Fix #4557 rework: Keep original type untpd.New

We need to keep the original type

 - to allow IDE naviagtion
 - to make PrepareTransparent work correctly

Author: odersky

compiler/src/dotty/tools/dotc/ast/untpd.scala

@@ -301,20 +301,23 @@ object untpd extends Trees.Instance[Untyped] with UntypedTreeInfo {
 
   // ------ Additional creation methods for untyped only -----------------
 
-  /**     new pre.C[Ts](args1)...(args_n)
+  /**     new T(args1)...(args_n)
    *  ==>
-   *      (new pre.C).<init>[Ts](args1)...(args_n)
+   *      new T.<init>[Ts](args1)...(args_n)
+   *
+   *  where `Ts` are the class type arguments of `T` or its class type alias.
+   *  Note: we also keep any type arguments as parts of `T`. This is necessary to allow
+   *  navigation into these arguments from the IDE, and to do the right thing in
+   *  PrepareTransparent.
    */
   def New(tpt: Tree, argss: List[List[Tree]])(implicit ctx: Context): Tree = {
     val (tycon, targs) = tpt match {
       case AppliedTypeTree(tycon, targs) =>
         (tycon, targs)
       case TypedSplice(tpt1: tpd.Tree) =>
-        val tp = tpt1.tpe.dealias
-        val tycon = tp.typeConstructor
-        val argTypes = tp.argTypesLo
-        def wrap(tpe: Type) = TypeTree(tpe) withPos tpt.pos
-        (wrap(tycon), argTypes map wrap)
+        val argTypes = tpt1.tpe.dealias.argTypesLo
+        def wrap(tpe: Type) = TypeTree(tpe).withPos(tpt.pos)
+        (tpt, argTypes.map(wrap))
       case _ =>
         (tpt, Nil)
     }

tests/neg/wildbase.scala

@@ -1,5 +1,5 @@
 class A[T]
 
-class B extends A[_] // OK
+class B extends A[_] // error: type argument must be fully defined
 
-class C extends A[_ >: Any <: Nothing]  // error: conflicting bounds
+class C extends A[_ >: Any <: Nothing]  // error: conflicting bounds // error: type argument must be fully defined

tests/run/tasty-extractors-2.check

@@ -91,7 +91,7 @@ Type.SymRef(ClassDef("Unit", _, _, _, _), Type.ThisType(Type.SymRef(PackageDef("
 Term.Block(List(ClassDef("Foo12", DefDef("<init>", Nil, List(Nil), TypeTree.Synthetic(), None), List(Term.Apply(Term.Select(Term.New(TypeTree.Synthetic()), "<init>", Some(Signature(Nil, java.lang.Object))), Nil)), None, List(ValDef("a", TypeTree.Synthetic(), Some(Term.Literal(Constant.Int(11))))))), Term.Literal(Constant.Unit()))
 Type.SymRef(ClassDef("Unit", _, _, _, _), Type.ThisType(Type.SymRef(PackageDef("scala", _), NoPrefix())))
 
-Term.Block(List(ClassDef("Foo", DefDef("<init>", Nil, List(Nil), TypeTree.Synthetic(), None), List(Term.Apply(Term.Select(Term.New(TypeTree.Synthetic()), "<init>", Some(Signature(Nil, java.lang.Object))), Nil)), None, Nil), ClassDef("Bar", DefDef("<init>", Nil, List(Nil), TypeTree.Synthetic(), None), List(Term.Apply(Term.Select(Term.New(TypeTree.Synthetic()), "<init>", Some(Signature(Nil, Test$._$Foo))), Nil)), None, Nil)), Term.Literal(Constant.Unit()))
+Term.Block(List(ClassDef("Foo", DefDef("<init>", Nil, List(Nil), TypeTree.Synthetic(), None), List(Term.Apply(Term.Select(Term.New(TypeTree.Synthetic()), "<init>", Some(Signature(Nil, java.lang.Object))), Nil)), None, Nil), ClassDef("Bar", DefDef("<init>", Nil, List(Nil), TypeTree.Synthetic(), None), List(Term.Apply(Term.Select(Term.New(TypeTree.TypeIdent("Foo")), "<init>", Some(Signature(Nil, Test$._$Foo))), Nil)), None, Nil)), Term.Literal(Constant.Unit()))
 Type.SymRef(ClassDef("Unit", _, _, _, _), Type.ThisType(Type.SymRef(PackageDef("scala", _), NoPrefix())))
 
 Term.Block(List(ClassDef("Foo2", DefDef("<init>", Nil, List(Nil), TypeTree.Synthetic(), None), List(TypeTree.Synthetic()), None, Nil), ClassDef("Bar", DefDef("<init>", Nil, List(Nil), TypeTree.Synthetic(), None), List(Term.Apply(Term.Select(Term.New(TypeTree.Synthetic()), "<init>", Some(Signature(Nil, java.lang.Object))), Nil), TypeTree.TypeIdent("Foo2")), None, Nil)), Term.Literal(Constant.Unit()))