Address feedback from @smarter

Author: travisbrown

compiler/src/dotty/tools/dotc/parsing/Parsers.scala

@@ -1327,11 +1327,7 @@ object Parsers {
           else if (ctx.settings.YkindProjector.value) {
             val (newParams :+ newT, tparams) = replaceKindProjectorPlaceholders(params :+ t)
 
-            if (tparams.isEmpty) {
-              Function(params, t)
-            } else {
-              LambdaTypeTree(tparams, Function(newParams, newT))
-            }
+            lambdaAbstract(tparams, Function(newParams, newT))
           } else {
             Function(params, t)
           }
@@ -1424,16 +1420,22 @@ object Parsers {
       }
     }
 
+    private def makeKindProjectorTypeDef(name: TypeName, span: Option[Span]): TypeDef = {
+      val typeDef = TypeDef(name, TypeBoundsTree(EmptyTree, EmptyTree)).withFlags(Param)
+
+      span.fold(typeDef)(typeDef.withSpan)
+    }
+
     /** Replaces kind-projector's `*` in a list of types arguments with synthetic names,
      *  returning the new argument list and the synthetic type definitions.
      */
     private def replaceKindProjectorPlaceholders(params: List[Tree]): (List[Tree], List[TypeDef]) = {
       val tparams = new ListBuffer[TypeDef]
 
-      val newParams = params.map {
-        case Ident(tpnme.raw.STAR) =>
-          val name = tpnme.syntheticTypeParamName(tparams.length)
-          tparams += TypeDef(name, TypeBoundsTree(EmptyTree, EmptyTree))
+      val newParams = params.mapConserve {
+        case param @ Ident(tpnme.raw.STAR) =>
+          val name = WildcardParamName.fresh().toTypeName
+          tparams += makeKindProjectorTypeDef(name, None)
           Ident(name)
         case other => other
       }
@@ -1594,7 +1596,7 @@ object Parsers {
               args match {
                 case List(Function(params, body)) =>
                   val typeDefs = params.collect {
-                    case Ident(name) => TypeDef(name.toTypeName, TypeBoundsTree(EmptyTree, EmptyTree))
+                    case param @ Ident(name) => makeKindProjectorTypeDef(name.toTypeName, Some(param.span))
                   }
                   if (typeDefs.length != params.length) fail()
                   else LambdaTypeTree(typeDefs, body)
@@ -1604,11 +1606,7 @@ object Parsers {
             case _ =>
               val (newArgs, tparams) = replaceKindProjectorPlaceholders(args)
 
-              if (tparams.isEmpty) {
-                AppliedTypeTree(applied, args)
-              } else {
-                LambdaTypeTree(tparams, AppliedTypeTree(applied, newArgs))
-              }
+              lambdaAbstract(tparams, AppliedTypeTree(applied, newArgs))
           }
 
         } else {

tests/neg-custom-args/kind-projector.check

@@ -9,4 +9,4 @@
 -- Error: tests/neg-custom-args/kind-projector.scala:6:22 --------------------------------------------------------------
 6 |class Bar2 extends Foo[*] // error
   |                      ^
-  |                      Type argument X0 has not the same kind as its bound  <: [_$1] => Any
+  |                      Type argument _$4 has not the same kind as its bound  <: [_$1] => Any