Merge pull request #9614 from dotty-staging/fix-9603

Fix #9603: handle HK pattern bound type symbols

Author: nicolasstucki

compiler/src/dotty/tools/dotc/transform/patmat/Space.scala

@@ -466,16 +466,25 @@ class SpaceEngine(using Context) extends SpaceLogic {
 
     tp match {
       case tp @ AppliedType(tycon, args) =>
-        if (tycon.isRef(defn.ArrayClass)) tp.derivedAppliedType(tycon, args.map(arg => erase(arg, inArray = true)))
-        else tp.derivedAppliedType(tycon, args.map(arg => erase(arg, inArray = false)))
+        if tycon.typeSymbol.isPatternBound then return WildcardType
+
+        val args2 =
+          if (tycon.isRef(defn.ArrayClass)) args.map(arg => erase(arg, inArray = true))
+          else args.map(arg => erase(arg, inArray = false))
+        tp.derivedAppliedType(erase(tycon, inArray), args2)
+
       case OrType(tp1, tp2) =>
         OrType(erase(tp1, inArray), erase(tp2, inArray))
+
       case AndType(tp1, tp2) =>
         AndType(erase(tp1, inArray), erase(tp2, inArray))
+
       case tp @ RefinedType(parent, _, _) =>
         erase(parent)
+
       case tref: TypeRef if tref.typeSymbol.isPatternBound =>
         if (inArray) tref.underlying else WildcardType
+
       case _ => tp
     }
   }
@@ -526,7 +535,7 @@ class SpaceEngine(using Context) extends SpaceLogic {
     val mt: MethodType = unapp.widen match {
       case mt: MethodType => mt
       case pt: PolyType   =>
-        inContext(ctx.fresh.setNewTyperState()) {
+        inContext(ctx.fresh.setExploreTyperState()) {
           val tvars = pt.paramInfos.map(newTypeVar)
           val mt = pt.instantiate(tvars).asInstanceOf[MethodType]
           scrutineeTp <:< mt.paramInfos(0)

tests/patmat/i9603.scala

@@ -0,0 +1,22 @@
+sealed abstract class Resource[+F[_], +A] {
+  import Resource.{Allocate, Bind, Suspend}
+
+  def loop[G[x] >: F[x], B](current: Resource[G, Any]): G[B] =
+    current match {
+      case Allocate(r) => ???
+      case Bind(s, fs) => ???
+      case Suspend(r) => ???
+    }
+}
+
+object Resource {
+
+  final case class Allocate[F[_], A](resource: F[A])
+      extends Resource[F, A]
+
+  final case class Bind[F[_], S, +A](source: Resource[F, S], fs: S => Resource[F, A])
+      extends Resource[F, A]
+
+  final case class Suspend[F[_], A](resource: F[Resource[F, A]]) extends Resource[F, A]
+
+}