Migrate deprecated usages of Operations#union (opensearch-project#19397)

Migrate usages of org.apache.lucene.util.automaton.Operations#union(Automaton, Automaton) to Operations#union(Collection<Automation>)

Signed-off-by: Sergei Ustimenko <[email protected]>
Signed-off-by: fdesu <[email protected]>

Author: fdesu

CHANGELOG.md

@@ -46,6 +46,7 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 - Optimize source conversion in gRPC search hits using zero-copy BytesRef ([#19280](https://github.com/opensearch-project/OpenSearch/pull/19280))
 - Allow plugins to copy folders into their config dir during installation ([#19343](https://github.com/opensearch-project/OpenSearch/pull/19343))
 - Add failureaccess as runtime dependency to transport-grpc module  ([#19339](https://github.com/opensearch-project/OpenSearch/pull/19339))
+- Migrate usages of deprecated `Operations#union` from Lucene ([#19397](https://github.com/opensearch-project/OpenSearch/pull/19397))
 
 ### Fixed
 - Fix unnecessary refreshes on update preparation failures ([#15261](https://github.com/opensearch-project/OpenSearch/issues/15261))

server/src/main/java/org/opensearch/common/lucene/search/AutomatonQueries.java

@@ -41,6 +41,7 @@
 import org.apache.lucene.util.automaton.Operations;
 
 import java.util.ArrayList;
+import java.util.Arrays;
 import java.util.Iterator;
 import java.util.List;
 
@@ -177,7 +178,7 @@ public static Automaton toCaseInsensitiveChar(int codepoint) {
         int altCase = Character.isLowerCase(codepoint) ? Character.toUpperCase(codepoint) : Character.toLowerCase(codepoint);
         Automaton result;
         if (altCase != codepoint) {
-            result = Operations.union(case1, Automata.makeChar(altCase));
+            result = Operations.union(Arrays.asList(case1, Automata.makeChar(altCase)));
         } else {
             result = case1;
         }

server/src/main/java/org/opensearch/common/xcontent/support/XContentMapValues.java

@@ -301,8 +301,11 @@ private static boolean hasNoWildcardsOrDots(String[] fields) {
      *  For instance, if the original simple regex is `foo`, this will translate
      *  it into `foo` OR `foo.*`. */
     private static Automaton makeMatchDotsInFieldNames(Automaton automaton) {
+        Automaton automatonMatchingFields = Operations.concatenate(
+            Arrays.asList(automaton, Automata.makeChar('.'), Automata.makeAnyString())
+        );
         return Operations.determinize(
-            Operations.union(automaton, Operations.concatenate(Arrays.asList(automaton, Automata.makeChar('.'), Automata.makeAnyString()))),
+            Operations.union(Arrays.asList(automaton, automatonMatchingFields)),
             Operations.DEFAULT_DETERMINIZE_WORK_LIMIT
         );
     }

server/src/main/java/org/opensearch/indices/SystemIndices.java

@@ -34,7 +34,6 @@
 
 import org.apache.logging.log4j.LogManager;
 import org.apache.logging.log4j.Logger;
-import org.apache.lucene.util.automaton.Automata;
 import org.apache.lucene.util.automaton.Automaton;
 import org.apache.lucene.util.automaton.CharacterRunAutomaton;
 import org.apache.lucene.util.automaton.Operations;
@@ -45,7 +44,6 @@
 import java.util.Collection;
 import java.util.List;
 import java.util.Map;
-import java.util.Optional;
 import java.util.stream.Collectors;
 
 /**
@@ -143,11 +141,9 @@ public boolean validateSystemIndex(String index) {
     }
 
     private static CharacterRunAutomaton buildCharacterRunAutomaton(Collection<SystemIndexDescriptor> descriptors) {
-        Optional<Automaton> automaton = descriptors.stream()
+        List<Automaton> automatons = descriptors.stream()
             .map(descriptor -> Regex.simpleMatchToAutomaton(descriptor.getIndexPattern()))
-            .reduce(Operations::union);
-        return new CharacterRunAutomaton(
-            Operations.determinize(automaton.orElse(Automata.makeEmpty()), Operations.DEFAULT_DETERMINIZE_WORK_LIMIT)
-        );
+            .collect(Collectors.toList());
+        return new CharacterRunAutomaton(Operations.determinize(Operations.union(automatons), Operations.DEFAULT_DETERMINIZE_WORK_LIMIT));
     }
 }