Thanks for working on this, @geekodour.

My thinking is that this isn't the right way to do this. Showing output like "--foo=false" seems quite confusing. If someone actually passes that they'll get an error:

package main

import (
	"fmt"

	"github.com/alecthomas/kingpin"
)

var boolFlag = kingpin.Flag("foo", "Foo").Default("true").Bool()

func main() {
	kingpin.Parse()
	fmt.Printf("%v\n", *boolFlag)
}

$> go run ./foo/main.go --foo=false
main: error: unexpected false, try --help
exit status 1

I think the original suggestion of showing --foo or --no-foo depending on the flag's default value was the right approach. It'd also be nice to change the help output to clarify this, so we'd get something like this:

--no-foo    Disable the foo feature. The default is to enable this feature.
--bar       Enable the bar feature. The default is to disable this feature.

The exact wording of that needs some work, since enable/disable may not work for every flag.

Yes, thanks for the PR, but I agree with @autarch. Whatever the help displays should be usable by the user.