existingdir with default validated and stops program run on unused-subcommand

[deweysasser]

Summary

If you have multiple subcommands, which have constrained arguments (e.g. existingdir with default
values) those constraints must pass even if the subcommand is not invoked.

I would expect uninvoked subcommands to NOT interrupt program run.

Kong Code

type Options struct {
	Cmd1         Subcommand1 `cmd:""`
	Cmd2         Subcommand2 `cmd:""`
}

type Subcommand1 struct {
	Dir1 string `group:"dir" help:"get a directory" type:"existingdir" default:"dir1"`
}

type Subcommand2 struct {
	Dir2 string `group:"dir" help:"get a directory" type:"existingdir" default:"dir2"`
}

Output

$ mkdir -p dir1 &&  go run main.go cmd-1 --dir-1 dir1
--dir-2: stat /Users/dsasser/personal/kong-bug-demo/dir2: no such file or directory
exit status 1

Expected Output

The expectation is that the program would run, as the constraints on the operable subcommand have been satisfied.

Note that if the default value is left off the parameters in the subcommands, the program runs as expected.

Running example

A running example of this problem can be found here

Notes

This may be related to #190