voonhous commented on code in PR #19205:
URL: https://github.com/apache/hudi/pull/19205#discussion_r3794375023


##########
hudi-spark-datasource/hudi-spark/src/test/java/org/apache/hudi/functional/TestMetaFieldsModeE2E.java:
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@@ -0,0 +1,830 @@
+/*
+ * 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.hudi.functional;
+
+import org.apache.hudi.DataSourceReadOptions;
+import org.apache.hudi.DataSourceWriteOptions;
+import org.apache.hudi.SparkAdapterSupport$;
+import org.apache.hudi.common.config.HoodieMetadataConfig;
+import org.apache.hudi.common.model.HoodieRecord;
+import org.apache.hudi.common.model.MetaFieldsMode;
+import org.apache.hudi.common.table.HoodieTableConfig;
+import org.apache.hudi.common.table.HoodieTableMetaClient;
+import org.apache.hudi.common.table.timeline.HoodieInstant;
+import org.apache.hudi.testutils.SparkClientFunctionalTestHarness;
+
+import org.apache.spark.sql.Dataset;
+import org.apache.spark.sql.Row;
+import org.apache.spark.sql.RowFactory;
+import org.apache.spark.sql.SaveMode;
+import org.apache.spark.sql.functions;
+import org.apache.spark.sql.types.DataTypes;
+import org.apache.spark.sql.types.StructField;
+import org.apache.spark.sql.types.StructType;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.EnumSource;
+
+import java.util.Arrays;
+import java.util.Collections;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+import java.util.stream.Collectors;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertNotNull;
+import static org.junit.jupiter.api.Assertions.assertNull;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+/**
+ * Spark-datasource end-to-end tests for the {@code hoodie.meta.fields.mode} 
property on CoW tables.
+ * Every {@link MetaFieldsMode} value is exercised via a write / re-read round 
trip; on-disk column
+ * population is verified by reading the parquet files back and inspecting the 
meta-column values.
+ */
+class TestMetaFieldsModeE2E extends SparkClientFunctionalTestHarness {
+
+  private static StructType simpleSchema() {
+    return DataTypes.createStructType(new StructField[]{
+        DataTypes.createStructField("column1", DataTypes.StringType, true),
+        DataTypes.createStructField("column2", DataTypes.StringType, true),
+        DataTypes.createStructField("column3", DataTypes.StringType, true)
+    }).asNullable();
+  }
+
+  private Map<String, String> baseOptions() {
+    Map<String, String> opts = new HashMap<>();
+    opts.put(DataSourceWriteOptions.RECORDKEY_FIELD().key(), "column1");
+    opts.put(DataSourceWriteOptions.PARTITIONPATH_FIELD().key(), "column2");
+    opts.put(DataSourceWriteOptions.ORDERING_FIELDS().key(), "column3");
+    opts.put(HoodieTableConfig.NAME.key(), "test_meta_fields_mode");
+    opts.put(DataSourceWriteOptions.TABLE_TYPE().key(), "COPY_ON_WRITE");
+    opts.put(HoodieMetadataConfig.ENABLE.key(), "false");
+    return opts;
+  }
+
+  private void writeRows(List<Row> records, StructType schema, Map<String, 
String> options, String path, SaveMode mode) {
+    spark().createDataset(records,
+            
SparkAdapterSupport$.MODULE$.sparkAdapter().getCatalystExpressionUtils().getEncoder(schema))
+        .write()
+        .format("hudi")
+        .options(options)
+        .mode(mode)
+        .save(path);
+  }
+
+  private HoodieTableConfig writeSampleAndGetTableConfig(Map<String, String> 
options, String path) {
+    writeRows(Arrays.asList(
+            RowFactory.create("k1", "p1", "v1"),
+            RowFactory.create("k2", "p1", "v2")),
+        simpleSchema(), options, path, SaveMode.Overwrite);
+    HoodieTableMetaClient metaClient =
+        
HoodieTableMetaClient.builder().setBasePath(path).setConf(storageConf()).build();
+    return metaClient.getTableConfig();
+  }
+
+  /**
+   * End-to-end assertion of the on-disk meta columns after a write. Reads the 
parquet files back
+   * (bypassing Hudi's own read path so we see the raw column values) and 
asserts which meta
+   * columns are non-null.
