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sbt 1.5.0-RC2

Hi everyone. On behalf of the sbt project, I am happy to announce sbt 1.5.0-RC2. This is the fifth feature release of sbt 1.x, a binary compatible release focusing on new features. sbt 1.x is released under Semantic Versioning, and the plugins are expected to work throughout the 1.x series.

The headline features of sbt 1.5.0 are:

How to upgrade

You can upgrade to sbt 1.5.0-RC2 by putting the following in project/


Changes since RC-1

Scala 3 support

sbt 1.5.0 adds built-in Scala 3 support, contributed by Scala Center. Main implementation was done by Adrien Piquerez ([@adpi2][@adpi2]) based on EPFL/LAMP’s sbt-dotty.

After this resolver is added, you can now use Scala 3.0.0-RC1 like any other Scala version.

ThisBuild / scalaVersion := "3.0.0-RC1"

This will compile the following Hello.scala:

package example

@main def hello(arg: String*): Unit =
  if arg.isEmpty then println("hello")
  else println(s"hi ${arg.head}")

Scala 2.13-3.x sandwich

Scala 3.0.x shares the standard library with Scala 2.13, and since Scala 2.13.4, they can mutually consume the output of each other as external library. This allows you to create Scala 2.13-3.x sandwich, a layering of dependencies coming from different Scala versions.

sbt 1.5.0 introduces new cross building operand to use _3 variant when scalaVersion is 2.13.x, and vice versa:

("a" % "b" % "1.0").cross(CrossVersion.for3Use2_13)

("a" % "b" % "1.0").cross(CrossVersion.for2_13Use3)

These are analogous to %% operator that selects _2.13 etc based on scalaVersion.

Warning: Libraries such as Cats may encode a particular notion in different ways for Scala 2.13 and 3.0. For example, arity abstraction may use Shapeless HList in Scala 2.13, but built-in Tuple types in Scala 3.0. Thus it’s generally not safe to have _2.13 and _3 versions of the same library in the classpath, even transitively. Library authors should generally treat Scala 3.0 as any other major version, and generally prefer to cross publish _3 variant to avoid the conflict. Application developers should be free to use .cross(CrossVersion.for3Use2_13) as long as the transitive dependency graph will not introduce _2.13 variant of a library you already have in _3 variant.

[lm#361][lm361] by [@adpi2][@adpi2]

Deprecation of sbt 0.13 syntax

sbt 1.5.0 deprecates both the sbt 0.13 style shell syntax proj/cofing:intask::key and sbt 0.13 styld build.sbt DSL key in (Compile, intask) in favor of the unified slash syntax.

See for details.

Eviction error

sbt 1.5.0 removes eviction warning, and replaces it with stricter eviction error. Unlike the eviction warning that was based on speculation, eviction error only uses the [ThisBuild / versionScheme information][versionScheme] supplied by the library authors.

For example:

lazy val use = project
    name := "use",
    libraryDependencies ++= Seq(
      "org.http4s" %% "http4s-blaze-server" % "0.21.11",
      // is published with early-semver
      "org.typelevel" %% "cats-effect" % "3.0.0-M4",

The above build will fail to build use/compile with the following error:

[error] stack trace is suppressed; run last use / update for the full output
[error] (use / update) found version conflict(s) in library dependencies; some are suspected to be binary incompatible:
[error]   * org.typelevel:cats-effect_2.12:3.0.0-M4 (early-semver) is selected over {2.2.0, 2.0.0, 2.0.0, 2.2.0}
[error]       +- use:use_2.12:0.1.0-SNAPSHOT                        (depends on 3.0.0-M4)
[error]       +- org.http4s:http4s-core_2.12:0.21.11                (depends on 2.2.0)
[error]       +- io.chrisdavenport:vault_2.12:2.0.0                 (depends on 2.0.0)
[error]       +- io.chrisdavenport:unique_2.12:2.0.0                (depends on 2.0.0)
[error]       +- co.fs2:fs2-core_2.12:2.4.5                         (depends on 2.2.0)
[error] this can be overridden using libraryDependencySchemes or evictionErrorLevel

This is because Cats Effect 2.x and 3.x are found in the classpath, and Cats Effect has declared that it uses early-semver. If the user wants to opt-out of this, the user can do so per module:

ThisBuild / libraryDependencySchemes += "org.typelevel" %% "cats-effect" % "always"

or globally as:

ThisBuild / evictionErrorLevel := Level.Info

On the other hand, if you want to bring back the guessing feature in eviction warning, you can do using the following settings:

ThisBuild / assumedVersionScheme := VersionScheme.PVP
ThisBuild / assumedVersionSchemeJava := VersionScheme.EarlySemVer
ThisBuild / assumedEvictionErrorLevel := Level.Warn

[@eed3si9n][@eed3si9n] implemented this in [#6221][6221], inspired in part by Scala Center’s sbt-eviction-rules, which was implemented by Alexandre Archambault ([@alxarchambault][@alxarchambault]) and Julien Richard-Foy ([@julienrf][@julienrf]).

ThisBuild / packageTimestamp setting

In sbt 1.4.0 we started wiping out the timestamps in JAR to make the builds more repeatable. This had an unintended consequence of breaking Play’s last-modified response header.

To opt out of this default, the user can use:

ThisBuild / packageTimestamp := Package.keepTimestamps

// or

ThisBuild / packageTimestamp := Package.gitCommitDateTimestamp

[#6237][6237] by [@eed3si9n][@eed3si9n]

Other updates


sbt 1.5.0-RC2 was brought to you by 27 contributors. Eugene Yokota (eed3si9n), Adrien Piquerez, Ethan Atkins, João Ferreira, Matthias Kurz, Eric Peters, Sam Halliday, Erlend Hamnaberg, Erwan Queffélec, Guillaume Massé, Martin Duhem, Mirco Dotta, Arthur McGibbon, Brice Jaglin, Cyrille Chepelov, Dale Wijnand, Eric Meisel, Guillaume Martres, Jason Pickens, Julien Richard-Foy, Kenji Yoshida (xuwei-k), Luc Henninger, Marcos Pereira, Marko Elezovic, Naoki Takezoe, Ondra Pelech, Rafał Sumisławski. Thanks!

Thanks to everyone who’s helped improve sbt and Zinc 1 by using them, reporting bugs, improving our documentation, porting builds, porting plugins, and submitting and reviewing pull requests.

For anyone interested in helping sbt, there are many avenues for you to help, depending on your interest. If you’re interested, Contributing, “help wanted”, “good first issue”, and Discussions are good starting points. [versionScheme]: [@adpi2]: [@jtjeferreira]: [@takezoe]: [@eed3si9n]: [@julienrf]: [@alxarchambault]: [@bjaglin]: [@RafalSumislawski]: [@melezov]: [@MasseGuillaume]: [@steinybot]: [@arixmkii]: [lm361]: [lm367]: [6296]: [5515]: [6254]: [6221]: [6283]: [6237]: [6316]: [6310]: [6326]: [6266]: [6335]: [6351]: [6403]: [6401]: [6397]: [6408]: [launcher86]: [launcher89]: [launcher92]: [launcher93]: [zinc968]: [lm372]: