Fix #8647: Remove TypeParamRef from instantiated test

Author: OlivierBlanvillain

compiler/src/dotty/tools/dotc/core/TypeComparer.scala

@@ -2359,7 +2359,7 @@ class TypeComparer(initctx: Context) extends ConstraintHandling[AbsentContext] w
                     x && {
                       t match {
                         case tp: TypeRef if tp.symbol.isAbstractOrParamType => false
-                        case _: SkolemType | _: TypeVar | _: TypeParamRef => false
+                        case _: SkolemType | _: TypeVar => false
                         case _ => foldOver(x, t)
                       }
                     }

tests/pos/8647.scala

@@ -0,0 +1,53 @@
+final class Two[A, B]()
+
+final class Blaaa
+
+final class Bla[X]
+
+object Test1 {
+
+  type Foo[X] = X match
+    case Two[Blaaa, _] =>
+      String
+    case Two[String, _] =>
+      Int
+
+  def test: Foo[Two[String, String]] = 1
+}
+
+object Test2 {
+  type Foo[X] = X match
+    case Two[Bla[_], _] =>
+      String
+    case Two[String, _] =>
+      Int
+
+  def test: Foo[Two[String, String]] = 1
+}
+
+
+object Test3 {
+  type Id[W] = W
+
+  type M[X, Y] = X match {
+    case Int   => String
+    case Id[x] => Y match {
+      case Two[Bla[a], _] => Int
+      case _ => String
+    }
+  }
+  val x: M[Boolean, Two[Boolean, Boolean]] = ""
+}
+
+object Test4 {
+  type Id[W] = W
+
+  type M[X, Y] = X match {
+    case Int   => String
+    case Id[x] => Y match {
+      case Two[Bla[`x`], _] => Int
+      case _ => String
+    }
+  }
+  val x: M[Boolean, Two[Bla[Boolean], Boolean]] = 1
+}