stevomitric commented on code in PR #55326:
URL: https://github.com/apache/spark/pull/55326#discussion_r3431509278


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sql/core/src/main/scala/org/apache/spark/sql/execution/datasources/parquet/types/ops/ParquetTypeOps.scala:
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@@ -0,0 +1,227 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.spark.sql.execution.datasources.parquet.types.ops
+
+import java.time.ZoneId
+
+import org.apache.parquet.io.api.{Converter, RecordConsumer}
+import org.apache.parquet.schema.Type
+import org.apache.parquet.schema.Type.Repetition
+
+import org.apache.spark.sql.catalyst.expressions.SpecializedGetters
+import org.apache.spark.sql.catalyst.util.RebaseDateTime.RebaseSpec
+import 
org.apache.spark.sql.execution.datasources.parquet.{HasParentContainerUpdater, 
ParentContainerUpdater, ParquetToSparkSchemaConverter}
+import org.apache.spark.sql.internal.SQLConf
+import org.apache.spark.sql.types.{DataType, StructType, TimeType}
+
+/**
+ * Optional trait for Parquet storage format integration in the Types 
Framework.
+ *
+ * Implement this trait to enable Parquet read/write support for a framework 
type. Each framework
+ * type that supports Parquet provides a concrete implementation and registers 
it in the companion
+ * object's apply() method.
+ *
+ * The trait covers these Parquet concerns:
+ *   - Schema conversion: Spark DataType -> Parquet schema type (write path)
+ *   - Value write: writing values to Parquet RecordConsumer
+ *   - Row-based read: creating Parquet converters for reading into InternalRow
+ *   - Type gates: declaring Parquet support (supportDataType) and the 
vectorized-read
+ *     capability flag (isBatchReadSupported)
+ *   - Schema clipping: declaring internal struct schema for column pruning
+ *
+ * NOT yet on the trait (deferred to follow-ups): vectorized-read batch 
updaters and
+ * filter-pushdown predicates. Only the isBatchReadSupported capability gate 
exists today;
+ * the actual vectorized updater and filter predicate hooks are not 
implemented here.
+ *
+ * DISPATCH PATTERN: Framework FIRST at all integration sites. Each Parquet 
infrastructure
+ * method wraps itself with:
+ * {{{
+ *   ParquetTypeOps(dt).map(_.method(...)).getOrElse(methodDefault(dt, ...))
+ * }}}
+ * The original code is extracted to a *Default method unchanged. For a 
framework-managed type
+ * the ops handles it; for any other type ParquetTypeOps(dt) is None and the 
*Default fallback
+ * executes the original code path.
+ *
+ * STRUCT-BACKED TYPES: Types stored as Parquet groups should override the
+ * extended newConverter overload (which provides 
schemaConverter/convertTz/rebase specs for
+ * recursive field conversion) and declare parquetStructSchema for column 
pruning.
+ *
+ * @see TimeTypeParquetOps for a reference implementation (primitive 
Long-backed type)
+ * @since 4.3.0
+ */
+private[parquet] trait ParquetTypeOps extends Serializable {
+
+  // ==================== Schema Conversion ====================
+
+  /**
+   * Converts this Spark DataType to a Parquet schema Type (for the write 
path).
+   *
+   * For primitive types: returns a PrimitiveType with the appropriate 
annotation.
+   * For struct-backed types: returns a GroupType with sub-fields and a 
logical type annotation.
+   *
+   * @param fieldName the column/field name in the Parquet schema
+   * @param repetition REQUIRED, OPTIONAL, or REPEATED
+   * @param inShredded whether the field is nested within a shredded Variant 
schema
+   * @return the Parquet Type for this DataType
+   */
+  def convertToParquetType(
+      fieldName: String, repetition: Repetition, inShredded: Boolean = false): 
Type
+
+  // ==================== Value Write ====================
+
+  /**
+   * Creates a value writer that writes values of this type to a Parquet 
RecordConsumer.
+   *
+   * The writer is a closure that captures the RecordConsumer and is called 
once per row during
+   * Parquet file writing. The RecordConsumer is instance-specific (one per 
output file).
+   *
+   * IMPORTANT: The RecordConsumer is passed as a lazy supplier (() => 
RecordConsumer) because
+   * makeWriter is called during ParquetWriteSupport.init(), when 
recordConsumer is still null.
+   * It gets set later in prepareForWrite(). The closure must evaluate the 
supplier at write
+   * time, not at creation time. The existing infrastructure closures work 
because they capture
+   * `this.recordConsumer` (a var field - Scala closures over vars capture the 
reference, not
+   * the value). The supplier lambda achieves the same lazy evaluation for ops 
code.
+   *
+   * For primitive types: directly calls recordConsumer.addLong/addBinary/etc. 
with any
+   * necessary conversion (e.g., nanos to micros for TimeType).
+   *
+   * @param recordConsumer lazy supplier for the Parquet output stream (null 
during init)
+   * @param makeFieldWriter callback into ParquetWriteSupport for recursive 
field writer creation
+   *                        (struct-backed types use this to create writers 
for sub-fields)
+   * @return a closure that writes a value from a row at the given ordinal
+   */
+  def makeWriter(
+      recordConsumer: () => RecordConsumer,
+      makeFieldWriter: DataType => (SpecializedGetters, Int) => Unit
