Fix reading map value contains variant null value

lib/trino-parquet/src/main/java/io/trino/parquet/reader/ParquetReader.java

@@ -519,21 +519,16 @@ private ColumnChunk readVariant(VariantField field)
 
         int positionCount = metadataChunk.getBlock().getPositionCount();
         BlockBuilder variantBlock = VARCHAR.createBlockBuilder(null, max(1, positionCount));
-        if (positionCount == 0) {
-            variantBlock.appendNull();
-        }
-        else {
-            ColumnChunk valueChunk = readColumnChunk(field.getValue());
-            for (int position = 0; position < positionCount; position++) {
-                Slice metadata = VARBINARY.getSlice(metadataChunk.getBlock(), position);
-                if (metadata.length() == 0) {
-                    variantBlock.appendNull();
-                    continue;
-                }
-                Slice value = VARBINARY.getSlice(valueChunk.getBlock(), position);
-                Variant variant = new Variant(value.getBytes(), metadata.getBytes());
-                VARCHAR.writeSlice(variantBlock, utf8Slice(variant.toJson(zoneId)));
+        ColumnChunk valueChunk = readColumnChunk(field.getValue());
+        for (int position = 0; position < positionCount; position++) {
+            Slice metadata = VARBINARY.getSlice(metadataChunk.getBlock(), position);
+            if (metadata.length() == 0) {
+                variantBlock.appendNull();
+                continue;
             }
+            Slice value = VARBINARY.getSlice(valueChunk.getBlock(), position);
+            Variant variant = new Variant(value.getBytes(), metadata.getBytes());
+            VARCHAR.writeSlice(variantBlock, utf8Slice(variant.toJson(zoneId)));
         }
         return new ColumnChunk(variantBlock.build(), metadataChunk.getDefinitionLevels(), metadataChunk.getRepetitionLevels());
     }

plugin/trino-delta-lake/src/test/java/io/trino/plugin/deltalake/TestDeltaLakeBasic.java

@@ -1613,6 +1613,9 @@ public void testVariant()
         assertQueryFails("INSERT INTO variant VALUES (2, null, null, null, null, 'new data')", "Unsupported writer features: .*");
     }
 
+    /**
+     * @see databricks154.test_variant_null
+     */
     @Test
     public void testVariantReadNull()
             throws Exception
@@ -1626,11 +1629,22 @@ public void testVariantReadNull()
                 .matches("VALUES 3");
 
         assertThat(query("SELECT * FROM " + tableName + " WHERE id = 3"))
-                .matches("VALUES (3, JSON 'null')");
+                .skippingTypesCheck()
+                .matches("VALUES (3, JSON 'null', NULL)");
         assertThat(query("SELECT * FROM " + tableName + " WHERE id = 4"))
-                .matches("VALUES (4, CAST(NULL AS JSON))");
+                .skippingTypesCheck()
+                .matches("VALUES (4, NULL, NULL)");
         assertThat(query("SELECT id FROM " + tableName + " WHERE x IS NULL"))
                 .matches("VALUES 4");
+
+        assertThat(query("TABLE " + tableName))
+                .skippingTypesCheck()
+                .matches("VALUES " +
+                        "(1, JSON '{\"a\":1}', MAP(ARRAY['key1'], ARRAY[NULL]))," +
+                        "(2, JSON '{\"a\":2}', MAP(ARRAY['key1'], ARRAY[JSON '{\"key\":\"value\"}']))," +
+                        "(3, JSON 'null', NULL)," +
+                        "(4, NULL, NULL)," +
+                         "(5, JSON '{\"a\":5}', NULL)");
     }
 
     /**

plugin/trino-delta-lake/src/test/resources/databricks154/test_variant_null/README.md

@@ -3,14 +3,15 @@ Data generated using Databricks 15.4:
 ```sql
 CREATE TABLE test_variant_null (
 id INT,
-x VARIANT
+x VARIANT,
+y MAP<STRING, VARIANT>
 ) USING DELTA
 LOCATION ?;
 
-INSERT INTO test_variant_null values 
-(1, parse_json('{"a":1}')), 
-(2, parse_json('{"a":2}')), 
-(3, parse_json('null')), 
-(4, NULL),
-(5, parse_json('{"a":5}'));
+INSERT INTO test_variant_null values
+(1, parse_json('{"a":1}'), map('key1', NULL)),
+(2, parse_json('{"a":2}'), map('key1', parse_json('{"key":"value"}'))),
+(3, parse_json('null'), NULL),
+(4, NULL, NULL),
+(5, parse_json('{"a":5}'), NULL);
 ```

plugin/trino-delta-lake/src/test/resources/databricks154/test_variant_null/_delta_log/00000000000000000000.json

