Expected behavior is unclear when using types and non-camelcase

[kirbysayshi]

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Hello!

I came across a gotcha and wanted to document it for future users of this library.

As demonstrated by this sandbox https://codesandbox.io/s/meow-kebab-case-behavior-9rpoc, the type hints are inconsistent with the actual shape of the parsed object. The code below is from the sandbox to demonstrate:

import meow from "meow";

const cli = meow("", {
  flags: {
    "input-file": {
      type: "string",
      alias: "i",
      default: "INPUT"
    }
  }
});

const camel = cli.flags.inputFile;
const kebab = cli.flags["input-file"];

type C = typeof camel; // unknown
type K = typeof kebab; // string;

console.log(camel, kebab);
// yet this outputs:
// > INPUT undefined

This leads to some tricky behavior when using meow, TS, and normalized names. Specifically, type hints and autocompletion will show cli.flags['input-file'] as the type-safe suggestion, when it's actually undefined.

I don't think it's possible for meow to handle this due to how TS generics work. But hopefully this saves someone else time that I spent trying to figure this out :D Unfortunately I don't know of a type-safe workaround.

And there's always the chance I'm doing something wrong, and if so, sorry for the noise. Thanks for the library!

[sindresorhus]

// @NiGhTTraX Is there anything we can do to improve this other than better docs about it?

[NiGhTTraX]

Unfortunately, no. We can't express the normalization of the flags through the type system. However, unnormalizedFlags should contain the flag under its original name with the correct type so in your case cli.unnormalizedFlags['input-file'] // number. It would be nice if this behavior were documented.

[Robbie-Cook]

I tell you h'wat - you can: https://github.com/microsoft/TypeScript/pull/40336

[Robbie-Cook]

Note the Split<>

[sindresorhus]

We can now use https://github.com/sindresorhus/type-fest/blob/master/ts41/camel-case.d.ts PR welcome :)

[sindresorhus]

Fixed by https://github.com/sindresorhus/meow/issues/155