+   */
+  private void assertMetaColumnPopulation(String path, MetaFieldsMode 
expectedMode) {
+    Dataset<Row> raw = spark().read().parquet(path + "/*/*.parquet");
+    Row first = raw.select(
+        HoodieRecord.COMMIT_TIME_METADATA_FIELD,
+        HoodieRecord.COMMIT_SEQNO_METADATA_FIELD,
+        HoodieRecord.RECORD_KEY_METADATA_FIELD,
+        HoodieRecord.PARTITION_PATH_METADATA_FIELD,
+        HoodieRecord.FILENAME_METADATA_FIELD).first();
+
+    if (expectedMode.isCommitTimePopulated()) {
+      assertNotNull(first.get(0), "expected _hoodie_commit_time to be 
populated for mode " + expectedMode);
+    } else {
+      assertNull(first.get(0), "expected _hoodie_commit_time to be null for 
mode " + expectedMode);
+    }
+    if (expectedMode.isFileNamePopulated()) {
+      assertNotNull(first.get(4), "expected _hoodie_file_name to be populated 
for mode " + expectedMode);
+    } else {
+      assertNull(first.get(4), "expected _hoodie_file_name to be null for mode 
" + expectedMode);
+    }
+    // Record key, partition path, and commit seq no are ALL-only.
+    if (expectedMode == MetaFieldsMode.ALL) {
+      assertNotNull(first.get(2), "record key must be populated in ALL mode");
+      assertNotNull(first.get(3), "partition path must be populated in ALL 
mode");
+      assertNotNull(first.get(1), "commit seq no must be populated in ALL 
mode");
+    } else {
+      assertNull(first.get(2), "record key must be null outside ALL mode, got: 
" + first.get(2));
+      assertNull(first.get(3), "partition path must be null outside ALL mode, 
got: " + first.get(3));
+      assertNull(first.get(1), "commit seq no must be null outside ALL mode, 
got: " + first.get(1));
+    }
+  }
+
+  @Test
+  void allModePersistsAndPopulatesAllColumns() {
+    Map<String, String> options = baseOptions();
+    // ALL is the default; no need to set the mode explicitly.
+    options.put(DataSourceWriteOptions.OPERATION().key(), 
DataSourceWriteOptions.BULK_INSERT_OPERATION_OPT_VAL());
+
+    HoodieTableConfig tc = writeSampleAndGetTableConfig(options, basePath());
+
+    assertTrue(tc.populateMetaFields());
+    assertEquals(MetaFieldsMode.ALL, tc.getMetaFieldsMode());
+    assertMetaColumnPopulation(basePath(), MetaFieldsMode.ALL);
+  }
+
+  @Test
+  void noneModePersistsAndLeavesAllColumnsNull() {
+    Map<String, String> options = baseOptions();
+    options.put(HoodieTableConfig.POPULATE_META_FIELDS.key(), "false");
+    options.put(DataSourceWriteOptions.OPERATION().key(), 
DataSourceWriteOptions.BULK_INSERT_OPERATION_OPT_VAL());
+
+    HoodieTableConfig tc = writeSampleAndGetTableConfig(options, basePath());
+
+    assertFalse(tc.populateMetaFields());
+    assertEquals(MetaFieldsMode.NONE, tc.getMetaFieldsMode());
+    assertMetaColumnPopulation(basePath(), MetaFieldsMode.NONE);
+  }
+
+  @Test
+  void commitTimeOnlyModePopulatesOnlyCommitTime() {
+    Map<String, String> options = baseOptions();
+    options.put(HoodieTableConfig.POPULATE_META_FIELDS.key(), "false");
+    options.put(HoodieTableConfig.META_FIELDS_MODE.key(), 
MetaFieldsMode.COMMIT_TIME_ONLY.name());
+    options.put(DataSourceWriteOptions.OPERATION().key(), 