@@ -1,3 +1,3 @@
-{"commitInfo":{"timestamp":1752418845893,"userId":"4222103729284476","userName":"[email protected]","operation":"CREATE TABLE","operationParameters":{"partitionBy":"[]","clusterBy":"[]","description":null,"isManaged":"false","properties":"{\"delta.enableDeletionVectors\":\"true\"}","statsOnLoad":false},"notebook":{"notebookId":"2325234880148729"},"clusterId":"1002-064054-nbosugsx","isolationLevel":"WriteSerializable","isBlindAppend":true,"operationMetrics":{},"tags":{"restoresDeletedRows":"false"},"engineInfo":"Databricks-Runtime/15.4.x-scala2.12","txnId":"7a8ee623-3291-4bb7-9b54-e1d7fa6f7bbb"}}
-{"metaData":{"id":"f363d3d3-6ad6-4228-a48a-53d4e60f58a3","format":{"provider":"parquet","options":{}},"schemaString":"{\"type\":\"struct\",\"fields\":[{\"name\":\"id\",\"type\":\"integer\",\"nullable\":true,\"metadata\":{}},{\"name\":\"x\",\"type\":\"variant\",\"nullable\":true,\"metadata\":{}}]}","partitionColumns":[],"configuration":{"delta.enableDeletionVectors":"true"},"createdTime":1752418845102}}
+{"commitInfo":{"timestamp":1758692471407,"userId":"4222103729284476","userName":"[email protected]","operation":"CREATE TABLE","operationParameters":{"partitionBy":"[]","clusterBy":"[]","description":null,"isManaged":"false","properties":"{\"delta.enableDeletionVectors\":\"true\"}","statsOnLoad":false},"notebook":{"notebookId":"2325234880148729"},"clusterId":"1002-064054-nbosugsx","isolationLevel":"WriteSerializable","isBlindAppend":true,"operationMetrics":{},"tags":{"restoresDeletedRows":"false"},"engineInfo":"Databricks-Runtime/15.4.x-scala2.12","txnId":"756c0581-29cf-436f-a2fe-8251bf671f32"}}
+{"metaData":{"id":"94ac345a-e904-4882-a9d9-bea4fcc8dd06","format":{"provider":"parquet","options":{}},"schemaString":"{\"type\":\"struct\",\"fields\":[{\"name\":\"id\",\"type\":\"integer\",\"nullable\":true,\"metadata\":{}},{\"name\":\"x\",\"type\":\"variant\",\"nullable\":true,\"metadata\":{}},{\"name\":\"y\",\"type\":{\"type\":\"map\",\"keyType\":\"string\",\"valueType\":\"variant\",\"valueContainsNull\":true},\"nullable\":true,\"metadata\":{}}]}","partitionColumns":[],"configuration":{"delta.enableDeletionVectors":"true"},"createdTime":1758692471256}}
 {"protocol":{"minReaderVersion":3,"minWriterVersion":7,"readerFeatures":["deletionVectors","variantType-preview"],"writerFeatures":["deletionVectors","variantType-preview"]}}

plugin/trino-delta-lake/src/test/resources/databricks154/test_variant_null/_delta_log/00000000000000000001.json

@@ -1,2 +1,2 @@
-{"commitInfo":{"timestamp":1752418883651,"userId":"4222103729284476","userName":"[email protected]","operation":"WRITE","operationParameters":{"mode":"Append","statsOnLoad":false,"partitionBy":"[]"},"notebook":{"notebookId":"2325234880148729"},"clusterId":"1002-064054-nbosugsx","readVersion":0,"isolationLevel":"WriteSerializable","isBlindAppend":true,"operationMetrics":{"numFiles":"1","numOutputRows":"5","numOutputBytes":"1094"},"tags":{"noRowsCopied":"true","restoresDeletedRows":"false"},"engineInfo":"Databricks-Runtime/15.4.x-scala2.12","txnId":"57b16f5c-8c44-4349-b47e-7a70373f38e5"}}
-{"add":{"path":"part-00000-3dae12c4-61bc-4177-bd36-2c936db81e90-c000.snappy.parquet","partitionValues":{},"size":1094,"modificationTime":1752418883000,"dataChange":true,"stats":"{\"numRecords\":5,\"minValues\":{\"id\":1},\"maxValues\":{\"id\":5},\"nullCount\":{\"id\":0,\"x\":1},\"tightBounds\":true}","tags":{"INSERTION_TIME":"1752418883000000","MIN_INSERTION_TIME":"1752418883000000","MAX_INSERTION_TIME":"1752418883000000","OPTIMIZE_TARGET_SIZE":"268435456"}}}
+{"commitInfo":{"timestamp":1758692482446,"userId":"4222103729284476","userName":"[email protected]","operation":"WRITE","operationParameters":{"mode":"Append","statsOnLoad":false,"partitionBy":"[]"},"notebook":{"notebookId":"2325234880148729"},"clusterId":"1002-064054-nbosugsx","readVersion":0,"isolationLevel":"WriteSerializable","isBlindAppend":true,"operationMetrics":{"numFiles":"1","numOutputRows":"5","numOutputBytes":"1945"},"tags":{"noRowsCopied":"true","restoresDeletedRows":"false"},"engineInfo":"Databricks-Runtime/15.4.x-scala2.12","txnId":"ce6e305b-2e60-4371-9f9d-6356857ad279"}}
+{"add":{"path":"part-00000-a4542d9d-2170-4716-b8ee-9a9879ee0289-c000.snappy.parquet","partitionValues":{},"size":1945,"modificationTime":1758692483000,"dataChange":true,"stats":"{\"numRecords\":5,\"minValues\":{\"id\":1},\"maxValues\":{\"id\":5},\"nullCount\":{\"id\":0,\"x\":1,\"y\":3},\"tightBounds\":true}","tags":{"INSERTION_TIME":"1758692483000000","MIN_INSERTION_TIME":"1758692483000000","MAX_INSERTION_TIME":"1758692483000000","OPTIMIZE_TARGET_SIZE":"268435456"}}}