From 464ea1b97e2408767a333aabd5f440109c07f5d6 Mon Sep 17 00:00:00 2001
From: Ethan Atkins <contact@ethanatkins.com>
Date: Wed, 8 Jul 2020 11:15:48 -0700
Subject: [PATCH] Add improved classloader construction short circuit

In order for sbt to function well, it needs the test interface, jansi
and forked jline jars provided by a classloader that is parent to all
other sbt classloaders. To do this for just the test interface jar, I
just checked if the top loader in the app configuration had the correct
name. Now that there are three jars, this is more complicated so I
updated the launcher to create a top loader with the method getEarlyJars
implemented and returning the three needed jars. This is a much more
scalable design.

If sbt is entered with a configuration that does not have a top loader
with the getEarlyJars method defined, then we just fall back on
constructing the default layered classlaoder from the configuration
classpath.

The motivation for this change is that I discovered that sbt immediately
crashed when I tried to run a non-snapshot version. After this change, I
verified that both snapshot and non-snapshot versions of the latest sbt
code could load with both an obsolete and up-to-date launcher.
---
 .../sbt/internal/XMainConfiguration.scala     | 29 +++++++++----------
 1 file changed, 14 insertions(+), 15 deletions(-)

diff --git a/main/src/main/scala/sbt/internal/XMainConfiguration.scala b/main/src/main/scala/sbt/internal/XMainConfiguration.scala
index d83826c37..1e72eb139 100644
--- a/main/src/main/scala/sbt/internal/XMainConfiguration.scala
+++ b/main/src/main/scala/sbt/internal/XMainConfiguration.scala
@@ -9,7 +9,7 @@ package sbt.internal
 
 import java.io.File
 import java.lang.reflect.InvocationTargetException
-import java.net.{ URL, URLClassLoader }
+import java.net.URL
 import java.util.concurrent.{ ExecutorService, Executors }
 import ClassLoaderClose.close
 
@@ -60,21 +60,20 @@ private[sbt] class XMainConfiguration {
   def run(moduleName: String, configuration: xsbti.AppConfiguration): xsbti.MainResult = {
     val topLoader = configuration.provider.scalaProvider.launcher.topLoader
     val updatedConfiguration =
-      if (topLoader.getClass.getCanonicalName.contains("TestInterfaceLoader")) {
-        topLoader match {
-          case u: URLClassLoader =>
-            val urls = u.getURLs
-            var i = 0
-            while (i < urls.length && i >= 0) {
-              if (urls(i).toString.contains("jline")) i = -2
-              else i += 1
-            }
-            if (i < 0) configuration
-            else makeConfiguration(configuration)
-          case _ => configuration
+      try {
+        val method = topLoader.getClass.getMethod("getEarlyJars")
+        val jars = method.invoke(topLoader).asInstanceOf[Array[URL]]
+        var canReuseConfiguration = jars.length == 3
+        var j = 0
+        while (j < jars.length && canReuseConfiguration) {
+          val s = jars(j).toString
+          canReuseConfiguration =
+            s.contains("jline") || s.contains("test-interface") || s.contains("jansi")
+          j += 1
         }
-      } else {
-        makeConfiguration(configuration)
+        if (canReuseConfiguration) configuration else makeConfiguration(configuration)
+      } catch {
+        case _: NoSuchMethodException => makeConfiguration(configuration)
       }
     val loader = updatedConfiguration.provider.loader
     Thread.currentThread.setContextClassLoader(loader)