From 1d497f586a313aeb92039bd14d90db132c72d91e Mon Sep 17 00:00:00 2001
From: odersky <odersky@gmail.com>
Date: Tue, 28 Mar 2023 14:24:34 +0200
Subject: [PATCH] Recognize named arguments in isFunctionWithUnknownParamType

---
 compiler/src/dotty/tools/dotc/ast/TreeInfo.scala       | 2 ++
 compiler/src/dotty/tools/dotc/typer/Applications.scala | 2 +-
 tests/pos/i17155.scala                                 | 7 +++++++
 3 files changed, 10 insertions(+), 1 deletion(-)
 create mode 100644 tests/pos/i17155.scala

diff --git a/compiler/src/dotty/tools/dotc/ast/TreeInfo.scala b/compiler/src/dotty/tools/dotc/ast/TreeInfo.scala
index 73f45bd7369b..c2147b6af2d3 100644
--- a/compiler/src/dotty/tools/dotc/ast/TreeInfo.scala
+++ b/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
   }
diff --git a/compiler/src/dotty/tools/dotc/typer/Applications.scala b/compiler/src/dotty/tools/dotc/typer/Applications.scala
index 345a8693063b..79d6501ccb2d 100644
--- a/compiler/src/dotty/tools/dotc/typer/Applications.scala
+++ b/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
         }
diff --git a/tests/pos/i17155.scala b/tests/pos/i17155.scala
new file mode 100644
index 000000000000..7b58dbe4a13a
--- /dev/null
+++ b/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
\ No newline at end of file