fixes #25419; lift magic types to typeclasses (#25421)

fixes #25419

compiler/semstmts.nim

@@ -1845,6 +1845,13 @@ proc typeSectionFinalPass(c: PContext, n: PNode) =
           let baseType = s.typ.safeSkipTypes(abstractPtrs)
           if baseType.kind in {tyObject, tyTuple} and not baseType.n.isNil:
             checkForMetaFields(c, baseType.n, hasError)
+
+        if s.typ.kind in {tySet, tyArray, tySequence, tyUncheckedArray} and s.typ.elementType.kind == tyNone:
+          # magic generics are not filled but tyNone is added to its elements by default,
+          # we lift them to tyBuiltInTypeClass here
+          s.typ = newTypeS(tyBuiltInTypeClass, c,
+                    newTypeS(s.typ.kind, c))
+
         if not hasError:
           checkConstructedType(c.config, s.info, s.typ)
   #instAllTypeBoundOp(c, n.info)

tests/types/tissues_types.nim

@@ -116,3 +116,13 @@ block:
   s(something)
   s(otherthing, something)
   s(something, otherthing)
+
+block:
+  type 
+    Test = set
+    Test2 = seq
+    Test3 = array
+
+  doAssert set is Test
+  doAssert seq is Test2
+  doAssert array is Test3