From 65b171c3abb1d8c5cd50e10f6722f0a39fd9ad46 Mon Sep 17 00:00:00 2001
From: Yichen Xu <yichen.x@outlook.com>
Date: Mon, 9 Aug 2021 02:26:43 +0800
Subject: [PATCH 01/14] Approximate GADT lower bound for HKTs

---
 compiler/src/dotty/tools/dotc/core/TypeComparer.scala | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/compiler/src/dotty/tools/dotc/core/TypeComparer.scala b/compiler/src/dotty/tools/dotc/core/TypeComparer.scala
index eee0e802528c..038330c2f6a1 100644
--- a/compiler/src/dotty/tools/dotc/core/TypeComparer.scala
+++ b/compiler/src/dotty/tools/dotc/core/TypeComparer.scala
@@ -1167,6 +1167,15 @@ class TypeComparer(@constructorOnly initctx: Context) extends ConstraintHandling
         else
           fallback(tycon2bounds.lo)
 
+      def compareTyConGadtBounds: Boolean =
+        tycon2 match
+          case tycon2: TypeRef =>
+            val tycon2sym = tycon2.symbol
+            tycon2sym.onGadtBounds { bounds2 =>
+              compareLower(bounds2, tyconIsTypeRef = false)
+            }
+          case _ => false
+
       tycon2 match {
         case param2: TypeParamRef =>
           isMatchingApply(tp1) ||
@@ -1174,6 +1183,7 @@ class TypeComparer(@constructorOnly initctx: Context) extends ConstraintHandling
           compareLower(bounds(param2), tyconIsTypeRef = false)
         case tycon2: TypeRef =>
           isMatchingApply(tp1) ||
+          compareTyConGadtBounds ||
           defn.isCompiletimeAppliedType(tycon2.symbol) && compareCompiletimeAppliedType(tp2, tp1, fromBelow = true) || {
             tycon2.info match {
               case info2: TypeBounds =>

From 23f2d7591e9c930b6e645bf99522f2ced7ef834c Mon Sep 17 00:00:00 2001
From: Yichen Xu <yichen.x@outlook.com>
Date: Mon, 9 Aug 2021 02:28:18 +0800
Subject: [PATCH 02/14] Properly record the usage of GADT bounds

---
 .../dotty/tools/dotc/core/TypeComparer.scala  | 20 ++++++++++---------
 1 file changed, 11 insertions(+), 9 deletions(-)

diff --git a/compiler/src/dotty/tools/dotc/core/TypeComparer.scala b/compiler/src/dotty/tools/dotc/core/TypeComparer.scala
index 038330c2f6a1..a964a56c0b3d 100644
--- a/compiler/src/dotty/tools/dotc/core/TypeComparer.scala
+++ b/compiler/src/dotty/tools/dotc/core/TypeComparer.scala
@@ -1167,14 +1167,16 @@ class TypeComparer(@constructorOnly initctx: Context) extends ConstraintHandling
         else
           fallback(tycon2bounds.lo)
 
-      def compareTyConGadtBounds: Boolean =
-        tycon2 match
-          case tycon2: TypeRef =>
-            val tycon2sym = tycon2.symbol
-            tycon2sym.onGadtBounds { bounds2 =>
-              compareLower(bounds2, tyconIsTypeRef = false)
-            }
-          case _ => false
+      def byGadtBounds: Boolean =
+        {
+          tycon2 match
+            case tycon2: TypeRef =>
+              val tycon2sym = tycon2.symbol
+              tycon2sym.onGadtBounds { bounds2 =>
+                compareLower(bounds2, tyconIsTypeRef = false)
+              }
+            case _ => false
+        } && { GADTused = true; true }
 
       tycon2 match {
         case param2: TypeParamRef =>
@@ -1183,7 +1185,7 @@ class TypeComparer(@constructorOnly initctx: Context) extends ConstraintHandling
           compareLower(bounds(param2), tyconIsTypeRef = false)
         case tycon2: TypeRef =>
           isMatchingApply(tp1) ||
-          compareTyConGadtBounds ||
+          byGadtBounds ||
           defn.isCompiletimeAppliedType(tycon2.symbol) && compareCompiletimeAppliedType(tp2, tp1, fromBelow = true) || {
             tycon2.info match {
               case info2: TypeBounds =>

