Implement Promise.retryWithDelay

Closes #45

lib/init.lua

@@ -1925,6 +1925,36 @@ function Promise.retry(callback, times, ...)
 	end)
 end
 
+--[=[
+	Repeatedly calls a Promise-returning function up to `times` number of times, waiting `seconds` seconds between each
+	retry, until the returned Promise resolves.
+
+	If the amount of retries is exceeded, the function will return the latest rejected Promise.
+
+	@since v3.2.0
+	@param callback (...: P) -> Promise<T>
+	@param times number
+	@param seconds number
+	@param ...? P
+]=]
+function Promise.retryWithDelay(callback, times, seconds, ...)
+	assert(isCallable(callback), "Parameter #1 to Promise.retry must be a function")
+	assert(type(times) == "number", "Parameter #2 (times) to Promise.retry must be a number")
+	assert(type(seconds) == "number", "Parameter #3 (seconds) to Promise.retry must be a number")
+
+	local args, length = { ... }, select("#", ...)
+
+	return Promise.resolve(callback(...)):catch(function(...)
+		if times > 0 then
+			Promise.delay(seconds):await()
+
+			return Promise.retryWithDelay(callback, times - 1, seconds, unpack(args, 1, length))
+		else
+			return Promise.reject(...)
+		end
+	end)
+end
+
 --[=[
 	Converts an event into a Promise which resolves the next time the event fires.
 

lib/init.spec.lua

@@ -1611,6 +1611,37 @@ return function()
 		end)
 	end)
 
+	describe("Promise.retryWithDelay", function()
+		it("should retry after a delay", function()
+			local counter = 0
+
+			local promise = Promise.retryWithDelay(function(parameter)
+				expect(parameter).to.equal("foo")
+
+				counter = counter + 1
+
+				if counter == 3 then
+					return Promise.resolve("ok")
+				end
+
+				return Promise.reject("fail")
+			end, 3, 10, "foo")
+
+			expect(counter).to.equal(1)
+
+			advanceTime(11)
+
+			expect(counter).to.equal(2)
+
+			advanceTime(11)
+
+			expect(counter).to.equal(3)
+
+			expect(promise:getStatus()).to.equal(Promise.Status.Resolved)
+			expect(promise._values[1]).to.equal("ok")
+		end)
+	end)
+
 	describe("Promise.fromEvent", function()
 		it("should convert a Promise into an event", function()
 			local event = Instance.new("BindableEvent")