DataSourceWriteOptions.BULK_INSERT_OPERATION_OPT_VAL());
+
+    HoodieTableConfig tc = writeSampleAndGetTableConfig(options, basePath());
+
+    assertEquals(MetaFieldsMode.COMMIT_TIME_ONLY.name(),
+        tc.getProps().getProperty(HoodieTableConfig.META_FIELDS_MODE.key()));
+    assertEquals(MetaFieldsMode.COMMIT_TIME_ONLY, tc.getMetaFieldsMode());
+    assertMetaColumnPopulation(basePath(), MetaFieldsMode.COMMIT_TIME_ONLY);
+  }
+
+  @Test
+  void fileNameOnlyModePopulatesOnlyFileName() {
+    Map<String, String> options = baseOptions();
+    options.put(HoodieTableConfig.POPULATE_META_FIELDS.key(), "false");
+    options.put(HoodieTableConfig.META_FIELDS_MODE.key(), 
MetaFieldsMode.FILE_NAME_ONLY.name());
+    options.put(DataSourceWriteOptions.OPERATION().key(), 
DataSourceWriteOptions.BULK_INSERT_OPERATION_OPT_VAL());
+
+    HoodieTableConfig tc = writeSampleAndGetTableConfig(options, basePath());
+
+    assertEquals(MetaFieldsMode.FILE_NAME_ONLY, tc.getMetaFieldsMode());
+    assertMetaColumnPopulation(basePath(), MetaFieldsMode.FILE_NAME_ONLY);
+  }
+
+  @Test
+  void commitTimeAndFileNameModePopulatesBoth() {
+    Map<String, String> options = baseOptions();
+    options.put(HoodieTableConfig.POPULATE_META_FIELDS.key(), "false");
+    options.put(HoodieTableConfig.META_FIELDS_MODE.key(), 
MetaFieldsMode.COMMIT_TIME_AND_FILE_NAME.name());
+    options.put(DataSourceWriteOptions.OPERATION().key(), 
DataSourceWriteOptions.BULK_INSERT_OPERATION_OPT_VAL());
+
+    HoodieTableConfig tc = writeSampleAndGetTableConfig(options, basePath());
+
+    assertEquals(MetaFieldsMode.COMMIT_TIME_AND_FILE_NAME, 
tc.getMetaFieldsMode());
+    assertMetaColumnPopulation(basePath(), 
MetaFieldsMode.COMMIT_TIME_AND_FILE_NAME);
+  }
+
+  @Test
+  void explicitlyContradictingTheModeIsRejectedAtTableCreation() {
+    // A selective mode implies populate.meta.fields=false. Stating the 
boolean as true alongside it
+    // is a contradiction, and the user is told rather than having half their 
request discarded.
+    // This is the datasource end of the check in 
HoodieTableMetaClient.TableBuilder.
+    Map<String, String> options = baseOptions();
+    options.put(HoodieTableConfig.POPULATE_META_FIELDS.key(), "true");
+    options.put(HoodieTableConfig.META_FIELDS_MODE.key(), 
MetaFieldsMode.COMMIT_TIME_ONLY.name());
+    options.put(DataSourceWriteOptions.OPERATION().key(), 
DataSourceWriteOptions.BULK_INSERT_OPERATION_OPT_VAL());
+
+    Throwable thrown = assertThrows(Throwable.class, () ->
+        writeSampleAndGetTableConfig(options, basePath()));
+
+    String rootMessage = rootMessageOf(thrown);
+    assertTrue(rootMessage.contains(HoodieTableConfig.META_FIELDS_MODE.key())
+            && 
rootMessage.contains(HoodieTableConfig.POPULATE_META_FIELDS.key()),
+        "the error must name both properties so the user knows which to drop, 
got: " + rootMessage);
+  }
+
+  @Test
+  void selectiveModeWithoutTheLegacyBooleanDerivesItAsFalse() {
+    // The ordinary case: state only the mode. The boolean is derived, never 
carried through
+    // verbatim -- a pre-1.3.0 reader ignores the mode property, so leaving 
populate=true would make
+    // it treat a selectively-written table as ALL.
