SOLR-18164: Remove use of .singleton

gradle/validation/forbidden-apis/defaults.all.txt

@@ -63,6 +63,9 @@ java.util.Collections#emptySet()
 @defaultMessage Use Map.of()
 java.util.Collections#emptyMap()
 
+@defaultMessage Use Set.of()
+java.util.Collections#singleton(**)
+
 java.util.Locale#forLanguageTag(java.lang.String) @ use new Locale.Builder().setLanguageTag(...).build() which has error handling
 java.util.Locale#toString() @ use Locale#toLanguageTag() for a standardized BCP47 locale name
 

solr/core/src/java/org/apache/solr/api/ApiBag.java

@@ -417,8 +417,7 @@ public static List<CommandOperation> getCommandOperations(
       ContentStream stream, Map<String, JsonSchemaValidator> validators, boolean validate) {
     List<CommandOperation> parsedCommands = null;
     try {
-      parsedCommands =
-          CommandOperation.readCommands(Collections.singleton(stream), new NamedList<>());
+      parsedCommands = CommandOperation.readCommands(Set.of(stream), new NamedList<>());
     } catch (IOException e) {
       throw new SolrException(SolrException.ErrorCode.BAD_REQUEST, "Unable to parse commands", e);
     }

solr/core/src/java/org/apache/solr/cloud/api/collections/AddReplicaCmd.java

@@ -32,9 +32,9 @@
 import java.lang.invoke.MethodHandles;
 import java.util.ArrayList;
 import java.util.Collection;
-import java.util.Collections;
 import java.util.List;
 import java.util.Map;
+import java.util.Set;
 import java.util.concurrent.TimeUnit;
 import java.util.stream.Collectors;
 import org.apache.solr.client.solrj.cloud.SolrCloudManager;
@@ -287,7 +287,7 @@ private ModifiableSolrParams getReplicaParams(
                 ccc.getZkStateReader(),
                 ccc.getSolrCloudManager().getTimeSource(),
                 collectionName,
-                Collections.singleton(createReplica.coreName))
+                Set.of(createReplica.coreName))
             .get(createReplica.coreName)
             .getName());
 

solr/core/src/java/org/apache/solr/cloud/api/collections/CollectionHandlingUtils.java

@@ -376,7 +376,7 @@ static void cleanBackup(
       BackupRepository repository, URI backupUri, BackupId backupId, CollectionCommandContext ccc)
       throws Exception {
     new DeleteBackupCmd(ccc)
-        .deleteBackupIds(backupUri, repository, Collections.singleton(backupId), new NamedList<>());
+        .deleteBackupIds(backupUri, repository, Set.of(backupId), new NamedList<>());
   }
 
   static void deleteBackup(

solr/core/src/java/org/apache/solr/cloud/api/collections/DeleteBackupCmd.java

@@ -270,7 +270,7 @@ private void deleteBackupId(
           "Backup ID [" + bid + "] not found; cannot be deleted");
     }
 
-    deleteBackupIds(backupPath, repository, Collections.singleton(backupId), results);
+    deleteBackupIds(backupPath, repository, Set.of(backupId), results);
   }
 
   static final class PurgeGraph {

solr/core/src/java/org/apache/solr/cloud/api/collections/DeleteCollectionCmd.java

@@ -23,7 +23,6 @@
 
 import java.lang.invoke.MethodHandles;
 import java.util.ArrayList;
-import java.util.Collections;
 import java.util.List;
 import java.util.Map;
 import java.util.Objects;
@@ -53,7 +52,7 @@ public class DeleteCollectionCmd implements CollApiCmds.CollectionApiCommand {
   private static final Logger log = LoggerFactory.getLogger(MethodHandles.lookup().lookupClass());
 
   private static final Set<String> okayExceptions =
-      Collections.singleton(NonExistentCoreException.class.getName());
+      Set.of(NonExistentCoreException.class.getName());
 
   private final CollectionCommandContext ccc;
 

solr/core/src/java/org/apache/solr/core/SolrCore.java

@@ -1588,7 +1588,7 @@ private static void writeNewIndexProps(Directory dir, String tmpFileName, String
       IndexOutput out = dir.createOutput(tmpFileName, DirectoryFactory.IOCONTEXT_NO_CACHE);
       os = new OutputStreamWriter(new IndexOutputOutputStream(out), StandardCharsets.UTF_8);
       p.store(os, IndexFetcher.INDEX_PROPERTIES);
-      dir.sync(Collections.singleton(tmpFileName));
+      dir.sync(Set.of(tmpFileName));
     } catch (Exception e) {
       throw new SolrException(
           ErrorCode.SERVER_ERROR, "Unable to write " + IndexFetcher.INDEX_PROPERTIES, e);

solr/core/src/java/org/apache/solr/core/SolrPaths.java

@@ -20,7 +20,6 @@
 import java.lang.invoke.MethodHandles;
 import java.nio.file.FileSystems;
 import java.nio.file.Path;
-import java.util.Collections;
 import java.util.HashSet;
 import java.util.Set;
 import org.apache.commons.exec.OS;
@@ -36,7 +35,7 @@ public final class SolrPaths {
   public static final Path ALL_PATH = Path.of("_ALL_");
 
