LUCENE-8292: Make TermsEnum fully abstract (#574)

lucene/CHANGES.txt

@@ -133,6 +133,8 @@ API Changes
 * LUCENE-8609: Remove IndexWriter#numDocs() and IndexWriter#maxDoc() in favor
   of IndexWriter#getDocStats(). (Simon Willnauer)
 
+* LUCENE-8292: Make TermsEnum fully abstract. (Simon Willnauer)
+
 Changes in Runtime Behavior
 
 * LUCENE-8333: Switch MoreLikeThis.setMaxDocFreqPct to use maxDoc instead of

lucene/MIGRATE.txt

@@ -1,11 +1,11 @@
 # Apache Lucene Migration Guide
 
-## TermsEnum.seekExact(BytesRef) is abstract (LUCENE-8662) ##
+## TermsEnum is now fully abstract (LUCENE-8292) ##
 
-TermsEnum.seekExact has been changed to abstract, so non-abstract subclass must implement it.
-The default implementation can be seekCeil(text) == SeekStatus.FOUND.
-This method is performance critical, so subclass SHOULD have its own implementation
-if possible instead of using the default implementation.
+TermsEnum has been changed to be fully abstract, so non-abstract subclass must implement all it's methods.
+Non-Performance critical TermsEnums can use BaseTermsEnum as a base class instead. The change was motivated
+by several performance issues with FilterTermsEnum that caused significant slowdowns and massive memory consumption due
+to not delegating all method from TermsEnum. See LUCENE-8292 and LUCENE-8662
 
 ## RAMDirectory, RAMFile, RAMInputStream, RAMOutputStream removed ##
 

lucene/backward-codecs/src/java/org/apache/lucene/codecs/lucene70/Lucene70DocValuesProducer.java

@@ -23,6 +23,7 @@ import java.util.Map;
 
 import org.apache.lucene.codecs.CodecUtil;
 import org.apache.lucene.codecs.DocValuesProducer;
+import org.apache.lucene.index.BaseTermsEnum;
 import org.apache.lucene.index.BinaryDocValues;
 import org.apache.lucene.index.CorruptIndexException;
 import org.apache.lucene.index.DocValues;
@@ -984,7 +985,7 @@ final class Lucene70DocValuesProducer extends DocValuesProducer implements Close
     }
   }
 
-  private static class TermsDict extends TermsEnum {
+  private static class TermsDict extends BaseTermsEnum {
 
     final TermsDictEntry entry;
     final LongValues blockAddresses;
@@ -1031,11 +1032,6 @@ final class Lucene70DocValuesProducer extends DocValuesProducer implements Close
       return term;
     }
 
-    @Override
-    public boolean seekExact(BytesRef text) throws IOException {
-      return seekCeil(text) == SeekStatus.FOUND;
-    }
-    
     @Override
     public void seekExact(long ord) throws IOException {
       if (ord < 0 || ord >= entry.termsDictSize) {

lucene/codecs/src/java/org/apache/lucene/codecs/blockterms/BlockTermsReader.java

@@ -29,6 +29,7 @@ import org.apache.lucene.codecs.BlockTermState;
 import org.apache.lucene.codecs.CodecUtil;
 import org.apache.lucene.codecs.FieldsProducer;
 import org.apache.lucene.codecs.PostingsReaderBase;
+import org.apache.lucene.index.BaseTermsEnum;
 import org.apache.lucene.index.CorruptIndexException;
 import org.apache.lucene.index.FieldInfo;
 import org.apache.lucene.index.ImpactsEnum;
@@ -286,7 +287,7 @@ public class BlockTermsReader extends FieldsProducer {
     }
 
     // Iterates through terms in this field
-    private final class SegmentTermsEnum extends TermsEnum {
+    private final class SegmentTermsEnum extends BaseTermsEnum {
       private final IndexInput in;
       private final BlockTermState state;
       private final boolean doOrd;
@@ -685,11 +686,6 @@ public class BlockTermsReader extends FieldsProducer {
         return ts;
       }
 
