error on large integer types as array index range (#23229)

fixes #17163, refs #23204

Types that aren't `tyRange` and are bigger than 16 bits, so `int32`,
`uint64`, `int` etc, are disallowed as array index range types.
`tyRange` is excluded because the max array size is backend independent
(except for the specific size of `high(uint64)` which crashes the
compiler) and so there should still be an escape hatch for people who
want bigger arrays.

(cherry picked from commit 3ab8b6b2cf)

compiler/semtypes.nim

@@ -407,13 +407,16 @@ proc semArray(c: PContext, n: PNode, prev: PType): PType =
     if indxB.kind in {tyGenericInst, tyAlias, tySink}: indxB = lastSon(indxB)
     if indxB.kind notin {tyGenericParam, tyStatic, tyFromExpr} and
         tfUnresolved notin indxB.flags:
-      if indxB.skipTypes({tyRange}).kind in {tyUInt, tyUInt64}:
-        discard
-      elif not isOrdinalType(indxB):
+      if not isOrdinalType(indxB):
         localError(c.config, n[1].info, errOrdinalTypeExpected % typeToString(indxB, preferDesc))
       elif enumHasHoles(indxB):
         localError(c.config, n[1].info, "enum '$1' has holes" %
                    typeToString(indxB.skipTypes({tyRange})))
+      elif indxB.kind != tyRange and
+          lengthOrd(c.config, indxB) > high(uint16).int:
+        # assume range type is intentional
+        localError(c.config, n[1].info,
+          "index type '$1' for array is too large" % typeToString(indxB))
     base = semTypeNode(c, n[2], nil)
     # ensure we only construct a tyArray when there was no error (bug #3048):
     result = newOrPrevType(tyArray, prev, c)

tests/array/tlargeindex.nim

@@ -0,0 +1,18 @@
+discard """
+  cmd: "nim check --hints:off $file"
+"""
+
+# issue #17163
+var e: array[int32, byte] #[tt.Error
+             ^ index type 'int32' for array is too large]#
+var f: array[uint32, byte] #[tt.Error
+             ^ index type 'uint32' for array is too large]#
+var g: array[int64, byte] #[tt.Error
+             ^ index type 'int64' for array is too large]#
+var h: array[uint64, byte] #[tt.Error
+             ^ index type 'uint64' for array is too large]#
+
+# crash in issue #23204
+proc y[N](): array[N, int] = default(array[N, int]) #[tt.Error
+                                           ^ index type 'int' for array is too large]#
+discard y[int]()