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:
##########
@@ -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:
   Short answer: yes, `format("hudi")` serves `_hoodie_commit_time` on a 
`COMMIT_TIME_ONLY` table. `appendWithoutRestatingTheModeKeepsTheTableSelective` 
(`TestMetaFieldsModeE2E:832-838`) asserts exactly that and is green, and I 
found no meta-field stripping or null-padding anywhere on the snapshot read 
path. 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 confirmations:
   
   1. The glob check you removed was failing on the clustered file, not on 
stale files. This fixture writes `SaveMode.Overwrite` with the mode set on that 
first write, so no file on disk predates `COMMIT_TIME_ONLY`; only 
post-clustering rows could fail it. Removing the call hid a second sighting.
   2. The asymmetry matches `writeRowSelectiveMetaFields` 
(`HoodieRowCreateHandle:184-201`): `_hoodie_file_name` is stamped fresh from 
the handle's own file, while `_hoodie_commit_time` is copied from the incoming 
row under preservation, which clustering defaults on. A correct file name plus 
a null commit time means the clustering input row was already null at ordinal 0.
   
   That input comes from `readRecordsForGroupAsRow`'s file-group read; why it 
returns null there but populated on the query path is the one open hop. 
`inputRecords.select("_hoodie_commit_time").show()` before 
`performClusteringWithRecordsAsRow` settles it in one run. Two suspects: the 
synthesized schema from `addMetadataFields(getTableSchema(false))` 
(`MultipleSparkJobExecutionStrategy:253-256`), and `SparkReaderContextFactory` 
leaving `sparkRequiredSchema` empty.
   
   Please restore the withdrawn assertion, re-point 
`assertMetaColumnPopulation` at the clustered table (the stale-file caveat does 
not apply here), and fix the input read. Clustering currently destroys the one 
column this mode exists to keep, and incremental reads crossing the clustering 
commit lose those rows -- a blocker, not a test gap.
   



##########
hudi-spark-datasource/hudi-spark/src/test/java/org/apache/hudi/functional/TestMetaFieldsModeE2E.java:
##########
@@ -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");

Review Comment:
   Checked the latest push (6c8f179): the matrix ({simple, single-field 
complex, non-partitioned} x hive_style on/off) and the HoodieBaseRelation 
comment correction are not in yet, so keeping this thread open until those land.
   
   On the split: agree, the writer-side field-count check can go to its own 
issue. We can defer.



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