+    Map<String, String> options = baseOptions();
+    options.put(HoodieTableConfig.META_FIELDS_MODE.key(), 
MetaFieldsMode.COMMIT_TIME_ONLY.name());
+    options.put(DataSourceWriteOptions.OPERATION().key(), 
DataSourceWriteOptions.BULK_INSERT_OPERATION_OPT_VAL());
+
+    HoodieTableConfig tc = writeSampleAndGetTableConfig(options, basePath());
+
+    assertEquals(MetaFieldsMode.COMMIT_TIME_ONLY, tc.getMetaFieldsMode());
+    assertMetaColumnPopulation(basePath(), MetaFieldsMode.COMMIT_TIME_ONLY);
+    assertFalse(tc.populateMetaFields(),
+        "legacy populate.meta.fields must be derived from the mode");
+  }
+
+  @Test
+  void noneModePersistsLegacyBooleanAsFalse() {
+    // The unsafe case this invariant protects: an old incremental reader that 
saw
+    // populate.meta.fields=true on a NONE table would run against all-null 
commit times and
+    // silently return zero rows. Stating only the mode -- the ordinary case 
-- must derive false.
+    Map<String, String> options = baseOptions();
+    options.put(HoodieTableConfig.META_FIELDS_MODE.key(), 
MetaFieldsMode.NONE.name());
+    options.put(DataSourceWriteOptions.OPERATION().key(), 
DataSourceWriteOptions.BULK_INSERT_OPERATION_OPT_VAL());
+
+    HoodieTableConfig tc = writeSampleAndGetTableConfig(options, basePath());
+
+    assertEquals(MetaFieldsMode.NONE, tc.getMetaFieldsMode());
+    assertFalse(tc.populateMetaFields(),
+        "NONE must persist populate.meta.fields=false so pre-1.3.0 readers do 
not treat it as ALL");
+  }
+
+  @Test
+  void allModePersistsLegacyBooleanAsTrue() {
+    Map<String, String> options = baseOptions();
+    options.put(HoodieTableConfig.META_FIELDS_MODE.key(), 
MetaFieldsMode.ALL.name());
+    options.put(DataSourceWriteOptions.OPERATION().key(), 
DataSourceWriteOptions.BULK_INSERT_OPERATION_OPT_VAL());
+
+    HoodieTableConfig tc = writeSampleAndGetTableConfig(options, basePath());
+
+    assertEquals(MetaFieldsMode.ALL, tc.getMetaFieldsMode());
+    assertTrue(tc.populateMetaFields(),
+        "ALL must persist populate.meta.fields=true for pre-1.3.0 readers");
+  }
+
+  @Test
+  void unknownModeValueIsRejected() {
+    Map<String, String> options = baseOptions();
+    options.put(HoodieTableConfig.POPULATE_META_FIELDS.key(), "false");
+    options.put(HoodieTableConfig.META_FIELDS_MODE.key(), "SOMETHING_BOGUS");
+    options.put(DataSourceWriteOptions.OPERATION().key(), 
DataSourceWriteOptions.BULK_INSERT_OPERATION_OPT_VAL());
+
+    Throwable thrown = assertThrows(Throwable.class, () ->
+        writeRows(Collections.singletonList(RowFactory.create("k1", "p1", 
"v1")),
+            simpleSchema(), options, basePath(), SaveMode.Overwrite));
+
+    String rootMessage = rootMessageOf(thrown);
+    assertTrue(rootMessage.contains("SOMETHING_BOGUS"),
+        "Expected error to name the rejected value, got: " + rootMessage);
+  }
+
+  // -------------------------------------------------------------------------
+  // Non-row-writer path coverage. Bulk insert with row.writer.enable=false 
forces the
+  // HoodieAvroParquetWriter path (via HoodieCreateHandle) instead of the 
internal-row writer path.
+  // Both paths must respect the mode identically.
