[FLINK-12300] Unused Import warning with DataStream[Seq[...]]

• Type: Bug
• Status: Open
• Priority: Not a Priority
• Resolution: Unresolved
• Affects Version/s: 1.8.0
• Component/s: API / Scala
• Labels: auto-deprioritized-major auto-deprioritized-minor
• Assignee: Unassigned
• Reporter: Michael
• Created: 23/Apr/19 09:04
• Updated: 25/Nov/21 22:38

Description

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

When enabling unused import warnings in build.sbt:

scalacOptions ++= Seq("-Xfatal-warnings", "-Ywarn-unused-import")

...and compiling a file with this content:

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))
  }
}

Then with Flink 1.8.0 this compile issue happens (while with Flink 1.7.2 everything compiles fine):

[error] /path/to/com/example/unusedimportissue/example.scala:1:0: Unused import
[error] package com.example.unusedimportissue
[error] ^

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?