From e4edcea8042615b714d5b44ace49cdb3f026da99 Mon Sep 17 00:00:00 2001
From: Yichen Xu <yichen.x@outlook.com>
Date: Wed, 18 Aug 2021 15:01:05 +0800
Subject: [PATCH 03/14] Fix the injectivity issue

---
 compiler/src/dotty/tools/dotc/core/TypeComparer.scala | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/compiler/src/dotty/tools/dotc/core/TypeComparer.scala b/compiler/src/dotty/tools/dotc/core/TypeComparer.scala
index a964a56c0b3d..37a46ff1d52b 100644
--- a/compiler/src/dotty/tools/dotc/core/TypeComparer.scala
+++ b/compiler/src/dotty/tools/dotc/core/TypeComparer.scala
@@ -9,6 +9,7 @@ import StdNames.nme
 import TypeOps.refineUsingParent
 import collection.mutable
 import util.Stats
+import scala.util.DynamicVariable
 import config.Config
 import config.Feature.migrateTo3
 import config.Printers.{constr, subtyping, gadts, matchTypes, noPrinter}
@@ -60,6 +61,11 @@ class TypeComparer(@constructorOnly initctx: Context) extends ConstraintHandling
   /** Indicates whether the subtype check used GADT bounds */
   private var GADTused: Boolean = false
 
+  /** Indicates whether we have touched HKT GADT bounds */
+  private val touchedHKGADT: DynamicVariable[Boolean] = new DynamicVariable(false)
+
+  private def HKGADTtouched[T](body: => T): T = touchedHKGADT.withValue(true) { body }
+
   private var myInstance: TypeComparer = this
   def currentInstance: TypeComparer = myInstance
 
@@ -1092,6 +1098,7 @@ class TypeComparer(@constructorOnly initctx: Context) extends ConstraintHandling
                     val tyconIsInjective =
                       (tycon1sym.isClass || tycon2sym.isClass)
                       && (!touchedGADTs || gadtIsInstantiated)
+                      && !touchedHKGADT.value
 
                     inFrozenGadtIf(!tyconIsInjective) {
                       if tycon1sym == tycon2sym && tycon1sym.isAliasType then
@@ -1173,7 +1180,7 @@ class TypeComparer(@constructorOnly initctx: Context) extends ConstraintHandling
             case tycon2: TypeRef =>
               val tycon2sym = tycon2.symbol
               tycon2sym.onGadtBounds { bounds2 =>
-                compareLower(bounds2, tyconIsTypeRef = false)
+                HKGADTtouched { compareLower(bounds2, tyconIsTypeRef = false) }
               }
             case _ => false
         } && { GADTused = true; true }

From ab6aa685b8fe9770318c054d7f0f9976c20359a8 Mon Sep 17 00:00:00 2001
From: Yichen Xu <yichen.x@outlook.com>
Date: Wed, 18 Aug 2021 15:11:36 +0800
Subject: [PATCH 04/14] Add pos testcase

---
 tests/pos/gadt-hkt-bounds.scala | 7 +++++++
 1 file changed, 7 insertions(+)
 create mode 100644 tests/pos/gadt-hkt-bounds.scala

diff --git a/tests/pos/gadt-hkt-bounds.scala b/tests/pos/gadt-hkt-bounds.scala
new file mode 100644
index 000000000000..7b9fb976fbfa
--- /dev/null
+++ b/tests/pos/gadt-hkt-bounds.scala
@@ -0,0 +1,7 @@
+type Const = [X] =>> Int
+
+trait Expr[F[_]]
+case class ConstExpr() extends Expr[Const]
+
+def foo[F[_], A](e: Expr[F]): F[A] = e match
+  case _: ConstExpr => 0

From 196033e7d0ee221e618ecf915d2c3fe44a34cf15 Mon Sep 17 00:00:00 2001
From: Yichen Xu <yichen.x@outlook.com>
Date: Wed, 18 Aug 2021 15:15:23 +0800
Subject: [PATCH 05/14] Add neg test

