[ES|QL] Add CHUNK function

server/src/main/java/module-info.java

@@ -486,7 +486,7 @@
     exports org.elasticsearch.inference.configuration;
     exports org.elasticsearch.inference.validation;
     exports org.elasticsearch.monitor.metrics;
-    exports org.elasticsearch.plugins.internal.rewriter to org.elasticsearch.inference;
+    exports org.elasticsearch.plugins.internal.rewriter;
     exports org.elasticsearch.lucene.util.automaton;
     exports org.elasticsearch.index.codec.perfield;
     exports org.elasticsearch.index.codec.vectors to org.elasticsearch.test.knn, org.elasticsearch.gpu;

x-pack/plugin/esql/qa/testFixtures/src/main/resources/chunk.csv-spec

@@ -0,0 +1,45 @@
+###############################################
+# Tests for Chunk function
+#
+
+chunkExample
+required_capability: chunk_function
+
+// tag::chunk-with-field[]
+FROM books
+| EVAL chunks = CHUNK(description, 1, 20)
+// end::chunk-with-field[]
+| KEEP book_no, title, chunks
+| SORT book_no
+| LIMIT 5
+;
+warningRegex:java.lang.IllegalArgumentException: single-value function encountered multi-value
+
+// tag::chunk-with-field-result[]
+book_no:keyword | title:text                                            | chunks:keyword
+1211            | The brothers Karamazov                                | null
+1463            | Realms of Tolkien: Images of Middle-earth             | null
+1502            | Selected Passages from Correspondence with Friends    | null
+1937            | The Best Short Stories of Dostoevsky (Modern Library) | null
+1985            | Brothers Karamazov                                    | null
+// end::chunk-with-field-result[]
+;
+
+
+chunkTextWithMatch
+required_capability: chunk_function
+
+FROM books 
+| WHERE MATCH(title, "Return")
+| EVAL chunks = CHUNK(description, 1, 20)
+| KEEP book_no, title, chunks;
+ignoreOrder:true
+warningRegex:java.lang.IllegalArgumentException: single-value function encountered multi-value
+
+book_no:keyword | title:text                                                        | chunks:keyword
+2714            | Return of the King Being the Third Part of The Lord of the Rings  | null
+7350            | Return of the Shadow                                              | null
+;
+
+
+

x-pack/plugin/esql/src/main/java/org/elasticsearch/xpack/esql/action/EsqlCapabilities.java

@@ -1504,7 +1504,12 @@ public enum Cap {
         /**
          * Support for the literal {@code m} suffix as an alias for {@code minute} in temporal amounts.
          */
-        TEMPORAL_AMOUNT_M;
+        TEMPORAL_AMOUNT_M,
+
+        /**
+         * Chunk function.
+         */
+        CHUNK_FUNCTION(Build.current().isSnapshot());
 
         private final boolean enabled;
 

x-pack/plugin/esql/src/main/java/org/elasticsearch/xpack/esql/expression/ExpressionWritables.java

@@ -78,6 +78,7 @@
 import org.elasticsearch.xpack.esql.expression.function.scalar.spatial.StYMax;
 import org.elasticsearch.xpack.esql.expression.function.scalar.spatial.StYMin;
 import org.elasticsearch.xpack.esql.expression.function.scalar.string.ByteLength;
+import org.elasticsearch.xpack.esql.expression.function.scalar.string.Chunk;
 import org.elasticsearch.xpack.esql.expression.function.scalar.string.LTrim;
 import org.elasticsearch.xpack.esql.expression.function.scalar.string.Length;
 import org.elasticsearch.xpack.esql.expression.function.scalar.string.RTrim;
@@ -239,6 +240,7 @@ public static List<NamedWriteableRegistry.Entry> unaryScalars() {
         entries.add(UrlEncode.ENTRY);
         entries.add(UrlEncodeComponent.ENTRY);
         entries.add(UrlDecode.ENTRY);
+        entries.add(Chunk.ENTRY);
         // mv functions
         entries.addAll(MvFunctionWritables.getNamedWriteables());
         return entries;

x-pack/plugin/esql/src/main/java/org/elasticsearch/xpack/esql/expression/function/EsqlFunctionRegistry.java

@@ -176,6 +176,7 @@
 import org.elasticsearch.xpack.esql.expression.function.scalar.spatial.StYMin;
 import org.elasticsearch.xpack.esql.expression.function.scalar.string.BitLength;
 import org.elasticsearch.xpack.esql.expression.function.scalar.string.ByteLength;
+import org.elasticsearch.xpack.esql.expression.function.scalar.string.Chunk;
 import org.elasticsearch.xpack.esql.expression.function.scalar.string.Concat;
 import org.elasticsearch.xpack.esql.expression.function.scalar.string.Contains;
 import org.elasticsearch.xpack.esql.expression.function.scalar.string.EndsWith;
@@ -553,7 +554,8 @@ private static FunctionDefinition[][] snapshotFunctions() {
                 def(L1Norm.class, L1Norm::new, "v_l1_norm"),
                 def(L2Norm.class, L2Norm::new, "v_l2_norm"),
                 def(Magnitude.class, Magnitude::new, "v_magnitude"),
-                def(Hamming.class, Hamming::new, "v_hamming") } };
+                def(Hamming.class, Hamming::new, "v_hamming"),
+                def(Chunk.class, tri(Chunk::new), "chunk") } };
     }
 
     public EsqlFunctionRegistry snapshotRegistry() {
@@ -1036,13 +1038,22 @@ public interface BinaryBuilder<T> {
     @SuppressWarnings("overloads")  // These are ambiguous if you aren't using ctor references but we always do
     protected static <T extends Function> FunctionDefinition def(Class<T> function, TernaryBuilder<T> ctorRef, String... names) {
         FunctionBuilder builder = (source, children, cfg) -> {
+            boolean hasMinimumOne = TwoOptionalArguments.class.isAssignableFrom(function);
             boolean hasMinimumTwo = OptionalArgument.class.isAssignableFrom(function);
-            if (hasMinimumTwo && (children.size() > 3 || children.size() < 2)) {
+            if (hasMinimumOne && (children.size() > 3 || children.isEmpty())) {
+                throw new QlIllegalArgumentException("expects minimum one, maximum three arguments");
+            } else if (hasMinimumTwo && (children.size() > 3 || children.size() < 2)) {
                 throw new QlIllegalArgumentException("expects two or three arguments");
-            } else if (hasMinimumTwo == false && children.size() != 3) {
+            } else if (hasMinimumOne == false && hasMinimumTwo == false && children.size() != 3) {
                 throw new QlIllegalArgumentException("expects exactly three arguments");
             }
-            return ctorRef.build(source, children.get(0), children.get(1), children.size() == 3 ? children.get(2) : null);
+
+            return ctorRef.build(
+                source,
+                children.get(0),
+                children.size() > 1 ? children.get(1) : null,
+                children.size() == 3 ? children.get(2) : null
+            );
         };
         return def(function, builder, names);
     }