From 922885f7eb2bba251ee9b95173ef9633daf32eee Mon Sep 17 00:00:00 2001
From: Dale Wijnand <dale.wijnand@gmail.com>
Date: Tue, 27 Jul 2021 14:03:30 +0100
Subject: [PATCH 1/2] Make accessing OriginalTree noop on Scala 2.12.0-2

---
 .../src/main/scala-2.12/xsbt/Compat.scala     | 31 ++++++++++++++++---
 1 file changed, 27 insertions(+), 4 deletions(-)

diff --git a/internal/compiler-bridge/src/main/scala-2.12/xsbt/Compat.scala b/internal/compiler-bridge/src/main/scala-2.12/xsbt/Compat.scala
index 13c9d77249..49c35d79d6 100644
--- a/internal/compiler-bridge/src/main/scala-2.12/xsbt/Compat.scala
+++ b/internal/compiler-bridge/src/main/scala-2.12/xsbt/Compat.scala
@@ -22,10 +22,7 @@ abstract class Compat {
 
   /** If given tree contains object tree attachment calls func on tree from attachment. */
   protected def processOriginalTreeAttachment(in: Tree)(func: Tree => Unit): Unit = {
-    import analyzer._
-    in.attachments.get[OriginalTreeAttachment].foreach { a =>
-      func(a.original)
-    }
+    Compat.OriginalTreeTraverser.Instance.traverseOriginal(in)(func)
   }
 }
 object Compat {
@@ -34,6 +31,32 @@ object Compat {
 
   // IMain in 2.13 accepts ReplReporter
   def replReporter(settings: Settings, writer: PrintWriter) = writer
+
+  sealed abstract class OriginalTreeTraverser private {
+    def traverseOriginal[T <: Global#Tree](t: T)(f: T => Unit): Unit
+  }
+
+  object OriginalTreeTraverser {
+    private[this] val cls = try {
+      Class.forName("scala.tools.nsc.typechecker.StdAttachments$OriginalTreeAttachment")
+    } catch { case _: Throwable => null }
+
+    private object Reflective extends OriginalTreeTraverser {
+      private[this] val ct = scala.reflect.ClassTag(cls)
+      private[this] val meth = cls.getMethod("original")
+      def traverseOriginal[T <: Global#Tree](t: T)(f: T => Unit): Unit =
+        t.attachments.get(ct) match {
+          case Some(attachment) => f(meth.invoke(attachment).asInstanceOf[T])
+          case None             =>
+        }
+    }
+
+    private object NoOp extends OriginalTreeTraverser {
+      def traverseOriginal[T <: Global#Tree](t: T)(f: T => Unit): Unit = ()
+    }
+
+    val Instance = if (cls == null) NoOp else Reflective
+  }
 }
 
 /** Defines compatibility utils for [[ZincCompiler]]. */

From 97ae167a669ee8c6b8414a64a17cd72bf9b631fb Mon Sep 17 00:00:00 2001
From: Jason Zaugg <jzaugg@gmail.com>
Date: Wed, 28 Jul 2021 10:52:13 +1000
Subject: [PATCH 2/2] Fix ClassCastException in reflective original tree lookup

---
 internal/compiler-bridge/src/main/scala-2.12/xsbt/Compat.scala | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/internal/compiler-bridge/src/main/scala-2.12/xsbt/Compat.scala b/internal/compiler-bridge/src/main/scala-2.12/xsbt/Compat.scala
index 49c35d79d6..48a691e6f8 100644
--- a/internal/compiler-bridge/src/main/scala-2.12/xsbt/Compat.scala
+++ b/internal/compiler-bridge/src/main/scala-2.12/xsbt/Compat.scala
@@ -42,7 +42,7 @@ object Compat {
     } catch { case _: Throwable => null }
 
     private object Reflective extends OriginalTreeTraverser {
-      private[this] val ct = scala.reflect.ClassTag(cls)
+      private[this] val ct = scala.reflect.ClassTag[AnyRef](cls)
       private[this] val meth = cls.getMethod("original")
       def traverseOriginal[T <: Global#Tree](t: T)(f: T => Unit): Unit =
         t.attachments.get(ct) match {