---
 tests/neg/gadt-hkt-hi-bounds.scala | 8 ++++++++
 1 file changed, 8 insertions(+)
 create mode 100644 tests/neg/gadt-hkt-hi-bounds.scala

diff --git a/tests/neg/gadt-hkt-hi-bounds.scala b/tests/neg/gadt-hkt-hi-bounds.scala
new file mode 100644
index 000000000000..0aec1fe74113
--- /dev/null
+++ b/tests/neg/gadt-hkt-hi-bounds.scala
@@ -0,0 +1,8 @@
+type Const = [X] =>> Int
+
+trait Expr[-F[_]]
+case class ConstExpr() extends Expr[Const]
+
+def foo[F[_], A](e: Expr[F]) = e match
+  case _: ConstExpr =>
+    val i: Int = ??? : F[A]   // limitation  // error

From d551238552bd9e6ea4da19034b6c0ac5816f41a3 Mon Sep 17 00:00:00 2001
From: Yichen Xu <yichen.x@outlook.com>
Date: Wed, 18 Aug 2021 15:15:29 +0800
Subject: [PATCH 06/14] Update pos test

---
 tests/pos/gadt-hkt-bounds.scala | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tests/pos/gadt-hkt-bounds.scala b/tests/pos/gadt-hkt-bounds.scala
index 7b9fb976fbfa..177b7fe044f3 100644
--- a/tests/pos/gadt-hkt-bounds.scala
+++ b/tests/pos/gadt-hkt-bounds.scala
@@ -1,6 +1,6 @@
 type Const = [X] =>> Int
 
-trait Expr[F[_]]
+trait Expr[+F[_]]
 case class ConstExpr() extends Expr[Const]
 
 def foo[F[_], A](e: Expr[F]): F[A] = e match

From 7cda5b5a5d196e7a0af9adacd8e4bc10a70762d2 Mon Sep 17 00:00:00 2001
From: Yichen Xu <yichen.x@outlook.com>
Date: Tue, 24 Aug 2021 01:55:48 +0800
Subject: [PATCH 07/14] Rename HKGadt state and use primitive boolean

---
 .../src/dotty/tools/dotc/core/TypeComparer.scala     | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/compiler/src/dotty/tools/dotc/core/TypeComparer.scala b/compiler/src/dotty/tools/dotc/core/TypeComparer.scala
index 37a46ff1d52b..3c724907818e 100644
--- a/compiler/src/dotty/tools/dotc/core/TypeComparer.scala
+++ b/compiler/src/dotty/tools/dotc/core/TypeComparer.scala
@@ -62,9 +62,13 @@ class TypeComparer(@constructorOnly initctx: Context) extends ConstraintHandling
   private var GADTused: Boolean = false
 
   /** Indicates whether we have touched HKT GADT bounds */
-  private val touchedHKGADT: DynamicVariable[Boolean] = new DynamicVariable(false)
+  private var HKGADTtouched: Boolean = false
 
-  private def HKGADTtouched[T](body: => T): T = touchedHKGADT.withValue(true) { body }
+  private def touchHKGadt[T](body: => T): T =
+    val savedHKGADTtouched = HKGADTtouched
+    val res = body
+    HKGADTtouched = savedHKGADTtouched
+    res
 
   private var myInstance: TypeComparer = this
   def currentInstance: TypeComparer = myInstance
@@ -1098,7 +1102,7 @@ class TypeComparer(@constructorOnly initctx: Context) extends ConstraintHandling
                     val tyconIsInjective =
                       (tycon1sym.isClass || tycon2sym.isClass)
                       && (!touchedGADTs || gadtIsInstantiated)
-                      && !touchedHKGADT.value
+                      && !HKGADTtouched
 
                     inFrozenGadtIf(!tyconIsInjective) {
                       if tycon1sym == tycon2sym && tycon1sym.isAliasType then
@@ -1180,7 +1184,7 @@ class TypeComparer(@constructorOnly initctx: Context) extends ConstraintHandling
             case tycon2: TypeRef =>
               val tycon2sym = tycon2.symbol
               tycon2sym.onGadtBounds { bounds2 =>
-                HKGADTtouched { compareLower(bounds2, tyconIsTypeRef = false) }
+                touchHKGadt { compareLower(bounds2, tyconIsTypeRef = false) }
               }
             case _ => false
         } && { GADTused = true; true }

From dfbe8d4f378e5c88475eaa6edbfa72045867ae60 Mon Sep 17 00:00:00 2001
From: Yichen Xu <yichen.x@outlook.com>
Date: Tue, 24 Aug 2021 11:18:12 +0800
Subject: [PATCH 08/14] Fix touchHKGadt

