Allow for unqualified apply as context functions

Fixes #15414

Author: odersky

compiler/src/dotty/tools/dotc/typer/Typer.scala

@@ -3981,7 +3981,9 @@ class Typer(@constructorOnly nestingLevel: Int = 0) extends Namer
 
     /** Convert constructor proxy reference to a new expression */
     def newExpr =
-      val Select(qual, nme.apply) = tree: @unchecked
+      val qual = (tree: @unchecked) match
+        case Select(qual, nme.apply) => qual
+        case Ident(nme.apply) => This(tree.symbol.owner.asClass).withSpan(tree.span)
       val tycon = tree.tpe.widen.finalResultType.underlyingClassRef(refinementOK = false)
       val tpt = qual match
         case Ident(name) =>

tests/new/i15414.scala

@@ -0,0 +1,4 @@
+class C()
+object C {
+  val c = apply()
+}