Fix scala-js#3661: Load linker via reflection from main build

This will allow us to give resources to the linker that the build
itself compiles first.

Author: gzm0

project/Build.scala

@@ -10,6 +10,7 @@ import Keys._
 import com.typesafe.tools.mima.plugin.MimaPlugin.autoImport._
 import de.heikoseeberger.sbtheader.HeaderPlugin.autoImport._
 
+import java.net.URLClassLoader
 import java.util.Arrays
 
 import scala.collection.mutable
@@ -104,6 +105,13 @@ object MyScalaJSPlugin extends AutoPlugin {
       jsEnv := new NodeJSEnv(
           NodeJSEnv.Config().withSourceMap(wantSourceMaps.value)),
 
+      scalaJSLinkerImpl := {
+        val deps = (fullClasspath in (Build.linker, Runtime)).value
+        val urls = Attributed.data(deps).map(_.toURI.toURL).toArray
+
+        LinkerImpl.default(new URLClassLoader(urls, getClass.getClassLoader))
+      },
+
       // Link source maps to GitHub sources
       addScalaJSCompilerOption(Def.setting {
         "mapSourceURI:" +

project/build.sbt

@@ -6,10 +6,13 @@ 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"
 
+// Bump guava for closure compiler used by linker.
+// Since it is loaded by reflection, the normal eviction doesn't work.
+// Expect that you need to update this if you update closure-compiler.
+libraryDependencies += "com.google.guava" % "guava-testlib" % "25.1-jre"
+
 libraryDependencies += "org.eclipse.jgit" % "org.eclipse.jgit.pgm" % "3.2.0.201312181205-r"
 
 unmanagedSourceDirectories in Compile ++= {
@@ -20,8 +23,6 @@ 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",