(new Document());
+      w.close();
+      dir.close();
+    } finally {
+      restoreIndexWriterMaxDocs();
+    }
+  }
+
+  // LUCENE-6299
+  public void testAcrossTwoIndexWriters() throws Exception {
+    setIndexWriterMaxDocs(1);
+    try {
+      Directory dir = newDirectory();
+      IndexWriter w = new IndexWriter(dir, new IndexWriterConfig(null));
+      w.addDocument(new Document());
+      w.close();
+      w = new IndexWriter(dir, new IndexWriterConfig(null));
+      try {
+        w.addDocument(new Document());
+        fail("didn't hit exception");
+      } catch (IllegalArgumentException iae) {
+        // expected
+      }
+      w.close();
+      dir.close();
+    } finally {
+      restoreIndexWriterMaxDocs();
+    }
+  }
+
+  // LUCENE-6299
+  public void testCorruptIndexExceptionTooLarge() throws Exception {
+    Directory dir = newDirectory();
+    IndexWriter w = new IndexWriter(dir, new IndexWriterConfig(null));
+    w.addDocument(new Document());
+    w.addDocument(new Document());
+    w.close();
+
+    setIndexWriterMaxDocs(1);
+    try {       
+      DirectoryReader.open(dir);
+      fail("didn't hit exception");
+    } catch (CorruptIndexException cie) {
+      // expected
+    } finally {
+      restoreIndexWriterMaxDocs();
+    }
+
+    dir.close();
+  }
+  
+  // LUCENE-6299
+  public void testCorruptIndexExceptionTooLargeWriter() throws Exception {
+    Directory dir = newDirectory();
+    IndexWriter w = new IndexWriter(dir, new IndexWriterConfig(null));
+    w.addDocument(new Document());
+    w.addDocument(new Document());
+    w.close();
+
+    setIndexWriterMaxDocs(1);
+    try {       
+      new IndexWriter(dir, new IndexWriterConfig(null));
+      fail("didn't hit exception");
+    } catch (CorruptIndexException cie) {
+      // expected
+    } finally {
+      restoreIndexWriterMaxDocs();
+    }
+
+    dir.close();
+  }
 }
Index: lucene/core/src/test/org/apache/lucene/search/TestSearcherManager.java
===================================================================
--- lucene/core/src/test/org/apache/lucene/search/TestSearcherManager.java	(revision 1662487)
+++ lucene/core/src/test/org/apache/lucene/search/TestSearcherManager.java	(working copy)
@@ -457,7 +457,7 @@
   }
 
   private static class MyFilterDirectoryReader extends FilterDirectoryReader {
-    public MyFilterDirectoryReader(DirectoryReader in) {
+    public MyFilterDirectoryReader(DirectoryReader in) throws IOException {
       super(in, 
             new FilterDirectoryReader.SubReaderWrapper() {
               @Override
@@ -470,7 +470,7 @@
     }
 
     @Override
-    protected DirectoryReader doWrapDirectoryReader(DirectoryReader in) {
+    protected DirectoryReader doWrapDirectoryReader(DirectoryReader in) throws IOException {
       return new MyFilterDirectoryReader(in);
     }
   }
Index: lucene/core/src/test/org/apache/lucene/store/TestMockDirectoryWrapper.java
===================================================================
--- lucene/core/src/test/org/apache/lucene/store/TestMockDirectoryWrapper.java	(revision 1662487)
+++ lucene/core/src/test/org/apache/lucene/store/TestMockDirectoryWrapper.java	(working copy)
@@ -19,8 +19,10 @@
 
 import java.io.IOException;
 
+import org.apache.lucene.document.Document;
 import org.apache.lucene.index.IndexWriter;
 import org.apache.lucene.index.IndexWriterConfig;
+import org.apache.lucene.index.RandomIndexWriter;
 import org.apache.lucene.util.IOUtils;
 import org.apache.lucene.util.LuceneTestCase;
 
