Issue with CompilerOptions.keyofStringsOnly = true

[stalniy]

The issue

FromSchema does not infer required properties when compilerOptions.keyofStringsOnly = true.

The reason

I'm working on a project where ts compiler option keyofStringsOnly is set to true. This makes keyof WHATEVER to return string type instead of string | number | symbol. That's why when you check whether number extends keyof S["required"] on this line, it return false.

In general, keyof operator is not safe to test whether type is an array or tuple because even for objects and interfaces it returns string | number.

Also if you check the output type of type indexesOfArray = keyof string[], you will see that ts returns number and names of all methods. Even keyof ReadonlyArray<string> because it contains numeric indexes, length and all non mutating array methods

How to fix

In order to fix the issue, you need to convert that and similar checks to check on ReadonlyArray<string> or on { length: number }

type GetRequired<S> = "required" extends keyof S
  ? S["required"] extends ReadonlyArray<string>  // <----
    ? S["required"][number]
    : never
  : never;

[stalniy]

any thoughts?

[ThomasAribart]

Good catch ! I'll have a look into it next week !

[stalniy]

I can create a PR if you are ok with the fix, so the only thing you need to do is to release a new version :) Please, it's quite critical for me and I don't want to create hack-arounds

[ThomasAribart]

@stalniy It's merge and deployed in v1.6.1 👍 Thanks for your contribution !

[stalniy]

Awesome! Thank you!