[GLUTEN-1433] [VL] Add config to disable TimestampNTZ validation fallback

backends-velox/src/test/scala/org/apache/gluten/functions/ScalarFunctionsValidateSuite.scala

@@ -1521,4 +1521,27 @@ abstract class ScalarFunctionsValidateSuite extends FunctionsValidateSuite {
         }
     }
   }
+  test("test_current_timestamp") {
+    val df = spark.sql("SELECT l_orderkey, current_timestamp() from lineitem limit 1")
+    val optimizedPlan = df.queryExecution.optimizedPlan.toString()
+    assert(
+      !optimizedPlan.contains("CurrentTimestamp"),
+      s"Expected CurrentTimestamp to be folded to a literal, but got: $optimizedPlan"
+    )
+    checkGlutenPlan[ProjectExecTransformer](df)
+    checkFallbackOperators(df, 0)
+    df.collect()
+  }
+
+  test("test_now") {
+    val df = spark.sql("SELECT l_orderkey, now() from lineitem limit 1")
+    val optimizedPlan = df.queryExecution.optimizedPlan.toString()
+    assert(
+      !optimizedPlan.contains("Now"),
+      s"Expected Now to be folded to a literal, but got: $optimizedPlan"
+    )
+    checkGlutenPlan[ProjectExecTransformer](df)
+    checkFallbackOperators(df, 0)
+    df.collect()
+  }
 }

gluten-substrait/src/main/scala/org/apache/gluten/extension/columnar/validator/Validators.scala

@@ -220,6 +220,28 @@ object Validators {
 
   private class FallbackByTimestampNTZ() extends Validator {
     override def validate(plan: SparkPlan): Validator.OutCome = {
+      // Check if TimestampNTZ validation is enabled via VeloxConfig
+      // Use reflection to avoid compile-time dependency on backends-velox module
+      val enableValidation =
+        try {
+          // scalastyle:off classforname
+          val veloxConfigClass = Class.forName("org.apache.gluten.config.VeloxConfig")
+          // scalastyle:on classforname
+          val getMethod = veloxConfigClass.getMethod("get")
+          val configInstance = getMethod.invoke(null)
+          val enableMethod = veloxConfigClass.getMethod("enableTimestampNtzValidation")
+          enableMethod.invoke(configInstance).asInstanceOf[Boolean]
+        } catch {
+          case _: Exception =>
+            // If VeloxConfig is not available (e.g., non-Velox backend), default to enabled
+            true
+        }
+
+      if (!enableValidation) {
+        // Validation is disabled, allow TimestampNTZ
+        return pass()
+      }
+
       def containsNTZ(dataType: DataType): Boolean = dataType match {
         case dt if dt.catalogString == "timestamp_ntz" => true
         case st: StructType => st.exists(f => containsNTZ(f.dataType))