Subsume platform cross building

Problem
-------
In sbt 1, platform cross building is implemented using in the user-land
using `%%%` operator, which clevery handles both Scala cross building
and appending platform suffix like sjs1.
However, in general symbolic `%%%` is confusing, and hard to explain.

Solution
--------
In sbt 2, we should subsume the idea of platform cross building,
so `%%` can act as the current `%%%` operator.
This adds a new setting called `platform`, which defaults to
`Platform.jvm` by default.
When a subprojects sets it to `Platform.sjs1`, `ModuleID`s defined using
`%%` operator will inject the platform suffix `_sjs1` **in addition**
to the Scala binary suffix `_2.13` etc.

Note: Explicit JVM dependencies will now require `.platform(Platform.jvm)`.

main/src/main/scala/sbt/Defaults.scala

@@ -270,6 +270,7 @@ object Defaults extends BuildCommon {
       pomIncludeRepository :== Classpaths.defaultRepositoryFilter,
       updateOptions := UpdateOptions(),
       forceUpdatePeriod :== None,
+      platform :== Platform.jvm,
       // coursier settings
       csrExtraCredentials :== Nil,
       csrLogger := LMCoursier.coursierLoggerTask.value,
@@ -703,7 +704,7 @@ object Defaults extends BuildCommon {
         case CrossValue.Full     => CrossVersion.full
         case CrossValue.Binary   => CrossVersion.binary
       }
-      val base = ModuleID(id.groupID, id.name, sv).withCrossVersion(cross)
+      val base = ModuleID(id.groupID, id.name, sv).withCrossVersion(cross).platform(Platform.jvm)
       CrossVersion(scalaV, binVersion)(base).withCrossVersion(Disabled())
     },
     crossSbtVersions := Vector((pluginCrossBuild / sbtVersion).value),
@@ -2960,7 +2961,9 @@ object Classpaths {
             case CrossValue.Full     => CrossVersion.binary
             case CrossValue.Binary   => CrossVersion.full
           }
-          val base = ModuleID(id.groupID, id.name, sbtVersion.value).withCrossVersion(cross)
+          val base = ModuleID(id.groupID, id.name, sbtVersion.value)
+            .withCrossVersion(cross)
+            .platform(Platform.jvm)
           CrossVersion(scalaVersion, binVersion)(base).withCrossVersion(Disabled())
         },
         shellPrompt := sbt.internal.ui.UITask.NoShellPrompt,
@@ -3084,6 +3087,7 @@ object Classpaths {
             overrideScalaVersion = true
           ).withScalaOrganization(scalaOrganization.value)
             .withScalaArtifacts(scalaArtifacts.value.toVector)
+            .withPlatform(platform.?.value)
         )
       }
     )).value,
@@ -3335,7 +3339,7 @@ object Classpaths {
           ScalaArtifacts.toolDependencies(sbtOrg, version) ++
             ScalaArtifacts.docToolDependencies(sbtOrg, version)
         } else ScalaArtifacts.toolDependencies(sbtOrg, version)
-      allToolDeps ++ pluginAdjust
+      allToolDeps.map(_.platform(Platform.jvm)) ++ pluginAdjust
     },
     // in case of meta build, exclude all sbt modules from the dependency graph, so we can use the sbt resolved by the launcher
     allExcludeDependencies := {
@@ -4162,7 +4166,8 @@ object Classpaths {
       version: String
   ): Seq[ModuleID] =
     if (auto)
-      modifyForPlugin(plugin, ScalaArtifacts.libraryDependency(org, version)) :: Nil
+      modifyForPlugin(plugin, ScalaArtifacts.libraryDependency(org, version))
+        .platform(Platform.jvm) :: Nil
     else
       Nil
 

