nowarn class conflict with Scala 2.12

[thesamet]

Now that Scala 2.12.13 backported @nowarn, projects that use sbt-assembly need to handle a class conflict:

[error] java.lang.RuntimeException: deduplicate: different file contents found in the following:
333
[error] /home/runner/.cache/coursier/v1/https/repo1.maven.org/maven2/org/scala-lang/modules/scala-collection-compat_2.12/2.3.2/scala-collection-compat_2.12-2.3.2.jar:scala/annotation/nowarn$.class
334
[error] /home/runner/.cache/coursier/v1/https/repo1.maven.org/maven2/org/scala-lang/scala-library/2.12.13/scala-library-2.12.13.jar:scala/annotation/nowarn$.class
335
[error] deduplicate: different file contents found in the following:
336
[error] /home/runner/.cache/coursier/v1/https/repo1.maven.org/maven2/org/scala-lang/modules/scala-collection-compat_2.12/2.3.2/scala-collection-compat_2.12-2.3.2.jar:scala/annotation/nowarn.class
337
[error] /home/runner/.cache/coursier/v1/https/repo1.maven.org/maven2/org/scala-lang/scala-library/2.12.13/scala-library-2.12.13.jar:scala/annotation/nowarn.class

I tested it with both scala-collection-compat 2.3.2 and 2.4.1.

The workaround I have been using to let sbt-assembly pick one by adding the following setting:

      assembly / assemblyMergeStrategy := {
        case PathList("scala", "annotation", "nowarn.class" | "nowarn$.class") =>
          MergeStrategy.first
        case x =>
          (assembly / assemblyMergeStrategy).value.apply(x)
      },

I wonder if nowarn can be removed from future versions of scala-collection-compat now that it's available in 2.12?

[SethTisue]

I wonder if nowarn can be removed from future versions of scala-collection-compat now that it's available in 2.12?

Yes, a pull request removing it from the 2.12 build (but leaving it in for 2.11) would be welcome.

Thank you for documenting the workaround here.