MNDQ.patch

diff --git a/lucene/core/src/java/org/apache/lucene/search/BooleanQuery.java b/lucene/core/src/java/org/apache/lucene/search/BooleanQuery.java
index 209a6dc..d0f5df0 100644
--- a/lucene/core/src/java/org/apache/lucene/search/BooleanQuery.java
+++ b/lucene/core/src/java/org/apache/lucene/search/BooleanQuery.java
@@ -165,6 +165,9 @@ public class BooleanQuery extends Query implements Iterable<BooleanClause> {
 
   @Override
   public Query rewrite(IndexReader reader) throws IOException {
+    if (clauses.size() == 0) {
+      return new MatchNoDocsQuery();
+    }
     if (minNrShouldMatch == 0 && clauses.size() == 1) {                    // optimize 1-clause queries
       BooleanClause c = clauses.get(0);
       if (!c.isProhibited()) {  // just return clause
diff --git a/lucene/core/src/java/org/apache/lucene/search/MatchNoDocsQuery.java b/lucene/core/src/java/org/apache/lucene/search/MatchNoDocsQuery.java
new file mode 100644
index 0000000..c2aff7d
--- /dev/null
+++ b/lucene/core/src/java/org/apache/lucene/search/MatchNoDocsQuery.java
@@ -0,0 +1,150 @@
+package org.apache.lucene.search;
+
+/*
+ * 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;
+import java.util.Set;
+
+import org.apache.lucene.index.IndexReader;
+import org.apache.lucene.index.LeafReaderContext;
+import org.apache.lucene.index.Term;
+import org.apache.lucene.util.Bits;
+import org.apache.lucene.util.ToStringUtils;
+
+/**
+ * A query that matches no documents.
+ */
+public class MatchNoDocsQuery extends Query {
+
+    private class MatchNoScorer extends Scorer {
+        final float score;
+
+        MatchNoScorer(IndexReader reader, Bits liveDocs, Weight w, float score) {
+            super(w);
+            this.score = score;
+        }
+
+        @Override
+        public int docID() {
+            return -1;
+        }
+
+        @Override
+        public int nextDoc() throws IOException {
+            return NO_MORE_DOCS;
+        }
+
+        @Override
+        public float score() {
+            return score;
+        }
+
+        @Override
+        public int freq() {
+            return 1;
+        }
+
+        @Override
+        public int advance(int target) throws IOException {
+            return NO_MORE_DOCS;
+        }
+
+        @Override
+        public long cost() {
+            // Cost of 0, because this immediately returns NO_MORE_DOCS
+            return 0;
+        }
+    }
+
+    private class MatchNoDocsWeight extends Weight {
+        private float queryWeight;
+        private float queryNorm;
+
+        public MatchNoDocsWeight(IndexSearcher searcher) {
+            super(MatchNoDocsQuery.this);
+        }
+
+        @Override
+        public String toString() {
+            return "weight(" + MatchNoDocsQuery.this + ")";
+        }
+
+        @Override
+        public float getValueForNormalization() {
+            queryWeight = getBoost();
+            return queryWeight * queryWeight;
+        }
+
+        @Override
+        public void normalize(float queryNorm, float topLevelBoost) {
+            this.queryNorm = queryNorm * topLevelBoost;
+            queryWeight *= this.queryNorm;
+        }
+
+        @Override
+        public Scorer scorer(LeafReaderContext context, Bits acceptDocs) throws IOException {
+            return new MatchNoScorer(context.reader(), acceptDocs, this, queryWeight);
+        }
+
+        @Override
+        public Explanation explain(LeafReaderContext context, int doc) {
+            // explain query weight
+            ComplexExplanation queryExpl = new ComplexExplanation
+                    (true, queryWeight, "MatchNoDocsQuery, product of:");
+            if (getBoost() != 1.0f) {
+                queryExpl.addDetail(new Explanation(getBoost(),"boost"));
+            }
+            queryExpl.addDetail(new Explanation(queryNorm,"queryNorm"));