main/src/main/scala/sbt/Keys.scala

@@ -192,6 +192,7 @@ object Keys {
   val scalaBinaryVersion = settingKey[String]("The Scala version substring describing binary compatibility.").withRank(BPlusSetting)
   val crossScalaVersions = settingKey[Seq[String]]("The versions of Scala used when cross-building.").withRank(BPlusSetting)
   val crossVersion = settingKey[CrossVersion]("Configures handling of the Scala version when cross-building.").withRank(CSetting)
+  val platform = settingKey[String]("Configures the default suffix to be used for %% operator.").withRank(CSetting)
   val classpathOptions = settingKey[ClasspathOptions]("Configures handling of Scala classpaths.").withRank(DSetting)
   val discoveredSbtPlugins = taskKey[PluginDiscovery.DiscoveredNames]("The names of sbt plugin-related modules (modules that extend Build, Plugin, AutoPlugin) defined by this project.").withRank(CTask)
   val sbtPlugin = settingKey[Boolean]("If true, enables adding sbt as a dependency and auto-generation of the plugin descriptor file.").withRank(BMinusSetting)

main/src/main/scala/sbt/coursierint/CoursierInputsTasks.scala

@@ -49,6 +49,7 @@ object CoursierInputsTasks {
       description: String,
       homepage: Option[URL],
       vsOpt: Option[String],
+      projectPlatform: Option[String],
       log: Logger
   ): CProject = {
 
@@ -59,7 +60,8 @@ object CoursierInputsTasks {
       dependencies,
       configMap,
       sv,
-      sbv
+      sbv,
+      projectPlatform,
     )
     val proj1 = auOpt match {
       case Some(au) =>
@@ -88,6 +90,7 @@ object CoursierInputsTasks {
         description.value,
         homepage.value,
         versionScheme.value,
+        scalaModuleInfo.value.flatMap(_.platform),
         streams.value.log
       )
     }

project/Dependencies.scala

@@ -15,7 +15,7 @@ object Dependencies {
   // sbt modules
   private val ioVersion = nightlyVersion.getOrElse("1.8.0")
   private val lmVersion =
-    sys.props.get("sbt.build.lm.version").orElse(nightlyVersion).getOrElse("2.0.0-alpha10")
+    sys.props.get("sbt.build.lm.version").orElse(nightlyVersion).getOrElse("2.0.0-alpha11")
   val zincVersion = nightlyVersion.getOrElse("2.0.0-alpha6")
 
   private val sbtIO = "org.scala-sbt" %% "io" % ioVersion
@@ -80,7 +80,7 @@ object Dependencies {
   def addSbtZincCompileCore = addSbtModule(sbtZincPath, "zincCompileCore", zincCompileCore)
 
   // val lmCoursierShaded = "io.get-coursier" %% "lm-coursier-shaded" % "2.0.10"
-  val lmCoursierShaded = "org.scala-sbt" %% "librarymanagement-coursier" % "2.0.0-alpha4"
+  val lmCoursierShaded = "org.scala-sbt" %% "librarymanagement-coursier" % "2.0.0-alpha5"
 
   lazy val sjsonNewVersion = "0.13.0"
   def sjsonNew(n: String) = Def.setting(

sbt-app/src/main/scala/sbt/Import.scala

@@ -328,6 +328,7 @@ trait Import {
   val Patterns = sbt.librarymanagement.Patterns
   type Patterns = sbt.librarymanagement.Patterns
   type PatternsBasedRepository = sbt.librarymanagement.PatternsBasedRepository
+  val Platform = sbt.librarymanagement.Platform
   val PublishConfiguration = sbt.librarymanagement.PublishConfiguration
   type PublishConfiguration = sbt.librarymanagement.PublishConfiguration
   type RawRepository = sbt.librarymanagement.RawRepository

sbt-app/src/sbt-test/dependency-management/platform/build.sbt

@@ -0,0 +1,15 @@
+lazy val check = taskKey[Unit]("Runs the check")
+
+scalaVersion := "2.13.10"
+platform := Platform.sjs1
+
+// By default platformOpt field is set to None
+// Given %% lm engines will sustitute it with the subproject's platform suffix on `update`
+libraryDependencies += "com.github.scopt" %% "scopt" % "4.1.0"
+
+TaskKey[Unit]("check") := {
+  val ur = update.value
+  val files = ur.matching(moduleFilter(organization = "com.github.scopt", name = "scopt_sjs1_2.13", revision = "*"))
+  assert(files.nonEmpty, s"sjs1 scopt module was not found in update report: $ur")
+}
+csrCacheDirectory := baseDirectory.value / "coursier-cache"

sbt-app/src/sbt-test/dependency-management/platform/test

@@ -0,0 +1 @@
+> check