Don't force scala version if autoScalaLibrary is false

modules/sbt-coursier/src/main/scala/coursier/Tasks.scala

@@ -814,6 +814,8 @@ object Tasks {
 
       val (currentProject, fallbackDependencies, configGraphs) = currentProjectTask.value
 
+      val autoScalaLib = autoScalaLibrary.value
+
       val resolvers = resolversTask.value
 
       // TODO Warn about possible duplicated modules from source repositories?
@@ -909,7 +911,7 @@ object Tasks {
         forceVersions =
           // order matters here
           userForceVersions ++
-            (if (configs("compile") || configs("scala-tool")) forcedScalaModules(so, sv) else Map()) ++
+            (if (autoScalaLib && (configs("compile") || configs("scala-tool"))) forcedScalaModules(so, sv) else Map()) ++
             interProjectDependencies.map(_.moduleVersion),
         projectCache = parentProjectCache,
         mapDependencies = if (typelevel && (configs("compile") || configs("scala-tool"))) typelevelOrgSwap else None

modules/sbt-coursier/src/sbt-test/sbt-coursier-group-1/auto-scala-library/build.sbt

@@ -0,0 +1,20 @@
+autoScalaLibrary := false
+libraryDependencies += "com.chuusai" % "shapeless_2.12" % "2.3.2"
+
+val checkScalaLibrary = TaskKey[Unit]("checkScalaLibrary")
+
+checkScalaLibrary := {
+  val scalaLibsJars = managedClasspath
+    .in(Compile)
+    .value
+    .map(_.data.getName)
+    .filter(_.startsWith("scala-library"))
+    .sorted
+  val expectedScalaLibsJars = Seq(
+    "scala-library-2.12.0.jar"
+  )
+  assert(
+    scalaLibsJars == expectedScalaLibsJars,
+    s"$scalaLibsJars != $expectedScalaLibsJars"
+  )
+}

modules/sbt-coursier/src/sbt-test/sbt-coursier-group-1/auto-scala-library/project/plugins.sbt

@@ -0,0 +1,11 @@
+{
+  val pluginVersion = sys.props.getOrElse(
+    "plugin.version",
+    throw new RuntimeException(
+      """|The system property 'plugin.version' is not defined.
+         |Specify this property using the scriptedLaunchOpts -D.""".stripMargin
+    )
+  )
+
+  addSbtPlugin("io.get-coursier" % "sbt-coursier" % pluginVersion)
+}

modules/sbt-coursier/src/sbt-test/sbt-coursier-group-1/auto-scala-library/test

@@ -0,0 +1 @@
+> checkScalaLibrary