-      @Override
-      public boolean seekExact(BytesRef text) throws IOException {
-        return seekCeil(text) == SeekStatus.FOUND;
-      }
-      
       @Override
       public void seekExact(long ord) throws IOException {
         //System.out.println("BTR.seek by ord ord=" + ord);

lucene/codecs/src/java/org/apache/lucene/codecs/blocktreeords/OrdsIntersectTermsEnum.java

@@ -20,10 +20,10 @@ package org.apache.lucene.codecs.blocktreeords;
 import java.io.IOException;
 
 import org.apache.lucene.codecs.blocktreeords.FSTOrdsOutputs.Output;
+import org.apache.lucene.index.BaseTermsEnum;
 import org.apache.lucene.index.ImpactsEnum;
 import org.apache.lucene.index.PostingsEnum;
 import org.apache.lucene.index.TermState;
-import org.apache.lucene.index.TermsEnum;
 import org.apache.lucene.store.IndexInput;
 import org.apache.lucene.util.ArrayUtil;
 import org.apache.lucene.util.BytesRef;
@@ -34,7 +34,7 @@ import org.apache.lucene.util.automaton.RunAutomaton;
 import org.apache.lucene.util.fst.FST;
 
 // NOTE: cannot seek!
-final class OrdsIntersectTermsEnum extends TermsEnum {
+final class OrdsIntersectTermsEnum extends BaseTermsEnum {
   final IndexInput in;
 
   private OrdsIntersectTermsEnumFrame[] stack;

lucene/codecs/src/java/org/apache/lucene/codecs/blocktreeords/OrdsSegmentTermsEnum.java

@@ -25,10 +25,10 @@ import java.io.PrintStream;
 
 import org.apache.lucene.codecs.BlockTermState;
 import org.apache.lucene.codecs.blocktreeords.FSTOrdsOutputs.Output;
+import org.apache.lucene.index.BaseTermsEnum;
 import org.apache.lucene.index.ImpactsEnum;
 import org.apache.lucene.index.PostingsEnum;
 import org.apache.lucene.index.TermState;
-import org.apache.lucene.index.TermsEnum;
 import org.apache.lucene.store.ByteArrayDataInput;
 import org.apache.lucene.store.IndexInput;
 import org.apache.lucene.util.ArrayUtil;
@@ -41,7 +41,7 @@ import org.apache.lucene.util.fst.FST;
 import org.apache.lucene.util.fst.Util;
 
 /** Iterates through terms in this field. */
-public final class OrdsSegmentTermsEnum extends TermsEnum {
+public final class OrdsSegmentTermsEnum extends BaseTermsEnum {
 
   // Lazy init:
   IndexInput in;

lucene/codecs/src/java/org/apache/lucene/codecs/bloom/BloomFilteringPostingsFormat.java

@@ -32,6 +32,7 @@ import org.apache.lucene.codecs.FieldsProducer;
 import org.apache.lucene.codecs.NormsProducer;
 import org.apache.lucene.codecs.PostingsFormat;
 import org.apache.lucene.codecs.bloom.FuzzySet.ContainsResult;
+import org.apache.lucene.index.BaseTermsEnum;
 import org.apache.lucene.index.FieldInfo;
 import org.apache.lucene.index.Fields;
 import org.apache.lucene.index.ImpactsEnum;
@@ -291,7 +292,7 @@ public final class BloomFilteringPostingsFormat extends PostingsFormat {
       }
     }
 
-    static final class BloomFilteredTermsEnum extends TermsEnum {
+    static final class BloomFilteredTermsEnum extends BaseTermsEnum {
       private Terms delegateTerms;
       private TermsEnum delegateTermsEnum;
       private final FuzzySet filter;

lucene/codecs/src/java/org/apache/lucene/codecs/memory/DirectPostingsFormat.java

@@ -27,6 +27,7 @@ import org.apache.lucene.codecs.FieldsConsumer;
 import org.apache.lucene.codecs.FieldsProducer;
 import org.apache.lucene.codecs.PostingsFormat;
 import org.apache.lucene.codecs.lucene50.Lucene50PostingsFormat;
+import org.apache.lucene.index.BaseTermsEnum;
 import org.apache.lucene.index.FieldInfo;
 import org.apache.lucene.index.Fields;
 import org.apache.lucene.index.ImpactsEnum;
@@ -699,7 +700,7 @@ public final class DirectPostingsFormat extends PostingsFormat {
       return hasPayloads;
     }
 
