Fix #7852: avoid reading stale .tasty files from jars

Somehow, if we don't close the classloader used to read .tasty files
from jars, a subsequent compilation run might end up reading a stale
version of the .tasty file which does not exist on disk anymore. I don't
understand why this happens since we don't reuse the classloader itself,
but that's life sometimes ¯\_(ツ)_/¯

Author: smarter

compiler/src/dotty/tools/dotc/core/classfile/ClassfileParser.scala

@@ -780,22 +780,29 @@ class ClassfileParser(
               Array.empty
             case Some(jar: ZipArchive) => // We are in a jar
               val cl = new URLClassLoader(Array(jar.jpath.toUri.toURL), /*parent =*/ null)
-              val path = classfile.path.stripSuffix(".class") + ".tasty"
-              val stream = cl.getResourceAsStream(path)
-              if (stream != null) {
-                val tastyOutStream = new ByteArrayOutputStream()
-                val buffer = new Array[Byte](1024)
-                var read = stream.read(buffer, 0, buffer.length)
-                while (read != -1) {
-                  tastyOutStream.write(buffer, 0, read)
-                  read = stream.read(buffer, 0, buffer.length)
+              try {
+                val path = classfile.path.stripSuffix(".class") + ".tasty"
+                val stream = cl.getResourceAsStream(path)
+                if (stream != null) {
+                  val tastyOutStream = new ByteArrayOutputStream()
+                  val buffer = new Array[Byte](1024)
+                  var read = stream.read(buffer, 0, buffer.length)
+                  while (read != -1) {
+                    tastyOutStream.write(buffer, 0, read)
+                    read = stream.read(buffer, 0, buffer.length)
+                  }
+                  tastyOutStream.flush()
+                  tastyOutStream.toByteArray
+                }
+                else {
+                  ctx.error(s"Could not find $path in $jar")
+                  Array.empty
                 }
-                tastyOutStream.flush()
-                tastyOutStream.toByteArray
               }
-              else {
-                ctx.error(s"Could not find $path in $jar")
-                Array.empty
+              finally {
+                // If we don't close the classloader, spooky things happen (see
+                // scripted test source-dependencies/export-jars2).
+                cl.close()
               }
             case _ =>
               val plainFile = new PlainFile(io.File(classfile.jpath).changeExtension("tasty"))

sbt-dotty/sbt-test/source-dependencies/export-jars/changes/B.scala renamed to sbt-dotty/sbt-test/source-dependencies/export-jars/changes/B1.scala

@@ -0,0 +1 @@
+class A

sbt-dotty/sbt-test/source-dependencies/export-jars2/a/A.scala

@@ -0,0 +1,4 @@
+class B {
+  val x = new A
+}
+

sbt-dotty/sbt-test/source-dependencies/export-jars2/b/B.scala

@@ -0,0 +1,10 @@
+lazy val a = Project("a", file("a"))
+  .settings(
+    exportJars := true
+  )
+
+lazy val b = Project("b", file("b"))
+  .dependsOn(a)
+  .settings(
+    exportJars := true
+  )

sbt-dotty/sbt-test/source-dependencies/export-jars2/build.sbt

@@ -0,0 +1,2 @@
+
+class A

sbt-dotty/sbt-test/source-dependencies/export-jars2/changes/A1.scala

@@ -0,0 +1,5 @@
+
+class B {
+  val x = new A
+}
+

sbt-dotty/sbt-test/source-dependencies/export-jars2/changes/B1.scala

@@ -0,0 +1,12 @@
+import sbt._
+import Keys._
+
+object DottyInjectedPlugin extends AutoPlugin {
+  override def requires = plugins.JvmPlugin
+  override def trigger = allRequirements
+
+  override val projectSettings = Seq(
+    scalaVersion := sys.props("plugin.scalaVersion"),
+    scalacOptions += "-language:Scala2Compat"
+  )
+}

sbt-dotty/sbt-test/source-dependencies/export-jars2/project/DottyInjectedPlugin.scala

@@ -0,0 +1 @@
+addSbtPlugin("ch.epfl.lamp" % "sbt-dotty" % sys.props("plugin.version"))

sbt-dotty/sbt-test/source-dependencies/export-jars2/project/plugins.sbt

@@ -0,0 +1,7 @@
+> compile
+$ copy-file changes/A1.scala a/A.scala
+$ copy-file changes/B1.scala b/B.scala
+# This used to fail with "Tasty UUID (...) file did not correspond the tasty UUID (...) declared in the classfile"
+# because we were somehow reading the .tasty file from the previous compilation run, even though it does not exist
+# on disk anymore (#7852)
+> compile