---
 compiler/src/dotty/tools/dotc/core/TypeComparer.scala | 1 +
 1 file changed, 1 insertion(+)

diff --git a/compiler/src/dotty/tools/dotc/core/TypeComparer.scala b/compiler/src/dotty/tools/dotc/core/TypeComparer.scala
index 3c724907818e..226de5ab7670 100644
--- a/compiler/src/dotty/tools/dotc/core/TypeComparer.scala
+++ b/compiler/src/dotty/tools/dotc/core/TypeComparer.scala
@@ -66,6 +66,7 @@ class TypeComparer(@constructorOnly initctx: Context) extends ConstraintHandling
 
   private def touchHKGadt[T](body: => T): T =
     val savedHKGADTtouched = HKGADTtouched
+    HKGADTtouched = true
     val res = body
     HKGADTtouched = savedHKGADTtouched
     res

From abb4155c01da54601d40ee412b31fe9105366c2a Mon Sep 17 00:00:00 2001
From: Yichen Xu <yichen.x@outlook.com>
Date: Wed, 25 Aug 2021 12:29:40 +0800
Subject: [PATCH 09/14] Utilize frozenGadt instead of using a new state
 variable

---
 .../src/dotty/tools/dotc/core/TypeComparer.scala   | 14 ++------------
 1 file changed, 2 insertions(+), 12 deletions(-)

diff --git a/compiler/src/dotty/tools/dotc/core/TypeComparer.scala b/compiler/src/dotty/tools/dotc/core/TypeComparer.scala
index 226de5ab7670..bd95d7323334 100644
--- a/compiler/src/dotty/tools/dotc/core/TypeComparer.scala
+++ b/compiler/src/dotty/tools/dotc/core/TypeComparer.scala
@@ -61,16 +61,6 @@ class TypeComparer(@constructorOnly initctx: Context) extends ConstraintHandling
   /** Indicates whether the subtype check used GADT bounds */
   private var GADTused: Boolean = false
 
-  /** Indicates whether we have touched HKT GADT bounds */
-  private var HKGADTtouched: Boolean = false
-
-  private def touchHKGadt[T](body: => T): T =
-    val savedHKGADTtouched = HKGADTtouched
-    HKGADTtouched = true
-    val res = body
-    HKGADTtouched = savedHKGADTtouched
-    res
-
   private var myInstance: TypeComparer = this
   def currentInstance: TypeComparer = myInstance
 
@@ -1103,7 +1093,7 @@ class TypeComparer(@constructorOnly initctx: Context) extends ConstraintHandling
                     val tyconIsInjective =
                       (tycon1sym.isClass || tycon2sym.isClass)
                       && (!touchedGADTs || gadtIsInstantiated)
-                      && !HKGADTtouched
+                      && !frozenGadt
 
                     inFrozenGadtIf(!tyconIsInjective) {
                       if tycon1sym == tycon2sym && tycon1sym.isAliasType then
@@ -1185,7 +1175,7 @@ class TypeComparer(@constructorOnly initctx: Context) extends ConstraintHandling
             case tycon2: TypeRef =>
               val tycon2sym = tycon2.symbol
               tycon2sym.onGadtBounds { bounds2 =>
-                touchHKGadt { compareLower(bounds2, tyconIsTypeRef = false) }
+                inFrozenGadt { compareLower(bounds2, tyconIsTypeRef = false) }
               }
             case _ => false
         } && { GADTused = true; true }

From 28c63814af708c273e835bee9ad2fbac76d523ab Mon Sep 17 00:00:00 2001
From: Yichen Xu <yichen.x@outlook.com>
Date: Thu, 26 Aug 2021 00:46:02 +0800
Subject: [PATCH 10/14] Remove unused import

---
 compiler/src/dotty/tools/dotc/core/TypeComparer.scala | 1 -
 1 file changed, 1 deletion(-)

diff --git a/compiler/src/dotty/tools/dotc/core/TypeComparer.scala b/compiler/src/dotty/tools/dotc/core/TypeComparer.scala
index bd95d7323334..c2c1e08d154a 100644
--- a/compiler/src/dotty/tools/dotc/core/TypeComparer.scala
+++ b/compiler/src/dotty/tools/dotc/core/TypeComparer.scala
@@ -9,7 +9,6 @@ import StdNames.nme
 import TypeOps.refineUsingParent
 import collection.mutable
 import util.Stats
-import scala.util.DynamicVariable
 import config.Config
 import config.Feature.migrateTo3
 import config.Printers.{constr, subtyping, gadts, matchTypes, noPrinter}