   /** Special singleton path set containing only {@link #ALL_PATH}. */
-  private static final Set<Path> ALL_PATHS = Collections.singleton(ALL_PATH);
+  private static final Set<Path> ALL_PATHS = Set.of(ALL_PATH);
 
   private SolrPaths() {} // don't create this
 

solr/core/src/java/org/apache/solr/core/backup/ShardBackupMetadata.java

@@ -28,6 +28,7 @@
 import java.util.List;
 import java.util.Map;
 import java.util.Optional;
+import java.util.Set;
 import org.apache.lucene.store.IOContext;
 import org.apache.lucene.store.IndexInput;
 import org.apache.solr.common.util.Utils;
@@ -111,7 +112,7 @@ public void store(BackupRepository repository, URI folderURI, ShardBackupId shar
     final String filename = shardBackupId.getBackupMetadataFilename();
     URI fileURI = repository.resolve(folderURI, filename);
     if (repository.exists(fileURI)) {
-      repository.delete(folderURI, Collections.singleton(filename));
+      repository.delete(folderURI, Set.of(filename));
     }
 
     try (OutputStream os = repository.createOutput(repository.resolve(folderURI, filename))) {

solr/core/src/java/org/apache/solr/handler/IndexFetcher.java

@@ -956,7 +956,7 @@ private void logReplicationTimeAndConfFiles(
       try (Writer outFile =
           new OutputStreamWriter(new IndexOutputOutputStream(out), StandardCharsets.UTF_8)) {
         props.store(outFile, "Replication details");
-        dir.sync(Collections.singleton(tmpFileName));
+        dir.sync(Set.of(tmpFileName));
       }
 
       solrCore.getDirectoryFactory().renameWithOverwrite(dir, tmpFileName, REPLICATION_PROPERTIES);
@@ -1952,7 +1952,7 @@ private static class DirectoryFile implements FileInterface {
 
     @Override
     public void sync() throws IOException {
-      copy2Dir.sync(Collections.singleton(saveAs));
+      copy2Dir.sync(Set.of(saveAs));
     }
 
     @Override

solr/core/src/java/org/apache/solr/handler/MoreLikeThisHandler.java

@@ -21,10 +21,10 @@
 import java.lang.invoke.MethodHandles;
 import java.util.ArrayList;
 import java.util.Collection;
-import java.util.Collections;
 import java.util.Iterator;
 import java.util.List;
 import java.util.Map;
+import java.util.Set;
 import java.util.regex.Pattern;
 import net.jcip.annotations.NotThreadSafe;
 import org.apache.lucene.document.Document;
@@ -447,7 +447,7 @@ public DocListAndSet getMoreLikeThis(
           buffered.append(chunk, 0, len);
         }
 
-        Collection<Object> streamValue = Collections.singleton(buffered.get().toString());
+        Collection<Object> streamValue = Set.of(buffered.get().toString());
         Map<String, Collection<Object>> multifieldDoc = CollectionUtil.newHashMap(fields.length);
         for (String field : fields) {
           multifieldDoc.put(field, streamValue);

solr/core/src/java/org/apache/solr/handler/RequestHandlerBase.java

@@ -24,8 +24,8 @@
 import java.io.IOException;
 import java.lang.invoke.MethodHandles;
 import java.util.Collection;
-import java.util.Collections;
 import java.util.Optional;
+import java.util.Set;
 import org.apache.solr.api.Api;
 import org.apache.solr.api.ApiBag;
 import org.apache.solr.api.ApiSupport;
@@ -421,8 +421,7 @@ public PluginInfo getPluginInfo() {
 
   @Override
   public Collection<Api> getApis() {
-    return Collections.singleton(
-        new ApiBag.ReqHandlerToApi(this, ApiBag.constructSpec(pluginInfo)));
+    return Set.of(new ApiBag.ReqHandlerToApi(this, ApiBag.constructSpec(pluginInfo)));
   }
 
