SQL: Refactor Literals serialization method

Since other classes besides intervals can be serialized as part of
the Cursor, the getNamedWritables method should be moved from Intervals
to a more generic class Literals.

Relates to elastic#39973

x-pack/plugin/sql/src/main/java/org/elasticsearch/xpack/sql/expression/literal/Intervals.java

@@ -7,8 +7,6 @@
 package org.elasticsearch.xpack.sql.expression.literal;
 
 import org.elasticsearch.common.Strings;
-import org.elasticsearch.common.io.stream.NamedWriteableRegistry;
-import org.elasticsearch.common.io.stream.NamedWriteableRegistry.Entry;
 import org.elasticsearch.xpack.sql.SqlIllegalArgumentException;
 import org.elasticsearch.xpack.sql.expression.Foldables;
 import org.elasticsearch.xpack.sql.expression.Literal;
@@ -22,7 +20,6 @@
 import java.time.Period;
 import java.time.temporal.TemporalAmount;
 import java.util.ArrayList;
-import java.util.Collection;
 import java.util.LinkedHashMap;
 import java.util.List;
 import java.util.Map;
@@ -412,12 +409,4 @@ public static TemporalAmount parseInterval(Source source, String value, DataType
         return PARSERS.get(intervalType).parse(source, value);
     }
 
-    public static Collection<? extends Entry> getNamedWriteables() {
-        List<NamedWriteableRegistry.Entry> entries = new ArrayList<>();
-
-        entries.add(new Entry(IntervalDayTime.class, IntervalDayTime.NAME, IntervalDayTime::new));
-        entries.add(new Entry(IntervalYearMonth.class, IntervalYearMonth.NAME, IntervalYearMonth::new));
-
-        return entries;
-    }
-}
+}

x-pack/plugin/sql/src/main/java/org/elasticsearch/xpack/sql/expression/literal/Literals.java

@@ -0,0 +1,36 @@
+/*
+ * Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
+ * or more contributor license agreements. Licensed under the Elastic License;
+ * you may not use this file except in compliance with the Elastic License.
+ */
+
+package org.elasticsearch.xpack.sql.expression.literal;
+
+import org.elasticsearch.common.io.stream.NamedWriteableRegistry;
+
+import java.util.ArrayList;
+import java.util.Collection;
+import java.util.List;
+
+/**
+ * Utility class for common literal-related functions
+ */
+public final class Literals {
+
+    private Literals() {
+
+    }
+
+    /**
+     * All custom types that are not serializable by default can be be serialized as a part of Cursor (i.e as constant in ConstantProcessor)
+     * should implement NamedWriteables interface and register their de-serialization methods here.
+     */
+    public static Collection<? extends NamedWriteableRegistry.Entry> getNamedWriteables() {
+        List<NamedWriteableRegistry.Entry> entries = new ArrayList<>();
+
+        entries.add(new NamedWriteableRegistry.Entry(IntervalDayTime.class, IntervalDayTime.NAME, IntervalDayTime::new));
+        entries.add(new NamedWriteableRegistry.Entry(IntervalYearMonth.class, IntervalYearMonth.NAME, IntervalYearMonth::new));
+
+        return entries;
+    }
+}

x-pack/plugin/sql/src/main/java/org/elasticsearch/xpack/sql/session/Cursors.java

@@ -19,7 +19,7 @@
 import org.elasticsearch.xpack.sql.execution.search.extractor.BucketExtractors;
 import org.elasticsearch.xpack.sql.execution.search.extractor.HitExtractors;
 import org.elasticsearch.xpack.sql.expression.function.scalar.Processors;
-import org.elasticsearch.xpack.sql.expression.literal.Intervals;
+import org.elasticsearch.xpack.sql.expression.literal.Literals;
 import org.elasticsearch.xpack.sql.plugin.TextFormatterCursor;
 
 import java.io.ByteArrayOutputStream;
@@ -57,7 +57,7 @@ public static List<NamedWriteableRegistry.Entry> getNamedWriteables() {
         entries.addAll(BucketExtractors.getNamedWriteables());
 
         // and custom types
-        entries.addAll(Intervals.getNamedWriteables());
+        entries.addAll(Literals.getNamedWriteables());
 
         return entries;
     }
@@ -102,4 +102,4 @@ public static Cursor decodeFromString(String info) {
             throw new SqlIllegalArgumentException("Unexpected failure decoding cursor", ex);
         }
     }
-}
+}