fix false positives in bootstrap

Author: liufengyun

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

@@ -417,14 +417,13 @@ class SpaceEngine(implicit ctx: Context) extends SpaceLogic {
     case Bind(_, pat) => project(pat)
     case UnApply(fun, _, pats) =>
       if (pat.tpe.classSymbol.is(CaseClass))
-        // FIXME: why dealias is needed here?
-        Kon(pat.tpe.stripAnnots.dealias, pats.map(pat => project(pat)))
+        Kon(pat.tpe.stripAnnots, pats.map(pat => project(pat)))
       else if (fun.symbol.owner == scalaSeqFactoryClass && fun.symbol.name == nme.unapplySeq)
         projectList(pats)
       else if (fun.symbol.info.resultType.isRef(scalaSomeClass))
-        Kon(pat.tpe.stripAnnots.dealias, pats.map(pat => project(pat)))
+        Kon(pat.tpe.stripAnnots, pats.map(pat => project(pat)))
       else
-        Fun(pat.tpe.stripAnnots.dealias, fun.tpe, pats.map(pat => project(pat)))
+        Fun(pat.tpe.stripAnnots, fun.tpe, pats.map(pat => project(pat)))
     case Typed(pat @ UnApply(_, _, _), _) => project(pat)
     case Typed(expr, _) => Typ(expr.tpe.stripAnnots, true)
     case _ =>
@@ -470,7 +469,7 @@ class SpaceEngine(implicit ctx: Context) extends SpaceLogic {
   /** Is `tp1` a subtype of `tp2`?  */
   def isSubType(tp1: Type, tp2: Type): Boolean = {
     // check SI-9657 and tests/patmat/gadt.scala
-    val res = erase(tp1) <:< erase(tp2)
+    val res = tp1 <:< erase(tp2)
     debug.println(s"${tp1.show} <:< ${tp2.show} = $res")
     res
   }

tests/patmat/dotty.scala

@@ -0,0 +1,30 @@
+object IntEqualityTestTreeMaker {
+  def unapply(xs: Int): Option[Int] = ???
+}
+
+class Test {
+  def isBelow(n: Int, s: String): Boolean = false
+
+  def foo(xs: List[(Int, String)]): Unit = (xs filter (isBelow _).tupled) match {
+    case Nil =>
+    case matches =>
+  }
+
+  def linkCompanions(xs: List[(Int, Int)]): Unit = {
+    xs.groupBy(_._1).foreach {
+      case (_, List(x1, x2)) =>
+      case _ => ()
+    }
+  }
+
+  def bar(xs: List[(Int, String)]): Unit = xs match {
+    case (x, s) :: Nil =>
+    case Nil =>
+    case _ =>
+  }
+
+  def patmat(alts: List[List[Int]]): Unit = alts.forall {
+    case List(IntEqualityTestTreeMaker(_)) => false
+    case _ => true
+  }
+}