More explicit test of trait parameter initialization order

As suggested by @retronym

Author: odersky

tests/run/traitParamInit.scala

@@ -0,0 +1,30 @@
+object Trace {
+  private var results = List[Any]()
+  def apply[A](a: A) = {results ::= a; a}
+  def fetchAndClear(): Seq[Any] = try results.reverse finally results = Nil
+}
+trait T(a: Any) {
+  val ta = a
+  Trace(s"T.<init>($ta)")
+  val t_val = Trace("T.val")
+}
+
+trait U(a: Any) extends T {
+  val ua = a
+  Trace(s"U.<init>($ua)")
+}
+
+object Test {
+  def check(expected: Any) = {
+    val actual = Trace.fetchAndClear()
+    if (actual != expected)
+      sys.error(s"\n$actual\n$expected")
+  }
+  def main(args: Array[String]): Unit = {
+    new T(Trace("ta")) with U(Trace("ua")) {}
+    check(List("ta", "T.<init>(ta)", "T.val", "ua", "U.<init>(ua)"))
+
+    new U(Trace("ua")) with T(Trace("ta")) {}
+    check(List("ta", "T.<init>(ta)", "T.val", "ua", "U.<init>(ua)"))
+  }
+}