-    private final class DirectTermsEnum extends TermsEnum {
+    private final class DirectTermsEnum extends BaseTermsEnum {
 
       private final BytesRef scratch = new BytesRef();
       private int termOrd;
@@ -944,7 +945,7 @@ public final class DirectPostingsFormat extends PostingsFormat {
       }
     }
 
-    private final class DirectIntersectTermsEnum extends TermsEnum {
+    private final class DirectIntersectTermsEnum extends BaseTermsEnum {
       private final RunAutomaton runAutomaton;
       private final CompiledAutomaton compiledAutomaton;
       private int termOrd;
@@ -1508,10 +1509,6 @@ public final class DirectPostingsFormat extends PostingsFormat {
         throw new UnsupportedOperationException();
       }
       
-      @Override
-      public boolean seekExact(BytesRef text) throws IOException {
-        return seekCeil(text) == SeekStatus.FOUND;
-      }
     }
   }
 

lucene/codecs/src/java/org/apache/lucene/codecs/memory/FSTOrdTermsReader.java

@@ -305,7 +305,7 @@ public class FSTOrdTermsReader extends FieldsProducer {
     }
 
     // Only wraps common operations for PBF interact
-    abstract class BaseTermsEnum extends TermsEnum {
+    abstract class BaseTermsEnum extends org.apache.lucene.index.BaseTermsEnum {
 
       /* Current term's ord, starts from 0 */
       long ord;
@@ -626,11 +626,6 @@ public class FSTOrdTermsReader extends FieldsProducer {
         super.decodeStats();
       }
 
-      @Override
-      public boolean seekExact(BytesRef text) throws IOException {
-        return seekCeil(text) == SeekStatus.FOUND;
-      }
-      
       @Override
       public SeekStatus seekCeil(BytesRef target) throws IOException {
         throw new UnsupportedOperationException();

lucene/codecs/src/java/org/apache/lucene/codecs/memory/FSTTermsReader.java

@@ -259,7 +259,7 @@ public class FSTTermsReader extends FieldsProducer {
     }
 
     // Only wraps common operations for PBF interact
-    abstract class BaseTermsEnum extends TermsEnum {
+    abstract class BaseTermsEnum extends org.apache.lucene.index.BaseTermsEnum {
 
       /* Current term stats + decoded metadata (customized by PBF) */
       final BlockTermState state;
@@ -519,11 +519,6 @@ public class FSTTermsReader extends FieldsProducer {
         state.totalTermFreq = meta.totalTermFreq;
       }
 
-      @Override
-      public boolean seekExact(BytesRef text) throws IOException {
-        return seekCeil(text) == SeekStatus.FOUND;
-      }
-      
       @Override
       public SeekStatus seekCeil(BytesRef target) throws IOException {
         decoded = false;

lucene/codecs/src/java/org/apache/lucene/codecs/simpletext/SimpleTextFieldsReader.java

@@ -27,6 +27,7 @@ import java.util.Map;
 import java.util.TreeMap;
 
 import org.apache.lucene.codecs.FieldsProducer;
+import org.apache.lucene.index.BaseTermsEnum;
 import org.apache.lucene.index.FieldInfo;
 import org.apache.lucene.index.FieldInfos;
 import org.apache.lucene.index.ImpactsEnum;
@@ -111,7 +112,7 @@ class SimpleTextFieldsReader extends FieldsProducer {
     }
   }
 
-  private class SimpleTextTermsEnum extends TermsEnum {
+  private class SimpleTextTermsEnum extends BaseTermsEnum {
     private final IndexOptions indexOptions;
     private int docFreq;
     private long totalTermFreq;

lucene/codecs/src/java/org/apache/lucene/codecs/simpletext/SimpleTextTermVectorsReader.java

@@ -25,6 +25,7 @@ import java.util.SortedMap;
 import java.util.TreeMap;
 
 import org.apache.lucene.codecs.TermVectorsReader;
+import org.apache.lucene.index.BaseTermsEnum;
 import org.apache.lucene.index.Fields;
 import org.apache.lucene.index.ImpactsEnum;
 import org.apache.lucene.index.IndexFileNames;
@@ -338,7 +339,7 @@ public class SimpleTextTermVectorsReader extends TermVectorsReader {
     private BytesRef payloads[];
   }
 
