Make generic choices type const

[matthyk]

While working on #59 I noticed that since TypeScript 5.0 it is possible to declare generic types as const. This infers the value as const. The advantage of this is that the command type is more strictly typed. For this to work we need PR #59, but I wanted to make these new changes in a separate PR.

program
  .addOption(new Option('-o, --opt', '').choices(['a', 'b', 'c']))
  .action(function () {
    expectType<Command<[], { opt?: true | 'a' | 'b' | 'c' }>>(this)
  })

instead of

program
  .addOption(new Option('-o, --opt', '').choices(['a', 'b', 'c']))
  .action(function () {
    expectType<Command<[], { opt?: true | string }>>(this)
  })

[shadowspawn]

Oh nice. This is independent of #59 and the work-around is actually covered in the README:

Use a "const assertion" on the choices to narrow the option type from string

[shadowspawn]

Typescript 5 is somewhat "recent" and I think might have to wait for a breaking major update of this package in the future to adopt this, or do more work and support multiple versions: https://www.typescriptlang.org/docs/handbook/declaration-files/publishing.html#version-selection-with-typesversions

(Assuming we don't already require Typescript 5! Hmm, should have a test that runs against oldest supported TypeScript.)

[shadowspawn]

DefinitelyTyped has a handy graphic of their 2-year TypeScript testing support: https://github.com/DefinitelyTyped/DefinitelyTyped#support-window

[matthyk]

Since one can achieve the same with as const, we should stick to the timeline from DefinitelyTyped

[shadowspawn]

I am keeping an eye out for Typescript dependencies in other projects.

A new version of typescript-eslint is supporting TypeScript >=4.7.4:

• https://typescript-eslint.io/blog/announcing-typescript-eslint-v7#breaking-changes

[mrazauskas]

should have a test that runs against oldest supported TypeScript

@shadowspawn

To draw your attention, TSTyche is a type testing tool that is able to use specified version of TypeScript: tstyche --target 4.8,latest. This simple!

It also has test() helper with .only and .skip modifiers. Also --watch mode. And much more.

---

Note that the install size of tstyche is only around 220kB. This is because the installed TypeScript is loaded by default.

In contrary tsds install size is 48.0MB. They ship their own copy to TypeScript. (Or maybe even two? Because the install size of the latest version of typescript package is 20.9MB.)

[shadowspawn]

Thanks @mrazauskas , I had not seen TSTyche.