@@ -91,4 +93,16 @@
     dir.close();
   }
   
+  public void testMDWinsideOfMDW() throws Exception {
+    // add MDW inside another MDW
+    Directory dir = new MockDirectoryWrapper(random(), newMockDirectory());
+    RandomIndexWriter iw = new RandomIndexWriter(random(), dir);
+    for (int i = 0; i < 20; i++) {
+      iw.addDocument(new Document());
+    }
+    iw.commit();
+    iw.close();
+    dir.close();
+  }
+  
 }
Index: lucene/highlighter/src/java/org/apache/lucene/search/postingshighlight/PostingsHighlighter.java
===================================================================
--- lucene/highlighter/src/java/org/apache/lucene/search/postingshighlight/PostingsHighlighter.java	(revision 1662487)
+++ lucene/highlighter/src/java/org/apache/lucene/search/postingshighlight/PostingsHighlighter.java	(working copy)
@@ -31,7 +31,6 @@
 import java.util.TreeSet;
 
 import org.apache.lucene.analysis.Analyzer;
-import org.apache.lucene.index.PostingsEnum;
 import org.apache.lucene.index.FieldInfo;
 import org.apache.lucene.index.IndexOptions;
 import org.apache.lucene.index.IndexReader;
@@ -39,6 +38,7 @@
 import org.apache.lucene.index.LeafReader;
 import org.apache.lucene.index.LeafReaderContext;
 import org.apache.lucene.index.MultiReader;
+import org.apache.lucene.index.PostingsEnum;
 import org.apache.lucene.index.ReaderUtil;
 import org.apache.lucene.index.StoredFieldVisitor;
 import org.apache.lucene.index.Term;
@@ -100,7 +100,14 @@
   // unnecessary.
   
   /** for rewriting: we don't want slow processing from MTQs */
-  private static final IndexReader EMPTY_INDEXREADER = new MultiReader();
+  private static final IndexReader EMPTY_INDEXREADER;
+  static {
+    try {
+      EMPTY_INDEXREADER = new MultiReader();
+    } catch (IOException bogus) {
+      throw new RuntimeException(bogus);
+    }
+  }
   
   /** Default maximum content size to process. Typically snippets
    *  closer to the beginning of the document better summarize its content */
Index: lucene/misc/src/java/org/apache/lucene/uninverting/UninvertingReader.java
===================================================================
--- lucene/misc/src/java/org/apache/lucene/uninverting/UninvertingReader.java	(revision 1662487)
+++ lucene/misc/src/java/org/apache/lucene/uninverting/UninvertingReader.java	(working copy)
@@ -146,7 +146,7 @@
    * can be used normally (e.g. passed to {@link DirectoryReader#openIfChanged(DirectoryReader)})
    * and so on. 
    */
-  public static DirectoryReader wrap(DirectoryReader in, final Map<String,Type> mapping) {
+  public static DirectoryReader wrap(DirectoryReader in, final Map<String,Type> mapping) throws IOException {
     return new UninvertingDirectoryReader(in, mapping);
   }
   
@@ -153,7 +153,7 @@
   static class UninvertingDirectoryReader extends FilterDirectoryReader {
     final Map<String,Type> mapping;
     
-    public UninvertingDirectoryReader(DirectoryReader in, final Map<String,Type> mapping) {
+    public UninvertingDirectoryReader(DirectoryReader in, final Map<String,Type> mapping) throws IOException {
       super(in, new FilterDirectoryReader.SubReaderWrapper() {
         @Override
         public LeafReader wrap(LeafReader reader) {
@@ -164,7 +164,7 @@
     }
 
     @Override
-    protected DirectoryReader doWrapDirectoryReader(DirectoryReader in) {
+    protected DirectoryReader doWrapDirectoryReader(DirectoryReader in) throws IOException {
       return new UninvertingDirectoryReader(in, mapping);
     }
   }
Index: lucene/test-framework/src/java/org/apache/lucene/index/AssertingDirectoryReader.java
===================================================================
--- lucene/test-framework/src/java/org/apache/lucene/index/AssertingDirectoryReader.java	(revision 1662487)
+++ lucene/test-framework/src/java/org/apache/lucene/index/AssertingDirectoryReader.java	(working copy)
@@ -17,6 +17,8 @@
  * limitations under the License.
  */
 
+import java.io.IOException;
+
 /**
  * A {@link DirectoryReader} that wraps all its subreaders with
  * {@link AssertingLeafReader}
@@ -30,12 +32,12 @@
     }
   }
 
-  public AssertingDirectoryReader(DirectoryReader in) {
+  public AssertingDirectoryReader(DirectoryReader in) throws IOException {
     super(in, new AssertingSubReaderWrapper());
   }
 
   @Override
-  protected DirectoryReader doWrapDirectoryReader(DirectoryReader in) {
+  protected DirectoryReader doWrapDirectoryReader(DirectoryReader in) throws IOException {
     return new AssertingDirectoryReader(in);
   }
 