-  private static class SimpleTVTermsEnum extends TermsEnum {
+  private static class SimpleTVTermsEnum extends BaseTermsEnum {
     SortedMap<BytesRef,SimpleTVPostings> terms;
     Iterator<Map.Entry<BytesRef,SimpleTextTermVectorsReader.SimpleTVPostings>> iterator;
     Map.Entry<BytesRef,SimpleTextTermVectorsReader.SimpleTVPostings> current;
@@ -358,11 +359,6 @@ public class SimpleTextTermVectorsReader extends TermVectorsReader {
       }
     }
 
-    @Override
-    public boolean seekExact(BytesRef text) throws IOException {
-      return seekCeil(text) == SeekStatus.FOUND;
-    }
-    
     @Override
     public void seekExact(long ord) throws IOException {
       throw new UnsupportedOperationException();

lucene/core/src/java/org/apache/lucene/codecs/blocktree/IntersectTermsEnum.java

@@ -19,11 +19,11 @@ package org.apache.lucene.codecs.blocktree;
 
 import java.io.IOException;
 
+import org.apache.lucene.index.BaseTermsEnum;
 import org.apache.lucene.index.ImpactsEnum;
 import org.apache.lucene.index.PostingsEnum;
 import org.apache.lucene.index.TermState;
 import org.apache.lucene.index.Terms;
-import org.apache.lucene.index.TermsEnum;
 import org.apache.lucene.store.IndexInput;
 import org.apache.lucene.util.ArrayUtil;
 import org.apache.lucene.util.BytesRef;
@@ -44,7 +44,7 @@ import org.apache.lucene.util.fst.Outputs;
  *  Likewise, in next it scans until it finds a term that matches the
  *  current automaton transition. */
 
-final class IntersectTermsEnum extends TermsEnum {
+final class IntersectTermsEnum extends BaseTermsEnum {
 
   //static boolean DEBUG = BlockTreeTermsWriter.DEBUG;
 

lucene/core/src/java/org/apache/lucene/codecs/blocktree/SegmentTermsEnum.java

@@ -21,10 +21,10 @@ import java.io.IOException;
 import java.io.PrintStream;
 
 import org.apache.lucene.codecs.BlockTermState;
+import org.apache.lucene.index.BaseTermsEnum;
 import org.apache.lucene.index.ImpactsEnum;
 import org.apache.lucene.index.PostingsEnum;
 import org.apache.lucene.index.TermState;
-import org.apache.lucene.index.TermsEnum;
 import org.apache.lucene.store.ByteArrayDataInput;
 import org.apache.lucene.store.IndexInput;
 import org.apache.lucene.util.ArrayUtil;
@@ -36,7 +36,7 @@ import org.apache.lucene.util.fst.Util;
 
 /** Iterates through terms in this field. */
 
-final class SegmentTermsEnum extends TermsEnum {
+final class SegmentTermsEnum extends BaseTermsEnum {
 
   // Lazy init:
   IndexInput in;

lucene/core/src/java/org/apache/lucene/codecs/compressing/CompressingTermVectorsReader.java

@@ -26,6 +26,7 @@ import java.util.NoSuchElementException;
 
 import org.apache.lucene.codecs.CodecUtil;
 import org.apache.lucene.codecs.TermVectorsReader;
+import org.apache.lucene.index.BaseTermsEnum;
 import org.apache.lucene.index.CorruptIndexException;
 import org.apache.lucene.index.SlowImpactsEnum;
 import org.apache.lucene.index.PostingsEnum;
@@ -825,7 +826,7 @@ public final class CompressingTermVectorsReader extends TermVectorsReader implem
 
   }
 
-  private static class TVTermsEnum extends TermsEnum {
+  private static class TVTermsEnum extends BaseTermsEnum {
 
     private int numTerms, startPos, ord;
     private int[] prefixLengths, suffixLengths, termFreqs, positionIndex, positions, startOffsets, lengths, payloadIndex;
@@ -906,11 +907,6 @@ public final class CompressingTermVectorsReader extends TermVectorsReader implem
       }
     }
 
