Merge pull request #1695 from dotty-staging/fix-#1662

Fix #1662: Add missing case for singleton

Author: odersky

src/dotty/tools/dotc/ast/tpd.scala

@@ -306,8 +306,8 @@ object tpd extends Trees.Instance[Type] with TypedTreeInfo {
       case _ =>
         false
     }
-    typeIsElidable || 
-    tp.symbol.is(JavaStatic) || 
+    typeIsElidable ||
+    tp.symbol.is(JavaStatic) ||
     tp.symbol.hasAnnotation(defn.ScalaStaticAnnot)
   }
 
@@ -343,6 +343,7 @@ object tpd extends Trees.Instance[Type] with TypedTreeInfo {
   def singleton(tp: Type)(implicit ctx: Context): Tree = tp match {
     case tp: TermRef => ref(tp)
     case tp: ThisType => This(tp.cls)
+    case tp: SkolemType => singleton(tp.narrow)
     case SuperType(qual, _) => singleton(qual)
     case ConstantType(value) => Literal(value)
   }

tests/neg/i1662.scala

@@ -0,0 +1,6 @@
+class Lift {
+  def apply(f: F0) // error
+  class F0
+  object F0 { implicit def f2f0(String): F0 = ??? } // error
+  (new Lift)("")
+}