   /**

solr/core/src/java/org/apache/solr/handler/admin/ColStatus.java

@@ -20,7 +20,6 @@
 import java.io.IOException;
 import java.lang.invoke.MethodHandles;
 import java.util.Collection;
-import java.util.Collections;
 import java.util.Map;
 import java.util.Set;
 import java.util.TreeMap;
@@ -78,7 +77,7 @@ public void getColStatus(NamedList<Object> results) {
     if (col == null) {
       collections = clusterState.getCollectionNames();
     } else {
-      collections = Collections.singleton(col);
+      collections = Set.of(col);
     }
     boolean withFieldInfo = props.getBool(FIELD_INFO_PROP, false);
     boolean withCoreInfo = props.getBool(CORE_INFO_PROP, false);

solr/core/src/java/org/apache/solr/handler/component/QueryElevationComponent.java

@@ -444,7 +444,7 @@ protected ElevationProvider loadElevationProvider(Document doc) {
         String e = DOMUtil.getAttr(child, EXCLUDE, null);
         if (e != null) {
           if (Boolean.valueOf(e)) {
-            elevationBuilder.addExcludedIds(Collections.singleton(id));
+            elevationBuilder.addExcludedIds(Set.of(id));
             continue;
           }
         }

solr/core/src/java/org/apache/solr/handler/component/RealTimeGetComponent.java

@@ -584,10 +584,7 @@ private static SolrDocument mergePartialDocWithFullDocFromIndex(
         searcher
             .getDocFetcher()
             .decorateDocValueFields(
-                doc,
-                docid,
-                Collections.singleton(VERSION_FIELD),
-                new DocValuesIteratorCache(searcher, false));
+                doc, docid, Set.of(VERSION_FIELD), new DocValuesIteratorCache(searcher, false));
       }
 
       long docVersion = (long) doc.getFirstValue(VERSION_FIELD);

solr/core/src/java/org/apache/solr/handler/component/ResponseLogComponent.java

@@ -17,7 +17,6 @@
 package org.apache.solr.handler.component;
 
 import java.io.IOException;
-import java.util.Collections;
 import java.util.Set;
 import org.apache.solr.common.params.SolrParams;
 import org.apache.solr.response.ResultContext;
@@ -90,7 +89,7 @@ protected void processIds(
 
     StringBuilder sb = new StringBuilder();
 
-    Set<String> fields = Collections.singleton(schema.getUniqueKeyField().getName());
+    Set<String> fields = Set.of(schema.getUniqueKeyField().getName());
     SolrDocumentFetcher docFetcher = searcher.getDocFetcher();
     for (DocIterator iter = dl.iterator(); iter.hasNext(); ) {
 
@@ -106,7 +105,7 @@ protected void processScores(
       throws IOException {
 
     StringBuilder sb = new StringBuilder();
-    Set<String> fields = Collections.singleton(schema.getUniqueKeyField().getName());
+    Set<String> fields = Set.of(schema.getUniqueKeyField().getName());
     SolrDocumentFetcher docFetcher = searcher.getDocFetcher();
     for (DocIterator iter = dl.iterator(); iter.hasNext(); ) {
       sb.append(schema.printableUniqueKey(docFetcher.doc(iter.nextDoc(), fields)))

solr/core/src/java/org/apache/solr/response/TextResponseWriter.java

@@ -20,7 +20,6 @@
 import java.io.Writer;
 import java.util.Calendar;
 import java.util.Collection;
-import java.util.Collections;
 import java.util.HashSet;
 import java.util.Iterator;
 import java.util.Set;
@@ -87,9 +86,7 @@ public TextResponseWriter(Writer writer, SolrQueryRequest req, SolrQueryResponse
       this.rawReturnFields = NO_RAW_FIELDS;
     } else {
       this.rawFields =
-          rawFields.size() == 1
-              ? Collections.singleton(rawFields.iterator().next())
-              : new HashSet<>(rawFields);
+          rawFields.size() == 1 ? Set.of(rawFields.iterator().next()) : new HashSet<>(rawFields);
       this.rawShim = new RawShimTextResponseWriter(this);
       this.rawReturnFields = returnFields;
     }

solr/core/src/java/org/apache/solr/response/transform/RawValueTransformerFactory.java

@@ -17,7 +17,6 @@
 package org.apache.solr.response.transform;
 
 import java.util.Collection;
-import java.util.Collections;
 import java.util.Map;
 import java.util.Set;
 import org.apache.solr.common.SolrDocument;
@@ -123,7 +122,7 @@ public String getName() {
 
