Recognize named arguments in isFunctionWithUnknownParamType (#17161)

fixes #17155

Author: bishabosha

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

@@ -399,6 +399,8 @@ trait UntypedTreeInfo extends TreeInfo[Untyped] { self: Trees.Instance[Untyped]
       Some(tree)
     case Block(Nil, expr) =>
       functionWithUnknownParamType(expr)
+    case NamedArg(_, expr) =>
+      functionWithUnknownParamType(expr)
     case _ =>
       None
   }

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

@@ -448,7 +448,7 @@ trait Applications extends Compatibility {
       def rec(t: Type): Type = {
         t.widen match{
           case funType: MethodType => funType
-          case funType: PolyType => 
+          case funType: PolyType =>
             rec(instantiateWithTypeVars(funType))
           case tp => tp
         }

tests/pos/i17155.scala

@@ -0,0 +1,7 @@
+def foo[A, B](arr: Array[A], pf: PartialFunction[A, B]): Seq[B] = arr.toSeq.collect(pf)
+def foo[A, B](list: List[A], pf: PartialFunction[A, B]): Seq[B] = list.collect(pf) // no errors if this is commented out
+
+val arr = Array(1, 2, 3)
+val resOkay = foo(arr = arr, { case n if n % 2 != 0 => n.toString }) // compiles
+val resNope = foo(arr = arr, pf = { case n if n % 2 != 0 => n.toString }) // Error 1
+val resNope2 = foo[Int, String](arr = arr, pf = { case n if n % 2 != 0 => n.toString }) // Error 2