[SPARK-38700][SQL] Use error classes in the execution errors of save mode

core/src/main/resources/error/error-classes.json

@@ -196,6 +196,9 @@
   "UNSUPPORTED_OPERATION" : {
     "message" : [ "The operation is not supported: <operation>" ]
   },
+  "UNSUPPORTED_SAVE_MODE" : {
+    "message" : [ "The saveMode is not supported: <saveMode> (<pathExists>)" ]
+  },
   "UNTYPED_SCALA_UDF" : {
     "message" : [ "You're using untyped Scala UDF, which does not have the input type information. Spark may blindly pass null to the Scala closure with primitive-type argument, and the closure will see the default value of the Java type for the null argument, e.g. `udf((x: Int) => x, IntegerType)`, the result is 0 for null input. To get rid of this error, you could:\n1. use typed Scala UDF APIs(without return type parameter), e.g. `udf((x: Int) => x)`\n2. use Java UDF APIs, e.g. `udf(new UDF1[String, Integer] { override def call(s: String): Integer = s.length() }, IntegerType)`, if input types are all non primitive\n3. set \"spark.sql.legacy.allowUntypedScalaUDF\" to true and use this API with caution" ]
   },

sql/catalyst/src/main/scala/org/apache/spark/sql/errors/QueryExecutionErrors.scala

@@ -582,8 +582,9 @@ object QueryExecutionErrors extends QueryErrorsBase {
        """.stripMargin)
   }
 
-  def unsupportedSaveModeError(saveMode: String, pathExists: Boolean): Throwable = {
-    new IllegalStateException(s"unsupported save mode $saveMode ($pathExists)")
+  def saveModeUnsupportedError(saveMode: Any, pathExists: Boolean): Throwable = {
+    new SparkIllegalStateException(errorClass = "UNSUPPORTED_SAVE_MODE",
+      messageParameters = Array(toSQLValue(saveMode), toSQLValue(pathExists)))
   }
 
   def cannotClearOutputDirectoryError(staticPrefixPath: Path): Throwable = {

sql/core/src/main/scala/org/apache/spark/sql/execution/datasources/InsertIntoHadoopFsRelationCommand.scala

@@ -133,7 +133,7 @@ case class InsertIntoHadoopFsRelationCommand(
         case (SaveMode.Ignore, exists) =>
           !exists
         case (s, exists) =>
-          throw QueryExecutionErrors.unsupportedSaveModeError(s.toString, exists)
+          throw QueryExecutionErrors.saveModeUnsupportedError(s, exists)
       }
     }
 

sql/core/src/test/scala/org/apache/spark/sql/errors/QueryExecutionErrorsSuite.scala

@@ -22,7 +22,7 @@ import java.util.Locale
 import test.org.apache.spark.sql.connector.JavaSimpleWritableDataSource
 
 import org.apache.spark.{SparkArithmeticException, SparkException, SparkIllegalStateException, SparkRuntimeException, SparkUnsupportedOperationException, SparkUpgradeException}
-import org.apache.spark.sql.{AnalysisException, DataFrame, QueryTest}
+import org.apache.spark.sql.{AnalysisException, DataFrame, QueryTest, SaveMode}
 import org.apache.spark.sql.catalyst.util.BadRecordException
 import org.apache.spark.sql.connector.SimpleWritableDataSource
 import org.apache.spark.sql.execution.QueryExecutionException
@@ -424,4 +424,17 @@ class QueryExecutionErrorsSuite
       matchMsg = true
     )
   }
+
+  test("UNSUPPORTED_SAVE_MODE: unsupported null saveMode") {
+    withTempPath { path =>
+      val e = intercept[SparkIllegalStateException] {
+        val saveMode: SaveMode = null
+        Seq(1, 2).toDS().write.mode(saveMode).parquet(path.getAbsolutePath)
+      }
+      checkErrorClass(
+        exception = e,
+        errorClass = "UNSUPPORTED_SAVE_MODE",
+        msg = "The saveMode is not supported: NULL (false)")
+    }
+  }
 }