voonhous commented on code in PR #18065:
URL: https://github.com/apache/hudi/pull/18065#discussion_r3419686168


##########
hudi-hadoop-common/src/main/java/org/apache/hudi/avro/HoodieAvroWriteSupport.java:
##########
@@ -20,38 +20,289 @@
 package org.apache.hudi.avro;
 
 import org.apache.hudi.common.bloom.BloomFilter;
+import org.apache.hudi.common.config.HoodieConfig;
+import org.apache.hudi.common.config.HoodieStorageConfig;
 import org.apache.hudi.common.schema.HoodieSchema;
+import org.apache.hudi.common.schema.HoodieSchemaField;
+import org.apache.hudi.common.schema.HoodieSchemaType;
+import org.apache.hudi.common.schema.HoodieSchemaUtils;
 import org.apache.hudi.common.util.CollectionUtils;
 import org.apache.hudi.common.util.Option;
+import org.apache.hudi.common.util.ReflectionUtils;
 import org.apache.hudi.common.util.StringUtils;
+import org.apache.hudi.exception.HoodieException;
 
+import org.apache.avro.Schema;
+import org.apache.avro.generic.GenericData;
+import org.apache.avro.generic.GenericRecord;
+import org.apache.avro.generic.IndexedRecord;
 import org.apache.parquet.avro.AvroWriteSupport;
 import org.apache.parquet.hadoop.api.WriteSupport;
 import org.apache.parquet.schema.MessageType;
 
+import java.util.ArrayList;
 import java.util.Collections;
 import java.util.HashMap;
+import java.util.LinkedHashMap;
+import java.util.List;
 import java.util.Map;
 import java.util.Properties;
+import java.util.regex.Matcher;
+import java.util.regex.Pattern;
+
+import static 
org.apache.hudi.common.config.HoodieStorageConfig.PARQUET_VARIANT_FORCE_SHREDDING_SCHEMA_FOR_TEST;
+import static 
org.apache.hudi.common.config.HoodieStorageConfig.PARQUET_VARIANT_SHREDDING_PROVIDER_CLASS;
+import static 
org.apache.hudi.common.config.HoodieStorageConfig.PARQUET_VARIANT_WRITE_SHREDDING_ENABLED;
 
 /**
- * Wrap AvroWriterSupport for plugging in the bloom filter.
+ * Wrap AvroWriterSupport for plugging in the bloom filter and variant 
shredding support.
+ *
+ * <p>When variant columns are configured for shredding (via {@link 
HoodieSchema.Variant#isShredded()}),
+ * this class transforms variant records at write time to populate {@code 
typed_value} columns
+ * by parsing variant binary data using a {@link VariantShreddingProvider} 
loaded via reflection.</p>
  */
 public class HoodieAvroWriteSupport<T> extends AvroWriteSupport<T> {
 
   private final Option<HoodieBloomFilterWriteSupport<String>> 
bloomFilterWriteSupportOpt;
   private final Map<String, String> footerMetadata = new HashMap<>();
   protected final Properties properties;
 
+  /**
+   * Whether variant write shredding is enabled via config.
+   */
+  private final boolean variantWriteShreddingEnabled;
+
+  /**
+   * The effective (possibly shredded) HoodieSchema used for writing.
+   */
+  private final HoodieSchema effectiveHoodieSchema;
+
+  /**
+   * The effective Avro schema (derived from effectiveHoodieSchema).
+   */
+  private final Schema effectiveAvroSchema;
+
+  /**
+   * Variant fields that need shredding, keyed by their index in the effective 
schema.
+   * Empty if no shredding is needed.
+   */
+  private final Map<Integer, ShreddedVariantField> shreddedVariantFields;
+
+  /**
+   * Provider for variant shredding (loaded via reflection). Null if no 
shredding is needed.
+   */
+  private final VariantShreddingProvider shreddingProvider;
+
+  /**
+   * Names of all variant-typed top-level fields, regardless of shredding. 
Used to fail fast on the
+   * not-yet-supported read-then-reshred path (compaction/clustering over an 
already-shredded base
+   * file). See https://github.com/apache/hudi/issues/18931.
+   */
+  private final String[] variantFieldNames;
+
   public HoodieAvroWriteSupport(MessageType schema, HoodieSchema hoodieSchema, 
Option<BloomFilter> bloomFilterOpt,
                                 Properties properties) {
-    super(schema, hoodieSchema.toAvroSchema(), ConvertingGenericData.INSTANCE);
+    this(schema, hoodieSchema, generateEffectiveSchema(hoodieSchema, 
properties), bloomFilterOpt, properties);
+  }
+
+  private HoodieAvroWriteSupport(MessageType schema, HoodieSchema 
hoodieSchema, HoodieSchema effectiveSchema,
+                                 Option<BloomFilter> bloomFilterOpt, 
Properties properties) {
+    super(schema, effectiveSchema.toAvroSchema(), 
ConvertingGenericData.INSTANCE);
     this.bloomFilterWriteSupportOpt = 
bloomFilterOpt.map(HoodieBloomFilterAvroWriteSupport::new);
     this.properties = properties;
     String vectorMeta = 
HoodieSchema.buildVectorColumnsMetadataValue(hoodieSchema);
     if (!vectorMeta.isEmpty()) {
       footerMetadata.put(HoodieSchema.VECTOR_COLUMNS_METADATA_KEY, vectorMeta);
     }
+
+    this.effectiveHoodieSchema = effectiveSchema;

