From c3564dfac837b1a070ff260ac7cc7708d9f86b85 Mon Sep 17 00:00:00 2001
From: Matt Bovel <matthieu@bovel.net>
Date: Mon, 28 Apr 2025 11:05:32 +0000
Subject: [PATCH] Tighten condition to preserve denotation in IntegrateMap

---
 compiler/src/dotty/tools/dotc/core/Types.scala |  8 ++++++--
 tests/pos/23056.scala                          | 18 ++++++++++++++++++
 2 files changed, 24 insertions(+), 2 deletions(-)
 create mode 100644 tests/pos/23056.scala

diff --git a/compiler/src/dotty/tools/dotc/core/Types.scala b/compiler/src/dotty/tools/dotc/core/Types.scala
index ebff52b002a1..2cd66464da3c 100644
--- a/compiler/src/dotty/tools/dotc/core/Types.scala
+++ b/compiler/src/dotty/tools/dotc/core/Types.scala
@@ -3858,8 +3858,12 @@ object Types extends TypeUtils {
 
       override final def derivedSelect(tp: NamedType, pre: Type): Type =
         if tp.prefix eq pre then tp
-        else if tp.symbol.exists then NamedType(pre, tp.name, tp.denot.asSeenFrom(pre))
-        else NamedType(pre, tp.name)
+        else
+          pre match
+            case ref: ParamRef if (ref.binder eq self) && tp.symbol.exists =>
+              NamedType(pre, tp.name, tp.denot.asSeenFrom(pre))
+            case _ =>
+              tp.derivedSelect(pre)
 
     final def derivedLambdaType(paramNames: List[ThisName] = this.paramNames,
                           paramInfos: List[PInfo] = this.paramInfos,
diff --git a/tests/pos/23056.scala b/tests/pos/23056.scala
new file mode 100644
index 000000000000..e38909e16c61
--- /dev/null
+++ b/tests/pos/23056.scala
@@ -0,0 +1,18 @@
+def Test = {
+  val ops: CompileOps[Option, Option, Any]  = ???
+  ops.to(List).map(_.reverse) // error
+}
+
+trait CompileOps[F[_], G[_], O]:
+  def to(collector: Collector[O]): G[collector.Out]
+trait Collector[-A] {
+  type Out
+}
+
+object Collector:
+  type Aux[A, X] = Collector[A] { type Out = X }
+
+  given [A, C[_]]: Conversion[
+    scala.collection.IterableFactory[C],
+    Collector.Aux[A, C[A]]
+  ] = ???