[2.0.x] fix: keep worker classloader open for shutdown hooks (#9639)

sbt-app/src/sbt-test/tests/fork-shutdown-hook/build.sbt

@@ -0,0 +1,21 @@
+Global / localCacheDirectory := baseDirectory.value / "diskcache"
+scalaVersion := "3.8.4"
+
+Test / fork := true
+
+libraryDependencies += "org.scalameta" %% "munit" % "1.0.4" % Test
+
+val check = TaskKey[Unit]("check", "Verify the shutdown hook could load classes.")
+
+check := Def.uncached {
+  val file = baseDirectory.value / "hook-result.txt"
+  val deadline = System.currentTimeMillis + 30000
+  def content: String = if (file.exists) IO.read(file).trim else ""
+  while (content.isEmpty || content.startsWith("PENDING")) {
+    if (System.currentTimeMillis > deadline)
+      sys.error(s"shutdown hook never completed: '$content'")
+    Thread.sleep(500)
+  }
+  val result = content
+  if (!result.startsWith("OK")) sys.error(s"shutdown hook failed: '$result'")
+}

sbt-app/src/sbt-test/tests/fork-shutdown-hook/src/test/scala/LazilyLoaded.scala

@@ -0,0 +1,5 @@
+package repro
+
+object LazilyLoaded {
+  val marker: String = "loaded"
+}

sbt-app/src/sbt-test/tests/fork-shutdown-hook/src/test/scala/ShutdownHookTest.scala

@@ -0,0 +1,20 @@
+package repro
+
+import java.nio.file.{ Files, Paths }
+
+class ShutdownHookTest extends munit.FunSuite {
+  test("shutdown hook can load classes after the test run") {
+    val out = Paths.get("hook-result.txt")
+    Files.writeString(out, "PENDING: shutdown hook did not run" + System.lineSeparator)
+    val _ = sys.addShutdownHook {
+      val result =
+        try {
+          Class.forName("repro.LazilyLoaded$")
+          "OK: classloader still works at JVM shutdown"
+        } catch {
+          case t: Throwable => s"FAIL: $t"
+        }
+      Files.writeString(out, result + System.lineSeparator)
+    }
+  }
+}

sbt-app/src/sbt-test/tests/fork-shutdown-hook/test

@@ -0,0 +1,2 @@
+> testFull
+> check

worker/src/main/java/sbt/internal/worker1/WorkerMain.java

@@ -188,12 +188,11 @@ public final class WorkerMain {
         throw new RuntimeException("missing jvmRunInfo element");
       }
       RunInfo.JvmRunInfo jvmRunInfo = info.jvmRunInfo;
-      try (URLClassLoader cl = createClassLoader(jvmRunInfo, ClassLoader.getSystemClassLoader())) {
-        Class<?> mainClass = cl.loadClass(jvmRunInfo.mainClass);
-        Method mainMethod = mainClass.getMethod("main", String[].class);
-        String[] mainArgs = jvmRunInfo.args.stream().toArray(String[]::new);
-        mainMethod.invoke(null, (Object) mainArgs);
-      }
+      URLClassLoader cl = createClassLoader(jvmRunInfo, ClassLoader.getSystemClassLoader());
+      Class<?> mainClass = cl.loadClass(jvmRunInfo.mainClass);
+      Method mainMethod = mainClass.getMethod("main", String[].class);
+      String[] mainArgs = jvmRunInfo.args.stream().toArray(String[]::new);
+      mainMethod.invoke(null, (Object) mainArgs);
     } else {
       throw new RuntimeException("only jvm is supported");
     }
@@ -207,9 +206,8 @@ public final class WorkerMain {
       if (jvmRunInfo.classpath.isEmpty()) {
         ForkTestMain.main(id, info, this.jsonOut, parent);
       } else {
-        try (URLClassLoader cl = createClassLoader(jvmRunInfo, parent)) {
-          ForkTestMain.main(id, info, this.jsonOut, cl);
-        }
+        URLClassLoader cl = createClassLoader(jvmRunInfo, parent);
+        ForkTestMain.main(id, info, this.jsonOut, cl);
       }
     } else {
       throw new RuntimeException("only jvm is supported");