Review Comment:
   Resolved in c14ae042 - folded the two passes into a single one that collects 
the variant field names and the shredded subset together.



##########
hudi-spark-datasource/hudi-spark/src/test/scala/org/apache/spark/sql/hudi/dml/schema/TestVariantDataType.scala:
##########
@@ -542,4 +546,160 @@ class TestVariantDataType extends HoodieSparkSqlTestBase {
 
     spark.sql(s"drop table $tableName")
   }
+
+  test("Test Shredded Variant Write and Read + Validate Parquet Schema after 
Write") {
+    assume(HoodieSparkUtils.gteqSpark4_0, "Variant type requires Spark 4.0 or 
higher")
+
+    // Test 1: Shredding enabled with forced schema → parquet should have 
typed_value
+    withRecordType()(withTempDir { tmp =>
+      val tableName = generateTableName
+      spark.sql(
+        s"""
+           |create table $tableName (
+           |  id int,
+           |  name string,
+           |  v variant,
+           |  ts long
+           |) using hudi
+           | location '${tmp.getCanonicalPath}'
+           | tblproperties (
+           |  primaryKey = 'id',
+           |  type = 'cow',
+           |  preCombineField = 'ts'
+           | )
+        """.stripMargin)
+
+      spark.sql("set hoodie.parquet.variant.write.shredding.enabled = true")
+      spark.sql("set hoodie.parquet.variant.allow.reading.shredded = true")
+      spark.sql("set hoodie.parquet.variant.force.shredding.schema.for.test = 
a int, b string")
+
+      spark.sql(
+        s"""
+           |insert into $tableName values
+           |  (1, 'row1', parse_json('{"a": 1, "b": "hello"}'), 1000)
+        """.stripMargin)
+      checkAnswer(s"select id, name, cast(v as string), ts from $tableName 
order by id")(
+        Seq(1, "row1", "{\"a\":1,\"b\":\"hello\"}", 1000)
+      )
+
+      // Verify parquet schema has shredded structure with typed_value
+      val parquetFiles = listDataParquetFiles(tmp.getCanonicalPath)
+      assert(parquetFiles.nonEmpty, "Should have at least one data parquet 
file")
+
+      parquetFiles.foreach { filePath =>
+        val schema = readParquetSchema(filePath)
+        val variantGroup = getFieldAsGroup(schema, "v")
+        assert(groupContainsField(variantGroup, "typed_value"),
+          s"Shredded variant should have typed_value field. 
Schema:\n$variantGroup")
+        val valueField = 
variantGroup.getType(variantGroup.getFieldIndex("value"))
+        assert(valueField.getRepetition == Type.Repetition.OPTIONAL,
+          "Shredded variant value field should be OPTIONAL")
+        val metadataField = 
variantGroup.getType(variantGroup.getFieldIndex("metadata"))
+        assert(metadataField.getRepetition == Type.Repetition.REQUIRED,
+          "Shredded variant metadata field should be REQUIRED")
+      }
+    })
+  }
+
+  test("Test Unshredded Variant Write and Read + Validate Parquet Schema after 
Write") {
+    assume(HoodieSparkUtils.gteqSpark4_0, "Variant type requires Spark 4.0 or 
higher")
+    // Shredding disabled parquet should NOT have typed_value
+    withRecordType()(withTempDir { tmp =>
+      val tableName = generateTableName
+      spark.sql(
+        s"""
+           |create table $tableName (
+           |  id int,
+           |  name string,
+           |  v variant,
+           |  ts long
+           |) using hudi
+           | location '${tmp.getCanonicalPath}'
+           | tblproperties (
+           |  primaryKey = 'id',
