From 3b992918f661d07ab80889ce512a7f6df5917f72 Mon Sep 17 00:00:00 2001
From: Dale Wijnand <dale.wijnand@gmail.com>
Date: Wed, 4 Oct 2023 13:53:17 +0100
Subject: [PATCH] Fix info of ASF nested class

Class M1#F asSeenFrom M2 has type parameters with info of the original
owner/prefix (M1).  So running asSeenFrom against that info fixes the
eta-expanded lambda.
---
 compiler/src/dotty/tools/dotc/typer/Namer.scala | 8 ++++++--
 tests/pos/i18569.scala                          | 9 +++++++++
 2 files changed, 15 insertions(+), 2 deletions(-)
 create mode 100644 tests/pos/i18569.scala

diff --git a/compiler/src/dotty/tools/dotc/typer/Namer.scala b/compiler/src/dotty/tools/dotc/typer/Namer.scala
index 8ed881ca0d81..904cba8f67b5 100644
--- a/compiler/src/dotty/tools/dotc/typer/Namer.scala
+++ b/compiler/src/dotty/tools/dotc/typer/Namer.scala
@@ -1175,8 +1175,12 @@ class Namer { typer: Typer =>
             if mbr.isType then
               val forwarderName = checkNoConflict(alias.toTypeName, isPrivate = false, span)
               var target = pathType.select(sym)
-              if target.typeParams.nonEmpty then
-                target = target.EtaExpand(target.typeParams)
+              val tparams = target.typeParamSymbols
+              if tparams.nonEmpty then
+                target = HKTypeLambda(tparams.map(_.paramName))(
+                  tl => tparams.map(p =>
+                    HKTypeLambda.toPInfo(tl.integrate(tparams, p.info.asSeenFrom(pathType, sym.owner)))),
+                  tl => tl.integrate(tparams, target.appliedTo(tparams.map(_.paramRef))))
               newSymbol(
                 cls, forwarderName,
                 Exported | Final,
diff --git a/tests/pos/i18569.scala b/tests/pos/i18569.scala
new file mode 100644
index 000000000000..7dcdd5e68d6e
--- /dev/null
+++ b/tests/pos/i18569.scala
@@ -0,0 +1,9 @@
+trait M1:
+  trait A
+  trait F[T <: A]
+
+object M2 extends M1
+
+trait Test:
+  export M2.*
+  def y: F[A]