From 2da3c588a00452c9b775d318c2ce2987b33ab4ba Mon Sep 17 00:00:00 2001
From: Yichen Xu <yichen.x@outlook.com>
Date: Thu, 26 Aug 2021 23:47:32 +0800
Subject: [PATCH 11/14] Remove workaround

---
 compiler/src/dotty/tools/dotc/core/TypeComparer.scala | 1 -
 1 file changed, 1 deletion(-)

diff --git a/compiler/src/dotty/tools/dotc/core/TypeComparer.scala b/compiler/src/dotty/tools/dotc/core/TypeComparer.scala
index c2c1e08d154a..6fda9b304411 100644
--- a/compiler/src/dotty/tools/dotc/core/TypeComparer.scala
+++ b/compiler/src/dotty/tools/dotc/core/TypeComparer.scala
@@ -1092,7 +1092,6 @@ class TypeComparer(@constructorOnly initctx: Context) extends ConstraintHandling
                     val tyconIsInjective =
                       (tycon1sym.isClass || tycon2sym.isClass)
                       && (!touchedGADTs || gadtIsInstantiated)
-                      && !frozenGadt
 
                     inFrozenGadtIf(!tyconIsInjective) {
                       if tycon1sym == tycon2sym && tycon1sym.isAliasType then

From 0b323dc8a51b55e6ef10d2ff06764343787da1d3 Mon Sep 17 00:00:00 2001
From: Yichen Xu <yichen.x@outlook.com>
Date: Wed, 25 Aug 2021 14:05:37 +0800
Subject: [PATCH 12/14] Fix inFrozenGadtIf

---
 compiler/src/dotty/tools/dotc/core/TypeComparer.scala | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/compiler/src/dotty/tools/dotc/core/TypeComparer.scala b/compiler/src/dotty/tools/dotc/core/TypeComparer.scala
index 6fda9b304411..b86722a7ba98 100644
--- a/compiler/src/dotty/tools/dotc/core/TypeComparer.scala
+++ b/compiler/src/dotty/tools/dotc/core/TypeComparer.scala
@@ -172,7 +172,7 @@ class TypeComparer(@constructorOnly initctx: Context) extends ConstraintHandling
 
   private inline def inFrozenGadtIf[T](cond: Boolean)(inline op: T): T = {
     val savedFrozenGadt = frozenGadt
-    frozenGadt = cond
+    frozenGadt ||= cond
     try op finally frozenGadt = savedFrozenGadt
   }
 

From 8b45a005530281c6ed59f552eecc5f624bdb2a65 Mon Sep 17 00:00:00 2001
From: Yichen Xu <yichen.x@outlook.com>
Date: Sun, 29 Aug 2021 10:47:33 +0800
Subject: [PATCH 13/14] Also approximate with HKT's GADT higher bounds

---
 .../dotty/tools/dotc/core/TypeComparer.scala  | 20 ++++++++++++++-----
 tests/{neg => pos}/gadt-hkt-hi-bounds.scala   |  2 +-
 ...-bounds.scala => gadt-hkt-lo-bounds.scala} |  0
 3 files changed, 16 insertions(+), 6 deletions(-)
 rename tests/{neg => pos}/gadt-hkt-hi-bounds.scala (73%)
 rename tests/pos/{gadt-hkt-bounds.scala => gadt-hkt-lo-bounds.scala} (100%)

