Try shared class loader

Author: adpi2

project/Build.scala

@@ -337,8 +337,7 @@ object Build {
         scalaLibrary,
         dottyLibrary,
         dottyCompiler,
-        allJars,
-        appConfiguration.value
+        allJars
       )
     },
     // sbt-dotty defines `scalaInstance in doc` so we need to override it manually

sbt-dotty/src/dotty/tools/sbtplugin/DottyPlugin.scala

@@ -539,27 +539,30 @@ object DottyPlugin extends AutoPlugin {
       scalaLibraryJar,
       dottyLibraryJar,
       compilerJar,
-      allJars,
-      appConfiguration.value
+      allJars
     )
   }
 
   // Adapted from private mkScalaInstance in sbt
   def makeScalaInstance(
-    state: State, dottyVersion: String, scalaLibrary: File, dottyLibrary: File, compiler: File, all: Seq[File], appConfiguration: AppConfiguration
+    state: State, dottyVersion: String, scalaLibrary: File, dottyLibrary: File, compiler: File, all: Seq[File]
   ): ScalaInstance = {
     /**
       * The compiler bridge must load the xsbti classes from the sbt
       * classloader, and similarly the Scala repl must load the sbt provided
-      * jline terminal. To do so we add the `appConfiguration` loader in
-      * the parent hierarchy of the scala 3 instance loader.
-      *
-      * The [[FilteringClassLoader]] ensures that the JNA, JDK and xsbti
-      * classes only are loaded from the sbt loader. That is necessary because
-      * the sbt class loader contains the Scala 2.12 library and compiler
-      * bridge.
+      * jline terminal.
       */
-    val topLoader = new FilteringClassLoader(appConfiguration.provider.loader)
+    val topLoader = new ClassLoader(null) {
+      val sharedPrefixes = List(
+        "xsbti.",
+        "org.jline."
+      )
+
+      override def loadClass(name: String): Class[_] = {
+        if (sharedPrefixes.exists(name.startsWith(_))) getClass.getClassLoader.loadClass(name)
+        else super.loadClass(name)
+      }
+    }
 
     val libraryJars = Array(dottyLibrary, scalaLibrary)
     val libraryLoader = state.classLoaderCache.cachedCustomClassloader(
@@ -583,27 +586,3 @@ object DottyPlugin extends AutoPlugin {
       None)
   }
 }
-
-private class FilteringClassLoader(parent: ClassLoader) extends ClassLoader(parent) {
-  private val prefixes = List(
-    "xsbti.",
-    "org.jline.",
-    "java.",
-    "sun.",
-    "jdk.internal.reflect.",
-    "javax."
-  )
-
-  override def loadClass(name: String, resolve: Boolean): Class[_] = {
-    if (prefixes.exists(name.startsWith(_))) super.loadClass(name, resolve)
-    else null
-  }
-
-  override def getResource(name: String): URL = {
-    null
-  }
-
-  override def getResources(name: String): Enumeration[URL] = {
-    Collections.enumeration(Collections.emptyList());
-  }
-}