Merge pull request #11340 from dotty-staging/fix-11250

Fix unpickling of match type aliases

Author: odersky

compiler/src/dotty/tools/dotc/core/tasty/TreeUnpickler.scala

@@ -858,10 +858,7 @@ class TreeUnpickler(reader: TastyReader,
                 rhs.tpe.typeParams
             }
             sym.info = sym.opaqueToBounds(
-              rhs.tpe match {
-                case _: TypeBounds | _: ClassInfo => checkNonCyclic(sym, rhs.tpe, reportErrors = false)
-                case _ => rhs.tpe.toBounds
-              },
+              checkNonCyclic(sym, rhs.tpe.toBounds, reportErrors = false),
               rhs, rhs.tpe.typeParams)
             if sym.isOpaqueAlias then sym.typeRef.recomputeDenot() // make sure we see the new bounds from now on
             sym.resetFlag(Provisional)

compiler/src/dotty/tools/dotc/typer/TypeAssigner.scala

@@ -463,7 +463,9 @@ trait TypeAssigner {
   def assignType(tree: untpd.TypeBoundsTree, lo: Tree, hi: Tree, alias: Tree)(using Context): TypeBoundsTree =
     tree.withType(
       if !alias.isEmpty then alias.tpe
-      else if lo eq hi then TypeAlias(lo.tpe)
+      else if lo eq hi then
+        if lo.tpe.isMatch then MatchAlias(lo.tpe)
+        else TypeAlias(lo.tpe)
       else TypeBounds(lo.tpe, hi.tpe))
 
   def assignType(tree: untpd.Bind, sym: Symbol)(using Context): Bind =

compiler/test/dotc/pos-test-pickling.blacklist

@@ -34,6 +34,7 @@ i7872.scala
 6687.scala
 i11236.scala
 i11247.scala
+i11250
 
 # Opaque type
 i5720.scala

tests/pos/i11250/1.scala

@@ -0,0 +1,29 @@
+package shapeless3.data
+
+import scala.compiletime._
+
+trait Monoidal {
+  type to[_] <: Tuple
+  type length[m] = Monoidal.length[to[m]]
+}
+
+object Monoidal {
+  import Tuple._
+
+  type length[m <: Tuple] = Size[m]
+}
+
+trait UnboundedMonoidal[T0[_, _], U0] extends Monoidal {
+  type to[t] <: Tuple = t match {
+    case T0[hd, tl] => hd *: to[tl]
+    case U0 => EmptyTuple
+  }
+}
+
+object pairs extends UnboundedMonoidal[Tuple2, Unit]
+
+object MonoidalTest { // Compiles fine here
+  type p = (Int, (String, (Boolean, Unit)))
+  summon[pairs.length[p] =:= 3]
+}
+

tests/pos/i11250/2.scala

@@ -0,0 +1,7 @@
+package shapeless3.data
+
+object MonoidalTest2 { // But not here
+  type p = (Int, (String, (Boolean, Unit)))
+  summon[pairs.length[p] =:= 3]
+}
+