-    @Override
-    public boolean seekExact(BytesRef text) throws IOException {
-      return seekCeil(text) == SeekStatus.FOUND;
-    }
-    
     @Override
     public void seekExact(long ord) throws IOException {
       throw new UnsupportedOperationException();

lucene/core/src/java/org/apache/lucene/codecs/lucene80/Lucene80DocValuesProducer.java

@@ -23,6 +23,7 @@ import java.util.Map;
 
 import org.apache.lucene.codecs.CodecUtil;
 import org.apache.lucene.codecs.DocValuesProducer;
+import org.apache.lucene.index.BaseTermsEnum;
 import org.apache.lucene.index.BinaryDocValues;
 import org.apache.lucene.index.CorruptIndexException;
 import org.apache.lucene.index.DocValues;
@@ -926,7 +927,7 @@ final class Lucene80DocValuesProducer extends DocValuesProducer implements Close
     }
   }
 
-  private static class TermsDict extends TermsEnum {
+  private static class TermsDict extends BaseTermsEnum {
 
     final TermsDictEntry entry;
     final LongValues blockAddresses;
@@ -973,11 +974,6 @@ final class Lucene80DocValuesProducer extends DocValuesProducer implements Close
       return term;
     }
 
-    @Override
-    public boolean seekExact(BytesRef text) throws IOException {
-      return seekCeil(text) == SeekStatus.FOUND;
-    }
-    
     @Override
     public void seekExact(long ord) throws IOException {
       if (ord < 0 || ord >= entry.termsDictSize) {

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

@@ -0,0 +1,75 @@
+/*
+ * 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.
+ */
+
+package org.apache.lucene.index;
+
+import java.io.IOException;
+
+import org.apache.lucene.util.AttributeSource;
+import org.apache.lucene.util.BytesRef;
+
+/**
+ * A base TermsEnum that adds default implementations for
+ * <ul>
+ *   <li>{@link #attributes()}</li>
+ *   <li>{@link #termState()}</li>
+ *   <li>{@link #seekExact(BytesRef)}</li>
+ *   <li>{@link #seekExact(BytesRef, TermState)}</li>
+ * </ul>
+ *
+ * In some cases, the default implementation may be slow and consume huge memory, so subclass SHOULD have its own
+ * implementation if possible.
+ */
+public abstract class BaseTermsEnum extends TermsEnum {
+
+  private AttributeSource atts = null;
+  
+  /** Sole constructor. (For invocation by subclass
+   *  constructors, typically implicit.) */
+  protected BaseTermsEnum() {
+    super();
+  }
+
+  @Override
+  public TermState termState() throws IOException {
+    return new TermState() {
+      @Override
+      public void copyFrom(TermState other) {
+        throw new UnsupportedOperationException();
+      }
+    };
+  }
+
+  @Override
+  public boolean seekExact(BytesRef text) throws IOException {
+    return seekCeil(text) == SeekStatus.FOUND;
+  }
+
+  @Override
+  public void seekExact(BytesRef term, TermState state) throws IOException {
+    if (!seekExact(term)) {
+      throw new IllegalArgumentException("term=" + term + " does not exist");
+    }
+  }
+
+  public AttributeSource attributes() {
+    if (atts == null) {
+      atts = new AttributeSource();
+    }
+    return atts;
+  }
+}

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

@@ -223,6 +223,16 @@ public abstract class FilterLeafReader extends LeafReader {
     public ImpactsEnum impacts(int flags) throws IOException {
       return in.impacts(flags);
     }
+
+    @Override
+    public void seekExact(BytesRef term, TermState state) throws IOException {
+      in.seekExact(term, state);
+    }
+
+    @Override
+    public TermState termState() throws IOException {
+      return in.termState();
+    }
   }
 
   /** Base class for filtering {@link PostingsEnum} implementations. */

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

@@ -124,7 +124,7 @@ class FreqProxFields extends Fields {
     }
   }
 
-  private static class FreqProxTermsEnum extends TermsEnum {
+  private static class FreqProxTermsEnum extends BaseTermsEnum {
     final FreqProxTermsWriterPerField terms;
     final int[] sortedTermIDs;
     final FreqProxPostingsArray postingsArray;
@@ -180,11 +180,6 @@ class FreqProxFields extends Fields {
       }
     }
 
