Revert recent changes to opaque type proxy generation

compiler/src/dotty/tools/dotc/inlines/Inliner.scala

@@ -162,28 +162,9 @@ object Inliner:
           else Nil
         case _ => Nil
       val refinements = openOpaqueAliases(cls.givenSelfType)
-
-      // Map references in the refinements from the proxied termRef
-      // to the recursive type of the refined type
-      // e.g.: Obj.type{type A = Obj.B; type B = Int} -> Obj.type{type A = <recthis>.B; type B = Int}
-      def mapRecTermRefReferences(recType: RecType, refinedType: Type) =
-        new TypeMap {
-          def apply(tp: Type) = tp match
-            case RefinedType(a: RefinedType, b, info) => RefinedType(apply(a), b, apply(info))
-            case RefinedType(a, b, info) => RefinedType(a, b, apply(info))
-            case TypeRef(prefix, des) => TypeRef(apply(prefix), des)
-            case termRef: TermRef if termRef == ref => recType.recThis
-            case _ => mapOver(tp)
-        }.apply(refinedType)
-
       val refinedType = refinements.foldLeft(ref: Type): (parent, refinement) =>
         RefinedType(parent, refinement._1, TypeAlias(refinement._2))
-
-      val recType = RecType.closeOver ( recType =>
-        mapRecTermRefReferences(recType, refinedType)
-      )
-
-      val refiningSym = newSym(InlineBinderName.fresh(), Synthetic, recType, span)
+      val refiningSym = newSym(InlineBinderName.fresh(), Synthetic, refinedType, span)
       refiningSym.termRef
 
     def unapply(refiningRef: TermRef)(using Context): Option[TermRef] =
@@ -402,9 +383,6 @@ class Inliner(val call: tpd.Tree)(using Context):
    */
   private val opaqueProxies = new mutable.ListBuffer[(TermRef, TermRef)]
 
-  /** TermRefs for which we already started synthesising proxies */
-  private val visitedTermRefs = new mutable.HashSet[TermRef]
-
   protected def hasOpaqueProxies = opaqueProxies.nonEmpty
 
   /** Map first halves of opaqueProxies pairs to second halves, using =:= as equality */
@@ -432,15 +410,12 @@ class Inliner(val call: tpd.Tree)(using Context):
         for cls <- ref.widen.baseClasses do
           if cls.containsOpaques
              && (forThisProxy || inlinedMethod.isContainedIn(cls))
-             && !visitedTermRefs.contains(ref)
+             && mapRef(ref).isEmpty
           then
-            visitedTermRefs += ref
             val refiningRef = OpaqueProxy(ref, cls, call.span)
             val refiningSym = refiningRef.symbol.asTerm
             val refinedType = refiningRef.info
-            val refiningDef = addProxiesForRecurrentOpaques(
-              ValDef(refiningSym, tpd.ref(ref).cast(refinedType), inferred = true).withSpan(span)
-            )
+            val refiningDef = ValDef(refiningSym, tpd.ref(ref).cast(refinedType), inferred = true).withSpan(span)
             inlining.println(i"add opaque alias proxy $refiningDef for $ref in $tp")
             bindingsBuf += refiningDef
             opaqueProxies += ((ref, refiningSym.termRef))
@@ -460,27 +435,6 @@ class Inliner(val call: tpd.Tree)(using Context):
           }
     )
 
-  /** Transforms proxies that reference other opaque types, like for:
-   * object Obj1 { opaque type A = Int }
-   * object Obj2 { opaque type B = A }
-   * and proxy$1 of type Obj2.type{type B = Obj1.A}
-   * creates proxy$2 of type Obj1.type{type A = Int}
-   * and transforms proxy$1 into Obj2.type{type B = proxy$2.A}
-   */
-  private def addProxiesForRecurrentOpaques(binding: ValDef)(using Context): ValDef =
-    def fixRefinedTypes(ref: Type): Unit  =
-      ref match
-        case recType: RecType => fixRefinedTypes(recType.underlying)
-        case RefinedType(parent, name, info) =>
-          addOpaqueProxies(info.widen, binding.span, true)
-          fixRefinedTypes(parent)
-        case _ =>
-    fixRefinedTypes(binding.symbol.info)
-    binding.symbol.info = mapOpaques.typeMap(binding.symbol.info)
-    mapOpaques.transform(binding).asInstanceOf[ValDef]
-      .showing(i"transformed this binding exposing opaque aliases: $result", inlining)
-  end addProxiesForRecurrentOpaques
-
   /** If `binding` contains TermRefs that refer to objects with opaque
    *  type aliases, add proxy definitions that expose these aliases
    *  and substitute such TermRefs with theproxies. Example from pos/opaque-inline1.scala:

tests/pos/i22974a/Maybe_1.scala

@@ -0,0 +1,14 @@
+package pack
+import Maybe._
+opaque type Maybe[+A] >: (Absent | Present[A]) = Absent | Present[A]
+object Maybe:
+  sealed abstract class Absent
+  case object Absent extends Absent
+  object internal:
+    case class PresentAbsent(val depth: Int)
+  opaque type Present[+A] = A | internal.PresentAbsent
+
+  extension [A](self: Maybe[A]) {
+    inline def flatten[B]: Maybe[B] = ???
+    inline def isDefined: Boolean = ???
+  }

tests/pos/i22974a/macro_1.scala

@@ -0,0 +1,6 @@
+import scala.quoted._
+
+inline def passThorugh(inline condition: Boolean): Any =
+  ${ passThorughImpl('{condition}) }
+
+def passThorughImpl(condition: Expr[Boolean])(using Quotes): Expr[Any] = condition

tests/pos/i22974a/main_2.scala

@@ -0,0 +1,6 @@
+object Test {
+  def main(): Unit =
+    import pack.Maybe
+    val res: Maybe[Maybe[Int]] = ???
+    passThorugh(res.flatten.isDefined)
+}

tests/pos/i22974b.scala

@@ -0,0 +1,18 @@
+object outer:
+  opaque type Queue = Queue.Unsafe
+  object Queue:
+    abstract class Unsafe
+    opaque type Unbounded = Queue
+    object Unbounded:
+      inline def initWith()(f: Unbounded => Unit): Unit =
+        f(Unsafe.init())
+
+      opaque type Unsafe <: Queue.Unsafe = Queue
+      object Unsafe:
+        def init[A](): Unsafe = ???
+
+object Resource:
+  def run: Unit =
+    outer.Queue.Unbounded.initWith() { q =>
+      ???
+    }

tests/pos/i22974c.scala

@@ -0,0 +1,18 @@
+object other:
+  sealed abstract class Absent
+  case object Absent extends Absent
+  case class PresentAbsent(val depth: Int)
+  opaque type Present[+A] = A | PresentAbsent
+  opaque type Maybe[+A] >: (Absent | Present[A]) = Absent | Present[A]
+
+  extension [A](self: Maybe[A]) {
+    inline def flatten[B]: Maybe[B] = if self.isEmpty then Absent else ???
+    def isEmpty: Boolean = self.isInstanceOf[Absent]
+  }
+
+class Test {
+  def main(): Unit =
+    import other.Maybe
+    val res: Maybe[Maybe[Int]] = ???
+    res.flatten
+}