Panic with ${env} in help for positional arguments #556
Description
I would like to use ${env} in the help message of a positional argument. It would make it consistent with my options. When I try to, help in Kong 1.12.1 panics saying "undefined variable".
Here is an demo.
Option with ${env}
module test
go 1.25.0
require github.com/alecthomas/kong v1.12.1
package main
import (
"github.com/alecthomas/kong"
)
var cli struct {
Foo string `help:"Foo (${env})" env:"FOO"`
}
func main() {
ctx := kong.Parse(&cli)
err := ctx.Run()
ctx.FatalIfErrorf(err)
}Let's build and run:
> go build && ./test -h
Usage: test [flags]
Flags:
-h, --help Show context-sensitive help.
--foo=STRING Foo (FOO)
Argument with ${env}
Let's use arg:"" to turn Foo into a positional argument, leaving everything else unchanged:
package main
import (
"github.com/alecthomas/kong"
)
var cli struct {
Foo string `arg:"" help:"Foo (${env})" env:"FOO"`
}
func main() {
ctx := kong.Parse(&cli)
err := ctx.Run()
ctx.FatalIfErrorf(err)
}The program panics:
> go build && ./test -h
panic: help for <foo>: undefined variable ${env}
goroutine 1 [running]:
github.com/alecthomas/kong.Parse({0x598660?, 0x757830?}, {0x0?, 0xc000110068?, 0x0?})
/home/dbohdan/go/pkg/mod/github.com/alecthomas/kong@v1.12.1/global.go:11 +0xa5
main.main()
/tmp/demo/main.go:12 +0x28
Argument without ${env}
Now let's remove ${env} from the description:
package main
import (
"github.com/alecthomas/kong"
)
var cli struct {
Foo string `arg:"" help:"Foo" env:"FOO"`
}
func main() {
ctx := kong.Parse(&cli)
err := ctx.Run()
ctx.FatalIfErrorf(err)
}It works again:
> go build && ./test -h
Usage: test <foo>
Arguments:
<foo> Foo ($FOO)
Flags:
-h, --help Show context-sensitive help.