Index: lucene/test-framework/src/java/org/apache/lucene/index/BaseStoredFieldsFormatTestCase.java
===================================================================
--- lucene/test-framework/src/java/org/apache/lucene/index/BaseStoredFieldsFormatTestCase.java	(revision 1662487)
+++ lucene/test-framework/src/java/org/apache/lucene/index/BaseStoredFieldsFormatTestCase.java	(working copy)
@@ -599,7 +599,7 @@
 
   private static class DummyFilterDirectoryReader extends FilterDirectoryReader {
 
-    public DummyFilterDirectoryReader(DirectoryReader in) {
+    public DummyFilterDirectoryReader(DirectoryReader in) throws IOException {
       super(in, new SubReaderWrapper() {
         @Override
         public LeafReader wrap(LeafReader reader) {
@@ -609,7 +609,7 @@
     }
 
     @Override
-    protected DirectoryReader doWrapDirectoryReader(DirectoryReader in) {
+    protected DirectoryReader doWrapDirectoryReader(DirectoryReader in) throws IOException {
       return new DummyFilterDirectoryReader(in);
     }
     
Index: lucene/test-framework/src/java/org/apache/lucene/index/MismatchedDirectoryReader.java
===================================================================
--- lucene/test-framework/src/java/org/apache/lucene/index/MismatchedDirectoryReader.java	(revision 1662487)
+++ lucene/test-framework/src/java/org/apache/lucene/index/MismatchedDirectoryReader.java	(working copy)
@@ -17,6 +17,7 @@
  * limitations under the License.
  */
 
+import java.io.IOException;
 import java.util.Random;
 
 /**
@@ -38,12 +39,12 @@
     }
   }
 
-  public MismatchedDirectoryReader(DirectoryReader in, Random random) {
+  public MismatchedDirectoryReader(DirectoryReader in, Random random) throws IOException {
     super(in, new MismatchedSubReaderWrapper(random));
   }
 
   @Override
-  protected DirectoryReader doWrapDirectoryReader(DirectoryReader in) {
+  protected DirectoryReader doWrapDirectoryReader(DirectoryReader in) throws IOException {
     return new AssertingDirectoryReader(in);
   }
 }
Index: lucene/test-framework/src/java/org/apache/lucene/search/QueryUtils.java
===================================================================
--- lucene/test-framework/src/java/org/apache/lucene/search/QueryUtils.java	(revision 1662487)
+++ lucene/test-framework/src/java/org/apache/lucene/search/QueryUtils.java	(working copy)
@@ -22,6 +22,7 @@
 import java.util.Random;
 
 import junit.framework.Assert;
+
 import org.apache.lucene.analysis.MockAnalyzer;
 import org.apache.lucene.document.Document;
 import org.apache.lucene.index.AllDeletedFilterReader;
@@ -133,7 +134,7 @@
   public static class FCInvisibleMultiReader extends MultiReader {
     private final Object cacheKey = new Object();
   
-    public FCInvisibleMultiReader(IndexReader... readers) {
+    public FCInvisibleMultiReader(IndexReader... readers) throws IOException {
       super(readers);
     }
     
Index: lucene/test-framework/src/java/org/apache/lucene/store/BaseDirectoryWrapper.java
===================================================================
--- lucene/test-framework/src/java/org/apache/lucene/store/BaseDirectoryWrapper.java	(revision 1662487)
+++ lucene/test-framework/src/java/org/apache/lucene/store/BaseDirectoryWrapper.java	(working copy)
@@ -28,13 +28,13 @@
 // do NOT make any methods in this class synchronized, volatile
 // do NOT import anything from the concurrency package.
 // no randoms, no nothing.
-public class BaseDirectoryWrapper extends FilterDirectory {
+public abstract class BaseDirectoryWrapper extends FilterDirectory {
   
   private boolean checkIndexOnClose = true;
   private boolean crossCheckTermVectorsOnClose = true;
   protected volatile boolean isOpen = true;
 
-  public BaseDirectoryWrapper(Directory delegate) {
+  protected BaseDirectoryWrapper(Directory delegate) {
     super(delegate);
   }
 
