Command derive setup for both cargo extension and standalone usage

[MiniaczQ]

Hi, I'm trying to port clap from v2 to v4 in the tarpaulin crate.

One of the features is how both cargo tarpaulin --help and cargo-tarpaulin --help calls work exactly the same.
While porting I accidentally regressed this functionality.
The cargo run -- --help works, while cargo run -- tarpaulin --help throws an error about unknown command:

#[derive(Debug, Parser)]
#[command(name = "cargo-tarpaulin")]
#[command(bin_name = "cargo")]
#[command(author, version, about, long_about = None)]
pub enum CargoTarpaulinCli {
    Tarpaulin(TarpaulinCli),
}

match CargoTarpaulinCli::try_parse() {
    Ok(CargoTarpaulinCli::Tarpaulin(tarpaulin_cli)) => tarpaulin_cli,
    Err(_) => TarpaulinCli::parse(),
}

Reversing the order of parsing yields exactly opposite results, so still incorrect.

This is how it was originally done in clap v2.

let args = App::new("cargo-tarpaulin");
// app building
let args = args.subcommand_matches("tarpaulin").unwrap_or(&args);

How could I achieve the same functionality without reverting to builder-style commands?

Other

I've tried looking around through issues, discussions and examples, but couldn't find this exact use case.

Merge request in question

[epage]

Would the following work?

#!/usr/bin/env nargo

/*!
```cargo
[dependencies]
clap = { version = "4", features = ["derive"] }
```
*/

use clap::Parser;

#[derive(Debug, Parser)]
#[command(name = "cargo-tarpaulin")]
#[command(bin_name = "cargo")]
#[command(author, version, about, long_about = None)]
pub enum CargoTarpaulinCli {
    Tarpaulin(TarpaulinCli),
}

#[derive(Debug, Parser)]
pub struct TarpaulinCli {}

fn main() {
    let cli = match CargoTarpaulinCli::try_parse() {
        Ok(CargoTarpaulinCli::Tarpaulin(tarpaulin_cli)) => tarpaulin_cli,
        Err(err) if !err.use_stderr() => err.exit(),
        Err(_) => TarpaulinCli::parse(),
    };
    dbg!(cli);
}

We bubble --version and --help information up via errors, so we need to distinguish them to decide whether it should work or not.

Alternatively, you could do

#!/usr/bin/env nargo

/*!
```cargo
[dependencies]
clap = { version = "4", features = ["derive"] }
```
*/

use clap::Parser;

#[derive(Debug, Parser)]
#[command(name = "cargo-tarpaulin")]
#[command(bin_name = "cargo")]
#[command(author, version, about, long_about = None)]
#[command(arg_required_else_help = true)]
#[command(args_conflicts_with_subcommands = true)]
pub struct CargoTarpaulinCli {
    #[command(subcommand)]
    indirect: Option<CargoTarpaulinCommand>,
    #[command(flatten)]
    direct: Option<TarpaulinCli>,
}

#[derive(Debug, Parser)]
pub enum CargoTarpaulinCommand {
    Tarpaulin(TarpaulinCli),
}

#[derive(Debug, Parser)]
pub struct TarpaulinCli {}

fn main() {
    let cli = match CargoTarpaulinCli::parse() {
        CargoTarpaulinCli {
            indirect: Some(CargoTarpaulinCommand::Tarpaulin(cli)),
            direct: None,
        } => cli,
        CargoTarpaulinCli {
            indirect: None,
            direct: Some(cli),
        } => cli,
        CargoTarpaulinCli { .. } => unreachable!(),
    };
    dbg!(cli);
}

[MiniaczQ]

Thank you for the fast response 😄

The first option works the same way the original did, for cargo run -- --help it prints cargos help instead of tarpaulins.
I tried switching the commands around and it does work that way!

match TarpaulinCli::try_parse() {
    Ok(tarpaulin_cli) => tarpaulin_cli,
    Err(err) if !err.use_stderr() => err.exit(),
    Err(_) => match CargoTarpaulinCommand::parse() {
        CargoTarpaulinCommand::Tarpaulin(tarpaulin_cli) => tarpaulin_cli,
    },
}

Second option also does work and is very explicit, but I think I'll roll with the previous one