Fix scala-js#3661: Load linker reflectively

This gives us the following advantages:

- Allows us to give resources to the linker that the build itself
  compiles first (unblocks scala-js#3537).
- Hides linker dependencies away from other sbt plugins. Notably the
  Google Closure Compiler and Guava (fixes scala-js#3193).

Author: gzm0

Jenkinsfile

@@ -298,7 +298,7 @@ def Tasks = [
   "bootstrap": '''
     setJavaVersion $java
     npm install &&
-    sbt ++$scala linker/test &&
+    sbt ++$scala! linker/test &&
     sbt ++$scala irJS/test linkerJS/test &&
     sbt 'set scalaJSStage in Global := FullOptStage' \
         'set scalaJSStage in testSuite := FastOptStage' \
@@ -315,14 +315,14 @@ def Tasks = [
   "tools": '''
     setJavaVersion $java
     npm install &&
-    sbt ++$scala ir/test logging/compile linkerInterface/compile \
+    sbt ++$scala! ir/test logging/compile linkerInterface/compile \
         linker/compile jsEnvs/test nodeJSEnv/test testAdapter/test \
         ir/mimaReportBinaryIssues logging/mimaReportBinaryIssues \
         linkerInterface/mimaReportBinaryIssues linker/mimaReportBinaryIssues \
         jsEnvs/mimaReportBinaryIssues jsEnvsTestKit/mimaReportBinaryIssues \
         nodeJSEnv/mimaReportBinaryIssues \
         testAdapter/mimaReportBinaryIssues &&
-    sbt ++$scala ir/compile:doc logging/compile:doc \
+    sbt ++$scala! ir/compile:doc logging/compile:doc \
         linkerInterface/compile:doc \
         linker/compile:doc jsEnvs/compile:doc \
         jsEnvsTestKit/compile:doc nodeJSEnv/compile:doc \
@@ -332,7 +332,7 @@ def Tasks = [
   "tools-sbtplugin": '''
     setJavaVersion $java
     npm install &&
-    sbt ++$scala ir/test logging/compile linkerInterface/compile \
+    sbt ++$scala! ir/test logging/compile linkerInterface/compile \
         linker/compile jsEnvs/test nodeJSEnv/test testAdapter/test \
         sbtPlugin/package \
         ir/mimaReportBinaryIssues logging/mimaReportBinaryIssues \
@@ -341,7 +341,7 @@ def Tasks = [
         nodeJSEnv/mimaReportBinaryIssues \
         testAdapter/mimaReportBinaryIssues \
         sbtPlugin/mimaReportBinaryIssues &&
-    sbt ++$scala library/scalastyle javalanglib/scalastyle javalib/scalastyle \
+    sbt ++$scala! library/scalastyle javalanglib/scalastyle javalib/scalastyle \
         ir/scalastyle compiler/scalastyle \
         compiler/test:scalastyle \
         logging/scalastyle logging/test:scalastyle \
@@ -359,7 +359,7 @@ def Tasks = [
         jUnitPlugin/scalastyle jUnitRuntime/scalastyle \
         jUnitTestOutputsJVM/scalastyle jUnitTestOutputsJVM/test:scalastyle \
         jUnitTestOutputsJS/scalastyle jUnitTestOutputsJS/test:scalastyle &&
-    sbt ++$scala ir/compile:doc logging/compile:doc \
+    sbt ++$scala! ir/compile:doc logging/compile:doc \
         linkerInterface/compile:doc \
         linker/compile:doc jsEnvs/compile:doc \
         jsEnvsTestKit/compile:doc nodeJSEnv/compile:doc \
@@ -381,8 +381,7 @@ def Tasks = [
     sbt ++2.11.12 compiler/publishLocal library/publishLocal \
                   testInterface/publishLocal testBridge/publishLocal \
                   jUnitPlugin/publishLocal jUnitRuntime/publishLocal &&
-    sbt ++$toolsscala \
-        ir/publishLocal logging/publishLocal \
+    sbt ir/publishLocal logging/publishLocal \
         linkerInterface/publishLocal \
         linker/publishLocal jsEnvs/publishLocal \
         nodeJSEnv/publishLocal testAdapter/publishLocal \
@@ -402,19 +401,19 @@ def Tasks = [
   "partest-noopt": '''
     setJavaVersion $java
     npm install &&
-    sbt ++$scala package "partestSuite/testOnly -- --showDiff"
+    sbt ++$scala! package "partestSuite/testOnly -- --showDiff"
   ''',
 