-    @Override
-    public boolean seekExact(BytesRef text) throws IOException {
-      return seekCeil(text) == SeekStatus.FOUND;
-    }
-    
     public void seekExact(long ord) {
       this.ord = (int) ord;
       int textStart = postingsArray.textStarts[sortedTermIDs[this.ord]];

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

@@ -32,7 +32,7 @@ import org.apache.lucene.util.PriorityQueue;
  *
  * @lucene.experimental
  */
-public final class MultiTermsEnum extends TermsEnum {
+public final class MultiTermsEnum extends BaseTermsEnum {
 
   private static final Comparator<TermsEnumWithSlice> INDEX_COMPARATOR = new Comparator<TermsEnumWithSlice>() {
     @Override

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

@@ -25,7 +25,7 @@ import org.apache.lucene.util.BytesRefBuilder;
 /** Implements a {@link TermsEnum} wrapping a provided
  * {@link SortedDocValues}. */
 
-class SortedDocValuesTermsEnum extends TermsEnum {
+class SortedDocValuesTermsEnum extends BaseTermsEnum {
   private final SortedDocValues values;
   private int currentOrd = -1;
   private final BytesRefBuilder scratch;

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

@@ -25,7 +25,7 @@ import java.io.IOException;
 /** Implements a {@link TermsEnum} wrapping a provided
  * {@link SortedSetDocValues}. */
 
-class SortedSetDocValuesTermsEnum extends TermsEnum {
+class SortedSetDocValuesTermsEnum extends BaseTermsEnum {
   private final SortedSetDocValues values;
   private long currentOrd = -1;
   private final BytesRefBuilder scratch;

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

@@ -42,21 +42,16 @@ import org.apache.lucene.util.BytesRefIterator;
  * @lucene.experimental */
 public abstract class TermsEnum implements BytesRefIterator {
 
-  private AttributeSource atts = null;
-
   /** Sole constructor. (For invocation by subclass 
    *  constructors, typically implicit.) */
   protected TermsEnum() {
   }
 
   /** Returns the related attributes. */
-  public AttributeSource attributes() {
-    if (atts == null) atts = new AttributeSource();
-    return atts;
-  }
+  public abstract AttributeSource attributes();
   
   /** Represents returned result from {@link #seekCeil}. */
-  public static enum SeekStatus {
+  public enum SeekStatus {
     /** The term was not found, and the end of iteration was hit. */
     END,
     /** The precise term was found. */
@@ -70,15 +65,11 @@ public abstract class TermsEnum implements BytesRefIterator {
    * unpositioned. For some codecs, seekExact may be substantially faster than {@link #seekCeil}.
    * <p>
    * 
-   * The default implementation can be <code>seekCeil(text) == SeekStatus.FOUND; </code><br>
-   * But this method is performance critical. In some cases, the default implementation may be slow and consume huge memory,
-   * so subclass SHOULD have its own implementation if possible.
-   * 
+   *
    * @return true if the term is found; return false if the enum is unpositioned.
    */
   public abstract boolean seekExact(BytesRef text) throws IOException;
 
-
   /** Seeks to the specified term, if it exists, or to the
    *  next (ceiling) term.  Returns SeekStatus to
    *  indicate whether exact term was found, a different
@@ -114,11 +105,7 @@ public abstract class TermsEnum implements BytesRefIterator {
    * @param term the term the TermState corresponds to
    * @param state the {@link TermState}
    * */
-  public void seekExact(BytesRef term, TermState state) throws IOException {
-    if (!seekExact(term)) {
-      throw new IllegalArgumentException("term=" + term + " does not exist");
-    }
-  }
+  public abstract void seekExact(BytesRef term, TermState state) throws IOException;
 
   /** Returns current term. Do not call this when the enum
    *  is unpositioned. */
@@ -192,14 +179,7 @@ public abstract class TermsEnum implements BytesRefIterator {
    * @see TermState
    * @see #seekExact(BytesRef, TermState)
    */
-  public TermState termState() throws IOException {
-    return new TermState() {
-      @Override
-      public void copyFrom(TermState other) {
-        throw new UnsupportedOperationException();
-      }
-    };
-  }
+  public abstract TermState termState() throws IOException;
 
