Add test

Author: odersky

tests/neg/i12049.check

@@ -0,0 +1,50 @@
+-- [E007] Type Mismatch Error: tests/neg/i12049.scala:6:16 -------------------------------------------------------------
+6 |val x: String = ??? : M[B] // error
+  |                ^^^^^^^^^^
+  |                Found:    M[B]
+  |                Required: String
+  |
+  |                Note: a match type could not be fully reduced:
+  |
+  |                  trying to reduce  M[B]
+  |                  failed since selector  B
+  |                  does not match  case A => Int
+  |                  and cannot be shown to be disjoint from it either.
+  |                  Therefore, reduction cannot advance to the remaining case
+  |
+  |                    case B => String
+
+longer explanation available when compiling with `-explain`
+-- [E007] Type Mismatch Error: tests/neg/i12049.scala:14:17 ------------------------------------------------------------
+14 |val y3: String = ??? : Last[Int *: Int *: Boolean *: String *: EmptyTuple]  // error
+   |                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |                 Found:    Last[EmptyTuple.type]
+   |                 Required: String
+   |
+   |                 Note: a match type could not be fully reduced:
+   |
+   |                   trying to reduce  Last[EmptyTuple.type]
+   |                   failed since selector  EmptyTuple.type
+   |                   matches none of the cases
+   |
+   |                     case _ *: _ *: t => Last[t]
+   |                     case t *: EmptyTuple => t
+
+longer explanation available when compiling with `-explain`
+-- [E007] Type Mismatch Error: tests/neg/i12049.scala:22:20 ------------------------------------------------------------
+22 |val z3: (A, B, A) = ??? : Reverse[(A, B, A)] // error
+   |                    ^^^^^^^^^^^^^^^^^^^^^^^^
+   |                    Found:    Tuple.Concat[Reverse[A *: EmptyTuple.type], (B, A)]
+   |                    Required: (A, B, A)
+   |
+   |                    Note: a match type could not be fully reduced:
+   |
+   |                      trying to reduce  Tuple.Concat[Reverse[A *: EmptyTuple.type], (B, A)]
+   |                      trying to reduce  Reverse[A *: EmptyTuple.type]
+   |                      failed since selector  A *: EmptyTuple.type
+   |                      matches none of the cases
+   |
+   |                        case t1 *: t2 *: ts => Tuple.Concat[Reverse[ts], (t2, t1)]
+   |                        case EmptyTuple => EmptyTuple
+
+longer explanation available when compiling with `-explain`

tests/neg/i12049.scala

@@ -3,5 +3,20 @@ trait B
 type M[X] = X match
   case A => Int
   case B => String
-val x: String = ??? : M[B]
+val x: String = ??? : M[B] // error
 
+type Last[X <: Tuple] = X match
+  case _ *: _ *: t => Last[t]
+  case t *: EmptyTuple => t
+
+val y1: Int = ??? : Last[Int *: EmptyTuple]
+val y2: String = ??? : Last[Int *: Boolean *: String *: EmptyTuple]
+val y3: String = ??? : Last[Int *: Int *: Boolean *: String *: EmptyTuple]  // error
+
+type Reverse[X <: Tuple] = X match
+  case t1 *: t2 *: ts => Tuple.Concat[Reverse[ts], (t2, t1)]
+  case EmptyTuple => EmptyTuple
+
+val z1: (B, A) = ??? : Reverse[(A, B)]
+val z2: (B, A, B, A) = ??? : Reverse[(A, B, A, B)]
+val z3: (A, B, A) = ??? : Reverse[(A, B, A)] // error