   "partest-fastopt": '''
     setJavaVersion $java
     npm install &&
-    sbt ++$scala package "partestSuite/testOnly -- --fastOpt --showDiff"
+    sbt ++$scala! package "partestSuite/testOnly -- --fastOpt --showDiff"
   ''',
 
   "partest-fullopt": '''
     setJavaVersion $java
     npm install &&
-    sbt ++$scala package "partestSuite/testOnly -- --fullOpt --showDiff"
+    sbt ++$scala! package "partestSuite/testOnly -- --fullOpt --showDiff"
   '''
 ]
 
@@ -455,7 +454,7 @@ allJavaVersions.each { javaVersion ->
   quickMatrix.add([task: "tools", scala: "2.11.12", java: javaVersion])
 }
 quickMatrix.add([task: "partestc", scala: "2.12.1", java: mainJavaVersion])
-quickMatrix.add([task: "sbtplugin-test", toolsscala: "2.12.8", java: mainJavaVersion])
+quickMatrix.add([task: "sbtplugin-test", java: mainJavaVersion])
 
 // The 'full' matrix
 def fullMatrix = quickMatrix.clone()

project/Build.scala

@@ -104,6 +104,13 @@ object MyScalaJSPlugin extends AutoPlugin {
       jsEnv := new NodeJSEnv(
           NodeJSEnv.Config().withSourceMap(wantSourceMaps.value)),
 
+      scalaJSLinkerImpl := {
+        val v = (scalaVersion in Build.linker).value
+        assert(v.startsWith("2.12."), "The linker is configured with a Scala " +
+            s"version ($v) that is not compatible with this build (2.12.x). ")
+        LinkerImpl.default(Attributed.data((fullClasspath in (Build.linker, Runtime)).value))
+      },
+
       // Link source maps to GitHub sources
       addScalaJSCompilerOption(Def.setting {
         "mapSourceURI:" +
@@ -412,6 +419,10 @@ object Build {
       scalacOptions += "-Xfatal-warnings"
   )
 
+  val freezeVersionForToolsSettings = Def.settings(
+      crossScalaVersions := Seq("2.12.8")
+  )
+
   private def publishToBintraySettings = Def.settings(
       publishTo := {
         val proj = bintrayProjectName.value
@@ -554,6 +565,7 @@ object Build {
 
   lazy val irProject: Project = Project(id = "ir", base = file("ir")).settings(
       commonIrProjectSettings,
+      freezeVersionForToolsSettings,
       libraryDependencies +=
         "com.novocode" % "junit-interface" % "0.9" % "test"
   )
@@ -638,7 +650,8 @@ object Build {
   )
 
   lazy val logging: Project = (project in file("logging/jvm")).settings(
-      commonLoggingSettings
+      commonLoggingSettings,
+      freezeVersionForToolsSettings,
   )
 
   lazy val loggingJS: Project = (project in file("logging/js")).enablePlugins(
@@ -670,6 +683,7 @@ object Build {
 
   lazy val linkerInterface: Project = (project in file("linker-interface/jvm")).settings(
       commonLinkerInterfaceSettings,
+      freezeVersionForToolsSettings,
   ).dependsOn(irProject, logging)
 
   lazy val linkerInterfaceJS: Project = (project in file("linker-interface/js")).settings(
@@ -711,6 +725,7 @@ object Build {
 
   lazy val linker: Project = (project in file("linker/jvm")).settings(
       commonLinkerSettings,
+      freezeVersionForToolsSettings,
       libraryDependencies ++= Seq(
           "com.google.javascript" % "closure-compiler" % "v20190513",
           "com.novocode" % "junit-interface" % "0.9" % "test"
@@ -732,6 +747,7 @@ object Build {
 
   lazy val jsEnvs: Project = (project in file("js-envs")).settings(
       commonSettings,
+      freezeVersionForToolsSettings,
       publishSettings,
       fatalWarningsSettings,
       name := "Scala.js JS Envs",
@@ -742,6 +758,7 @@ object Build {
 
   lazy val jsEnvsTestKit: Project = (project in file("js-envs-test-kit")).settings(
       commonSettings,
+      freezeVersionForToolsSettings,
       publishSettings,
       fatalWarningsSettings,
       name := "Scala.js JS Envs Test Kit",
@@ -756,6 +773,7 @@ object Build {
 
