Revert "[SPARK-26216][SQL][FOLLOWUP] use abstract class instead of trait for UserDefinedFunction"

This reverts commit bba506f.

Author: Robert Kruszewski

project/MimaExcludes.scala

@@ -179,43 +179,14 @@ object MimaExcludes {
       case _ => true
     },
 
-    // [SPARK-26216][SQL] Do not use case class as public API (UserDefinedFunction)
-    ProblemFilters.exclude[MissingClassProblem]("org.apache.spark.sql.expressions.UserDefinedFunction$"),
-    ProblemFilters.exclude[AbstractClassProblem]("org.apache.spark.sql.expressions.UserDefinedFunction"),
-    ProblemFilters.exclude[DirectMissingMethodProblem]("org.apache.spark.sql.expressions.UserDefinedFunction.inputTypes"),
-    ProblemFilters.exclude[DirectMissingMethodProblem]("org.apache.spark.sql.expressions.UserDefinedFunction.nullableTypes_="),
-    ProblemFilters.exclude[DirectMissingMethodProblem]("org.apache.spark.sql.expressions.UserDefinedFunction.dataType"),
-    ProblemFilters.exclude[DirectMissingMethodProblem]("org.apache.spark.sql.expressions.UserDefinedFunction.f"),
-    ProblemFilters.exclude[DirectMissingMethodProblem]("org.apache.spark.sql.expressions.UserDefinedFunction.this"),
-    ProblemFilters.exclude[DirectAbstractMethodProblem]("org.apache.spark.sql.expressions.UserDefinedFunction.asNonNullable"),
-    ProblemFilters.exclude[ReversedAbstractMethodProblem]("org.apache.spark.sql.expressions.UserDefinedFunction.asNonNullable"),
-    ProblemFilters.exclude[DirectAbstractMethodProblem]("org.apache.spark.sql.expressions.UserDefinedFunction.nullable"),
-    ProblemFilters.exclude[ReversedAbstractMethodProblem]("org.apache.spark.sql.expressions.UserDefinedFunction.nullable"),
-    ProblemFilters.exclude[DirectAbstractMethodProblem]("org.apache.spark.sql.expressions.UserDefinedFunction.asNondeterministic"),
-    ProblemFilters.exclude[ReversedAbstractMethodProblem]("org.apache.spark.sql.expressions.UserDefinedFunction.asNondeterministic"),
-    ProblemFilters.exclude[DirectAbstractMethodProblem]("org.apache.spark.sql.expressions.UserDefinedFunction.deterministic"),
-    ProblemFilters.exclude[ReversedAbstractMethodProblem]("org.apache.spark.sql.expressions.UserDefinedFunction.deterministic"),
-    ProblemFilters.exclude[DirectAbstractMethodProblem]("org.apache.spark.sql.expressions.UserDefinedFunction.apply"),
-    ProblemFilters.exclude[ReversedAbstractMethodProblem]("org.apache.spark.sql.expressions.UserDefinedFunction.apply"),
-    ProblemFilters.exclude[DirectAbstractMethodProblem]("org.apache.spark.sql.expressions.UserDefinedFunction.withName"),
-    ProblemFilters.exclude[ReversedAbstractMethodProblem]("org.apache.spark.sql.expressions.UserDefinedFunction.withName"),
-    ProblemFilters.exclude[DirectMissingMethodProblem]("org.apache.spark.sql.expressions.UserDefinedFunction.productElement"),
-    ProblemFilters.exclude[DirectMissingMethodProblem]("org.apache.spark.sql.expressions.UserDefinedFunction.productArity"),
-    ProblemFilters.exclude[DirectMissingMethodProblem]("org.apache.spark.sql.expressions.UserDefinedFunction.copy$default$2"),
-    ProblemFilters.exclude[DirectMissingMethodProblem]("org.apache.spark.sql.expressions.UserDefinedFunction.canEqual"),
-    ProblemFilters.exclude[DirectMissingMethodProblem]("org.apache.spark.sql.expressions.UserDefinedFunction.copy"),
-    ProblemFilters.exclude[DirectMissingMethodProblem]("org.apache.spark.sql.expressions.UserDefinedFunction.copy$default$1"),
-    ProblemFilters.exclude[DirectMissingMethodProblem]("org.apache.spark.sql.expressions.UserDefinedFunction.productIterator"),
-    ProblemFilters.exclude[DirectMissingMethodProblem]("org.apache.spark.sql.expressions.UserDefinedFunction.productPrefix"),
-    ProblemFilters.exclude[DirectMissingMethodProblem]("org.apache.spark.sql.expressions.UserDefinedFunction.copy$default$3"),
-
     // [SPARK-11215][ML] Add multiple columns support to StringIndexer
     ProblemFilters.exclude[DirectMissingMethodProblem]("org.apache.spark.ml.feature.StringIndexer.validateAndTransformSchema"),
     ProblemFilters.exclude[DirectMissingMethodProblem]("org.apache.spark.ml.feature.StringIndexerModel.validateAndTransformSchema"),
 
     // [SPARK-26616][MLlib] Expose document frequency in IDFModel
     ProblemFilters.exclude[DirectMissingMethodProblem]("org.apache.spark.mllib.feature.IDFModel.this"),
     ProblemFilters.exclude[IncompatibleResultTypeProblem]("org.apache.spark.mllib.feature.IDF#DocumentFrequencyAggregator.idf")
+    ProblemFilters.exclude[IncompatibleTemplateDefProblem]("org.apache.spark.sql.expressions.UserDefinedFunction")
   )
 
   // Exclude rules for 2.4.x

sql/core/src/main/scala/org/apache/spark/sql/expressions/UserDefinedFunction.scala

@@ -38,7 +38,7 @@ import org.apache.spark.sql.types.DataType
  * @since 1.3.0
  */
 @Stable
-sealed abstract class UserDefinedFunction {
+sealed trait UserDefinedFunction {
 
   /**
    * Returns true when the UDF can return a nullable value.