@@ -72,10 +72,4 @@
   public boolean getCrossCheckTermVectorsOnClose() {
     return crossCheckTermVectorsOnClose;
   }
-
-  // why does this class override this method?
-  @Override
-  public void copyFrom(Directory from, String src, String dest, IOContext context) throws IOException {
-    in.copyFrom(from, src, dest, context);
-  }
 }
Index: lucene/test-framework/src/java/org/apache/lucene/store/MockDirectoryWrapper.java
===================================================================
--- lucene/test-framework/src/java/org/apache/lucene/store/MockDirectoryWrapper.java	(revision 1662487)
+++ lucene/test-framework/src/java/org/apache/lucene/store/MockDirectoryWrapper.java	(working copy)
@@ -209,23 +209,6 @@
     useSlowOpenClosers = v;
   }
 
-  /**
-   * Returns true if {@link #in} must sync its files.
-   * Currently, only {@link NRTCachingDirectory} requires sync'ing its files
-   * because otherwise they are cached in an internal {@link RAMDirectory}. If
-   * other directories require that too, they should be added to this method.
-   */
-  private boolean mustSync() {
-    Directory delegate = in;
-    while (delegate instanceof FilterDirectory) {
-      if (delegate instanceof NRTCachingDirectory) {
-        return true;
-      }
-      delegate = ((FilterDirectory) delegate).getDelegate();
-    }
-    return delegate instanceof NRTCachingDirectory;
-  }
-  
   @Override
   public synchronized void sync(Collection<String> names) throws IOException {
     maybeYield();
@@ -233,16 +216,13 @@
     if (crashed) {
       throw new IOException("cannot sync after crash");
     }
-    // don't wear out our hardware so much in tests.
-    if (LuceneTestCase.rarely(randomState) || mustSync()) {
-      for (String name : names) {
-        // randomly fail with IOE on any file
-        maybeThrowIOException(name);
-        in.sync(Collections.singleton(name));
-        unSyncedFiles.remove(name);
-      }
-    } else {
-      unSyncedFiles.removeAll(names);
+    // always pass thru fsync, directories rely on this.
+    // 90% of time, we use DisableFsyncFS which omits the real calls.
+    for (String name : names) {
+      // randomly fail with IOE on any file
+      maybeThrowIOException(name);
+      in.sync(Collections.singleton(name));
+      unSyncedFiles.remove(name);
     }
   }
 
@@ -1051,20 +1031,38 @@
     public boolean isLocked() throws IOException {
       return delegateLock.isLocked();
     }
+  }  
+  
+  /** Use this when throwing fake {@code IOException},
+   *  e.g. from {@link MockDirectoryWrapper.Failure}. */
+  public static class FakeIOException extends IOException {
   }
 
-  // TODO: why does this class override this method?
-  // we should use the default implementation so all of our checks work?
   @Override
-  public synchronized void copyFrom(Directory from, String src, String dest, IOContext context) throws IOException {
-    maybeYield();
-    // randomize the IOContext here?
-    in.copyFrom(from, src, dest, context);
+  public String toString() {
+    if (maxSize != 0) {
+      return "MockDirectoryWrapper(" + in + ", current=" + maxUsedSize + ",max=" + maxSize + ")";
+    } else {
+      return super.toString();
+    }
   }
+
+
+  // don't override optional methods like copyFrom: we need the default impl for things like disk 
+  // full checks. we randomly exercise "raw" directories anyway. We ensure default impls are used:
   
-  /** Use this when throwing fake {@code IOException},
-   *  e.g. from {@link MockDirectoryWrapper.Failure}. */
-  public static class FakeIOException extends IOException {
+  @Override
+  public final ChecksumIndexInput openChecksumInput(String name, IOContext context) throws IOException {
+    return super.openChecksumInput(name, context);
   }
 
+  @Override
+  public final void copyFrom(Directory from, String src, String dest, IOContext context) throws IOException {
+    super.copyFrom(from, src, dest, context);
+  }
+
+  @Override
+  protected final void ensureOpen() throws AlreadyClosedException {
+    super.ensureOpen();
+  }
 }
Index: lucene/test-framework/src/java/org/apache/lucene/store/RawDirectoryWrapper.java
===================================================================
--- lucene/test-framework/src/java/org/apache/lucene/store/RawDirectoryWrapper.java	(revision 0)
+++ lucene/test-framework/src/java/org/apache/lucene/store/RawDirectoryWrapper.java	(working copy)
@@ -0,0 +1,49 @@
+package org.apache.lucene.store;
+
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+import java.io.IOException;
+
+/**
+ * Delegates all operations, even optional ones, to the wrapped directory.
+ * <p>
+ * This class is used if you want the most realistic testing, but still
+ * with a checkindex on close. If you want asserts and evil things,
+ * use MockDirectoryWrapper instead.
+ */
+public final class RawDirectoryWrapper extends BaseDirectoryWrapper {
+
+  public RawDirectoryWrapper(Directory delegate) {
+    super(delegate);
+  }
+  
+  @Override
+  public void copyFrom(Directory from, String src, String dest, IOContext context) throws IOException {
+    in.copyFrom(from, src, dest, context);
+  }
+  
+  @Override
+  public ChecksumIndexInput openChecksumInput(String name, IOContext context) throws IOException {
+    return in.openChecksumInput(name, context);
+  }
+
+  @Override
+  protected void ensureOpen() throws AlreadyClosedException {
+    in.ensureOpen();
+  }
+}