+  // -------------------------------------------------------------------------
+
+  @Test
+  void nonRowWriterPathAllMode() {
+    Map<String, String> options = baseOptions();
+    options.put(DataSourceWriteOptions.OPERATION().key(), 
DataSourceWriteOptions.INSERT_OPERATION_OPT_VAL());
+    options.put("hoodie.datasource.write.row.writer.enable", "false");
+
+    HoodieTableConfig tc = writeSampleAndGetTableConfig(options, basePath());
+    assertEquals(MetaFieldsMode.ALL, tc.getMetaFieldsMode());
+    assertMetaColumnPopulation(basePath(), MetaFieldsMode.ALL);
+  }
+
+  @Test
+  void nonRowWriterPathNoneMode() {
+    Map<String, String> options = baseOptions();
+    options.put(HoodieTableConfig.POPULATE_META_FIELDS.key(), "false");
+    options.put(DataSourceWriteOptions.OPERATION().key(), 
DataSourceWriteOptions.INSERT_OPERATION_OPT_VAL());
+    options.put("hoodie.datasource.write.row.writer.enable", "false");
+
+    HoodieTableConfig tc = writeSampleAndGetTableConfig(options, basePath());
+    assertEquals(MetaFieldsMode.NONE, tc.getMetaFieldsMode());
+    assertMetaColumnPopulation(basePath(), MetaFieldsMode.NONE);
+  }
+
+  @Test
+  void nonRowWriterPathCommitTimeOnly() {
+    Map<String, String> options = baseOptions();
+    options.put(HoodieTableConfig.POPULATE_META_FIELDS.key(), "false");
+    options.put(HoodieTableConfig.META_FIELDS_MODE.key(), 
MetaFieldsMode.COMMIT_TIME_ONLY.name());
+    options.put(DataSourceWriteOptions.OPERATION().key(), 
DataSourceWriteOptions.INSERT_OPERATION_OPT_VAL());
+    options.put("hoodie.datasource.write.row.writer.enable", "false");
+
+    HoodieTableConfig tc = writeSampleAndGetTableConfig(options, basePath());
+    assertEquals(MetaFieldsMode.COMMIT_TIME_ONLY, tc.getMetaFieldsMode());
+    assertMetaColumnPopulation(basePath(), MetaFieldsMode.COMMIT_TIME_ONLY);
+  }
+
+  @Test
+  void nonRowWriterPathFileNameOnly() {
+    Map<String, String> options = baseOptions();
+    options.put(HoodieTableConfig.POPULATE_META_FIELDS.key(), "false");
+    options.put(HoodieTableConfig.META_FIELDS_MODE.key(), 
MetaFieldsMode.FILE_NAME_ONLY.name());
+    options.put(DataSourceWriteOptions.OPERATION().key(), 
DataSourceWriteOptions.INSERT_OPERATION_OPT_VAL());
+    options.put("hoodie.datasource.write.row.writer.enable", "false");
+
+    HoodieTableConfig tc = writeSampleAndGetTableConfig(options, basePath());
+    assertEquals(MetaFieldsMode.FILE_NAME_ONLY, tc.getMetaFieldsMode());
+    assertMetaColumnPopulation(basePath(), MetaFieldsMode.FILE_NAME_ONLY);
+  }
+
+  @Test
+  void nonRowWriterPathCommitTimeAndFileName() {
+    Map<String, String> options = baseOptions();
+    options.put(HoodieTableConfig.POPULATE_META_FIELDS.key(), "false");
+    options.put(HoodieTableConfig.META_FIELDS_MODE.key(), 
MetaFieldsMode.COMMIT_TIME_AND_FILE_NAME.name());
+    options.put(DataSourceWriteOptions.OPERATION().key(), 
DataSourceWriteOptions.INSERT_OPERATION_OPT_VAL());
+    options.put("hoodie.datasource.write.row.writer.enable", "false");
+
+    HoodieTableConfig tc = writeSampleAndGetTableConfig(options, basePath());
+    assertEquals(MetaFieldsMode.COMMIT_TIME_AND_FILE_NAME, 
tc.getMetaFieldsMode());
+    assertMetaColumnPopulation(basePath(), 
MetaFieldsMode.COMMIT_TIME_AND_FILE_NAME);
+  }
+
+  // -------------------------------------------------------------------------
+  // Clustering coverage.
+  //
+  // These target 358fbfdd717a, where HoodieRowCreateHandle's selective path 
copied the *source
+  // row's* _hoodie_file_name during clustering, leaving records pointing at a 
file clustering had
+  // just replaced. asserting only assertNotNull cannot catch that — the stale 
value is non-null too
+  // — so the assertion here compares the column against the file actually 
holding the row.
