Add flags and options

[casey]

Recipes should be able to define options:

foo --bar BAZ:
  echo {{BAZ}}

Maybe flags too:

foo --BAZ:
  echo {{BAZ}} # is it "true" or "false"? Or "" or BAZ?

Large changes to the parsing of recipe parameters like this should be considered holistically, along with other possible changes, like $ to support exporting parameters as environment variables, or changing all just variables to being environment variables.

[casey]

It occurs to me that we could use clap to construct recipe argument parsers.

[hustcer]

@casey Will flags be supported ? It's a quite common use case , Thanks !

[hustcer]

flag shorthand can also be supported:
foo --bar(-b):

[sascha-wolf]

Just my two cents: I would already be super happy if I could explicitly refer to the argument's name:

foo bar=something:
	echo {{bar}}

$ just foo bar=stuff
stuff

Of course fully featured flags and options would be lovely but for my personal use-case (and I imagine other's as well) this would already be very helpful, because then I can do things like this:

watch folders='lib,test' cmd='just test':
  find {{ '{' }}{{folders}}{{ '}' }} -name '*.ex*' | entr -dc {{cmd}}

$ just watch cmd='<some other command>'

[colemannerd]

I've just started using Just and my org loves it!

One thing that would improve our usage is opts with enums. We use just to coordinate all of our environment scripts and so we have done things like standardize accounts or environments to a certain list. Right now, they're just strings that we then call a pre-recipe on to check that they are one of a list. It would be awesome if we had this functionality AND incorporaitng an enum for one of the opts. I know #1990 is also similar.