Printing help on bare command invocation

[xpe]

Thanks for this great library!

I've spent some time looking for the easiest path to tell clap show a full help message on a bare command invocation. (This is the behavior with commands such as java and cloc.)

These commands don't work:

let mut app = App::new("name me").args_from_usage("<input_file> 'Sets the input file to use'");
let matches = app.get_matches(); // moves `app`
app.print_help(); // will not compile since `app` has been moved

I understand there are (at least) these options to make the API work as I intend:

1. Clone app before passing it to get_matches.
2. Find a function similar to get_matches that does not move app. (I'm not sure if one exists.)

I have a design question: What is the rationale for get_matches moving the app value? Perhaps a borrow would work out better?

P.S. For some context, feel free to see: http://stackoverflow.com/questions/40951538/method-call-on-clap-app-moving-ownership-more-than-once

[kbknapp]

Thanks!

You have a few options. You can either use AppSettings::ArgRequiredElseHelp or you can keep the move from happening by using App::get_matches_from_safe_borrow.

The downside with the second approach is it returns a Result, and you'll also have to provide the args to match against, either by providing your own arbitrary Vec, std::env::args or std::env::args_os (if you wish to support invalid UTF-8).

An example of the second version, should you choose that route would be:

let matches = // build app like normal
    .get_matches_from_safe_borrow(std::env:args_os())
    .unwrap_or_else(|e| e.exit())

The e.exit() portion does exactly what clap normally does, presenting an error message and gracefully exiting.

Hope this helps!

[EvanLuo42]

Thanks!

You have a few options. You can either use AppSettings::ArgRequiredElseHelp or you can keep the move from happening by using App::get_matches_from_safe_borrow.

The downside with the second approach is it returns a Result, and you'll also have to provide the args to match against, either by providing your own arbitrary Vec, std::env::args or std::env::args_os (if you wish to support invalid UTF-8).

An example of the second version, should you choose that route would be:

let matches = // build app like normal
    .get_matches_from_safe_borrow(std::env:args_os())
    .unwrap_or_else(|e| e.exit())

The e.exit() portion does exactly what clap normally does, presenting an error message and gracefully exiting.

Hope this helps!

I used this way to create matches. It's like:

let mut command = Command::new("ctool");
let matches = command.
    .try_get_matches_from(std::env::args_os())
    .unwrap_or_else(|e| e.exit());

And I want to use custom error, I did like this:

let action_undefined_error = command.error(
        clap::ErrorKind::InvalidValue,
        "The given action is not supported, please enter base64, hex, etc."
    );

But it still gave:
borrow of moved value: command E0382 value borrowed here after move Note: this function takes ownership of the receiver self, which moves command

How to solve this.

[epage]

try_get_matches_from took ownership of command and then you are trying to use command again.

Options

• Create a fn command() -> Command<'static> and write your errors as command().error(...). This will slow things down but in the error case so its unlikely anyone will notice
• Use _mut variant for parsing, whether get_matches_mut or try_get_matches_from_mut.

[EvanLuo42]

try_get_matches_from took ownership of command and then you are trying to use command again.

Options

• Create a fn command() -> Command<'static> and write your errors as command().error(...). This will slow things down but in the error case so its unlikely anyone will notice
• Use _mut variant for parsing, whether get_matches_mut or try_get_matches_from_mut.

Thank you, it worked.