strictNullChecks: false breaks Jsonify typing

[jpwilliams]

Summary

Step returns use the Jsonify type to represent the result of a step being (de)serialized as it is passed to and from Inngest.

If strictNullChecks: false is set in a user's tsconfig.json, however, this type sets some properties to optional that shouldn't be optional.

Example

Here's a playground example with strictNullChecks: false set. Notice how foo is optional where it shouldn't be. https://tsplay.dev/WyVMKw

import { Inngest } from "inngest";

const inngest = new Inngest({ id: "my-app" });

inngest.createFunction(
  { id: "my-fn" },
  { event: "my/event" },
  async ({ step }) => {
    // `foo` should not be optional
    const obj = await step.run("get-obj", () => ({
      //  ^? const obj: { foo?: string; }
      foo: "bar",
    }));
  },
);

Cause

This issue was introduced in #512 and released in 3.15.5. Specifically, this piece here:

inngest-js/packages/inngest/src/helpers/jsonify.ts

Lines 306 to 317 in 56c7ee2

	? IsLiteral<keyof T> extends true
	? // JsonifyObject recursive call for its children
	JsonifyObject<UndefinedToOptional<T>> // An object with known keys can be processed directly
	: Simplify<
	JsonifyObject<UndefinedToOptional<T>> &
	// If the object has generic keys, this is a
	// mapped type and we need to process the
	// generic and known keys separately
	JsonifyObject<
	UndefinedToOptional<Pick<T, KnownKeys<T>>>
	>
	>

Solution

Some TypeScript packages that perform some similar functionality are very opinionated about required configuration options. For example, type-fest: sindresorhus/type-fest#668 (comment)

However, as we wish to fit as quietly into a user's existing codebase as possible, ideally we:

• Add unit tests with a project using this option, which may surface other small issues
• If we can, account for strictNullChecks: false in this UndefinedToOptional type

[linear]

INN-2920 `strictNullChecks: false` breaks `Jsonify` typing