refactor

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

@@ -175,14 +175,22 @@ object TypeCoercion {
       })
   }
 
+  /**
+   * Whether the data type contains StringType.
+   */
+  def hasStringType(dt: DataType): Boolean = dt match {
+    case StringType => true
+    case ArrayType(et, _) => hasStringType(et)
+    // Add StructType if we support string promotion for struct fields in the future.
+    case _ => false
+  }
+
   private def findWiderCommonType(types: Seq[DataType]): Option[DataType] = {
     // findWiderTypeForTwo doesn't satisfy the associative law, i.e. (a op b) op c may not equal
     // to a op (b op c). This is only a problem for StringType. Excluding StringType,
     // findWiderTypeForTwo satisfies the associative law. For instance, (TimestampType,
     // IntegerType, StringType) should have StringType as the wider common type.
-    val (stringTypes, nonStringTypes) = types.partition { t =>
-      t == StringType || t == ArrayType(StringType)
-    }
+    val (stringTypes, nonStringTypes) = types.partition(hasStringType(_))
     (stringTypes.distinct ++ nonStringTypes).foldLeft[Option[DataType]](Some(NullType))((r, c) =>
       r match {
         case Some(d) => findWiderTypeForTwo(d, c)