fix(validation): Use the error as a message when none exists otherwise

[softcraft-development]

While exploring yargs I discovered an edge-case error.

_runValidation assumes that parseErrors is an Error object with a message property. However, it's legitimate in JavaScript to throw arbitrary object. When that object is not an Error, it's most commonly a String, i.e.:

throw 'This is an error.'

See: https://jsfiddle.net/softcraft/gxka09nb/

When _runValidation feeds parseErrors.message to YError, it's undefined, and thus YError generates an error message with the (quite unhelpful) 'yargs error' string, not the value of parseErrors.

This change will allow _runValidation to use the value of parseErrors as a fallback if parseErrors.message doesn't exist. This allows throw "error!" to work successfully.

(I encountered this problem by throwing a String error from a coerce() function.)

[evocateur]

Yikes, that is quite the edge case. I like Nicholas Zakas's explanation of why throwing anything that isn't an Error() object is "suboptimal".

Be that as it may, yargs isn't a linter, so let's make the errors useful in more contexts. 🎉

[softcraft-development]

Agreed on avoiding throwing of non-Errors. I only hit this issue as I was doing some quick & dirty Yargs hacking in my project, and figured that the CLI layer was "thin" enough that I didn't need a full stack trace.

[bcoe]

@softcraft-development please try:

npm i yargs@next

It should have your changes.

[softcraft-development]

Looks good. Thanks!

[bcoe]

this is now available in yargs@13.1.0.