[SPARK-23462][SQL] improve missing field error message in StructType

sql/catalyst/src/main/scala/org/apache/spark/sql/types/StructType.scala

@@ -271,7 +271,9 @@ case class StructType(fields: Array[StructField]) extends DataType with Seq[Stru
    */
   def apply(name: String): StructField = {
     nameToField.getOrElse(name,
-      throw new IllegalArgumentException(s"""Field "$name" does not exist."""))
+      throw new IllegalArgumentException(
+        s"""Field "$name" does not exist.
+           |Available fields: ${fieldNamesSet.mkString(", ")}""".stripMargin))
   }
 
   /**
@@ -284,7 +286,8 @@ case class StructType(fields: Array[StructField]) extends DataType with Seq[Stru
     val nonExistFields = names -- fieldNamesSet
     if (nonExistFields.nonEmpty) {
       throw new IllegalArgumentException(
-        s"Field ${nonExistFields.mkString(",")} does not exist.")
+        s"""Fields ${nonExistFields.mkString(", ")} does not exist.
+           |Available fields: ${fieldNamesSet.mkString(", ")}""".stripMargin)
     }
     // Preserve the original order of fields.
     StructType(fields.filter(f => names.contains(f.name)))
@@ -297,7 +300,9 @@ case class StructType(fields: Array[StructField]) extends DataType with Seq[Stru
    */
   def fieldIndex(name: String): Int = {
     nameToIndex.getOrElse(name,
-      throw new IllegalArgumentException(s"""Field "$name" does not exist."""))
+      throw new IllegalArgumentException(
+        s"""Field "$name" does not exist.
+           |Available fields: ${fieldNamesSet.mkString(", ")}""".stripMargin))
   }
 
   private[sql] def getFieldIndex(name: String): Option[Int] = {

sql/catalyst/src/test/scala/org/apache/spark/sql/types/StructTypeSuite.scala

@@ -0,0 +1,40 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.spark.sql.types
+
+import org.apache.spark.SparkFunSuite
+
+class StructTypeSuite extends SparkFunSuite {
+
+  val s = StructType.fromDDL("a INT, b STRING")
+
+  test("lookup a single missing field should output existing fields") {
+    val e = intercept[IllegalArgumentException](s("c")).getMessage
+    assert(e.contains("Available fields: a, b"))
+  }
+
+  test("lookup a set of missing fields should output existing fields") {
+    val e = intercept[IllegalArgumentException](s(Set("a", "c"))).getMessage
+    assert(e.contains("Available fields: a, b"))
+  }
+
+  test("lookup fieldIndex for missing field should output existing fields") {
+    val e = intercept[IllegalArgumentException](s.fieldIndex("c")).getMessage
+    assert(e.contains("Available fields: a, b"))
+  }
+}