scalac-compat is a microlibrary containing a set of lightweight tools designed to tackle mismatches between different Scala compiler versions in cross-build projects.
Currently, it consists of two modules: scalac-compat-annotation and scala2-notgiven-features.
The module contains Scala version specific annotations that can help to tune a build in cases when different Scala compiler versions may treat same standard annotations differently.
The module is published for Scala 2.12.x, 2.13.x and 3.2.x:
// sbt
"org.typelevel" %% "scalac-compat-annotation" % "{{MODULE_VERSION}}"
// mill
ivy"org.typelevel::scalac-compat-annotation:{{MODULE_VERSION}}"
// Scala CLI
//> using dep org.typelevel::scalac-compat-annotation:{{MODULE_VERSION}}Then import the module annotations:
import org.typelevel.scalaccompat.annotation._There are a set of specializations defined for @scala.annotation.nowarn that either redirect to the standard annotation or to a no-op annotation depending on a particular Scala version:
| Scala version |
@nowarn2 |
@nowarn212 |
@nowarn213 |
@nowarn3 |
|---|---|---|---|---|
| 2.12 | @nowarn |
@nowarn |
no-op | no-op |
| 2.13 | @nowarn |
no-op | @nowarn |
no-op |
| 3 | no-op | no-op | no-op | @nowarn |
Consider a case when someone has to deal with scala.collection.Stream in a cross-build project. Stream is deprecated since Scala v2.13. However, simply applying @nowarn("cat=deprecation") to methods that attempt to reference to Stream may lead to another warning on Scala version prior to v2.13:
@nowarn annotation does not suppress any warnings
Thus the specialized @nowarn annotations can come in handy here:
import org.typelevel.scalaccompat.annotation._
@nowarn213("cat=deprecation")
@nowarn3("cat=deprecation")
def reinventTheWheel: Stream[Int] = {
Stream
.iterate((1, 1)) { case (a2, a1) => (a1, a2 + a1) }
.map(_._1)
}The @scala.annotation.unused annotation was introduced since Scala v2.13.x and does not exists in previous versions of Scala library. The compatibility @org.typelevel.scalaccompat.annotation.unused annotation simply redirects to the @scala.annotation.unused on versions where it exists while mimics the same behavior with @scala.annotation.nowarn for Scala v2.12.x:
| Scala version |
@scalaccompat.annotation.unusedredirects to |
|---|---|
| 2.12 | @scala.annotation.nowarn("cat=unused") |
| 2.13 | @scala.annotation.unused |
| 3 | @scala.annotation.unused |
// Notice that there is no need to import `scala.annotation.unused`.
import org.typelevel.scalaccompat.annotation._
// Compiles on all supported Scala versions.
def testUnusedParam(name: String, @unused unusedParam: String): Unit = {
// The `unusedParam` is not used withing the body.
println(s"Hello, $name")
}See more examples in ./annotation/src/test
Scala 3 introduced scala.util.NotGiven: a special class used to implement negation in implicit search.
While techniques existed to implement this functionality in some cases in Scala 2, the NotGiven trait
was not backported to Scala 2. This makes cross-compilation more frustrating than it needs to be, so
this module was created to make a single org.typelevel.scalaccompat.scala.util.NotGiven available to
Scala 2.12, 2.13, and 3.
This is based on prior work by Shapeless and fs2.
Participants are expected to follow the Scala Code of Conduct while discussing the project on GitHub and any other venues associated with the project. See the organizational Code of Conduct for more details.
All code in this repository is licensed under the Apache License, Version 2.0. See LICENSE.
