From 731e666603b35b9409b0529788467e529dc50b2b Mon Sep 17 00:00:00 2001
From: eugene yokota <eed3si9n@gmail.com>
Date: Mon, 3 Aug 2026 00:24:41 -0400
Subject: [PATCH] [2.x] fix: Fixes AccessDeniedException issue on Windows
 (#9538)

**Problem**
When test classloader holds on to the JAR file, Windows gets
AccessDefinedException on packageBin.

**Solution**
Flip the default to close the test class loader.
---
 main/src/main/scala/sbt/internal/ClassLoaders.scala | 10 +++++-----
 main/src/main/scala/sbt/internal/SysProp.scala      |  2 +-
 .../close-run/src/main/scala/Main.scala             | 13 -------------
 .../src/sbt-test/classloader-cache/close-run/test   |  1 -
 4 files changed, 6 insertions(+), 20 deletions(-)
 delete mode 100644 sbt-app/src/sbt-test/classloader-cache/close-run/src/main/scala/Main.scala
 delete mode 100644 sbt-app/src/sbt-test/classloader-cache/close-run/test

diff --git a/main/src/main/scala/sbt/internal/ClassLoaders.scala b/main/src/main/scala/sbt/internal/ClassLoaders.scala
index fcd315834..60d04f79d 100644
--- a/main/src/main/scala/sbt/internal/ClassLoaders.scala
+++ b/main/src/main/scala/sbt/internal/ClassLoaders.scala
@@ -224,11 +224,11 @@ private[sbt] object ClassLoaders {
               scalaReflectLayer,
               () =>
                 new ReverseLookupClassLoaderHolder(
-                  allDependencies,
-                  scalaReflectLayer,
-                  close,
-                  allowZombies,
-                  logger
+                  classpath = allDependencies,
+                  parent = scalaReflectLayer,
+                  closeThis = close,
+                  allowZombies = allowZombies,
+                  logger = logger,
                 )
             )
           } else scalaReflectLayer
diff --git a/main/src/main/scala/sbt/internal/SysProp.scala b/main/src/main/scala/sbt/internal/SysProp.scala
index 17c19c10b..41369c245 100644
--- a/main/src/main/scala/sbt/internal/SysProp.scala
+++ b/main/src/main/scala/sbt/internal/SysProp.scala
@@ -132,7 +132,7 @@ object SysProp:
    */
   lazy val color: Boolean = ITerminal.isColorEnabled
 
-  def closeClassLoaders: Boolean = getOrFalse("sbt.classloader.close")
+  def closeClassLoaders: Boolean = getOrTrue("sbt.classloader.close")
 
   def fileCacheSize: Long =
     SizeParser(System.getProperty("sbt.file.cache.size", "128M")).getOrElse(128L * 1024 * 1024)
diff --git a/sbt-app/src/sbt-test/classloader-cache/close-run/src/main/scala/Main.scala b/sbt-app/src/sbt-test/classloader-cache/close-run/src/main/scala/Main.scala
deleted file mode 100644
index a3964a2b3..000000000
--- a/sbt-app/src/sbt-test/classloader-cache/close-run/src/main/scala/Main.scala
+++ /dev/null
@@ -1,13 +0,0 @@
-object Main {
-  class Foo
-
-  def main(args: Array[String]): Unit = {
-    new Thread {
-      override def run(): Unit = {
-        Thread.sleep(500)
-        try new Foo
-        catch { case t: Throwable => sys.exit(1) }
-      }
-    }.start()
-  }
-}
diff --git a/sbt-app/src/sbt-test/classloader-cache/close-run/test b/sbt-app/src/sbt-test/classloader-cache/close-run/test
deleted file mode 100644
index 9e4c2371c..000000000
--- a/sbt-app/src/sbt-test/classloader-cache/close-run/test
+++ /dev/null
@@ -1 +0,0 @@
-> run
\ No newline at end of file