[SPARK-16489][SQL] checkEvaluation should fail if expression reuses variable names

Author: rxin

sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/expressions/ExpressionEvalHelper.scala

@@ -132,23 +132,28 @@ trait ExpressionEvalHelper extends GeneratorDrivenPropertyChecks {
       expression: Expression,
       expected: Any,
       inputRow: InternalRow = EmptyRow): Unit = {
-
+    // SPARK-16489 Explicitly doing code generation twice so code gen will fail if
+    // some expression is reusing variable names across different instances.
+    // This behavior is tested in ExpressionEvalHelperSuite.
     val plan = generateProject(
-      GenerateUnsafeProjection.generate(Alias(expression, s"Optimized($expression)")() :: Nil),
+      GenerateUnsafeProjection.generate(
+        Alias(expression, s"Optimized($expression)1")() ::
+          Alias(expression, s"Optimized($expression)2")() :: Nil),
       expression)
 
     val unsafeRow = plan(inputRow)
     val input = if (inputRow == EmptyRow) "" else s", input: $inputRow"
 
     if (expected == null) {
       if (!unsafeRow.isNullAt(0)) {
-        val expectedRow = InternalRow(expected)
+        val expectedRow = InternalRow(expected, expected)
         fail("Incorrect evaluation in unsafe mode: " +
           s"$expression, actual: $unsafeRow, expected: $expectedRow$input")
       }
     } else {
-      val lit = InternalRow(expected)
-      val expectedRow = UnsafeProjection.create(Array(expression.dataType)).apply(lit)
+      val lit = InternalRow(expected, expected)
+      val expectedRow =
+        UnsafeProjection.create(Array(expression.dataType, expression.dataType)).apply(lit)
       if (unsafeRow != expectedRow) {
         fail("Incorrect evaluation in unsafe mode: " +
           s"$expression, actual: $unsafeRow, expected: $expectedRow$input")

sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/expressions/ExpressionEvalHelperSuite.scala

@@ -0,0 +1,54 @@
+/*
+ * 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.catalyst.expressions
+
+import org.apache.spark.SparkFunSuite
+import org.apache.spark.sql.catalyst.InternalRow
+import org.apache.spark.sql.catalyst.expressions.codegen.{CodegenContext, ExprCode}
+import org.apache.spark.sql.types.{DataType, IntegerType}
+
+/**
+ * A test suite for testing [[ExpressionEvalHelper]].
+ *
+ * Yes, we should write test cases for test harnesses, in case
+ * they have behaviors that are easy to break.
+ */
+class ExpressionEvalHelperSuite extends SparkFunSuite with ExpressionEvalHelper {
+
+  test("SPARK-16489 checkEvaluation should fail if expression reuses variable names") {
+    val e = intercept[RuntimeException] { checkEvaluation(BadCodegenExpression(), 10) }
+    assert(e.getMessage.contains("some_variable"))
+  }
+}
+
+/**
+ * An expression that generates bad code (variable name "some_variable" is not unique across
+ * instances of the expression.
+ */
+case class BadCodegenExpression() extends LeafExpression {
+  override def nullable: Boolean = false
+  override def eval(input: InternalRow): Any = 10
+  override protected def doGenCode(ctx: CodegenContext, ev: ExprCode): ExprCode = {
+    ev.copy(code =
+      s"""
+        |int some_variable = 11;
+        |int ${ev.value} = 10;
+      """.stripMargin)
+  }
+  override def dataType: DataType = IntegerType
+}