From 5448a16ba4224068ef19db507c42858b975f11b2 Mon Sep 17 00:00:00 2001
From: Ethan Atkins <contact@ethanatkins.com>
Date: Fri, 20 Nov 2020 12:17:59 -0800
Subject: [PATCH] Prepend scala instance jars to sbt classpath

When using the launcher's classpath for the metabuild, the
scala-compiler jar can be missing. This is because the managedJars only
method returns the scala-library jar and not the rest of the scala
instance. To fix this, we can always prepend the scala instance jars to
the classpath.

In order to simulate the issue in scripted, I had to manually remove the
scala-compiler.jar from the scripted classpath or else the scripted test
that I added doesn't actually do anything because the scala-compiler.jar
would end up on the app.provider.mainClasspath.

Fixes #4452
---
 build.sbt                                                  | 4 +++-
 main/src/main/scala/sbt/Defaults.scala                     | 7 ++++---
 .../plugin-scala-compiler-dependency/project/Plugin.scala  | 3 +++
 .../sbt-test/project/plugin-scala-compiler-dependency/test | 2 ++
 4 files changed, 12 insertions(+), 4 deletions(-)
 create mode 100644 sbt/src/sbt-test/project/plugin-scala-compiler-dependency/project/Plugin.scala
 create mode 100644 sbt/src/sbt-test/project/plugin-scala-compiler-dependency/test

diff --git a/build.sbt b/build.sbt
index 986281f56..443a3661b 100644
--- a/build.sbt
+++ b/build.sbt
@@ -1362,7 +1362,9 @@ def scriptedTask(launch: Boolean): Def.Initialize[InputTask[Unit]] = Def.inputTa
     scriptedLaunchOpts.value ++ (if (launch) Some(launchJar) else None),
     scalaVersion.value,
     version.value,
-    (scriptedSbtReduxProj / Test / fullClasspathAsJars).value.map(_.data),
+    (scriptedSbtReduxProj / Test / fullClasspathAsJars).value
+      .map(_.data)
+      .filterNot(_.getName.contains("scala-compiler")),
     streams.value.log
   )
 }
diff --git a/main/src/main/scala/sbt/Defaults.scala b/main/src/main/scala/sbt/Defaults.scala
index c6200785f..95dc58118 100644
--- a/main/src/main/scala/sbt/Defaults.scala
+++ b/main/src/main/scala/sbt/Defaults.scala
@@ -2506,14 +2506,15 @@ object Classpaths {
         val isMeta = isMetaBuild.value
         val force = reresolveSbtArtifacts.value
         val app = appConfiguration.value
-        val sbtCp0 = app.provider.mainClasspath.toList
-        val sbtCp = sbtCp0 map { Attributed.blank(_) }
+        def isJansiOrJLine(f: File) = f.getName.contains("jline") || f.getName.contains("jansi")
+        val scalaInstanceJars = app.provider.scalaProvider.jars.filterNot(isJansiOrJLine)
+        val sbtCp = (scalaInstanceJars ++ app.provider.mainClasspath).map(Attributed.blank)
         val mjars = managedJars(
           classpathConfiguration.value,
           classpathTypes.value,
           update.value
         )
-        if (isMeta && !force) mjars ++ sbtCp
+        if (isMeta && !force) (mjars ++ sbtCp).distinct
         else mjars
       },
       exportedProducts := ClasspathImpl.trackedExportedProducts(TrackLevel.TrackAlways).value,
diff --git a/sbt/src/sbt-test/project/plugin-scala-compiler-dependency/project/Plugin.scala b/sbt/src/sbt-test/project/plugin-scala-compiler-dependency/project/Plugin.scala
new file mode 100644
index 000000000..56281e2a1
--- /dev/null
+++ b/sbt/src/sbt-test/project/plugin-scala-compiler-dependency/project/Plugin.scala
@@ -0,0 +1,3 @@
+import scala.tools.nsc
+
+object Plugin
diff --git a/sbt/src/sbt-test/project/plugin-scala-compiler-dependency/test b/sbt/src/sbt-test/project/plugin-scala-compiler-dependency/test
new file mode 100644
index 000000000..3d7a46a0a
--- /dev/null
+++ b/sbt/src/sbt-test/project/plugin-scala-compiler-dependency/test
@@ -0,0 +1,2 @@
+> show sbtVersion
+# we just want to test that the project loads