From 4e27694dd9090a3891bdf8531ddd4d3896af0956 Mon Sep 17 00:00:00 2001
From: Wojciech Mazur <wmazur@virtuslab.com>
Date: Wed, 18 Sep 2024 18:14:48 +0200
Subject: [PATCH 1/2] Revert "Reduce projections of type aliases with class
 type prefixes"

---
 .../src/dotty/tools/dotc/core/Types.scala     | 16 +++---------
 tests/pos/i19892.scala                        | 26 -------------------
 2 files changed, 4 insertions(+), 38 deletions(-)
 delete mode 100644 tests/pos/i19892.scala

diff --git a/compiler/src/dotty/tools/dotc/core/Types.scala b/compiler/src/dotty/tools/dotc/core/Types.scala
index 4b426bb8c741..2d3027504936 100644
--- a/compiler/src/dotty/tools/dotc/core/Types.scala
+++ b/compiler/src/dotty/tools/dotc/core/Types.scala
@@ -2598,22 +2598,14 @@ object Types extends TypeUtils {
       case _ => true
     }
 
-    /** Reduce a type ref P # X, where X is a type alias and P is a refined type or
-     *  a class type. If P is a refined type `T { X = U; ... }`, reduce P to U,
-     *  provided U does not refer with a RecThis to the same refined type. If P is a
-     *  class type, reduce it to the dealiasd version of P # X. This means that at typer
-     *  we create projections only for inner classes with class prefixes, since projections
-     *  of P # X where X is an abstract type are handled by skolemization. At later phases
-     *  these projections might arise, though.
+    /** Reduce a type-ref `T { X = U; ... } # X`  to   `U`
+     *  provided `U` does not refer with a RecThis to the
+     *  refinement type `T { X = U; ... }`
      */
     def reduceProjection(using Context): Type =
       if (isType) {
         val reduced = prefix.lookupRefined(name)
-        if reduced.exists then reduced
-        else prefix.stripTypeVar match
-          case pre: (AppliedType | TypeRef)
-          if prefix.dealias.typeSymbol.isClass && this.symbol.isAliasType => dealias
-          case _ => this
+        if reduced.exists then reduced else this
       }
       else this
 
diff --git a/tests/pos/i19892.scala b/tests/pos/i19892.scala
deleted file mode 100644
index 6f3e0bd6d06c..000000000000
--- a/tests/pos/i19892.scala
+++ /dev/null
@@ -1,26 +0,0 @@
-abstract class ZPartialServerEndpoint[R, A, B, I, E, O, -C]
-    extends EndpointOps[A, I, E, O, C]{
-  override type ThisType[-_R] = ZPartialServerEndpoint[R, A, B, I, E, O, _R]
-  override type EndpointType[_A, _I, _E, _O, -_R] =ZPartialServerEndpoint[R, _A, B, _I, _E, _O, _R]
-}
-
-trait EndpointOps[A, I, E, O, -R] {
-  type EndpointType[_A, _I, _E, _O, -_R]
-  type ThisType[-_R]
-  def out[T]: EndpointType[A, I, E, T, R]
-  def description(d: String): ThisType[R]
-}
-
-object Test {
-  def basicEndpoint[R](): ZPartialServerEndpoint[R, Any, Any, Unit, Any, Unit, Any] = ???
-
-  // commonts next to `.out[Any]` contain information about compilation time when chaining up to N `out` functions
-  val case1 =
-     basicEndpoint() // 1.5s
-        .out[Any] // 1.6s
-        .out[Any] // 1.7s
-        .out[Any] // 2s
-        .out[Any] // 4s
-        .out[Any] // 33s
-        .out[Any] // aborted after 5 min
-}
\ No newline at end of file

From 1b9d12cbf198b63c02687eda62354169399c7848 Mon Sep 17 00:00:00 2001
From: Wojciech Mazur <wmazur@virtuslab.com>
Date: Wed, 18 Sep 2024 18:15:07 +0200
Subject: [PATCH 2/2] Add regresion test for #21576

---
 tests/run/i21576.check |  3 +++
 tests/run/i21576.scala | 31 +++++++++++++++++++++++++++++++
 2 files changed, 34 insertions(+)
 create mode 100644 tests/run/i21576.check
 create mode 100644 tests/run/i21576.scala

diff --git a/tests/run/i21576.check b/tests/run/i21576.check
new file mode 100644
index 000000000000..1bbe534c2782
--- /dev/null
+++ b/tests/run/i21576.check
@@ -0,0 +1,3 @@
+public SubFlow(SubFlowDef<Flow1<In>>,SubFlowDef<Flow2<java.lang.Object>>)
+public SubFlowDef<Flow1<In>> SubFlow.delegate1()
+public SubFlowDef<Flow2<java.lang.Object>> SubFlow.delegate2()
diff --git a/tests/run/i21576.scala b/tests/run/i21576.scala
new file mode 100644
index 000000000000..6b5515ac7719
--- /dev/null
+++ b/tests/run/i21576.scala
@@ -0,0 +1,31 @@
+// scalajs: --skip
+import scala.annotation.unchecked.uncheckedVariance
+
+trait SubFlowDef[+F[+_]]
+final class Flow1[-In]{
+  type Repr[+O] = Flow1[In @uncheckedVariance]
+}
+final class Flow2[+Out]{
+  type Repr[+O] = Flow2[O]
+}
+class SubFlow[In, Out](
+    val delegate1: SubFlowDef[Flow1[In]#Repr],
+    val delegate2: SubFlowDef[Flow2[Out]#Repr]
+)
+
+object Test {
+  def main(args: Array[String]): Unit = {
+    classOf[SubFlow[?, ?]]
+      .getConstructors()
+      .map(_.toGenericString())
+      .sorted
+      .foreach(println)
+
+    classOf[SubFlow[?, ?]]
+      .getMethods()
+      .filter(_.getName().startsWith("delegate"))
+      .map(_.toGenericString())
+      .sorted
+      .foreach(println)
+  }
+}