Change in classpath ordering compared to Ivy

I have a little sbt project reproducer that upgrading from sbt 1.2.8 to sbt 1.3.5 (and, therefore, to Coursier) changes the order of the dependencies, which in turn breaks the project.

build.sbt

scalaVersion in ThisBuild := "2.13.1"

libraryDependencies += "com.typesafe.play" %% "play-test" % "2.8.0-RC1" % Test
libraryDependencies += "org.scalatest"     %% "scalatest" % "3.0.8"     % Test

src/test/scala/t/UnitSpec.scala

import com.typesafe.config.ConfigFactory
import org.scalatest.{ MustMatchers, WordSpec }

class UnitSpec extends WordSpec with MustMatchers {
  def conf = ConfigFactory.defaultReference()

  "Config" should {
    "return Akka HTTP server provider" in {
      val serverProvider = conf.getString("play.server.provider")
      serverProvider mustBe "play.core.server.AkkaHttpServerProvider"
    }

    "be able to load Netty settings" in {
      val nettyTransport = conf.getString("play.server.netty.transport")
      nettyTransport mustBe "jdk"
    }
  }
}

Using sbt 1.2.8, all works as expected:

17:36:22 $ sbtx -Dsbt.version=1.2.8 test
[warn] sbt version mismatch, current: 1.2.8, in build.properties: "1.3.5", use 'reboot' to use the new value.
[info] Loading settings for project global-plugins from global-plugins.sbt ...
[info] Loading global plugins from /Users/dnw/.dotfiles/.sbt/1.0/plugins
[info] Loading project definition from /s/t-sbt-cp-order/project
[info] Loading settings for project t-sbt-cp-order from build.sbt ...
[info] Set current project to t-sbt-cp-order (in build file:/s/t-sbt-cp-order/)
[info] UnitSpec:
[info] Config
[info] - should return Akka HTTP server provider
[info] - should be able to load Netty settings
[info] ScalaTest
[info] Run completed in 483 milliseconds.
[info] Total number of tests run: 2
[info] Suites: completed 1, aborted 0
[info] Tests: succeeded 2, failed 0, canceled 0, ignored 0, pending 0
[info] All tests passed.
[info] Passed: Total 2, Failed 0, Errors 0, Passed 2
[success] Total time: 2 s, completed 17-Dec-2019 17:36:33

Using sbt 1.3.5, it fails:

17:37:11 $ sbtx -Dsbt.version=1.3.5 test
[info] Loading settings for project global-plugins from global-plugins.sbt ...
[info] Loading global plugins from /Users/dnw/.dotfiles/.sbt/1.0/plugins
[info] Loading project definition from /s/t-sbt-cp-order/project
[info] Loading settings for project t-sbt-cp-order from build.sbt ...
[info] Set current project to t-sbt-cp-order (in build file:/s/t-sbt-cp-order/)
[info] UnitSpec:
[info] Config
[info] - should return Akka HTTP server provider *** FAILED ***
[info]   "play.core.server.[Netty]ServerProvider" was not equal to "play.core.server.[AkkaHttp]ServerProvider" (UnitSpec.scala:12)
[info] - should be able to load Netty settings
[info] ScalaTest
[info] Run completed in 480 milliseconds.
[info] Total number of tests run: 2
[info] Suites: completed 1, aborted 0
[info] Tests: succeeded 1, failed 1, canceled 0, ignored 0, pending 0
[info] *** 1 TEST FAILED ***
[error] Failed: Total 2, Failed 1, Errors 0, Passed 1
[error] Failed tests:
[error] 	UnitSpec
[error] (Test / test) sbt.TestsFailedException: Tests unsuccessful
[error] Total time: 2 s, completed 17-Dec-2019 17:37:21

Using sbt 1.3.5 without Coursier succeeds again:

17:37:46 $ sbtx -Dsbt.version=1.3.5 -Dsbt.coursier=false test
[info] Loading settings for project global-plugins from global-plugins.sbt ...
[info] Loading global plugins from /Users/dnw/.dotfiles/.sbt/1.0/plugins
[info] Loading project definition from /s/t-sbt-cp-order/project
[info] Loading settings for project t-sbt-cp-order from build.sbt ...
[info] Set current project to t-sbt-cp-order (in build file:/s/t-sbt-cp-order/)
[info] UnitSpec:
[info] Config
[info] - should return Akka HTTP server provider
[info] - should be able to load Netty settings
[info] ScalaTest
[info] Run completed in 441 milliseconds.
[info] Total number of tests run: 2
[info] Suites: completed 1, aborted 0
[info] Tests: succeeded 2, failed 0, canceled 0, ignored 0, pending 0
[info] All tests passed.
[info] Passed: Total 2, Failed 0, Errors 0, Passed 2
[success] Total time: 2 s, completed 17-Dec-2019 17:37:56

Originally opened against sbt as https://github.com/sbt/sbt/issues/5282.

[dwijnand]

Good news: I release a local version of lm-coursier-shaded and a local version of sbt 1.3.x using it, and this is now fixed.

I learnt that update’s caching doesn’t track lm-coursier-shaded’s version, which is why it was initially looking still unfixed.

Thanks for your help, Alex!!

[dwijnand]

I should try to get this fix in before 2.0.0 comes out of RC cycle!! (I wouldn’t want 2.0.0 to be “stable” and this change not to be acceptable.) Should I consider this urgent? Do you have an idea of a timeline for 2.0.0?