   lazy val nodeJSEnv: Project = (project in file("nodejs-env")).settings(
       commonSettings,
+      freezeVersionForToolsSettings,
       publishSettings,
       fatalWarningsSettings,
       name := "Scala.js Node.js env",
@@ -770,6 +788,7 @@ object Build {
 
   lazy val testAdapter = (project in file("test-adapter")).settings(
       commonSettings,
+      freezeVersionForToolsSettings,
       publishSettings,
       fatalWarningsSettings,
       name := "Scala.js sbt test adapter",
@@ -815,7 +834,7 @@ object Build {
 
         sbtJars.map(_.data -> docUrl).toMap
       }
-  ).dependsOn(linker, jsEnvs, nodeJSEnv, testAdapter)
+  ).dependsOn(linkerInterface, jsEnvs, nodeJSEnv, testAdapter)
 
   lazy val delambdafySetting = {
     scalacOptions ++= (
@@ -1274,6 +1293,7 @@ object Build {
 
   lazy val jUnitTestOutputsJVM = (project in file("junit-test/output-jvm")).settings(
       commonJUnitTestOutputsSettings,
+      freezeVersionForToolsSettings,
       name := "Tests for Scala.js JUnit output in JVM.",
       libraryDependencies ++= Seq(
           "org.scala-sbt" % "test-interface" % "1.0" % "test",
@@ -1303,6 +1323,7 @@ object Build {
 
   lazy val jUnitAsyncJVM = (project in file("junit-async/jvm")).settings(
       commonSettings,
+      freezeVersionForToolsSettings,
       name := "Scala.js internal JUnit async JVM support",
       publishArtifact in Compile := false
   )

project/build.sbt

@@ -6,8 +6,6 @@ addSbtPlugin("org.scalastyle" % "scalastyle-sbt-plugin" % "1.0.0")
 
 addSbtPlugin("org.portable-scala" % "sbt-platform-deps" % "1.0.0")
 
-libraryDependencies += "com.google.javascript" % "closure-compiler" % "v20190513"
-
 libraryDependencies += "com.google.jimfs" % "jimfs" % "1.1"
 
 libraryDependencies += "org.eclipse.jgit" % "org.eclipse.jgit.pgm" % "3.2.0.201312181205-r"
@@ -20,8 +18,6 @@ unmanagedSourceDirectories in Compile ++= {
     root / "logging/jvm/src/main/scala",
     root / "linker-interface/shared/src/main/scala",
     root / "linker-interface/jvm/src/main/scala",
-    root / "linker/shared/src/main/scala",
-    root / "linker/jvm/src/main/scala",
     root / "js-envs/src/main/scala",
     root / "nodejs-env/src/main/scala",
     root / "test-adapter/src/main/scala",

sbt-plugin-test/project/build.sbt

@@ -1,2 +1,5 @@
-addSbtPlugin("org.scala-js" % "sbt-scalajs" %
-  org.scalajs.ir.ScalaJSVersions.current)
+val scalaJSVersion = org.scalajs.ir.ScalaJSVersions.current
+
+addSbtPlugin("org.scala-js" % "sbt-scalajs" % scalaJSVersion)
+
+libraryDependencies += "org.scala-js" %% "scalajs-linker" % scalaJSVersion

sbt-plugin/src/main/scala/org/scalajs/sbtplugin/CacheBox.scala

@@ -0,0 +1,35 @@
+/*
+ * Scala.js (https://www.scala-js.org/)
+ *
+ * Copyright EPFL.
+ *
+ * Licensed under Apache License 2.0
+ * (https://www.apache.org/licenses/LICENSE-2.0).
+ *
+ * See the NOTICE file distributed with this work for
+ * additional information regarding copyright ownership.
+ */
+
+package org.scalajs.sbtplugin
+
+/** A CacheBox is a support class to abuse an sbt setting as a cache.
+ *
+ *  A CacheBox is needed, once the cached result needs to depend on a task,
+ *  since then it cannot simply be made a setting anymore.
+ */
+private[sbtplugin] final class CacheBox[T] {
+  private[this] var value: T = _
+
+  def ensure(f: => T): T = synchronized {
+    if (value == null) {
+      value = f
+    }
+    value
+  }
+
+  def foreach(f: T => Unit): Unit = synchronized {
+    if (value != null) {
+      f(value)
+    }
+  }
+}