Do not consider enums with holes as ordinals (#8264)

Make the compiler behave consistently with respect to what's written in
the manual.

Fixes #1239

compiler/semmagic.nim

@@ -171,7 +171,7 @@ proc semTypeTraits(c: PContext, n: PNode): PNode =
 proc semOrd(c: PContext, n: PNode): PNode =
   result = n
   let parType = n.sons[1].typ
-  if isOrdinalType(parType):
+  if isOrdinalType(parType, allowEnumWithHoles=true):
     discard
   elif parType.kind == tySet:
     result.typ = makeRangeType(c, firstOrd(c.config, parType), lastOrd(c.config, parType), n.info)

compiler/types.nim

@@ -133,18 +133,18 @@ proc elemType*(t: PType): PType =
   else: result = t.lastSon
   assert(result != nil)
 
-proc isOrdinalType*(t: PType): bool =
+proc enumHasHoles*(t: PType): bool =
+  var b = t.skipTypes({tyRange, tyGenericInst, tyAlias, tySink})
+  result = b.kind == tyEnum and tfEnumHasHoles in b.flags
+
+proc isOrdinalType*(t: PType, allowEnumWithHoles = false): bool =
   assert(t != nil)
   const
     # caution: uint, uint64 are no ordinal types!
     baseKinds = {tyChar,tyInt..tyInt64,tyUInt8..tyUInt32,tyBool,tyEnum}
     parentKinds = {tyRange, tyOrdinal, tyGenericInst, tyAlias, tySink, tyDistinct}
-  t.kind in baseKinds or (t.kind in parentKinds and isOrdinalType(t.sons[0]))
+  (t.kind in baseKinds and not (t.enumHasHoles and not allowEnumWithHoles)) or
-
+    (t.kind in parentKinds and isOrdinalType(t.lastSon))
-proc enumHasHoles*(t: PType): bool =
-  var b = t
-  while b.kind in {tyRange, tyGenericInst, tyAlias, tySink}: b = b.sons[0]
-  result = b.kind == tyEnum and tfEnumHasHoles in b.flags
 
 proc iterOverTypeAux(marker: var IntSet, t: PType, iter: TTypeIter,
                      closure: RootRef): bool

lib/system.nim

@@ -263,14 +263,14 @@ proc high*[T: Ordinal](x: T): T {.magic: "High", noSideEffect.}
   ##  high(2) #=> 9223372036854775807
   ##  high(int) #=> 9223372036854775807
 
-proc high*[T: Ordinal](x: typeDesc[T]): T {.magic: "High", noSideEffect.}
+proc high*[T: Ordinal|enum](x: typeDesc[T]): T {.magic: "High", noSideEffect.}
 proc high*[T](x: openArray[T]): int {.magic: "High", noSideEffect.}
 proc high*[I, T](x: array[I, T]): I {.magic: "High", noSideEffect.}
 proc high*[I, T](x: typeDesc[array[I, T]]): I {.magic: "High", noSideEffect.}
 proc high*(x: cstring): int {.magic: "High", noSideEffect.}
 proc high*(x: string): int {.magic: "High", noSideEffect.}
 
-proc low*[T: Ordinal](x: typeDesc[T]): T {.magic: "Low", noSideEffect.}
+proc low*[T: Ordinal|enum](x: typeDesc[T]): T {.magic: "Low", noSideEffect.}
 proc low*[T](x: openArray[T]): int {.magic: "Low", noSideEffect.}
 proc low*[I, T](x: array[I, T]): I {.magic: "Low", noSideEffect.}
 proc low*[T](x: T): T {.magic: "Low", noSideEffect.}
@@ -792,7 +792,7 @@ proc card*[T](x: set[T]): int {.magic: "Card", noSideEffect.}
   ##  var i = {1,2,3,4}
   ##  card(i) #=> 4
 
-proc ord*[T](x: T): int {.magic: "Ord", noSideEffect.}
+proc ord*[T: Ordinal|enum](x: T): int {.magic: "Ord", noSideEffect.}
   ## returns the internal int value of an ordinal value ``x``.
   ##
   ## .. code-block:: nim