+            queryExpl.setValue(0.0f);
+            queryExpl.setMatch(Boolean.FALSE);
+            return queryExpl;
+        }
+    }
+
+    @Override
+    public Weight createWeight(IndexSearcher searcher, boolean needsScores) {
+        return new MatchNoDocsWeight(searcher);
+    }
+
+    @Override
+    public void extractTerms(Set<Term> terms) {
+    }
+
+    @Override
+    public String toString(String field) {
+        StringBuilder buffer = new StringBuilder();
+        buffer.append("_none_");
+        buffer.append(ToStringUtils.boost(getBoost()));
+        return buffer.toString();
+    }
+
+    @Override
+    public boolean equals(Object o) {
+        if (!(o instanceof MatchNoDocsQuery)) {
+            return false;
+        }
+        MatchNoDocsQuery other = (MatchNoDocsQuery) o;
+        return this.getBoost() == other.getBoost();
+    }
+
+    @Override
+    public int hashCode() {
+        // nocommit - I don't know where 0x1AA71190 comes from here, it may need to be changed
+        return Float.floatToIntBits(getBoost()) ^ 0x1AA71190;
+    }
+}
diff --git a/lucene/core/src/test/org/apache/lucene/search/TestMatchNoDocsQuery.java b/lucene/core/src/test/org/apache/lucene/search/TestMatchNoDocsQuery.java
new file mode 100644
index 0000000..6f8adfc
--- /dev/null
+++ b/lucene/core/src/test/org/apache/lucene/search/TestMatchNoDocsQuery.java
@@ -0,0 +1,85 @@
+/*
+ * 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.search;
+
+import java.io.IOException;
+
+import org.apache.lucene.analysis.Analyzer;
+import org.apache.lucene.analysis.MockAnalyzer;
+import org.apache.lucene.document.Document;
+import org.apache.lucene.document.Field;
+import org.apache.lucene.index.DirectoryReader;
+import org.apache.lucene.index.IndexWriter;
+import org.apache.lucene.index.Term;
+import org.apache.lucene.index.IndexReader;
+import org.apache.lucene.store.Directory;
+
+import org.apache.lucene.util.LuceneTestCase;
+
+/**
+ * Tests MatchNoDocsQuery.
+ *
+ */
+public class TestMatchNoDocsQuery extends LuceneTestCase {
+  private Analyzer analyzer;
+
+  @Override
+  public void setUp() throws Exception {
+    super.setUp();
+    analyzer = new MockAnalyzer(random());
+  }
+
+  public void testQuery() throws Exception {
+    Directory dir = newDirectory();
+    IndexWriter iw = new IndexWriter(dir, newIndexWriterConfig(analyzer).setMaxBufferedDocs(2).setMergePolicy(newLogMergePolicy()));
+    addDoc("one", iw);
+    addDoc("two", iw);
+    addDoc("three four", iw);
+    IndexReader ir = DirectoryReader.open(iw, true);
+
+    IndexSearcher is = newSearcher(ir);
+    ScoreDoc[] hits;
+
+    hits = is.search(new MatchNoDocsQuery(), 1000).scoreDocs;
+    assertEquals(0, hits.length);
+
+    // An empty BooleanQuery rewrites to MatchNoDocsQuery()
+    BooleanQuery bq = new BooleanQuery();
+    Query rewritten = bq.rewrite(ir);
+    assertTrue(rewritten instanceof MatchNoDocsQuery);
+    hits = is.search(bq, 1000).scoreDocs;
+    assertEquals(0, hits.length);
+
+    iw.close();
+    ir.close();
+    dir.close();
+  }
+
+  public void testEquals() {
+    Query q1 = new MatchNoDocsQuery();
+    Query q2 = new MatchNoDocsQuery();
+    assertTrue(q1.equals(q2));
+  }
+
+  private void addDoc(String text, IndexWriter iw) throws IOException {
+    Document doc = new Document();
+    Field f = newTextField("key", text, Field.Store.YES);
+    doc.add(f);
+    iw.addDocument(doc);
+  }
+
+}
diff --git a/lucene/core/src/test/org/apache/lucene/search/TestWildcard.java b/lucene/core/src/test/org/apache/lucene/search/TestWildcard.java
index 3e8f8e7..8f4a5e2 100644
--- a/lucene/core/src/test/org/apache/lucene/search/TestWildcard.java
+++ b/lucene/core/src/test/org/apache/lucene/search/TestWildcard.java
@@ -97,7 +97,7 @@ public class TestWildcard
   }
   
