[SPARK-59023][SQL] Support none mode in spark.sql.ui.explainMode to skip plan description in SQL events

sql/catalyst/src/main/scala/org/apache/spark/sql/internal/SQLConf.scala

@@ -6665,14 +6665,15 @@ object SQLConf {
     .createWithDefault(false)
 
   val UI_EXPLAIN_MODE = buildConf("spark.sql.ui.explainMode")
-    .doc("Configures the query explain mode used in the Spark SQL UI. The value can be 'simple', " +
-      "'extended', 'codegen', 'cost', or 'formatted'. The default value is 'formatted'.")
+    .doc("Configures the query explain mode used in the Spark SQL UI. The value can be 'none', " +
+      "'simple', 'extended', 'codegen', 'cost', or 'formatted'. The default value is 'formatted'.")
     .version("3.1.0")
     .stringConf
     .transform(_.toUpperCase(Locale.ROOT))
-    .checkValue(mode => Set("SIMPLE", "EXTENDED", "CODEGEN", "COST", "FORMATTED").contains(mode),
-      "Invalid value for 'spark.sql.ui.explainMode'. Valid values are 'simple', 'extended', " +
-      "'codegen', 'cost' and 'formatted'.")
+    .checkValue(mode =>
+      Set("NONE", "SIMPLE", "EXTENDED", "CODEGEN", "COST", "FORMATTED").contains(mode),
+      "Invalid value for 'spark.sql.ui.explainMode'. Valid values are 'none', 'simple', " +
+      "'extended', 'codegen', 'cost' and 'formatted'.")
     .createWithDefault("formatted")
 
   val SOURCES_BINARY_FILE_MAX_LENGTH = buildConf("spark.sql.sources.binaryFile.maxLength")

sql/core/src/main/scala/org/apache/spark/sql/execution/SQLExecution.scala

@@ -120,6 +120,27 @@ object SQLExecution extends Logging {
     }
   }
 
+  private[sql] val NONE_EXPLAIN_MODE = "none"
+
+  private[sql] val NO_PLAN_DESCRIPTION =
+    s"No plan description because ${SQLConf.UI_EXPLAIN_MODE.key}=$NONE_EXPLAIN_MODE"
+
+  /**
+   * Returns the plan description carried by the SQL UI events, or a placeholder when the UI
+   * explain mode is `none`, in which case the explain string, which is expensive to build for
+   * large plans, is not generated at all.
+   *
+   * `none` is intentionally not an [[ExplainMode]]: it only makes sense for the UI events, and
+   * keeping it here avoids making `df.explain("none")` a valid public API.
+   */
+  private[sql] def planDescription(qe: QueryExecution, uiExplainMode: String): String = {
+    if (uiExplainMode.equalsIgnoreCase(NONE_EXPLAIN_MODE)) {
+      NO_PLAN_DESCRIPTION
+    } else {
+      qe.explainString(ExplainMode.fromString(uiExplainMode))
+    }
+  }
+
   /**
    * Wrap an action that will execute "queryExecution" to track all Spark jobs in the body so that
    * we can connect them with an execution.
@@ -209,9 +230,8 @@ object SQLExecution extends Logging {
                   sc.listenerBus.post(startEvent)
                   throw e
                 case Right(f) =>
-                  val planDescriptionMode =
-                    ExplainMode.fromString(sparkSession.sessionState.conf.uiExplainMode)
-                  val planDesc = queryExecution.explainString(planDescriptionMode)
+                  val planDesc = planDescription(
+                    queryExecution, sparkSession.sessionState.conf.uiExplainMode)
                   val planInfo = try {
                     SparkPlanInfo.fromSparkPlan(queryExecution.executedPlan)
                   } catch {

sql/core/src/main/scala/org/apache/spark/sql/execution/adaptive/AdaptiveSparkPlanExec.scala

@@ -1145,10 +1145,9 @@ case class AdaptiveSparkPlanExec(
       context.session.sparkContext.listenerBus.post(SparkListenerSQLAdaptiveSQLMetricUpdates(
         executionId, newMetrics))
     } else {
-      val planDescriptionMode = ExplainMode.fromString(conf.uiExplainMode)
       context.session.sparkContext.listenerBus.post(SparkListenerSQLAdaptiveExecutionUpdate(
         executionId,
-        context.qe.explainString(planDescriptionMode),
+        SQLExecution.planDescription(context.qe, conf.uiExplainMode),
         SparkPlanInfo.fromSparkPlan(context.qe.executedPlan)))
     }
   }

sql/core/src/test/scala/org/apache/spark/sql/execution/adaptive/AdaptiveQueryExecSuite.scala

@@ -2541,7 +2541,8 @@ class AdaptiveQueryExecSuite
           "== Optimized Logical Plan ==", "== Physical Plan ==")),
         ("codegen", Seq("WholeStageCodegen subtrees")),
         ("cost", Seq("== Optimized Logical Plan ==", "Statistics(sizeInBytes")),
-        ("formatted", Seq("== Physical Plan ==", "Output", "Arguments"))).foreach {
+        ("formatted", Seq("== Physical Plan ==", "Output", "Arguments")),
+        ("none", Seq(SQLExecution.NO_PLAN_DESCRIPTION))).foreach {
       case (mode, expected) =>
         checkPlanDescription(mode, expected)
     }

sql/core/src/test/scala/org/apache/spark/sql/execution/ui/SQLAppStatusListenerSuite.scala

@@ -369,7 +369,8 @@ abstract class SQLAppStatusListenerSuite extends SharedSparkSession with JsonTes
           "== Optimized Logical Plan ==", "== Physical Plan ==")),
         ("codegen", Seq("WholeStageCodegen subtrees")),
         ("cost", Seq("== Optimized Logical Plan ==", "Statistics(sizeInBytes")),
-        ("formatted", Seq("== Physical Plan ==", "Output", "Arguments"))).foreach {
+        ("formatted", Seq("== Physical Plan ==", "Output", "Arguments")),
+        ("none", Seq(SQLExecution.NO_PLAN_DESCRIPTION))).foreach {
       case (mode, expected) =>
         checkPlanDescription(mode, expected)
     }