ResolutionClassLoader (WIP)

cli/src/main/scala/coursier/cli/Coursier.scala

@@ -97,6 +97,9 @@ case class Launch(
   @ExtraName("M")
   @ExtraName("main")
     mainClass: String,
+  @ExtraName("c")
+  @HelpMessage("Assume coursier is a dependency of the launched app, and share the coursier dependency of the launcher with it - allows the launched app to get the resolution that launched it via ResolutionClassLoader")
+    addCoursier: Boolean,
   @Recurse
     common: CommonOptions
 ) extends CoursierCommand {
@@ -110,7 +113,29 @@ case class Launch(
     }
   }
 
-  val helper = new Helper(common, rawDependencies)
+  val extraForceVersions =
+    if (addCoursier)
+      ???
+    else
+      Seq.empty[String]
+
+  val dontFilterOut =
+    if (addCoursier) {
+      val url = classOf[coursier.core.Resolution].getProtectionDomain.getCodeSource.getLocation
+
+      if (url.getProtocol == "file")
+        Seq(new File(url.getPath))
+      else {
+        Console.err.println(s"Cannot get the location of the JAR of coursier ($url not a file URL)")
+        sys.exit(255)
+      }
+    } else
+      Seq.empty[File]
+
+  val helper = new Helper(
+    common.copy(forceVersion = common.forceVersion ++ extraForceVersions),
+    rawDependencies
+  )
 
   val files0 = helper.fetch(sources = false, javadoc = false)
 
@@ -118,7 +143,7 @@ case class Launch(
     files0.map(_.toURI.toURL).toArray,
     new ClasspathFilter(
       Thread.currentThread().getContextClassLoader,
-      Coursier.baseCp.map(new File(_)).toSet,
+      Coursier.baseCp.map(new File(_)).toSet -- dontFilterOut,
       exclude = true
     )
   )

core/jvm/src/main/scala/coursier/ResolutionClassLoader.scala

@@ -0,0 +1,37 @@
+package coursier
+
+import java.io.File
+import java.net.URLClassLoader
+
+import coursier.util.ClasspathFilter
+
+class ResolutionClassLoader(
+  val resolution: Resolution,
+  val artifacts: Seq[(Dependency, Artifact, File)],
+  parent: ClassLoader
+) extends URLClassLoader(
+  artifacts.map { case (_, _, f) => f.toURI.toURL }.toArray,
+  parent
+) {
+
+  /**
+   * Filtered version of this `ClassLoader`, exposing only `dependencies` and their
+   * their transitive dependencies, and filtering out the other dependencies from
+   * `resolution` - for `ClassLoader` isolation.
+   *
+   * An application launched by `coursier launch -C` has `ResolutionClassLoader` set as its
+   * context `ClassLoader` (can be obtain with `Thread.currentThread().getContextClassLoader`).
+   * If it aims at doing `ClassLoader` isolation, exposing only a dependency `dep` to the isolated
+   * things, `filter(dep)` provides a `ClassLoader` that loaded `dep` and all its transitive
+   * dependencies through the same loader as the contextual one, but that "exposes" only
+   * `dep` and its transitive dependencies, nothing more.
+   */
+  def filter(dependencies: Set[Dependency]): ClassLoader = {
+    val subRes = resolution.subset(dependencies)
+    val subArtifacts = subRes.dependencyArtifacts.map { case (_, a) => a }.toSet
+    val subFiles = artifacts.collect { case (_, a, f) if subArtifacts(a) => f }
+
+    new ClasspathFilter(this, subFiles.toSet, exclude = false)
+  }
+
+}