Add SetNonNullableDeep type

[som-sm]

Closes #795

Notes:

• Currently, there’s no way to remove nullables just from the rest element in an array type. For instance, you can’t get [string | null, …number[]] from [string | null, …(number | null)[]].

  Furthermore, it’s not very obvious what KeyPaths should be used to target the rest element. Using number would target all elements, not just the rest element (refer to the next point).

• Rest elements in array types behave slightly differently across versions when KeyPaths includes number. Refer the example below:

  // In v5.3 and below
  // `number` in `KeyPaths` DOESN'T affect the rest element
  type Test = SetNonNullableDeep<{a: [string | null, number | null, ...Array<boolean | null>]}, `a.${number}`>;
  //=> { a: [string, number, ...(boolean | null)[]]; }

  // In v5.4 and above
  // `number` in `KeyPaths` DOES affect the rest element
  type Test = SetNonNullableDeep<{a: [string | null, number | null, ...Array<boolean | null>]}, `a.${number}`>;
  //=> { a: [string, number, ...NonNullable<boolean | null>[]]; }

• SetNonNullableDeep currently doesn't deeply remove all nullables if KeyPaths is any. This will require a separate NonNullableDeep type, which I'll create it a separate PR.

[ogroppo]

Thanks for looking into this!

[som-sm]

Something really strange is happening here. If I remove the test on line 106, some tests in set-required-deep.ts start failing—tests that are completely unrelated to this. And there's no changes in SetRequiredDeep related files.

And this doesn't just fail locally, it also fails in CI.

@sindresorhus @Emiyaaaaa Do you have any idea why this could be happening?

weird-compressed.mov

[sindresorhus]

No idea. Probably some compiler quirk.

The minimum. Any more simplifications of this and it triggers the issue.

expectType<{a?: [string]}>({} as SetNonNullableDeep<{a?: [string]}, 'a.0'>);