Address comments from dongjoon-hyun, hvanhovell, beliefer, gatorsmile

This addresses the comments for #23398

sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/analysis/FunctionRegistry.scala

@@ -25,6 +25,7 @@ import scala.language.existentials
 import scala.reflect.ClassTag
 import scala.util.{Failure, Success, Try}
 
+import org.apache.spark.internal.Logging
 import org.apache.spark.sql.AnalysisException
 import org.apache.spark.sql.catalyst.FunctionIdentifier
 import org.apache.spark.sql.catalyst.analysis.FunctionRegistry.FunctionBuilder
@@ -87,7 +88,7 @@ trait FunctionRegistry {
   override def clone(): FunctionRegistry = throw new CloneNotSupportedException()
 }
 
-class SimpleFunctionRegistry extends FunctionRegistry {
+class SimpleFunctionRegistry extends FunctionRegistry with Logging {
 
   @GuardedBy("this")
   private val functionBuilders =
@@ -103,7 +104,10 @@ class SimpleFunctionRegistry extends FunctionRegistry {
       name: FunctionIdentifier,
       info: ExpressionInfo,
       builder: FunctionBuilder): Unit = synchronized {
-    functionBuilders.put(normalizeFuncName(name), (info, builder))
+    val normalizedName = normalizeFuncName(name)
+    if (functionBuilders.put(normalizedName, (info, builder)).isDefined) {
+      logWarning(s"The function $normalizedName replaced a previously registered function.")
+    }
   }
 
   override def lookupFunction(name: FunctionIdentifier, children: Seq[Expression]): Expression = {

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

@@ -99,8 +99,13 @@ object StaticSQLConf {
       .createWithDefault(false)
 
   val SPARK_SESSION_EXTENSIONS = buildStaticConf("spark.sql.extensions")
-    .doc("List of the class names used to configure Spark Session extensions. The classes should " +
-      "implement Function1[SparkSessionExtension, Unit], and must have a no-args constructor.")
+    .doc("A comma-separated list of classes that implement " +
+      "Function1[SparkSessionExtension, Unit] used to configure Spark Session extensions. The " +
+      "classes must have a no-args constructor. If multiple extensions are specified, they are " +
+      "applied in the specified order. For the case of rules and planner strategies, they are " +
+      "applied in the specified order. For the case of parsers, the last parser is used and each " +
+      "parser can delegate to its predecessor. For the case of function name conflicts, the last " +
+      "registered function name is used.")
     .stringConf
     .toSequence
     .createOptional

sql/core/src/test/scala/org/apache/spark/sql/SparkSessionExtensionSuite.scala

@@ -53,6 +53,12 @@ class SparkSessionExtensionSuite extends SparkFunSuite {
     }
   }
 
+  test("inject post hoc resolution analyzer rule") {
+    withSession(Seq(_.injectPostHocResolutionRule(MyRule))) { session =>
+      assert(session.sessionState.analyzer.postHocResolutionRules.contains(MyRule(session)))
+    }
+  }
+
   test("inject check analysis rule") {
     withSession(Seq(_.injectCheckRule(MyCheckRule))) { session =>
       assert(session.sessionState.analyzer.extendedCheckRules.contains(MyCheckRule(session)))
@@ -118,23 +124,36 @@ class SparkSessionExtensionSuite extends SparkFunSuite {
     try {
       assert(session.sessionState.planner.strategies.contains(MySparkStrategy(session)))
       assert(session.sessionState.analyzer.extendedResolutionRules.contains(MyRule(session)))
+      assert(session.sessionState.analyzer.postHocResolutionRules.contains(MyRule(session)))
+      assert(session.sessionState.analyzer.extendedCheckRules.contains(MyCheckRule(session)))
+      assert(session.sessionState.optimizer.batches.flatMap(_.rules).contains(MyRule(session)))
+      assert(session.sessionState.sqlParser.isInstanceOf[MyParser])
       assert(session.sessionState.functionRegistry
         .lookupFunction(MyExtensions.myFunction._1).isDefined)
     } finally {
       stop(session)
     }
   }
 
