fix #20272 range of uint64 shows signed upper bound (#20702)

compiler/types.nim

@@ -450,7 +450,10 @@ proc mutateType(t: PType, iter: TTypeMutator, closure: RootRef): PType =
 
 proc valueToString(a: PNode): string =
   case a.kind
-  of nkCharLit..nkUInt64Lit: result = $a.intVal
+  of nkCharLit, nkUIntLit..nkUInt64Lit:
+    result = $cast[uint64](a.intVal)
+  of nkIntLit..nkInt64Lit:
+    result = $a.intVal
   of nkFloatLit..nkFloat128Lit: result = $a.floatVal
   of nkStrLit..nkTripleStrLit: result = a.strVal
   else: result = "<invalid value>"

tests/misc/t6549.nim

@@ -0,0 +1,4 @@
+
+const l = $(range[low(uint64) .. high(uint64)])
+const r = "range 0..18446744073709551615(uint64)"
+doAssert l == r