Fix compilation to dealias types

Author: ausmarton

compiler/src/dotty/tools/dotc/printing/PlainPrinter.scala

@@ -193,7 +193,7 @@ class PlainPrinter(_ctx: Context) extends Printer {
         "<overloaded " ~ toTextRef(tp) ~ ">"
       case tp: TypeRef =>
         if (printWithoutPrefix.contains(tp.symbol))
-          selectionString(tp.dealias)
+          Str(selectionString(tp))
         else
           toTextPrefixOf(tp) ~ selectionString(tp)
       case tp: TermParamRef =>

tests/neg/i4986c.check

@@ -61,4 +61,7 @@
 -- [E172] Type Error: tests/neg/i4986c.scala:62:19 ---------------------------------------------------------------------
 62 |  i.m[Option[Long]] // error
    |                   ^
-   |                   String; List; [A, _] =>> List[Option[?]]; Int; Option[Long]; 
+   |                   String; List; [A, _] =>> List²[Option[?]]; Int; Option[Long]; 
+   |
+   |                   where:    List  is a type in package object scala which is an alias of List²
+   |                             List² is a class in package scala.collection.immutable

tests/neg/i9958.check

@@ -6,6 +6,9 @@
 8 |def b = f(a) // error
   |          ^
   |          Found:    G[[A <: Int] =>> List[A]]
-  |          Required: G[List]
+  |          Required: G[List²]
+  |
+  |          where:    List  is a class in package scala.collection.immutable
+  |                    List² is a type in package object scala which is an alias of List
   |
   | longer explanation available when compiling with `-explain`