SI-6551: don't insert apply call in polymorphic expression.

Don't rewrite an explicit apply method to dynamic polytypes.

Author: namin

src/compiler/scala/tools/nsc/typechecker/Typers.scala

@@ -1100,6 +1100,10 @@ trait Typers extends Modes with Adaptations with Tags {
           instantiateToMethodType(mt)
 
         case _ =>
+          def shouldInsertApply(tree: Tree) = inAllModes(mode, EXPRmode | FUNmode) && (tree.tpe match {
+            case _: MethodType | _: OverloadedType | _: PolyType => false
+            case _                                               => applyPossible
+          })
           def applyPossible = {
             def applyMeth = member(adaptToName(tree, nme.apply), nme.apply)
             dyna.acceptsApplyDynamic(tree.tpe) || (
@@ -1117,10 +1121,7 @@ trait Typers extends Modes with Adaptations with Tags {
             macroExpand(this, tree, mode, pt)
           else if ((mode & (PATTERNmode | FUNmode)) == (PATTERNmode | FUNmode))
             adaptConstrPattern()
-          else if (inAllModes(mode, EXPRmode | FUNmode) &&
-            !tree.tpe.isInstanceOf[MethodType] &&
-            !tree.tpe.isInstanceOf[OverloadedType] &&
-            applyPossible)
+          else if (shouldInsertApply(tree))
             insertApply()
           else if (!context.undetparams.isEmpty && !inPolyMode(mode)) { // (9)
             assert(!inHKMode(mode), modeString(mode)) //@M

test/files/pos/t6551.scala

@@ -0,0 +1,13 @@
+import language.dynamics
+
+object Test {
+  def main(args: Array[String]) {
+    class Lenser[T] extends Dynamic {
+      def selectDynamic(propName: String) = ???
+    }
+
+    def lens[T] = new Lenser[T]
+
+    val qq = lens[String]
+  }
+}