+  //
+  // Only the selective modes are covered: ALL and NONE route through writeRow 
/
+  // writeRowNoMetaFields and never enter the branch the fix touched.
+  // -------------------------------------------------------------------------
+
+  private Map<String, String> inlineClusteringOptions(MetaFieldsMode mode) {
+    Map<String, String> options = baseOptions();
+    options.put(HoodieTableConfig.META_FIELDS_MODE.key(), mode.name());
+    options.put(DataSourceWriteOptions.OPERATION().key(), 
DataSourceWriteOptions.BULK_INSERT_OPERATION_OPT_VAL());
+    options.put("hoodie.clustering.inline", "true");
+    options.put("hoodie.clustering.inline.max.commits", "1");
+    options.put("hoodie.clustering.plan.strategy.target.file.max.bytes", 
"10485760");
+    options.put("hoodie.clustering.plan.strategy.small.file.limit", 
"10485760");
+    return options;
+  }
+
+  /**
+   * Asserts clustering actually ran and that every surviving row's {@code 
_hoodie_file_name} names
+   * the file holding it.
+   *
+   * <p>Reads through Hudi rather than globbing the parquet directly: after 
inline clustering the
+   * pre-clustering file is still on disk (no cleaning has run), so a raw glob 
would also inspect
+   * rows that were replaced and are no longer served.
+   */
+  private void assertClusteredFileNamesPointAtTheirOwnFile(String path, 
MetaFieldsMode mode) {
+    HoodieTableMetaClient metaClient =
+        
HoodieTableMetaClient.builder().setBasePath(path).setConf(storageConf()).build();
+    assertEquals(mode, metaClient.getTableConfig().getMetaFieldsMode());
+    assertEquals(1, 
metaClient.getActiveTimeline().getCompletedReplaceTimeline().countInstants(),
+        "clustering must have produced a replacecommit, otherwise this test 
proves nothing");
+
+    List<Row> rows = spark().read().format("hudi").load(path)
+        .withColumn("__containing_file", functions.input_file_name())
+        .collectAsList();
+    assertFalse(rows.isEmpty(), "expected the clustered table to still serve 
rows");
+
+    for (Row row : rows) {
+      String fileName = row.getAs(HoodieRecord.FILENAME_METADATA_FIELD);
+      String containingFile = row.getAs("__containing_file").toString();
+      if (mode.isFileNamePopulated()) {
+        assertNotNull(fileName, "file name is opted in, so clustered rows must 
carry one");
+        assertTrue(containingFile.endsWith("/" + fileName),
+            "_hoodie_file_name must name the file holding the row after 
clustering, not the "
+                + "pre-clustering file it was read from; got " + fileName + " 
inside " + containingFile);
+      } else {
+        assertNull(fileName,
+            "file name is not opted in, so clustering must not populate it; 
got " + fileName);
+      }
+    }
+  }
+
+  @Test
+  void clusteringWritesTheNewFileNameUnderFileNameOnly() {
+    Map<String, String> options = 
inlineClusteringOptions(MetaFieldsMode.FILE_NAME_ONLY);
+    writeRows(Arrays.asList(
+            RowFactory.create("k1", "p1", "v1"),
+            RowFactory.create("k2", "p1", "v2"),
+            RowFactory.create("k3", "p1", "v3")),
+        simpleSchema(), options, basePath(), SaveMode.Overwrite);
+
+    assertClusteredFileNamesPointAtTheirOwnFile(basePath(), 
MetaFieldsMode.FILE_NAME_ONLY);
+  }
+
+  @Test
+  void clusteringWritesTheNewFileNameUnderCommitTimeAndFileName() {
+    Map<String, String> options = 
inlineClusteringOptions(MetaFieldsMode.COMMIT_TIME_AND_FILE_NAME);
+    writeRows(Arrays.asList(
+            RowFactory.create("k1", "p1", "v1"),
+            RowFactory.create("k2", "p1", "v2"),
+            RowFactory.create("k3", "p1", "v3")),
+        simpleSchema(), options, basePath(), SaveMode.Overwrite);
+
+    assertClusteredFileNamesPointAtTheirOwnFile(basePath(), 
MetaFieldsMode.COMMIT_TIME_AND_FILE_NAME);
+  }
+
+  @Test
+  void clusteringLeavesFileNameNullUnderCommitTimeOnly() {

Review Comment:
   Dug into the null. Short answer to your question: yes, `format("hudi")` does 
serve `_hoodie_commit_time` on a `COMMIT_TIME_ONLY` table, and this suite 
already proves it -- `appendWithoutRestatingTheModeKeepsTheTableSelective` 
reads through `format("hudi")` on a non-clustered `COMMIT_TIME_ONLY` table and 
asserts a non-null commit time on every row (`TestMetaFieldsModeE2E:832-838`), 
green at `6c8f179`. I also walked the snapshot read path looking for a 
meta-field special case and there is none: 
`FileGroupReaderSchemaHandler.generateRequiredSchema` returns the requested 
schema verbatim when the slice has no log files, and neither 
`HoodieFileGroupReaderBasedFileFormat` nor 
`SparkFileFormatInternalRowReaderContext` strips or null-pads meta columns. The 
read is faithful.
