Add backwards index overload for [] for JsonNode (#16501)

* Add backwards index overload for `[]` for JsonNode

* Add since

Co-authored-by: flywind <43030857+xflywind@users.noreply.github.com>

* Add docs, example, and changelog

Co-authored-by: flywind <43030857+xflywind@users.noreply.github.com>

changelog.md

@@ -89,6 +89,8 @@
 - Added `posix_utils.osReleaseFile` to get system identification from `os-release` file on Linux and the BSDs.
   https://www.freedesktop.org/software/systemd/man/os-release.html
 
+- Added `BackwardsIndex` overload for `JsonNode`.
+
 
 ## Language changes
 

lib/pure/json.nim

@@ -496,6 +496,19 @@ proc `[]`*(node: JsonNode, index: int): JsonNode {.inline.} =
   assert(node.kind == JArray)
   return node.elems[index]
 
+proc `[]`*(node: JsonNode, index: BackwardsIndex): JsonNode {.inline, since: (1, 5, 1).} =
+  ## Gets the node at `array.len-i` in an array through the `^` operator.
+  ##
+  ## i.e. `j[^i]` is a shortcut for `j[j.len-i]`.
+  runnableExamples:
+    let
+      j = parseJson("[1,2,3,4,5]")
+
+    doAssert j[^1].getInt == 5
+    doAssert j[^2].getInt == 4
+
+  `[]`(node, node.len - int(index))
+
 proc hasKey*(node: JsonNode, key: string): bool =
   ## Checks if `key` exists in `node`.
   assert(node.kind == JObject)