Github user mgaido91 commented on a diff in the pull request:
https://github.com/apache/spark/pull/19813#discussion_r154194781
--- Diff:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/codegen/ExpressionCodegen.scala
---
@@ -0,0 +1,259 @@
+/*
+ * 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.codegen
+
+import scala.collection.mutable
+
+import org.apache.spark.sql.catalyst.expressions._
+
+/**
+ * Defines APIs used in expression code generation.
+ */
+object ExpressionCodegen {
+
+ /**
+ * Given an expression, returns the all necessary parameters to evaluate
it, so the generated
+ * code of this expression can be split in a function.
+ * The 1st string in returned tuple is the parameter strings used to
call the function.
+ * The 2nd string in returned tuple is the parameter strings used to
declare the function.
+ *
+ * Returns `None` if it can't produce valid parameters.
+ *
+ * Params to include:
+ * 1. Evaluated columns referred by this, children or deferred
expressions.
+ * 2. Rows referred by this, children or deferred expressions.
+ * 3. Eliminated subexpressions referred bu children expressions.
+ */
+ def getExpressionInputParams(
+ ctx: CodegenContext,
+ expr: Expression): Option[(Seq[String], Seq[String])] = {
+ val (inputAttrs, inputVars) = getInputVarsForChildren(ctx, expr)
+ val inputRows = ctx.INPUT_ROW +: getInputRowsForChildren(ctx, expr)
--- End diff --
I see that as of now `ctx.INPUT_ROW` can't be `null` here, but can we add
an assertion and maybe a comment for the reason of this? I think this would
help people who might want to reuse this function in the future.
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