Fix subranges of distinct types (#18816) [backport]

compiler/typeallowed.nim

@@ -124,7 +124,7 @@ proc typeAllowedAux(marker: var IntSet, typ: PType, kind: TSymKind,
     result = typeAllowedAux(marker, lastSon(t), kind, c, flags)
   of tyRange:
     if skipTypes(t[0], abstractInst-{tyTypeDesc}).kind notin
-      {tyChar, tyEnum, tyInt..tyFloat128, tyInt..tyUInt64}: result = t
+      {tyChar, tyEnum, tyInt..tyFloat128, tyInt..tyUInt64, tyRange}: result = t
   of tyOpenArray:
     # you cannot nest openArrays/sinks/etc.
     if (kind != skParam or taIsOpenArray in flags) and views notin c.features:

tests/distinct/tdistinct.nim

@@ -167,6 +167,20 @@ template main() =
         s.Foo.add('c')
         doAssert s.string == "c" # was failing
       test()
+    block: #18061
+      type
+        A = distinct (0..100)
+        B = A(0) .. A(10)
+      proc test(b: B) = discard
+      let
+        a = A(10)
+        b = B(a)
+      test(b)
+
+      proc test(a: A) = discard
+      discard cast[B](A(1))
+      var c: B
+
 
 static: main()
 main()