LUAFDN-1514 Fix out-of-bounds error in charCodeAt (#182)

* Fix charCodeAt edge case

* Add comment

* Update rotriever and changelog

CHANGELOG.md

@@ -2,6 +2,9 @@
 
 ## Unreleased
 
+## 1.2.3
+* Fix an edge case in String.charCodeAt introduced in 1.2.2
+
 ## 1.2.2
 
 * Optimize charCodeAt by removing an iterations over all codepoints in the input string.

modules/string/src/__tests__/charCodeAt.spec.lua

@@ -76,6 +76,7 @@ return function()
 			local body = "\u{8123}a"
 
 			jestExpect(charCodeAt(body, 0)).toBe(Number.NaN)
+			jestExpect(charCodeAt(body, 3)).toBe(Number.NaN)
 			jestExpect(charCodeAt(body, 100)).toBe(Number.NaN)
 		end)
 

modules/string/src/charCodeAt.lua

@@ -30,13 +30,16 @@ return function(str: string, index: number): number
 		but it is cheaper to check string.len and handle utf8.offset than to check
 		utf.len, which iterates over all codepoints.
 	]]
-	if index < 1 or index > string.len(str) then
+	local length = string.len(str)
+	if index < 1 or index > length then
 		return NaN
 	end
 
 	-- utf8.offset returns nil for out of bounds
 	local offset = utf8.offset(str, index)
-	if offset == nil then
+
+	-- check that offset is not greater than the length of the string
+	if offset == nil or offset > length then
 		return NaN
 	end
 

rotriever.toml

@@ -1,5 +1,5 @@
 [workspace]
-version = "1.2.2"
+version = "1.2.3"
 members = ["modules/*"]
 default_member = "LuauPolyfill"
 authors = [