[jira] [Created] (FLINK-12300) Unused Import warning with DataStream[Seq[...]]

[Shang Yuanchun (Jira)]

Michael created FLINK-12300:
-------------------------------

             Summary: Unused Import warning with DataStream[Seq[...]]
                 Key: FLINK-12300
                 URL: https://issues.apache.org/jira/browse/FLINK-12300
             Project: Flink
          Issue Type: Bug
          Components: API / Scala
    Affects Versions: 1.8.0
            Reporter: Michael


There is a regression in Flink 1.8.0 compared to 1.7.2 using Scala...

When enabling unused import warnings in *build.sbt*:
{code:java}
scalacOptions ++= Seq("-Xfatal-warnings", "-Ywarn-unused-import")
{code}
...and compiling a file with this content:
{code:java}
package com.example.unusedimportissue

import org.apache.flink.streaming.api.scala._

object ExampleSeqDataStream {
  def doubleElement(numbers: DataStream[Int]): DataStream[Seq[Int]] = {
    numbers.map(x => Seq(x, x))
  }
}
{code}
Then with Flink 1.8.0 this compile issue happens (while with Flink 1.7.2 everything compiles fine):
{noformat}
[error] /path/to/com/example/unusedimportissue/example.scala:1:0: Unused import
[error] package com.example.unusedimportissue
[error] ^
{noformat}
If the result type {{DataStream[Seq[Int]]}} is replaced by {{DataStream[Int]}}, then this issue does not occur, so it is related to the {{Seq[...]}} type.

Maybe a Flink macro is generating an import that is not used, resulting in this error?



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