Add scalaCompilerBridgeBinaryJar task

The end goal is to rewrite Dotty's compiler-bridge in Java (this is easy
since the zinc-specific phases are in the compiler itself) to simplify
the bootstrapping process.

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

@@ -450,7 +450,8 @@ object Defaults extends BuildCommon {
       val _ = clean.value
       IvyActions.cleanCachedResolutionCache(ivyModule.value, streams.value.log)
     },
-    scalaCompilerBridgeSource := ZincUtil.getDefaultBridgeModule(scalaVersion.value)
+    scalaCompilerBridgeBinaryJar := None,
+    scalaCompilerBridgeSource := ZincUtil.getDefaultBridgeModule(scalaVersion.value),
   )
   // must be a val: duplication detected by object identity
   private[this] lazy val compileBaseGlobal: Seq[Setting[_]] = globalDefaults(
@@ -503,17 +504,27 @@ object Defaults extends BuildCommon {
       val zincDir = BuildPaths.getZincDirectory(st, g)
       val app = appConfiguration.value
       val launcher = app.provider.scalaProvider.launcher
-      val scalac = ZincUtil.scalaCompiler(
-        scalaInstance = scalaInstance.value,
-        classpathOptions = classpathOptions.value,
-        globalLock = launcher.globalLock,
-        componentProvider = app.provider.components,
-        secondaryCacheDir = Option(zincDir),
-        dependencyResolution = dependencyResolution.value,
-        compilerBridgeSource = scalaCompilerBridgeSource.value,
-        scalaJarsTarget = zincDir,
-        log = streams.value.log
-      )
+      val scalac =
+        scalaCompilerBridgeBinaryJar.value match {
+          case Some(jar) =>
+            ZincUtil.scalaCompiler(
+              scalaInstance = scalaInstance.value,
+              classpathOptions = classpathOptions.value,
+              compilerBridgeJar = jar
+            )
+          case _ =>
+            ZincUtil.scalaCompiler(
+              scalaInstance = scalaInstance.value,
+              classpathOptions = classpathOptions.value,
+              globalLock = launcher.globalLock,
+              componentProvider = app.provider.components,
+              secondaryCacheDir = Option(zincDir),
+              dependencyResolution = dependencyResolution.value,
+              compilerBridgeSource = scalaCompilerBridgeSource.value,
+              scalaJarsTarget = zincDir,
+              log = streams.value.log
+            )
+        }
       val compilers = ZincUtil.compilers(
         instance = scalaInstance.value,
         classpathOptions = classpathOptions.value,

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

@@ -220,7 +220,8 @@ object Keys {
   val crossSbtVersions = settingKey[Seq[String]]("The versions of Sbt used when cross-building an sbt plugin.")
   val printWarnings = taskKey[Unit]("Shows warnings from compilation, including ones that weren't printed initially.").withRank(BPlusTask)
   val fileInputOptions = settingKey[Seq[String]]("Options that take file input, which may invalidate the cache.").withRank(CSetting)
-  val scalaCompilerBridgeSource = settingKey[ModuleID]("Configures the module ID of the sources of the compiler bridge.").withRank(CSetting)
+  val scalaCompilerBridgeBinaryJar = taskKey[Option[File]]("Optionally, the jar of the compiler bridge. When not None, this takes precedence over scalaCompilerBridgeSource").withRank(CSetting)
+  val scalaCompilerBridgeSource = settingKey[ModuleID]("Configures the module ID of the sources of the compiler bridge when scalaCompilerBridgeBinaryJar is None").withRank(CSetting)
   val scalaArtifacts = settingKey[Seq[String]]("Configures the list of artifacts which should match the Scala binary version").withRank(CSetting)
   val enableBinaryCompileAnalysis = settingKey[Boolean]("Writes the analysis file in binary format")
   val crossJavaVersions = settingKey[Seq[String]]("The java versions used during JDK cross testing").withRank(BPlusSetting)

main/src/main/scala/sbt/internal/ConsoleProject.scala

@@ -21,7 +21,10 @@ object ConsoleProject {
     val cpImports = new Imports(extracted, state)
     val bindings = ("currentState" -> state) :: ("extracted" -> extracted) :: ("cpHelpers" -> cpImports) :: Nil
     val unit = extracted.currentUnit
-    val (_, dependencyResolution) = extracted.runTask(Keys.dependencyResolution, state)
+    val (state1, dependencyResolution) =
+      extracted.runTask(Keys.dependencyResolution, state)
+    val (_, scalaCompilerBridgeBinaryJar) =
+      extracted.runTask(Keys.scalaCompilerBridgeBinaryJar, state1)
     val scalaInstance = {
       val scalaProvider = state.configuration.provider.scalaProvider
       ScalaInstance(scalaProvider.version, scalaProvider.launcher)
@@ -30,17 +33,26 @@ object ConsoleProject {
     val zincDir = BuildPaths.getZincDirectory(state, g)
     val app = state.configuration
     val launcher = app.provider.scalaProvider.launcher
-    val compiler = ZincUtil.scalaCompiler(
-      scalaInstance = scalaInstance,
-      classpathOptions = ClasspathOptionsUtil.repl,
-      globalLock = launcher.globalLock,
-      componentProvider = app.provider.components,
-      secondaryCacheDir = Option(zincDir),
-      dependencyResolution = dependencyResolution,
-      compilerBridgeSource = extracted.get(Keys.scalaCompilerBridgeSource),
-      scalaJarsTarget = zincDir,
-      log = log
-    )
+    val compiler = scalaCompilerBridgeBinaryJar match {
+      case Some(jar) =>
+        ZincUtil.scalaCompiler(
+          scalaInstance = scalaInstance,
+          classpathOptions = ClasspathOptionsUtil.repl,
+          compilerBridgeJar = jar
+        )
+      case None =>
+        ZincUtil.scalaCompiler(
+          scalaInstance = scalaInstance,
+          classpathOptions = ClasspathOptionsUtil.repl,
+          globalLock = launcher.globalLock,
+          componentProvider = app.provider.components,
+          secondaryCacheDir = Option(zincDir),
+          dependencyResolution = dependencyResolution,
+          compilerBridgeSource = extracted.get(Keys.scalaCompilerBridgeSource),
+          scalaJarsTarget = zincDir,
+          log = log
+        )
+    }
     val imports = BuildUtil.getImports(unit.unit) ++ BuildUtil.importAll(bindings.map(_._1))
     val importString = imports.mkString("", ";\n", ";\n\n")
     val initCommands = importString + extra

sbt/src/sbt-test/dependency-management/compiler-bridge-binary/A.scala

@@ -0,0 +1 @@
+object A

sbt/src/sbt-test/dependency-management/compiler-bridge-binary/build.sbt

@@ -0,0 +1,16 @@
+scalaVersion := "2.12.6"
+
+// We can't use "%%" here without breaking the "== bridgeModule" check below
+val bridgeModule = "org.scala-sbt" % s"compiler-bridge_2.12" % "1.2.1"
+
+libraryDependencies += bridgeModule % Configurations.ScalaTool
+
+scalaCompilerBridgeSource := "shouldnotbeused" % "dummy" % "dummy"
+
+scalaCompilerBridgeBinaryJar := {
+  for {
+    toolReport <- update.value.configuration(Configurations.ScalaTool)
+    m <- toolReport.modules.find(m => m.module == bridgeModule)
+    (_, file) <- m.artifacts.find(art => art._1.`type` == Artifact.DefaultType)
+  } yield file
+}

sbt/src/sbt-test/dependency-management/compiler-bridge-binary/test

@@ -0,0 +1 @@
+> compile