   /** An empty TermsEnum for quickly returning an empty instance e.g.
    * in {@link org.apache.lucene.search.MultiTermQuery}
@@ -208,15 +188,10 @@ public abstract class TermsEnum implements BytesRefIterator {
    * This should not be a problem, as the enum is always empty and
    * the existence of unused Attributes does not matter.
    */
-  public static final TermsEnum EMPTY = new TermsEnum() {    
+  public static final TermsEnum EMPTY = new BaseTermsEnum() {
     @Override
     public SeekStatus seekCeil(BytesRef term) { return SeekStatus.END; }
     
-    @Override
-    public boolean seekExact(BytesRef text) throws IOException {
-      return seekCeil(text) == SeekStatus.FOUND;
-    }
-    
     @Override
     public void seekExact(long ord) {}
     

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

@@ -17,6 +17,7 @@
 package org.apache.lucene.search;
 
 
+import org.apache.lucene.index.BaseTermsEnum;
 import org.apache.lucene.index.ImpactsEnum;
 import org.apache.lucene.index.PostingsEnum;
 import org.apache.lucene.index.Term;
@@ -44,7 +45,7 @@ import java.util.Arrays;
  * {@link BytesRef#compareTo}.  Each term in the enumeration is
  * greater than all that precede it.</p>
  */
-public final class FuzzyTermsEnum extends TermsEnum {
+public final class FuzzyTermsEnum extends BaseTermsEnum {
 
   // NOTE: we can't subclass FilteredTermsEnum here because we need to sometimes change actualEnum:
   private TermsEnum actualEnum;

lucene/core/src/test/org/apache/lucene/index/TestCodecs.java

@@ -613,7 +613,7 @@ public class TestCodecs extends LuceneTestCase {
     }
   }
 
-  private static class DataTermsEnum extends TermsEnum {
+  private static class DataTermsEnum extends BaseTermsEnum {
     final FieldData fieldData;
     private int upto = -1;
 
@@ -653,11 +653,6 @@ public class TestCodecs extends LuceneTestCase {
       return SeekStatus.END;
     }
 
-    @Override
-    public boolean seekExact(BytesRef text) throws IOException {
-      return seekCeil(text) == SeekStatus.FOUND;
-    }
-    
     @Override
     public void seekExact(long ord) {
       throw new UnsupportedOperationException();

lucene/memory/src/java/org/apache/lucene/index/memory/MemoryIndex.java

@@ -1333,7 +1333,7 @@ public class MemoryIndex {
       }
     }
 
-    private class MemoryTermsEnum extends TermsEnum {
+    private class MemoryTermsEnum extends BaseTermsEnum {
       private final Info info;
       private final BytesRef br = new BytesRef();
       int termUpto = -1;

lucene/sandbox/src/java/org/apache/lucene/codecs/idversion/IDVersionSegmentTermsEnum.java

@@ -20,11 +20,11 @@ import java.io.IOException;
 import java.io.PrintStream;
 
 import org.apache.lucene.codecs.BlockTermState;
+import org.apache.lucene.index.BaseTermsEnum;
 import org.apache.lucene.index.ImpactsEnum;
 import org.apache.lucene.index.PostingsEnum;
 import org.apache.lucene.index.SlowImpactsEnum;
 import org.apache.lucene.index.TermState;
-import org.apache.lucene.index.TermsEnum;
 import org.apache.lucene.store.ByteArrayDataInput;
 import org.apache.lucene.store.IndexInput;
 import org.apache.lucene.util.ArrayUtil;
@@ -39,7 +39,7 @@ import org.apache.lucene.util.fst.Util;
  *  can cast it to call {@link #seekExact(BytesRef, long)} for
  *  optimistic-concurrency, and also {@link #getVersion} to get the
  *  version of the currently seek'd term. */
-public final class IDVersionSegmentTermsEnum extends TermsEnum {
+public final class IDVersionSegmentTermsEnum extends BaseTermsEnum {
 