Property changes on: lucene/test-framework/src/java/org/apache/lucene/store/RawDirectoryWrapper.java
___________________________________________________________________
Added: svn:eol-style
## -0,0 +1 ##
+native
\ No newline at end of property
Index: lucene/test-framework/src/java/org/apache/lucene/util/LuceneTestCase.java
===================================================================
--- lucene/test-framework/src/java/org/apache/lucene/util/LuceneTestCase.java	(revision 1662487)
+++ lucene/test-framework/src/java/org/apache/lucene/util/LuceneTestCase.java	(working copy)
@@ -82,6 +82,7 @@
 import com.carrotsearch.randomizedtesting.rules.NoInstanceHooksOverridesRule;
 import com.carrotsearch.randomizedtesting.rules.StaticFieldsInvariantRule;
 import com.carrotsearch.randomizedtesting.rules.SystemPropertiesInvariantRule;
+
 import org.apache.lucene.analysis.Analyzer;
 import org.apache.lucene.analysis.MockAnalyzer;
 import org.apache.lucene.document.Field;
@@ -110,6 +111,7 @@
 import org.apache.lucene.store.MockDirectoryWrapper;
 import org.apache.lucene.store.MockDirectoryWrapper.Throttling;
 import org.apache.lucene.store.NRTCachingDirectory;
+import org.apache.lucene.store.RawDirectoryWrapper;
 import org.apache.lucene.util.automaton.AutomatonTestUtil;
 import org.apache.lucene.util.automaton.CompiledAutomaton;
 import org.apache.lucene.util.automaton.RegExp;
@@ -1317,7 +1319,7 @@
     }
 
     if (bare) {
-      BaseDirectoryWrapper base = new BaseDirectoryWrapper(directory);
+      BaseDirectoryWrapper base = new RawDirectoryWrapper(directory);
       closeAfterSuite(new CloseableDirectory(base, suiteFailureMarker));
       return base;
     } else {
Index: solr/core/src/java/org/apache/solr/search/SolrIndexSearcher.java
===================================================================
--- solr/core/src/java/org/apache/solr/search/SolrIndexSearcher.java	(revision 1662487)
+++ solr/core/src/java/org/apache/solr/search/SolrIndexSearcher.java	(working copy)
@@ -67,13 +67,13 @@
 import org.apache.lucene.util.Bits;
 import org.apache.lucene.util.BytesRef;
 import org.apache.lucene.util.FixedBitSet;
+import org.apache.solr.common.SolrException.ErrorCode;
 import org.apache.solr.common.SolrException;
-import org.apache.solr.common.SolrException.ErrorCode;
 import org.apache.solr.common.params.ModifiableSolrParams;
 import org.apache.solr.common.util.NamedList;
 import org.apache.solr.common.util.SimpleOrderedMap;
+import org.apache.solr.core.DirectoryFactory.DirContext;
 import org.apache.solr.core.DirectoryFactory;
-import org.apache.solr.core.DirectoryFactory.DirContext;
 import org.apache.solr.core.SolrConfig;
 import org.apache.solr.core.SolrCore;
 import org.apache.solr.core.SolrInfoMBean;
@@ -167,7 +167,7 @@
   
   // TODO: wrap elsewhere and return a "map" from the schema that overrides get() ?
   // this reader supports reopen
-  private static DirectoryReader wrapReader(SolrCore core, DirectoryReader reader) {
+  private static DirectoryReader wrapReader(SolrCore core, DirectoryReader reader) throws IOException {
     assert reader != null;
     return ExitableDirectoryReader.wrap
         (UninvertingReader.wrap(reader, core.getLatestSchema().getUninversionMap(reader)),