[GitHub] [lucene-solr] jimczi commented on a change in pull request #620: LUCENE-8477: Automatically rewrite disjunctions when internal gaps matter

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jimczi commented on a change in pull request #620: LUCENE-8477: Automatically rewrite disjunctions when internal gaps matter
URL: https://github.com/apache/lucene-solr/pull/620#discussion_r269457511
 
 

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 File path: lucene/sandbox/src/java/org/apache/lucene/search/intervals/Disjunctions.java
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 @@ -0,0 +1,96 @@
+/*
+ * 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.intervals;
+
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.List;
+import java.util.function.Function;
+import java.util.stream.Collectors;
+
+import org.apache.lucene.search.BooleanQuery;
+
+final class Disjunctions {
+
+  // Given a list of sources that contain disjunctions, and a combiner function,
+  // pulls the disjunctions to the top of the source tree
+
+  // eg FUNC(a, b, OR(c, "d e")) => [FUNC(a, b, c), FUNC(a, b, "d e")]
+
+  public static List<IntervalsSource> pullUp(List<IntervalsSource> sources,
+                                             Function<List<IntervalsSource>, IntervalsSource> function) {
+
+    List<List<IntervalsSource>> rewritten = new ArrayList<>();
+    rewritten.add(new ArrayList<>());
+    for (IntervalsSource source : sources) {
+      List<IntervalsSource> disjuncts = splitDisjunctions(source);
+      if (disjuncts.size() == 1) {
+        rewritten.forEach(l -> l.add(disjuncts.get(0)));
+      }
+      else {
+        if (rewritten.size() * disjuncts.size() > BooleanQuery.getMaxClauseCount()) {
+          throw new IllegalArgumentException("Too many disjunctions to expand");
+        }
+        List<List<IntervalsSource>> toAdd = new ArrayList<>();
+        for (IntervalsSource disj : disjuncts) {
+          // clone the rewritten list, then append the disjunct
+          for (List<IntervalsSource> subList : rewritten) {
+            List<IntervalsSource> l = new ArrayList<>(subList);
+            l.add(disj);
+            toAdd.add(l);
+          }
+        }
+        rewritten = toAdd;
+      }
+    }
+    if (rewritten.size() == 1) {
+      return Collections.singletonList(function.apply(rewritten.get(0)));
+    }
+    return rewritten.stream().map(function).collect(Collectors.toList());
+  }
+
+  // Given a source containing disjunctions, and a mapping function,
+  // pulls the disjunctions to the top of the source tree
+  public static List<IntervalsSource> pullUp(IntervalsSource source, Function<IntervalsSource, IntervalsSource> function) {
+    List<IntervalsSource> disjuncts = splitDisjunctions(source);
+    if (disjuncts.size() == 1) {
+      return Collections.singletonList(function.apply(disjuncts.get(0)));
+    }
+    return disjuncts.stream().map(function).collect(Collectors.toList());
+  }
+
+  private static List<IntervalsSource> splitDisjunctions(IntervalsSource source) {
+    List<IntervalsSource> singletons = new ArrayList<>();
+    List<IntervalsSource> nonSingletons = new ArrayList<>();
+    for (IntervalsSource disj : source.pullUpDisjunctions()) {
+      if (disj.minExtent() == 1) {
 
 Review comment:
   can you add a comment explaining why we separate singleton source ? 

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