Callback parser should not need to stop parsing by calling os.Exit

[airnandez]

Hello,

when you use a callback parser, there is no other way of stopping parsing the command line arguments than to call os.Exit(). This is inconvenient if you need to do some clean up when you detect that parsing the command line arguments was not successful.

I would like to suggest modifying the signature of the callback parser so that it returns for instance a bool to tell go-options that the parsing process can continue or not.

In the return value of spec.Parse() we would need a way to know if the parsing ended successfully or not. For instance:

spec := options.NewOptions(mySpec).SetParseCallback(MyParseCallback)
opt := spec.Parse(os.Args[1:])
if ! opt.ParsingWasOK() {
// Do some cleanup here
}

In the current situation, we have to call the cleanup process in every 'case' of the 'switch' of the parse callback. If your command accepts several options, this may be a lot of code to repeat.

Best regards,

[gaal]

I agree this can be improved. Probably the callback function should return an error. I need to think about this some more though, because I don't like having to check a value on opt after calling Parse -- non-callback use wouldn't require it. Maybe get rid of SetParseCallback and add a OptionsSpec.ParseWithCallback, that looks the most promising so far.

BTW, if you're blocked on this, in the meantime you can override s.Exit to raise some bool value and not exit. Hacy but should tide you over.

[airnandez]

Hi Gaal,

for now I temporally turned around this problem by setting a bool flag in the closure of MyParseCallback and returning, instead of calling os.Exit(). Once spec.Parse() returns I check that boolean variable to know how to proceed.

The way you propose, namely to use a separate method on OptionsSpec for parsing with my custom callback looks fine for me. The callback would then be required to return an error when parsing should be stopped. I still would need a way to know whether the parsing process (using my custom callback) succeeded, so this may require to add a public field or a method to the Options type.