   /**
-   * Tests if a WildcardQuery with an empty term is rewritten to an empty BooleanQuery
+   * Tests if a WildcardQuery with an empty term is rewritten to a MatchNoDocsQuery
    */
   public void testEmptyTerm() throws IOException {
     Directory indexStore = getIndexStore("field", new String[]{"nowildcard", "nowildcardx"});
@@ -108,8 +108,7 @@ public class TestWildcard
     wq.setRewriteMethod(MultiTermQuery.SCORING_BOOLEAN_QUERY_REWRITE);
     assertMatches(searcher, wq, 0);
     Query q = searcher.rewrite(wq);
-    assertTrue(q instanceof BooleanQuery);
-    assertEquals(0, ((BooleanQuery) q).clauses().size());
+    assertTrue(q instanceof MatchNoDocsQuery);
     reader.close();
     indexStore.close();
   }
diff --git a/lucene/queryparser/src/java/org/apache/lucene/queryparser/simple/SimpleQueryParser.java b/lucene/queryparser/src/java/org/apache/lucene/queryparser/simple/SimpleQueryParser.java
index 5dff236..6f48d79 100644
--- a/lucene/queryparser/src/java/org/apache/lucene/queryparser/simple/SimpleQueryParser.java
+++ b/lucene/queryparser/src/java/org/apache/lucene/queryparser/simple/SimpleQueryParser.java
@@ -23,6 +23,7 @@ import org.apache.lucene.search.BooleanClause;
 import org.apache.lucene.search.BooleanQuery;
 import org.apache.lucene.search.FuzzyQuery;
 import org.apache.lucene.search.MatchAllDocsQuery;
+import org.apache.lucene.search.MatchNoDocsQuery;
 import org.apache.lucene.search.PrefixQuery;
 import org.apache.lucene.search.Query;
 import org.apache.lucene.util.QueryBuilder;
@@ -148,7 +149,11 @@ public class SimpleQueryParser extends QueryBuilder {
 
     State state = new State(data, buffer, 0, data.length);
     parseSubQuery(state);
-    return state.top;
+    if (state.top == null) {
+      return new MatchNoDocsQuery();
+    } else {
+      return state.top;
+    }
   }
 
   private void parseSubQuery(State state) {
diff --git a/lucene/queryparser/src/test/org/apache/lucene/queryparser/simple/TestSimpleQueryParser.java b/lucene/queryparser/src/test/org/apache/lucene/queryparser/simple/TestSimpleQueryParser.java
index 7b55a53..6bf7788 100644
--- a/lucene/queryparser/src/test/org/apache/lucene/queryparser/simple/TestSimpleQueryParser.java
+++ b/lucene/queryparser/src/test/org/apache/lucene/queryparser/simple/TestSimpleQueryParser.java
@@ -29,6 +29,7 @@ import org.apache.lucene.search.BooleanClause.Occur;
 import org.apache.lucene.search.BooleanQuery;
 import org.apache.lucene.search.FuzzyQuery;
 import org.apache.lucene.search.MatchAllDocsQuery;
+import org.apache.lucene.search.MatchNoDocsQuery;
 import org.apache.lucene.search.PhraseQuery;
 import org.apache.lucene.search.PrefixQuery;
 import org.apache.lucene.search.Query;
@@ -273,17 +274,19 @@ public class TestSimpleQueryParser extends LuceneTestCase {
   }
 
   public void testGarbageEmpty() throws Exception {
-    assertNull(parse(""));
-    assertNull(parse("  "));
-    assertNull(parse("  "));
-    assertNull(parse("\\ "));
-    assertNull(parse("\\ \\ "));
-    assertNull(parse("\"\""));
-    assertNull(parse("\" \""));
-    assertNull(parse("\" \"|\" \""));
-    assertNull(parse("(\" \"|\" \")"));
-    assertNull(parse("\" \" \" \""));
-    assertNull(parse("(\" \" \" \")"));
+    MatchNoDocsQuery expected = new MatchNoDocsQuery();
+
+    assertEquals(expected, parse(""));
+    assertEquals(expected, parse("  "));
+    assertEquals(expected, parse("  "));
+    assertEquals(expected, parse("\\ "));
+    assertEquals(expected, parse("\\ \\ "));
+    assertEquals(expected, parse("\"\""));
+    assertEquals(expected, parse("\" \""));
+    assertEquals(expected, parse("\" \"|\" \""));
+    assertEquals(expected, parse("(\" \"|\" \")"));
+    assertEquals(expected, parse("\" \" \" \""));
+    assertEquals(expected, parse("(\" \" \" \")"));
   }
 
   public void testGarbageAND() throws Exception {
@@ -643,4 +646,4 @@ public class TestSimpleQueryParser extends LuceneTestCase {
       parseKeyword(sb.toString(), TestUtil.nextInt(random(), 0, 1024)); // no exception
     }
   }
-}
\ No newline at end of file
+}