   // Lazy init:
   IndexInput in;

lucene/test-framework/src/java/org/apache/lucene/codecs/ramonly/RAMOnlyPostingsFormat.java

@@ -34,6 +34,7 @@ import org.apache.lucene.codecs.FieldsProducer;
 import org.apache.lucene.codecs.NormsProducer;
 import org.apache.lucene.codecs.PostingsFormat;
 import org.apache.lucene.codecs.TermStats;
+import org.apache.lucene.index.BaseTermsEnum;
 import org.apache.lucene.index.PostingsEnum;
 import org.apache.lucene.index.FieldInfo;
 import org.apache.lucene.index.Fields;
@@ -403,7 +404,7 @@ public final class RAMOnlyPostingsFormat extends PostingsFormat {
     }
   }
 
-  static class RAMTermsEnum extends TermsEnum {
+  static class RAMTermsEnum extends BaseTermsEnum {
     Iterator<String> it;
     String current;
     private final RAMField ramField;
@@ -444,11 +445,6 @@ public final class RAMOnlyPostingsFormat extends PostingsFormat {
       }
     }
     
-    @Override
-    public boolean seekExact(BytesRef text) throws IOException {
-      return seekCeil(text) == SeekStatus.FOUND;
-    }    
-
     @Override
     public void seekExact(long ord) {
       throw new UnsupportedOperationException();

lucene/test-framework/src/java/org/apache/lucene/index/RandomPostingsTester.java

@@ -519,7 +519,7 @@ public class RandomPostingsTester {
     }
   }
 
-  private static class SeedTermsEnum extends TermsEnum {
+  private static class SeedTermsEnum extends BaseTermsEnum {
     final SortedMap<BytesRef,SeedAndOrd> terms;
     final IndexOptions maxAllowed;
     final boolean allowPayloads;
@@ -564,11 +564,6 @@ public class RandomPostingsTester {
       }
     }
 
-    @Override
-    public boolean seekExact(BytesRef text) throws IOException {
-      return seekCeil(text) == SeekStatus.FOUND;
-    }
-    
     @Override
     public void seekExact(long ord) {
       throw new UnsupportedOperationException();

solr/core/src/java/org/apache/solr/query/SolrRangeQuery.java

@@ -20,6 +20,7 @@ import java.io.IOException;
 import java.util.ArrayList;
 import java.util.List;
 
+import org.apache.lucene.index.BaseTermsEnum;
 import org.apache.lucene.index.ImpactsEnum;
 import org.apache.lucene.index.IndexReader;
 import org.apache.lucene.index.LeafReaderContext;
@@ -176,7 +177,7 @@ public final class SolrRangeQuery extends ExtendedQueryBase implements DocSetPro
   }
 
 
-  private class RangeTermsEnum extends TermsEnum {
+  private class RangeTermsEnum extends BaseTermsEnum {
 
     TermsEnum te;
     BytesRef curr;

solr/core/src/java/org/apache/solr/uninverting/DocTermOrds.java

@@ -23,6 +23,7 @@ import java.util.List;
 import java.util.concurrent.TimeUnit;
 
 import org.apache.lucene.codecs.PostingsFormat;
+import org.apache.lucene.index.BaseTermsEnum;
 import org.apache.lucene.index.DocValues;
 import org.apache.lucene.index.DocValuesType;
 import org.apache.lucene.index.FieldInfo;
@@ -589,7 +590,7 @@ public class DocTermOrds implements Accountable {
    * "wrap" our own terms index around the original IndexReader. 
    * Only valid if there are terms for this field rom the original reader
    */
-  private final class OrdWrappedTermsEnum extends TermsEnum {
+  private final class OrdWrappedTermsEnum extends BaseTermsEnum {
     private final TermsEnum termsEnum;
     private BytesRef term;
     private long ord = -indexInterval-1;          // force "real" seek
@@ -703,11 +704,6 @@ public class DocTermOrds implements Accountable {
       }
     }
 
-    @Override
-    public boolean seekExact(BytesRef text) throws IOException {
-      return seekCeil(text) == SeekStatus.FOUND;
-    }
-    
     @Override
     public void seekExact(long targetOrd) throws IOException {
       int delta = (int) (targetOrd - ordBase - ord);