closes #3692: make instantiateTypeVar more care...

closes #3692: make instantiateTypeVar more careful so it does not change
T's info to >: T <: T.

review by odersky

3 files changed, 35 insertions, 1 deletions

diff --git a/src/compiler/scala/tools/nsc/typechecker/Infer.scala b/src/compiler/scala/tools/nsc/typechecker/Infer.scala
index d4979b0589..0c81bb3887 100644
--- a/src/compiler/scala/tools/nsc/typechecker/Infer.scala
+++ b/src/compiler/scala/tools/nsc/typechecker/Infer.scala
@@ -1250,6 +1250,8 @@ trait Infer {
       solve(tvars1, tvars1 map (_.origin.typeSymbol), tvars1 map (x => COVARIANT), false)
     }
 
+    // this is quite nasty: it destructively changes the info of the syms of e.g., method type params (see #3692, where the type param T's bounds were set to >: T <: T, so that parts looped)
+    // the changes are rolled back by restoreTypeBounds, but might be unintentially observed in the mean time
     def instantiateTypeVar(tvar: TypeVar) {
       val tparam = tvar.origin.typeSymbol
       if (false &&
@@ -1263,7 +1265,8 @@ trait Infer {
       } else {
         val (lo, hi) = instBounds(tvar)
         if (lo <:< hi) {
-          if (!((lo <:< tparam.info.bounds.lo) && (tparam.info.bounds.hi <:< hi))) {
+          if (!((lo <:< tparam.info.bounds.lo) && (tparam.info.bounds.hi <:< hi)) // bounds were improved
+             && tparam != lo.typeSymbolDirect && tparam != hi.typeSymbolDirect) { // don't create illegal cycles
             context.nextEnclosing(_.tree.isInstanceOf[CaseDef]).pushTypeBounds(tparam)
             tparam setInfo TypeBounds(lo, hi)
             if (settings.debug.value) log("new bounds of " + tparam + " = " + tparam.info)
diff --git a/test/files/neg/t3692.check b/test/files/neg/t3692.check
new file mode 100644
index 0000000000..ce89a6563d
--- /dev/null
+++ b/test/files/neg/t3692.check
@@ -0,0 +1,14 @@
+t3692.scala:11: warning: type Integer in package scala is deprecated: use <code>java.lang.Integer</code> instead
+      case m0: Map[Int, Int] => new java.util.HashMap[Integer, Integer]
+                                              ^
+t3692.scala:12: warning: type Integer in package scala is deprecated: use <code>java.lang.Integer</code> instead
+      case m1: Map[Int, V] => new java.util.HashMap[Integer, V]
+                                            ^
+t3692.scala:13: warning: type Integer in package scala is deprecated: use <code>java.lang.Integer</code> instead
+      case m2: Map[T, Int] => new java.util.HashMap[T, Integer]
+                                            ^
+t3692.scala:13: error: unreachable code
+      case m2: Map[T, Int] => new java.util.HashMap[T, Integer]
+                              ^
+three warnings found
+one error found
diff --git a/test/files/neg/t3692.scala b/test/files/neg/t3692.scala
new file mode 100644
index 0000000000..78b0e4b843
--- /dev/null
+++ b/test/files/neg/t3692.scala
@@ -0,0 +1,17 @@
+object ManifestTester {
+  def main(args: Array[String]) = {
+    val map = Map("John" -> 1, "Josh" -> 2)
+    new ManifestTester().toJavaMap(map)
+  }
+}
+
+class ManifestTester {
+  private final def toJavaMap[T, V](map: Map[T, V])(implicit m1: Manifest[T], m2: Manifest[V]): java.util.Map[_, _] = {
+    map match {
+      case m0: Map[Int, Int] => new java.util.HashMap[Integer, Integer]
+      case m1: Map[Int, V] => new java.util.HashMap[Integer, V]
+      case m2: Map[T, Int] => new java.util.HashMap[T, Integer]
+      case _ => new java.util.HashMap[T, V]
+    }
+  }
+}
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