Add string.split implementation (#190)

* init

* remove .history files

* fix bad test and add Roblox's internal tests

* change formatting to please linter

lib/libs/init.lua

@@ -1,5 +1,6 @@
 local names = {
 	"math",
+	"string",
 }
 
 local libs = {}
@@ -8,4 +9,4 @@ for _, name in ipairs(names) do
 	libs[name] = import("./" .. name)
 end
 
-return libs
+return libs

lib/libs/string.lua

@@ -0,0 +1,36 @@
+local rbxString = {}
+
+for key, value in pairs(string) do
+	rbxString[key] = value
+end
+
+rbxString.split = function(str, sep)
+	local result = {}
+
+	if sep == "" then
+		for i = 1, #str do
+			result[i] = str:sub(i, i)
+		end
+	else
+		if sep == nil then
+			sep = ","
+		end
+
+		local count = 1
+		local pos = 1
+		local a, b = str:find(sep, pos, true)
+
+		while a do
+			result[count] = str:sub(pos, a - 1)
+			count = count + 1
+			pos = b + 1
+			a, b = str:find(sep, pos, true)
+		end
+
+		result[count] = str:sub(pos)
+	end
+
+	return result
+end
+
+return rbxString

lib/libs/string_spec.lua

@@ -0,0 +1,98 @@
+local string = import("./string")
+
+describe("libs.string", function()
+	describe("split", function()
+		it("should be a function", function()
+			assert.is_function(string.split)
+		end)
+
+		it("should return an array of comma separated strings if sep is nil", function()
+			assert.are.same({"Hello", "world", "and", "lemur"}, string.split("Hello,world,and,lemur"))
+		end)
+
+		it("should return an array of all characters in a string if sep is the empty string", function()
+			assert.are.same({
+				"H",
+				"e",
+				"l",
+				"l",
+				"o",
+				",",
+				"w",
+				"o",
+				"r",
+				"l",
+				"d",
+				",",
+				"a",
+				"n",
+				"d",
+				",",
+				"l",
+				"e",
+				"m",
+				"u",
+				"r",
+			}, string.split("Hello,world,and,lemur", ""))
+		end)
+
+		it("should return an empty table if the string and sep is the empty string", function()
+			assert.are.same({}, string.split("", ""))
+		end)
+
+		it("should return the original string in a table if no sep is matched", function()
+			assert.are.same({"Hello, world"}, string.split("Hello, world", "K"))
+			assert.are.same({""}, string.split("", " "))
+		end)
+
+		it("should return empty strings at the front and back when seps are present there", function()
+			assert.are.same({"", "Validark", "Osyris", "Vorlias", ""}, string.split("/Validark/Osyris/Vorlias/", "/"))
+			assert.are.same({"", "Validark", "Osyris", "Vorlias"}, string.split("/Validark/Osyris/Vorlias", "/"))
+			assert.are.same({"Validark", "Osyris", "Vorlias", ""}, string.split("Validark/Osyris/Vorlias/", "/"))
+			assert.are.same({"Validark", "Osyris", "Vorlias"}, string.split("Validark/Osyris/Vorlias", "/"))
+		end)
+
+		it("should allow multi-character separators", function()
+			assert.are.same({"Hello", "world"}, string.split("Hello, world", ", "))
+		end)
+
+		it("should literally interpret Lua character classes", function()
+			assert.are.same({"Hello, world"}, string.split("Hello, world", "%l"))
+			assert.are.same({"Hel", "o, world"}, string.split("Hel%lo, world", "%l"))
+		end)
+
+		it("should match Roblox's internal tests", function()
+			-- Provided by tiffany352 at https://github.com/LPGhatguy/lemur/pull/190
+			local char = string.char
+			local ZWJ = char(0xe2, 0x80, 0x8d)
+			assert.are.same({ "" }, string.split("", ","))
+			assert.are.same({ "foo", "", "bar" }, string.split("foo,,bar", ","))
+			assert.are.same({ "", "foo" }, string.split(",foo", ","))
+			assert.are.same({ "foo", "" }, string.split("foo,", ","))
+			assert.are.same({ "", "" }, string.split(",", ","))
+			assert.are.same({ "", "", "" }, string.split(",,", ","))
+			assert.are.same({ "" }, string.split("", "~~~"))
+			assert.are.same({ "~~" }, string.split("~~", "~~~"))
+			assert.are.same({ "~~ ~~" }, string.split("~~ ~~", "~~~"))
+			assert.are.same({ "foo", "bar" }, string.split("foo~~~bar", "~~~"))
+			assert.are.same({ "foo", "", "bar" }, string.split("foo~~~~~~bar", "~~~"))
+			assert.are.same({ "", "foo" }, string.split("~~~foo", "~~~"))
+			assert.are.same({ "foo", "" }, string.split("foo~~~", "~~~"))
+			assert.are.same({ "", "" }, string.split("~~~", "~~~"))
+			assert.are.same({ "", "", "" }, string.split("~~~~~~", "~~~"))
+			assert.are.same({ "", "", "O" }, string.split("OOOOO", "OO"))
+			assert.are.same({ "   ws   " }, string.split("   ws   ", ","))
+			assert.are.same({ "foo ", " bar" }, string.split("foo , bar", ","))
+			assert.are.same({ "我很高兴", "你呢？" }, string.split("我很高兴，你呢？", "，"))
+			assert.are.same({ "👩", "👩", "👧", "👧" }, string.split("👩‍👩‍👧‍👧", ZWJ))
+			assert.are.same({ "foo", "bar" }, string.split("foo\0bar", "\0"))
+			assert.are.same({ "foo", "bar", "" }, string.split("foo\0bar\0", "\0"))
+			assert.are.same({ "foo", "bar" }, string.split("foo\0\0bar", "\0\0"))
+			assert.are.same({ "foo\0" }, string.split("foo\0", "\0\0"))
+			assert.are.same({ "foo", "\0" }, string.split("foo\0\0\0", "\0\0"))
+			assert.are.same({ }, string.split("", ""))
+			assert.are.same({ "a", "b", "c" }, string.split("abc", ""))
+			assert.are.same({ char(0xef), char(0xbc), char(0x9f) }, string.split("？", ""))
+		end)
+	end)
+end)