[Kernel] Enable writing to tables at version 7 when no invariants are…

… defined in the schema (#4027)

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#### Which Delta project/connector is this regarding?
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- [ ] Spark
- [ ] Standalone
- [ ] Flink
- [x] Kernel
- [ ] Other (fill in here)

## Description

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Currently, Kernel doesn't support the `invariants` feature and could not
write to tables on writer version 7 if their `writerFeatures` contains
`invariants`.

With this change, Kernel will allow `invariants` to be present in the
`writerFeatures` for tables on writer version 7, provided the schema
does not define any invariants. This unblocks Kernel from writing to
such tables.

## How was this patch tested?

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Tests are added in `TableFeaturesSuite.scala`. It also added a missing
integration test in `RowTrackingSuite.scala` that was previously blocked
by `invariants`.


## Does this PR introduce _any_ user-facing changes?

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No.

---------

Co-authored-by: Johan Lasperas <[email protected]>

kernel/kernel-api/src/main/java/io/delta/kernel/internal/TableFeatures.java

@@ -64,6 +64,8 @@ public class TableFeatures {
 
   public static final String ROW_TRACKING_FEATURE_NAME = "rowTracking";
 
+  public static final String INVARIANTS_FEATURE_NAME = "invariants";
+
   /** The minimum writer version required to support table features. */
   public static final int TABLE_FEATURES_MIN_WRITER_VERSION = 7;
 
@@ -136,10 +138,15 @@ public static void validateWriteSupportedTable(
         throw unsupportedWriterProtocol(tablePath, minWriterVersion);
       case 7:
         for (String writerFeature : protocol.getWriterFeatures()) {
-          if (!SUPPORTED_WRITER_FEATURES.contains(writerFeature)) {
+          if (writerFeature.equals(INVARIANTS_FEATURE_NAME)) {
+            // For version 7, we allow 'invariants' to be present in the protocol's writerFeatures
+            // to unblock certain use cases, provided that no invariants are defined in the schema.
+            validateNoInvariants(tableSchema);
+          } else if (!SUPPORTED_WRITER_FEATURES.contains(writerFeature)) {
             throw unsupportedWriterFeature(tablePath, writerFeature);
           }
         }
+
         // Eventually we may have a way to declare and enforce dependencies between features.
         // By putting this check for row tracking here, it makes it easier to spot that row
         // tracking defines such a dependency that can be implicitly checked.

kernel/kernel-api/src/test/scala/io/delta/kernel/internal/TableFeaturesSuite.scala

@@ -80,15 +80,30 @@ class TableFeaturesSuite extends AnyFunSuite {
     }
   }
 
-  Seq("invariants", "checkConstraints", "generatedColumns", "allowColumnDefaults", "changeDataFeed",
+  Seq("checkConstraints", "generatedColumns", "allowColumnDefaults", "changeDataFeed",
     "identityColumns", "deletionVectors", "timestampNtz", "v2Checkpoint", "icebergCompatV1",
-    "icebergCompatV2", "clustering",
-      "vacuumProtocolCheck").foreach { unsupportedWriterFeature =>
+    "icebergCompatV2", "clustering", "vacuumProtocolCheck").foreach { unsupportedWriterFeature =>
     test(s"validateWriteSupported: protocol 7 with $unsupportedWriterFeature") {
       checkUnsupported(createTestProtocol(minWriterVersion = 7, unsupportedWriterFeature))
     }
   }
 
+  test("validateWriteSupported: protocol 7 with invariants, schema doesn't contain invariants") {
+    checkSupported(
+      createTestProtocol(minWriterVersion = 7, "invariants"),
+      metadata = createTestMetadata(),
+      schema = createTestSchema(includeInvariant = false)
+    )
+  }
+
+  test("validateWriteSupported: protocol 7 with invariants, schema contains invariants") {
+    checkUnsupported(
+      createTestProtocol(minWriterVersion = 7, "invariants"),
+      metadata = createTestMetadata(),
+      schema = createTestSchema(includeInvariant = true)
+    )
+  }
+
   def checkSupported(
     protocol: Protocol,
     metadata: Metadata = null,

kernel/kernel-defaults/src/test/scala/io/delta/kernel/defaults/RowTrackingSuite.scala

@@ -296,7 +296,45 @@ class RowTrackingSuite extends DeltaTableWriteSuiteBase with ParquetSuiteBase {
   }
 
   test("Integration test - Write table with Spark then write with Kernel") {
-    // TODO: Implement this test. Creating and writing a table using Spark with row tracking also
-    //  enables the 'invariants' feature, which is not yet supported by the Kernel.
+    withTempDirAndEngine((tablePath, engine) => {
+      val tbl = "tbl"
+      withTable(tbl) {
+        spark.sql(
+          s"""CREATE TABLE $tbl (id LONG) USING delta
+             |LOCATION '$tablePath'
+             |TBLPROPERTIES (
+             |  'delta.feature.domainMetadata' = 'enabled',
+             |  'delta.feature.rowTracking' = 'supported'
+             |)
+             |""".stripMargin
+        )
+
+        // Write to the table using delta-spark
+        spark.range(0, 20).write.format("delta").mode("append").save(tablePath) // version 1
+        spark.range(20, 100).write.format("delta").mode("append").save(tablePath) // version 2
+
+        // Verify the table state
+        verifyBaseRowIDs(engine, tablePath, Seq(0, 20))
+        verifyDefaultRowCommitVersion(engine, tablePath, Seq(1, 2))
+        verifyHighWatermark(engine, tablePath, 99)
+
+        // Write to the table using Kernel
+        val schema = new StructType().add("id", LONG)
+        val dataBatch1 = generateData(schema, Seq.empty, Map.empty, 100, 1) // 100 rows
+        val dataBatch2 = generateData(schema, Seq.empty, Map.empty, 200, 1) // 200 rows
+        val dataBatch3 = generateData(schema, Seq.empty, Map.empty, 400, 1) // 400 rows
+        appendData(
+          engine,
+          tablePath,
+          schema = schema,
+          data = Seq(dataBatch1, dataBatch2, dataBatch3).map(Map.empty[String, Literal] -> _)
+        ) // version 3
+
+        // Verify the table state
+        verifyBaseRowIDs(engine, tablePath, Seq(0, 20, 100, 200, 400))
+        verifyDefaultRowCommitVersion(engine, tablePath, Seq(1, 2, 3, 3, 3))
+        verifyHighWatermark(engine, tablePath, 799)
+      }
+    })
   }
 }