Make classpathFromClassloader non quadratic, add tests

The tests ensure that we've fixed #7897.

Co-Authored-By: Guillaume Martres <[email protected]>

Author: nicolasstucki

sbt-dotty/sbt-test/sbt-dotty/i7897/build-no-fork.sbt

@@ -0,0 +1,5 @@
+scalaVersion := sys.props("plugin.scalaVersion")
+
+libraryDependencies += "ch.epfl.lamp" %% "dotty-staging" % scalaVersion.value
+
+fork := false

sbt-dotty/sbt-test/sbt-dotty/i7897/build.sbt

@@ -0,0 +1,5 @@
+scalaVersion := sys.props("plugin.scalaVersion")
+
+libraryDependencies += "ch.epfl.lamp" %% "dotty-staging" % scalaVersion.value
+
+fork := true

sbt-dotty/sbt-test/sbt-dotty/i7897/project/build.properties

@@ -0,0 +1 @@
+sbt.version=1.3.6

sbt-dotty/sbt-test/sbt-dotty/i7897/project/plugins.sbt

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

sbt-dotty/sbt-test/sbt-dotty/i7897/src/main/scala/hello/i7897.scala

@@ -0,0 +1,14 @@
+import scala.quoted._, staging._
+
+given Toolbox = Toolbox.make(getClass.getClassLoader)
+
+val f: Array[Int] => Int = run {
+  val stagedSum: Expr[Array[Int] => Int] = '{ (arr: Array[Int]) => 6 }
+  println(stagedSum.show)
+  stagedSum
+}
+
+object Main {
+  def main(args: Array[String]): Unit =
+    f.apply(Array(1, 2, 3)) // Returns 6
+}

sbt-dotty/sbt-test/sbt-dotty/i7897/test

@@ -0,0 +1,3 @@
+> run
+$ copy-file build-no-fork.sbt build.sbt
+> run

staging/src/scala/quoted/staging/QuoteDriver.scala

@@ -73,23 +73,19 @@ private class QuoteDriver(appClassloader: ClassLoader) extends Driver {
    *  the wrong thing.
    */
   private def classpathFromClassloader(cl: ClassLoader): String = {
-    @tailrec
-    def loop(cl: ClassLoader, suffixClasspath: String): String =
-      cl match {
-        case cl: URLClassLoader =>
-          val updatedClasspath = cl.getURLs
-            .map(url => Paths.get(url.toURI).toAbsolutePath.toString)
-            .mkString(
-              "",
-              File.pathSeparator,
-              if (suffixClasspath.isEmpty) "" else File.pathSeparator + suffixClasspath
-            )
-          loop(cl.getParent, updatedClasspath)
-        case _ =>
-          suffixClasspath
-      }
-
-    loop(cl, "")
+    val classpathBuff = List.newBuilder[String]
+    def collectClassLoaderPaths(cl: ClassLoader): Unit = cl match {
+      case cl: URLClassLoader =>
+        collectClassLoaderPaths(cl.getParent)
+        // Parent classloaders are searched before their child, so the part of
+        // the classpath coming from the child is added at the _end_ of the
+        // classpath.
+        classpathBuff ++=
+          cl.getURLs.iterator.map(url => Paths.get(url.toURI).toAbsolutePath.toString)
+      case _ =>
+    }
+    collectClassLoaderPaths(cl)
+    classpathBuff.result().mkString(java.io.File.pathSeparator)
   }
 }