Ignore private/sealed abstract class/traits

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

@@ -628,7 +628,15 @@ class SpaceEngine(using Context) extends SpaceLogic {
       case tp if tp.classSymbol.isAllOf(JavaEnumTrait) =>
         tp.classSymbol.children.map(sym => Typ(sym.termRef, true))
       case tp =>
-        val children = tp.classSymbol.children
+        def getChildren(sym: Symbol): List[Symbol] =
+          sym.children.flatMap { child =>
+            if child eq sym then Nil // i3145: sealed trait Baz, val x = new Baz {}, Baz.children returns Baz...
+            else if tp.classSymbol == defn.TupleClass || tp.classSymbol == defn.NonEmptyTupleClass then
+              List(child) // TupleN and TupleXXL classes are used for Tuple, but they aren't Tuple's children
+            else if (child.is(Private) || child.is(Sealed)) && child.isOneOf(AbstractOrTrait) then getChildren(child)
+            else List(child)
+          }
+        val children = getChildren(tp.classSymbol)
         debug.println(s"candidates for ${tp.show} : [${children.map(_.show).mkString(", ")}]")
 
         val parts = children.map { sym =>

tests/patmat/i14579.scala

@@ -0,0 +1,10 @@
+trait A {
+  sealed abstract class X
+  private class X1 extends X with X2 { }
+  private trait X2 extends X
+  sealed trait X3 extends X
+
+  def f(x: X) = x match {
+    case _: X1 => 0
+  }
+}

tests/patmat/patmatexhaust.check

@@ -5,7 +5,6 @@
 53: Pattern Match Exhaustivity: _: Gp
 59: Pattern Match Exhaustivity: Nil
 75: Pattern Match Exhaustivity: _: B
-87: Pattern Match Exhaustivity: _: C1
 100: Pattern Match Exhaustivity: _: C1
 114: Pattern Match Exhaustivity: D1, D2()
 126: Pattern Match Exhaustivity: _: C1

tests/patmat/patmatexhaust.scala

@@ -84,7 +84,7 @@ class TestSealedExhaustive { // compile only
     case class C3() extends C
     case object C4 extends C
 
-    def ma10(x: C) = x match {  // treat abstract sealed C1 is as inhabited.
+    def ma10(x: C) = x match {  // exhaustive: abstract sealed C1 is dead end.
       case C3()     => true
       case C2 | C4  => true
     }