Fixed 1541.

git-svn-id: http://lampsvn.epfl.ch/svn-repos/scala/scala/trunk@16654 5e8d7ff9-d8ef-0310-90f0-a4852d11357a

src/compiler/scala/tools/nsc/transform/TailCalls.scala

@@ -252,9 +252,13 @@ abstract class TailCalls extends Transform
                isSameTypes(ctx.tparams, targs map (_.tpe.typeSymbol)) &&
                isRecursiveCall(fun)) {
             fun match {
-              case Select(receiver, _) => 
-                // make sure the type of 'this' doesn't change through this recursive call
-                if (!forMSIL && (receiver.tpe.widen == ctx.currentMethod.enclClass.typeOfThis)) 
+              case Select(receiver, _) =>
+                val recTpe = receiver.tpe.widen
+                val enclTpe = ctx.currentMethod.enclClass.typeOfThis
+                // make sure the type of 'this' doesn't change through this polymorphic recursive call
+                if (!forMSIL && 
+                    (receiver.tpe.typeParams.isEmpty || 
+                      (receiver.tpe.widen == ctx.currentMethod.enclClass.typeOfThis))) 
                   rewriteTailCall(fun, receiver :: transformTrees(vargs, mkContext(ctx, false))) 
                 else 
                   defaultTree

test/files/run/tailcalls.check

@@ -51,3 +51,4 @@ test TailCall.b1 was successful
 test TailCall.b2 was successful
 test FancyTailCalls.tcTryLocal was successful
 test FancyTailCalls.differentInstance was successful
+test PolyObject.tramp was successful

test/files/run/tailcalls.scala

@@ -194,6 +194,15 @@ object FancyTailCalls {
   val f2 = new FancyTailCalls
 }
 
+object PolyObject extends Application {
+  def tramp[A](x: Int): Int = 
+    if (x > 0)
+      tramp[A](x - 1)
+    else 
+      0
+}
+
+
 class FancyTailCalls {
 
   def tcTryLocal(x: Int, v: Int): Int = {
@@ -370,7 +379,9 @@ object Test {
     val FancyTailCalls = new FancyTailCalls;
     check_success("FancyTailCalls.tcTryLocal",   FancyTailCalls.tcTryLocal(max, max), max)
     check_success("FancyTailCalls.differentInstance",   FancyTailCalls.differentInstance(max, 42), 42)
+    check_success("PolyObject.tramp", PolyObject.tramp[Int](max), 0)
   }
+  
 }
 
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