Merge pull request #13651 from dotty-staging/fix-13526

Normalize prototype before decomposing as a function

Author: OlivierBlanvillain

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

@@ -1144,7 +1144,7 @@ class Typer extends Namer
         case _ => mapOver(t)
     }
 
-    val pt1 = pt.stripTypeVar.dealias
+    val pt1 = pt.stripTypeVar.dealias.normalized
     if (pt1 ne pt1.dropDependentRefinement)
        && defn.isContextFunctionType(pt1.nonPrivateMember(nme.apply).info.finalResultType)
     then

tests/pos/i13526.scala

@@ -0,0 +1,15 @@
+type ~>[Args <: Tuple, Return] = Args match {
+  case (arg1, arg2) => ((arg1, arg2) => Return)
+}
+
+trait Builder[Args <: NonEmptyTuple] {
+  def apply(f: Args ~> String): String
+}
+
+class BuilderImpl[Args <: NonEmptyTuple] extends Builder[Args] {
+  override def apply(f: Args ~> String): String = ???
+}
+
+val builder = BuilderImpl[Int *: String *: EmptyTuple]()
+// builder { (i: Int, s: String) => "test" } // This line compiles
+val _ = builder { (i, s) => "test" } // Does not compile