Nested arrays cause 'item-end when a 'x' was expected" error (#476)

* Address issue with nested arrays

Some schemas with nested arrays ( e.g., NestedArray.avsc ) generate the following
error when deserialized with fastserde:

Attempt to process a item-end when a string was expected.

This PR adds a test case and addresses the issue

* Update test

* Fix fastserdetest.avsc

* Update fastserdetest.java

* Remove code to verify test pipeline fails

* Make name consistent

* Fix FastDeserializerGeneratorBase

* Use helper functions so test builds on all versions

* Fix case of ItemName

* Remove dependency of getSymbolPrintName

* Remove unnecessary whitespace change

* Add javadoc

---------

Co-authored-by: Andy Sautins <[email protected]>

fastserde/avro-fastserde-tests-common/src/test/avro/nestedArrayTest.avsc

@@ -0,0 +1,26 @@
+{
+   "namespace": "com.linkedin.avro.fastserde.generated.avro",
+    "name": "NestedArrayTest",
+    "type": "record",
+    "fields": [
+        {
+            "name": "NestedArrayItems",
+            "type": {
+                "type": "array",
+                "items": {
+                    "type": "array",
+                    "items": {
+                        "name": "NestedArrayItem",
+                        "type": "record",
+                        "fields": [
+                            {
+                                "name": "ItemName",
+                                "type": "string"
+                            }
+                        ]
+                    }
+                }
+            }
+        }
+    ]
+}

fastserde/avro-fastserde-tests-common/src/test/java/com/linkedin/avro/fastserde/FastNestedArrayTest.java

@@ -0,0 +1,37 @@
+package com.linkedin.avro.fastserde;
+
+import com.linkedin.avro.fastserde.generated.avro.NestedArrayItem;
+import com.linkedin.avro.fastserde.generated.avro.NestedArrayTest;
+
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.List;
+import org.apache.avro.io.Decoder;
+import org.testng.Assert;
+import org.testng.annotations.Test;
+
+
+public class FastNestedArrayTest {
+
+  @Test
+  public void testExample() throws Exception {
+
+     NestedArrayTest nestedArrayTest = new NestedArrayTest();
+
+    List<NestedArrayItem> items = new ArrayList<>();
+    NestedArrayItem item = new NestedArrayItem();
+    FastSerdeTestsSupport.setField(item, "ItemName", "itemName");
+    FastSerdeTestsSupport.setField(nestedArrayTest, "NestedArrayItems", Collections.singletonList(items));
+
+    Decoder decoder = FastSerdeTestsSupport.specificDataAsDecoder(nestedArrayTest, NestedArrayTest.SCHEMA$);
+
+    FastSpecificDatumReader<NestedArrayTest> fastSpecificDatumReader =
+        new FastSpecificDatumReader<>(NestedArrayTest.SCHEMA$);
+    FastDeserializer<NestedArrayTest> fastDeserializer =
+        fastSpecificDatumReader.getFastDeserializer().get();
+
+    NestedArrayTest actual = fastDeserializer.deserialize(decoder);
+
+    Assert.assertEquals(actual, nestedArrayTest);
+  }
+}

fastserde/avro-fastserde/src/main/java/com/linkedin/avro/fastserde/FastDeserializerGeneratorBase.java

@@ -6,6 +6,7 @@
 import java.util.Arrays;
 import java.util.Collections;
 import java.util.ListIterator;
+import java.util.Optional;
 import org.apache.avro.Schema;
 import com.linkedin.avro.fastserde.backport.Symbol;
 import org.apache.avro.util.Utf8;
@@ -71,6 +72,17 @@ protected static void assignBlockToBody(Object codeContainer, JBlock body) {
 
   public abstract FastDeserializer<T> generateDeserializer();
 
+  /**
+   * Retrieve the symbols associated with the FieldAction necessary
+   * to generate code to populate the field.
+   *
+   * When processing a nested array ( an array directly inside
+   * another array ) return the symbol.production to navigate the
+   * nested array properly.
+   *
+   * @param action FieldAction being process
+   * @return list of symbols associated with the input FieldAction
+   */
   protected ListIterator<Symbol> actionIterator(FieldAction action) {
     ListIterator<Symbol> actionIterator = null;
 
@@ -85,6 +97,14 @@ protected ListIterator<Symbol> actionIterator(FieldAction action) {
     while (actionIterator.hasNext()) {
       Symbol symbol = actionIterator.next();
 
+      if (Symbol.Kind.REPEATER.equals(symbol.kind)  &&
+          Symbol.Kind.TERMINAL.equals(((Symbol.Repeater)symbol).end)
+          && "array-end"
+          .equals(((Symbol.Repeater)symbol).end.toString())) {
+        actionIterator = Arrays.asList(reverseSymbolArray(symbol.production)).listIterator();
+        break;
+      }
+
       if (symbol instanceof Symbol.ErrorAction) {
         throw new FastDeserializerGeneratorException(((Symbol.ErrorAction) symbol).msg);
       }