Merge pull request #13635 from dotty-staging/fix-13633

Fix #13633: Add regression test

Author: nicolasstucki

tests/pos/13633.scala

@@ -0,0 +1,50 @@
+import scala.compiletime.{constValueTuple, constValue}
+
+object Sums extends App:
+
+  println(constValueTuple[Plus[(true, true, true), (true, true)]]) // works
+  println(constValueTuple[Plus1[(true, true, true), (true, true)]]) // fails
+  println(constValueTuple[
+    Reverse[PlusLoop[Reverse[(true, true, true)], Reverse[(true, true)], false]]]
+    ) // also works despite it's just an unfold of `Plus1` application
+
+  type Plus[A <: Tuple, B <: Tuple] <: Tuple = (A, B) match
+    case (EmptyTuple, EmptyTuple) => EmptyTuple
+    case (a, b)                   => Reverse[PlusLoop[Reverse[A], Reverse[B], false]]
+
+  type Plus1[A <: Tuple, B <: Tuple]         = Reverse[PlusLoop[Reverse[A], Reverse[B], false]]
+
+  type ReverseLoop[A, XS <: Tuple] <: Tuple = A match {
+    case EmptyTuple => XS
+    case x *: xs    => ReverseLoop[xs, x *: XS]
+  }
+
+  type Reverse[A] = ReverseLoop[A, EmptyTuple]
+
+  type PlusTri[A, B, C]                             = (A, B, C) match
+    case (false, false, false)                                              => (false, false)
+    case (true, false, false) | (false, true, false) | (false, false, true) => (false, true)
+    case (true, true, false) | (true, false, true) | (false, true, true)    => (true, false)
+    case (true, true, true)                                                 => (true, true)
+
+  type Inc[A <: Tuple] <: Tuple                     = A match
+    case EmptyTuple => true *: EmptyTuple
+    case t *: as    =>
+      t match
+        case false => true *: as
+        case true  => false *: Inc[as]
+
+  type IncT[A <: Tuple, O <: Boolean] <: Tuple      = O match
+    case false => A
+    case true  => Inc[A]
+
+  type PlusLoop[A <: Tuple, B <: Tuple, O] <: Tuple = (A, B) match
+    case (EmptyTuple, EmptyTuple) =>
+      O match
+        case true  => (true *: EmptyTuple)
+        case false => EmptyTuple
+    case (EmptyTuple, B)          => IncT[B, O]
+    case (A, EmptyTuple)          => IncT[A, O]
+    case (a *: as, b *: bs)       =>
+      PlusTri[a, b, O] match
+        case (x, y) => y *: PlusLoop[as, bs, x]