default value interferes with passing context to sub-commands

[bcoe]

setting a default value for a global option overrides the context object.

yargs()
          .command('batman', 'batman command', function (yargs) {
            yargs.command('robin', 'robin command', {}, function (_argv) {
              argv = _argv
            })
          })
          .option('state', {
            default: undefined,
            global: true
          })
          .parse('batman robin --what', {
            state: 'grumpy but rich'
          }, function (_err, argv, _output) {})

[maxrimue]

@bcoe I think I tracked down the problem. It seems like argv will always take precedence over any context passed to .parse(). For example, this will fail:

var parsed = yargs.parse('--foo bar', {
  foo: 'not bar'
})

parsed.foo.should.equal('not bar')

If I'm not totally wrong here, it seems that the problem lies in L875, where assign is called to merge context and argv, but in a way that argv takes precedence. Changing the order in this statement made the aforementioned test case pass.

Isn't the context object meant to take precedence over argv?

Edit: Never mind, finally got this 😄 I guess the problem is that when we merge argv and context, the default values are already in argv.

[maxrimue]

@bcoe I would propose we add a new parameter for the parser like: Parser.detailed(args, options, state) so that the parser can apply state in precedence over default values and give back the argv like that. What do you think? Would take on this when I know what to do.

[bcoe]

@maxrimue before we add any more configuration options; I think I'd be tempted to just swap the order of precedence. I argue that context should take precedence.

Would you be okay with making this one of the breaking changes in #742 (CC: @nexdrew).