diff --git a/compiler/src/dotty/tools/dotc/core/TypeComparer.scala b/compiler/src/dotty/tools/dotc/core/TypeComparer.scala
index b86722a7ba98..b0ee7c524f20 100644
--- a/compiler/src/dotty/tools/dotc/core/TypeComparer.scala
+++ b/compiler/src/dotty/tools/dotc/core/TypeComparer.scala
@@ -1225,11 +1225,21 @@ class TypeComparer(@constructorOnly initctx: Context) extends ConstraintHandling
             isSubType(bounds(param1).hi.applyIfParameterized(args1), tp2, approx.addLow)
         case tycon1: TypeRef =>
           val sym = tycon1.symbol
-          !sym.isClass && {
-            defn.isCompiletimeAppliedType(sym) && compareCompiletimeAppliedType(tp1, tp2, fromBelow = false) ||
-            recur(tp1.superType, tp2) ||
-            tryLiftedToThis1
-          }
+
+          def byGadtBounds: Boolean =
+            {
+              sym.onGadtBounds { bounds1 =>
+                inFrozenGadt { isSubType(bounds1.hi.applyIfParameterized(args1), tp2, approx.addLow) }
+              }
+            } && { GADTused = true; true }
+
+          {
+            !sym.isClass && {
+              defn.isCompiletimeAppliedType(sym) && compareCompiletimeAppliedType(tp1, tp2, fromBelow = false) ||
+              recur(tp1.superType, tp2) ||
+              tryLiftedToThis1
+            }
+          } || byGadtBounds
         case tycon1: TypeProxy =>
           recur(tp1.superType, tp2)
         case _ =>
diff --git a/tests/neg/gadt-hkt-hi-bounds.scala b/tests/pos/gadt-hkt-hi-bounds.scala
similarity index 73%
rename from tests/neg/gadt-hkt-hi-bounds.scala
rename to tests/pos/gadt-hkt-hi-bounds.scala
index 0aec1fe74113..fca06f375b6b 100644
--- a/tests/neg/gadt-hkt-hi-bounds.scala
+++ b/tests/pos/gadt-hkt-hi-bounds.scala
@@ -5,4 +5,4 @@ case class ConstExpr() extends Expr[Const]
 
 def foo[F[_], A](e: Expr[F]) = e match
   case _: ConstExpr =>
-    val i: Int = ??? : F[A]   // limitation  // error
+    val i: Int = ??? : F[A]
diff --git a/tests/pos/gadt-hkt-bounds.scala b/tests/pos/gadt-hkt-lo-bounds.scala
similarity index 100%
rename from tests/pos/gadt-hkt-bounds.scala
rename to tests/pos/gadt-hkt-lo-bounds.scala

From d1a04e22f8fd35a2344260515d4dff57a3f46f86 Mon Sep 17 00:00:00 2001
From: Yichen Xu <yichen.x@outlook.com>
Date: Mon, 30 Aug 2021 21:08:26 +0800
Subject: [PATCH 14/14] Remove redundant braces

---
 .../dotty/tools/dotc/core/TypeComparer.scala  | 19 ++++++++-----------
 1 file changed, 8 insertions(+), 11 deletions(-)

diff --git a/compiler/src/dotty/tools/dotc/core/TypeComparer.scala b/compiler/src/dotty/tools/dotc/core/TypeComparer.scala
index b0ee7c524f20..d167d55310a1 100644
--- a/compiler/src/dotty/tools/dotc/core/TypeComparer.scala
+++ b/compiler/src/dotty/tools/dotc/core/TypeComparer.scala
@@ -1227,19 +1227,16 @@ class TypeComparer(@constructorOnly initctx: Context) extends ConstraintHandling
           val sym = tycon1.symbol
 
           def byGadtBounds: Boolean =
-            {
-              sym.onGadtBounds { bounds1 =>
-                inFrozenGadt { isSubType(bounds1.hi.applyIfParameterized(args1), tp2, approx.addLow) }
-              }
+            sym.onGadtBounds { bounds1 =>
+              inFrozenGadt { isSubType(bounds1.hi.applyIfParameterized(args1), tp2, approx.addLow) }
             } && { GADTused = true; true }
 
-          {
-            !sym.isClass && {
-              defn.isCompiletimeAppliedType(sym) && compareCompiletimeAppliedType(tp1, tp2, fromBelow = false) ||
-              recur(tp1.superType, tp2) ||
-              tryLiftedToThis1
-            }
-          } || byGadtBounds
+
+          !sym.isClass && {
+            defn.isCompiletimeAppliedType(sym) && compareCompiletimeAppliedType(tp1, tp2, fromBelow = false) ||
+            recur(tp1.superType, tp2) ||
+            tryLiftedToThis1
+          }|| byGadtBounds
         case tycon1: TypeProxy =>
           recur(tp1.superType, tp2)
         case _ =>