     @Override
     public Collection<String> getRawFields() {
-      return Collections.singleton(display);
+      return Set.of(display);
     }
 
     @Override

solr/core/src/java/org/apache/solr/schema/SchemaManager.java

@@ -16,7 +16,6 @@
  */
 package org.apache.solr.schema;
 
-import static java.util.Collections.singleton;
 import static java.util.Collections.singletonList;
 import static java.util.Collections.singletonMap;
 import static org.apache.solr.client.api.model.SchemaChange.OPERATION_TYPE_PROP;
@@ -37,6 +36,7 @@
 import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
+import java.util.Set;
 import java.util.concurrent.TimeUnit;
 import org.apache.solr.client.api.model.AddCopyFieldOperation;
 import org.apache.solr.client.api.model.DeleteCopyFieldOperation;
@@ -355,7 +355,7 @@ public boolean perform(SchemaChange op, SchemaManager mgr) throws SchemaOperatio
         final var deleteFieldTypeOp = (DeleteFieldTypeOperation) op;
         String name = ensureNotNull("name", deleteFieldTypeOp.name);
         try {
-          mgr.managedIndexSchema = mgr.managedIndexSchema.deleteFieldTypes(singleton(name));
+          mgr.managedIndexSchema = mgr.managedIndexSchema.deleteFieldTypes(Set.of(name));
           return true;
         } catch (Exception e) {
           log.error("Could not delete field type", e);
@@ -385,7 +385,7 @@ public boolean perform(SchemaChange op, SchemaManager mgr) throws SchemaOperatio
         final var deleteFieldOp = (DeleteFieldOperation) op;
         String name = ensureNotNull("name", deleteFieldOp.name);
         try {
-          mgr.managedIndexSchema = mgr.managedIndexSchema.deleteFields(singleton(name));
+          mgr.managedIndexSchema = mgr.managedIndexSchema.deleteFields(Set.of(name));
           return true;
         } catch (Exception e) {
           log.error("Could not delete field", e);
@@ -399,7 +399,7 @@ public boolean perform(SchemaChange op, SchemaManager mgr) throws SchemaOperatio
         final var deleteDynFieldOp = (DeleteDynamicFieldOperation) op;
         String name = ensureNotNull("name", deleteDynFieldOp.name);
         try {
-          mgr.managedIndexSchema = mgr.managedIndexSchema.deleteDynamicFields(singleton(name));
+          mgr.managedIndexSchema = mgr.managedIndexSchema.deleteDynamicFields(Set.of(name));
           return true;
         } catch (Exception e) {
           log.error("Could not delete dynamic field", e);

solr/core/src/java/org/apache/solr/search/grouping/distributed/shardresultserializer/TopGroupsResultTransformer.java

@@ -22,11 +22,11 @@
 import java.lang.invoke.MethodHandles;
 import java.lang.reflect.Array;
 import java.util.ArrayList;
-import java.util.Collections;
 import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
 import java.util.Map.Entry;
+import java.util.Set;
 import org.apache.lucene.document.Document;
 import org.apache.lucene.search.FieldDoc;
 import org.apache.lucene.search.ScoreDoc;
@@ -331,6 +331,6 @@ protected NamedList<Object> serializeTopDocs(QueryCommandResult result) throws I
 
   private Document retrieveDocument(
       final SchemaField uniqueField, int doc, SolrDocumentFetcher docFetcher) throws IOException {
-    return docFetcher.doc(doc, Collections.singleton(uniqueField.getName()));
+    return docFetcher.doc(doc, Set.of(uniqueField.getName()));
   }
 }

solr/core/src/java/org/apache/solr/search/mlt/MLTContentQParserPlugin.java

@@ -19,8 +19,8 @@
 import java.io.IOException;
 import java.io.StringReader;
 import java.util.Collection;
-import java.util.Collections;
 import java.util.Map;
+import java.util.Set;
 import org.apache.lucene.queries.mlt.MoreLikeThis;
 import org.apache.lucene.search.Query;
 import org.apache.solr.common.SolrException;
@@ -57,7 +57,7 @@ protected Query likeContent(MoreLikeThis moreLikeThis, String content) throws IO
     if (fieldNames.length == 1) {
       return moreLikeThis.like(fieldNames[0], new StringReader(content));
     } else {
-      Collection<Object> streamValue = Collections.singleton(content);
+      Collection<Object> streamValue = Set.of(content);
       Map<String, Collection<Object>> multifieldDoc = CollectionUtil.newHashMap(fieldNames.length);
       for (String field : fieldNames) {
         multifieldDoc.put(field, streamValue);