Allow qualified types without argument name

Author: mbovel

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

@@ -2280,10 +2280,8 @@ object desugar {
       case PatDef(mods, pats, tpt, rhs) =>
         val pats1 = if (tpt.isEmpty) pats else pats map (Typed(_, tpt))
         flatTree(pats1 map (makePatDef(tree, mods, _, rhs)))
-      case QualifiedTypeTree(parent, None, qualifier) =>
-        ErrorReporting.errorTree(parent, em"missing parameter name in qualified type", tree.srcPos)
-      case QualifiedTypeTree(parent, Some(paramName), qualifier) =>
-        qualifiedType(parent, paramName, qualifier, tree.span)
+      case QualifiedTypeTree(parent, paramName, qualifier) =>
+        qualifiedType(parent, paramName.getOrElse(nme.WILDCARD), qualifier, tree.span)
       case ext: ExtMethods =>
         Block(List(ext), syntheticUnitLiteral.withSpan(ext.span))
       case f: FunctionWithMods if f.hasErasedParams => makeFunctionWithValDefs(f, pt)

tests/printing/qualified-types.check

@@ -20,6 +20,7 @@ package example {
           res:Boolean
         }
       )
+    type UninhabitedInt = Int @qualified[Int]((_: Int) => false)
     type Nested =
       Int @qualified[Int]((x: Int) =>
         {

tests/printing/qualified-types.scala

@@ -15,6 +15,8 @@ type Pos5 = {x: Int with
   res
 }
 
+type UninhabitedInt = Int with false
+
 type Nested = {x: Int with { val y: {z: Int with z > 0} = ??? ; x > y }}
 type Intersection = Int & {x: Int with x > 0}
 type ValRefinement = {val x: Int with x > 0}