+           |  type = 'cow',
+           |  preCombineField = 'ts'
+           | )
+              """.stripMargin)
+
+      spark.sql(s"set hoodie.parquet.variant.write.shredding.enabled = false")
+
+      spark.sql(
+        s"""
+           |insert into $tableName values
+           |  (1, 'row1', parse_json('{"a": 1, "b": "hello"}'), 1000)
+              """.stripMargin)
+
+      checkAnswer(s"select id, name, cast(v as string), ts from $tableName 
order by id")(
+        Seq(1, "row1", "{\"a\":1,\"b\":\"hello\"}", 1000)
+      )
+
+      // Verify parquet schema does NOT have typed_value
+      val parquetFiles = listDataParquetFiles(tmp.getCanonicalPath)
+      assert(parquetFiles.nonEmpty, "Should have at least one data parquet 
file")
+
+      parquetFiles.foreach { filePath =>
+        val schema = readParquetSchema(filePath)
+        val variantGroup = getFieldAsGroup(schema, "v")
+        assert(!groupContainsField(variantGroup, "typed_value"),
+          s"Non-shredded variant should NOT have typed_value field. 
Schema:\n$variantGroup")
+        val valueField = 
variantGroup.getType(variantGroup.getFieldIndex("value"))
+        assert(valueField.getRepetition == Type.Repetition.REQUIRED,
+          "Non-shredded variant value field should be REQUIRED")
+      }
+
+      // Verify data can still be read back for the non-shredded case
+      checkAnswer(s"select id, name, cast(v as string), ts from $tableName 
order by id")(
+        Seq(1, "row1", "{\"a\":1,\"b\":\"hello\"}", 1000)
+      )
+    })
+  }
+
+  /**
+   * Lists data parquet files in the table directory, excluding Hudi metadata 
files.
+   */
+  private def listDataParquetFiles(tablePath: String): Seq[String] = {
+    val conf = spark.sparkContext.hadoopConfiguration
+    val fs = FileSystem.get(new HadoopPath(tablePath).toUri, conf)
+    val iter = fs.listFiles(new HadoopPath(tablePath), true)
+    val files = scala.collection.mutable.ArrayBuffer[String]()
+    while (iter.hasNext) {
+      val file = iter.next()
+      val path = file.getPath.toString
+      if (path.endsWith(".parquet") && !path.contains(".hoodie")) {
+        files += path
+      }
+    }
+    files.toSeq
+  }
+
+  /**
+   * Reads the Parquet schema (MessageType) from a parquet file.
+   */
+  private def readParquetSchema(filePath: String): MessageType = {
+    val conf = spark.sparkContext.hadoopConfiguration
+    val inputFile = HadoopInputFile.fromPath(new HadoopPath(filePath), conf)
+    val reader = ParquetFileReader.open(inputFile)
+    try {
+      reader.getFooter.getFileMetaData.getSchema
+    } finally {
+      reader.close()
+    }
+  }
+
+  /**
+   * Gets a named field from a GroupType (MessageType) and returns it as a 
GroupType.
+   * Uses getFieldIndex(String) + getType(int) to avoid Scala overload 
resolution issues.
+   */
+  private def getFieldAsGroup(parent: GroupType, fieldName: String): GroupType 
= {
+    val idx: Int = parent.getFieldIndex(fieldName)
+    parent.getType(idx).asGroupType()
+  }
+
+  /**
+   * Checks whether a GroupType contains a field with the given name.
+   */
+  private def groupContainsField(group: GroupType, fieldName: String): Boolean 
= {
+    group.containsField(fieldName)

Review Comment:
   Resolved in c14ae042 - inlined `containsField` at both call sites and 
dropped the helper.



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