   
   So your assertion was not reading the wrong thing. The clustered files 
physically carry a null `_hoodie_commit_time`. This thread found a real bug.
   
   Two things point at the same place:
   
   1. The glob check you removed was failing for the same reason, not because 
of stale files. The helper comment says pre-clustering files "may predate the 
current mode", but in this fixture they cannot: 
`clusteringLeavesFileNameNullUnderCommitTimeOnly` writes with 
`SaveMode.Overwrite` and `inlineClusteringOptions` sets the mode on that very 
first write, so every parquet file on disk was written under 
`COMMIT_TIME_ONLY`. The pre-clustering file passes both glob assertions; only 
post-clustering rows can fail it. The raw-parquet failure was independent 
confirmation of the null, and removing the call hid it.
   
   2. The asymmetry you observed is exactly the shape of 
`writeRowSelectiveMetaFields` (`HoodieRowCreateHandle:184-201`): 
`_hoodie_file_name` is stamped fresh from the handle's own file, so it is 
always correct; `_hoodie_commit_time` is copied from the incoming row when 
`shouldPreserveHoodieMetadata` is set, which clustering defaults to true 
(`MultipleSparkJobExecutionStrategy:104`). For a clustered row to read back 
with a correct file name and a null commit time, 
`row.getUTF8String(COMMIT_TIME_METADATA_FIELD_ORD)` must already have been null 
-- the clustering input carried the null and preservation persisted it.
   
   The input rows come from `readRecordsForGroupAsRow`'s file-group read. Why 
that read returns null at ordinal 0 while the same machinery on the query path 
serves it populated is the one hop I could not settle by inspection. The two 
setups differ in exactly two ways, worth probing first:
   
   - Schema provenance: the query path prunes the schema resolved from commit 
metadata; clustering builds 
`addMetadataFields(TableSchemaResolver.getTableSchema(false), 
allowOperationMetadataField())` (`MultipleSparkJobExecutionStrategy:253-256`), 
i.e. synthesized meta fields, plus possibly `_hoodie_operation` at ordinal 5 
which the file does not have.
   - Reader context: the query path hands the parquet reader 
`sparkRequiredSchema`; `SparkReaderContextFactory.getContext()` leaves it empty 
and uses the broadcast non-vectorized reader.
   
   `inputRecords.select(_hoodie_commit_time).show()` before 
`performClusteringWithRecordsAsRow` will split "FG read returned null" from 
"writer dropped it" in one run.
   
   Given the above: please restore the withdrawn direct-comparison assertion 
(it is the regression test for this), re-point `assertMetaColumnPopulation` at 
the clustered `COMMIT_TIME_ONLY` table (the physical half; with this fixture 
the stale-file caveat does not apply), and fix the clustering input read. As it 
stands clustering destroys the one column a `COMMIT_TIME_ONLY` table exists to 
keep, and any incremental read window that crosses the clustering commit 
silently loses those rows -- so this is a blocker for the mode, not a test gap.
   



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