+  ): (SpecializedGetters, Int) => Unit
+
+  // ==================== Row-Based Read ====================
+
+  /**
+   * Creates a Parquet Converter for reading values of this type (simple 
version).
+   *
+   * Primitive types override this method. The converter typically extends
+   * ParquetPrimitiveConverter and overrides addLong/addBinary/etc. to perform 
any necessary
+   * conversion (e.g., micros to nanos for TimeType).
+   *
+   * WARNING: Struct-backed types must override the EXTENDED overload below 
instead. This simple
+   * version does not provide the schemaConverter, timezone, or rebase specs 
needed for recursive
+   * field conversion. Overriding only this method for a struct-backed type 
will compile but
+   * produce incorrect behavior at runtime (missing timezone conversion, 
calendar rebasing, etc.).
+   *
+   * @param parquetType the Parquet schema type for this field
+   * @param updater the parent container to set converted values into
+   * @return a Converter that reads Parquet values into the parent container
+   */
+  def newConverter(
+      parquetType: Type,
+      updater: ParentContainerUpdater): Converter with 
HasParentContainerUpdater
+
+  /**
+   * Creates a Parquet Converter for reading values of this type (extended 
version).
+   *
+   * Struct-backed types override this method to receive the extra context 
needed for recursive
+   * field conversion (schemaConverter for nested type resolution, timezone 
for timestamp
+   * conversion, rebase specs for calendar rebasing).
+   *
+   * Default delegates to the simple version - primitive types inherit this 
default and
+   * ignore the extra parameters.
+   *
+   * @param parquetType the Parquet schema type for this field
+   * @param updater the parent container to set converted values into
+   * @param schemaConverter for resolving nested Parquet schemas to Spark types
+   * @param convertTz timezone for timestamp conversion
+   * @param datetimeRebaseSpec calendar rebasing spec for datetime types
+   * @param int96RebaseSpec calendar rebasing spec for INT96 timestamps
+   * @return a Converter that reads Parquet values into the parent container
+   */
+  def newConverter(
+      parquetType: Type,
+      updater: ParentContainerUpdater,
+      schemaConverter: ParquetToSparkSchemaConverter,
+      convertTz: Option[ZoneId],
+      datetimeRebaseSpec: RebaseSpec,
+      int96RebaseSpec: RebaseSpec): Converter with HasParentContainerUpdater =
+    newConverter(parquetType, updater)
+
+  // ==================== Type Gates ====================
+
+  /**
+   * Whether this type is supported by the Parquet data source.
+   * Used by ParquetFileFormat.supportDataType.
+   */
+  def supportDataType: Boolean = true
+
+  /**
+   * Whether vectorized (batch) reading is supported for this type.
+   * Used by ParquetUtils.isBatchReadSupported. Default is false - types must 
opt in
+   * by overriding to true. When false, Spark uses the row-based read path 
(newConverter)
+   * which is always available.
+   *
+   * PRECONDITION: there is no framework vectorized-read hook yet, so 
returning true is only
+   * safe for a type the legacy Java vectorized path 
(ParquetVectorUpdaterFactory /
+   * VectorizedColumnReader) already handles. A new type that returns true 
without that
+   * legacy support would route into a factory that does not recognize it. 
TimeType is safe
+   * here precisely because the legacy path handles it; until the vectorized 
integration
+   * (follow-up) lands, other types should leave this false.
+   *
+   * @param sqlConf the active SQL configuration
+   */
+  def isBatchReadSupported(sqlConf: SQLConf): Boolean = false
+
+  // ==================== Schema Clipping (Struct-Backed Types) 
====================
+
+  /**
+   * The Parquet-level struct schema for column pruning.
+   *
+   * Struct-backed types (stored as a Parquet GROUP) return the field schema 
so that
+   * ParquetReadSupport.clipParquetType can prune sub-fields based on the 
query's
+   * requested columns.
+   *
+   * This is independent of PhysicalDataType - Parquet storage representation 
may differ from
+   * internal row representation. A type could be PhysicalBinaryType in rows 
but a GROUP in
+   * Parquet (e.g., a type stored as binary in rows but as a GROUP with 
metadata fields on disk).
+   *
+   * Primitive types return None (no sub-fields to clip).
+   */
+  def parquetStructSchema: Option[StructType] = None
+}
+
+/**
+ * Factory object for creating ParquetTypeOps instances.
+ *
+ * Provides forward lookup (DataType -> ops) for framework-first dispatch at 
Parquet
+ * integration sites. apply() returns Some only for framework-managed types, 
so callers
+ * fall back to the legacy path for everything else.
+ */
+private[parquet] object ParquetTypeOps {
+
+  /**
+   * Returns a ParquetTypeOps instance for the given DataType, if supported.
+   *
+   * Returns None if the type has no Parquet ops.
+   * This is the single registration point for all Parquet type operations.
+   */
+  def apply(dt: DataType): Option[ParquetTypeOps] = {
+    dt match {
+      case tt: TimeType => Some(TimeTypeParquetOps(tt))

Review Comment:
   This is not quite right. Stricter `requireCompatibleParquetType` rejection 
isn't *unconditional* see @cloud-fan comment



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