-  test("use multiple custom class for extensions") {
+  test("use multiple custom class for extensions in the specified order") {
     val session = SparkSession.builder()
       .master("local[1]")
       .config("spark.sql.extensions", Seq(
-        classOf[MyExtensions].getCanonicalName,
-        classOf[MyExtensions2].getCanonicalName).mkString(","))
+        classOf[MyExtensions2].getCanonicalName,
+        classOf[MyExtensions].getCanonicalName).mkString(","))
       .getOrCreate()
     try {
-      assert(session.sessionState.planner.strategies.contains(MySparkStrategy(session)))
-      assert(session.sessionState.analyzer.extendedResolutionRules.contains(MyRule(session)))
+      assert(session.sessionState.planner.strategies.containsSlice(
+        Seq(MySparkStrategy2(session), MySparkStrategy(session))))
+      val orderedRules = Seq(MyRule2(session), MyRule(session))
+      val orderedCheckRules = Seq(MyCheckRule2(session), MyCheckRule(session))
+      val parser = MyParser(session, CatalystSqlParser)
+      assert(session.sessionState.analyzer.extendedResolutionRules.containsSlice(orderedRules))
+      assert(session.sessionState.analyzer.postHocResolutionRules.containsSlice(orderedRules))
+      assert(session.sessionState.analyzer.extendedCheckRules.containsSlice(orderedCheckRules))
+      assert(session.sessionState.optimizer.batches.flatMap(_.rules).filter(orderedRules.contains)
+        .containsSlice(orderedRules ++ orderedRules)) // The optimizer rules are duplicated
+      assert(session.sessionState.sqlParser == parser)
       assert(session.sessionState.functionRegistry
         .lookupFunction(MyExtensions.myFunction._1).isDefined)
       assert(session.sessionState.functionRegistry
@@ -143,6 +162,48 @@ class SparkSessionExtensionSuite extends SparkFunSuite {
       stop(session)
     }
   }
+
+  test("allow an extension to be duplicated") {
+    val session = SparkSession.builder()
+      .master("local[1]")
+      .config("spark.sql.extensions", Seq(
+        classOf[MyExtensions].getCanonicalName,
+        classOf[MyExtensions].getCanonicalName).mkString(","))
+      .getOrCreate()
+    try {
+      assert(session.sessionState.planner.strategies.count(_ == MySparkStrategy(session)) == 2)
+      assert(session.sessionState.analyzer.extendedResolutionRules.count(_ == MyRule(session)) == 2)
+      assert(session.sessionState.analyzer.postHocResolutionRules.count(_ == MyRule(session)) == 2)
+      assert(session.sessionState.analyzer.extendedCheckRules.count(_ == MyCheckRule(session)) == 2)
+      assert(session.sessionState.optimizer.batches.flatMap(_.rules)
+        .count(_ == MyRule(session)) == 4) // The optimizer rules are duplicated
+      val outerParser = session.sessionState.sqlParser
+      assert(outerParser.isInstanceOf[MyParser])
+      assert(outerParser.asInstanceOf[MyParser].delegate.isInstanceOf[MyParser])
+      assert(session.sessionState.functionRegistry
+        .lookupFunction(MyExtensions.myFunction._1).isDefined)
+    } finally {
+      stop(session)
+    }
+  }
+
+  test("use the last registered function name when there are duplicates") {
+    val session = SparkSession.builder()
+      .master("local[1]")
+      .config("spark.sql.extensions", Seq(
+        classOf[MyExtensions2].getCanonicalName,
+        classOf[MyExtensions2Duplicate].getCanonicalName).mkString(","))
+      .getOrCreate()
+    try {
+      val lastRegistered = session.sessionState.functionRegistry
+        .lookupFunction(FunctionIdentifier("myFunction2"))
+      assert(lastRegistered.isDefined)
+      assert(lastRegistered.get.getExtended != MyExtensions2.myFunction._2.getExtended)
+      assert(lastRegistered.get.getExtended == MyExtensions2Duplicate.myFunction._2.getExtended)
+    } finally {
+      stop(session)
+    }
+  }
 }
 
 case class MyRule(spark: SparkSession) extends Rule[LogicalPlan] {
@@ -189,19 +250,54 @@ class MyExtensions extends (SparkSessionExtensions => Unit) {
   def apply(e: SparkSessionExtensions): Unit = {
     e.injectPlannerStrategy(MySparkStrategy)
     e.injectResolutionRule(MyRule)
+    e.injectPostHocResolutionRule(MyRule)
+    e.injectCheckRule(MyCheckRule)
+    e.injectOptimizerRule(MyRule)
+    e.injectParser(MyParser)
     e.injectFunction(MyExtensions.myFunction)
   }
 }
 
+case class MyRule2(spark: SparkSession) extends Rule[LogicalPlan] {
+  override def apply(plan: LogicalPlan): LogicalPlan = plan
+}
+
+case class MyCheckRule2(spark: SparkSession) extends (LogicalPlan => Unit) {
+  override def apply(plan: LogicalPlan): Unit = { }
+}
+
+case class MySparkStrategy2(spark: SparkSession) extends SparkStrategy {
+  override def apply(plan: LogicalPlan): Seq[SparkPlan] = Seq.empty
+}
+
 object MyExtensions2 {
 
   val myFunction = (FunctionIdentifier("myFunction2"),
     new ExpressionInfo("noClass", "myDb", "myFunction2", "usage", "extended usage" ),
-    (myArgs: Seq[Expression]) => Literal(5, IntegerType))
+    (_: Seq[Expression]) => Literal(5, IntegerType))
 }
 
 class MyExtensions2 extends (SparkSessionExtensions => Unit) {
   def apply(e: SparkSessionExtensions): Unit = {
+    e.injectPlannerStrategy(MySparkStrategy2)
+    e.injectResolutionRule(MyRule2)
+    e.injectPostHocResolutionRule(MyRule2)
+    e.injectCheckRule(MyCheckRule2)
+    e.injectOptimizerRule(MyRule2)
+    e.injectParser((_, _) => CatalystSqlParser)
     e.injectFunction(MyExtensions2.myFunction)
   }
 }
+
+object MyExtensions2Duplicate {
+
+  val myFunction = (FunctionIdentifier("myFunction2"),
+    new ExpressionInfo("noClass", "myDb", "myFunction2", "usage", "last wins" ),
+    (_: Seq[Expression]) => Literal(5, IntegerType))
+}
+
+class MyExtensions2Duplicate extends (SparkSessionExtensions => Unit) {
+  def apply(e: SparkSessionExtensions): Unit = {
+    e.injectFunction(MyExtensions2Duplicate.myFunction)
+  }
+}