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] 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