Require key type = VARCHAR to encode Avro maps

Author: martin-traverse

adapter/avro/src/main/java/org/apache/arrow/adapter/avro/ArrowToAvroUtils.java

@@ -691,6 +691,10 @@ private static BaseAvroProducer<?> createProducer(FieldVector vector, boolean nu
       case MAP:
         MapVector mapVector = (MapVector) vector;
         StructVector entryVector = (StructVector) mapVector.getDataVector();
+        Types.MinorType keyType = entryVector.getChildrenFromFields().get(0).getMinorType();
+        if (keyType != Types.MinorType.VARCHAR) {
+          throw new IllegalArgumentException("MAP key type must be VARCHAR for Avro encoding");
+        }
         VarCharVector keyVector = (VarCharVector) entryVector.getChildrenFromFields().get(0);
         FieldVector valueVector = entryVector.getChildrenFromFields().get(1);
         Producer<?> keyProducer = new AvroStringProducer(keyVector);