[SPARK-12480][FOLLOW-UP] use a single column vararg for hash

address comments in #10435

This makes the API easier to use if user programmatically generate the call to hash, and they will get analysis exception if the arguments of hash is empty.

Author: Wenchen Fan <wenchen@databricks.com>

Closes #10588 from cloud-fan/hash.

python/pyspark/sql/functions.py

@@ -1018,6 +1018,18 @@ def sha2(col, numBits):
     return Column(jc)
 
 
+@since(2.0)
+def hash(*cols):
+    """Calculates the hash code of given columns, and returns the result as a int column.
+
+    >>> sqlContext.createDataFrame([('ABC',)], ['a']).select(hash('a').alias('hash')).collect()
+    [Row(hash=1358996357)]
+    """
+    sc = SparkContext._active_spark_context
+    jc = sc._jvm.functions.hash(_to_seq(sc, cols, _to_java_column))
+    return Column(jc)
+
+
 # ---------------------- String/Binary functions ------------------------------
 
 _string_functions = {

sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/misc.scala

@@ -200,7 +200,7 @@ case class Murmur3Hash(children: Seq[Expression], seed: Int) extends Expression
 
   override def checkInputDataTypes(): TypeCheckResult = {
     if (children.isEmpty) {
-      TypeCheckResult.TypeCheckFailure("arguments of function hash cannot be empty")
+      TypeCheckResult.TypeCheckFailure("function hash requires at least one argument")
     } else {
       TypeCheckResult.TypeCheckSuccess
     }

sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/analysis/ExpressionTypeCheckingSuite.scala

@@ -163,6 +163,7 @@ class ExpressionTypeCheckingSuite extends SparkFunSuite {
     assertError(Coalesce(Seq('intField, 'booleanField)),
       "input to function coalesce should all be the same type")
     assertError(Coalesce(Nil), "input to function coalesce cannot be empty")
+    assertError(new Murmur3Hash(Nil), "function hash requires at least one argument")
     assertError(Explode('intField),
       "input to function explode should be array or map type")
   }

sql/core/src/main/scala/org/apache/spark/sql/functions.scala

@@ -1820,8 +1820,8 @@ object functions extends LegacyFunctions {
    * @since 2.0
    */
   @scala.annotation.varargs
-  def hash(col: Column, cols: Column*): Column = withExpr {
-    new Murmur3Hash((col +: cols).map(_.expr))
+  def hash(cols: Column*): Column = withExpr {
+    new Murmur3Hash(cols.map(_.expr))
   }
 
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