fix: render default arg/opt if equal to 0

[akwodkiewicz]

This PR fixes rendering of default values for arguments and flags.
Before the fix, if an arg/flag default was set to 0, it was not rendered.

I couldn't reopen or edit my existing PR, so this is an updated version of #248, but the base branch is set to main this time.

[RodEsp]

I'd rather see us explicitly call out equality to 0 to avoid other unintended values.

[akwodkiewicz]

I deliberately used my approach, because the default field is (incorrectly¹) typed as a string, so the compiler does not allow me to check for flag.default === 0, because it believes it's a (constant) false expression. My approach allowed me to leave the types unchanged (I did not want to cast fields to other types nor change the typings in other repositories) and still fix the bug.

I took a look at the oclif/parser and I believe this ² is probably why the type of a default is not a string, but anything that is assigned to the default parameter.

Footnotes

1. If the value was in fact a string, then Boolean('0') === true and the zero would be printed. And I wouldn't need to write this PR 😄 ↩

2. https://github.com/oclif/parser/blob/master/src/parse.ts#L214 ↩

[RodEsp]

@akwodkiewicz good point. I updated my original suggestions a little bit to account for that.

[akwodkiewicz]

@RodEsp, thanks for the changes. Should I add an inline comment explaining why we're calling .toString() on a string or will a commit message be sufficient?

[RodEsp]

@akwodkiewicz a comment would be great 🙂

[akwodkiewicz]

@RodEsp , I have made the changes

[RodEsp]

Thanks for the contribution @akwodkiewicz!