Unknown flags should be pointed out

[huonw]

$ cargo build --lib --rlease --feature foo 
Usage:
    cargo build [options]

This should say something along the lines of "invalid flag --rlease".

[alexcrichton]

cc @BurntSushi, does docopt give us an easy way to do this?

[BurntSushi]

Hmm, this is actually one of the few matching errors that docopt.rs tries to find. It should print in the error message:

extern crate docopt;

static USAGE: &'static str = "Usage: mycmd [-a]";

fn main() {
    let args = docopt::Docopt::new(USAGE)
                              .and_then(|d| d.parse())
                              .unwrap_or_else(|e| e.exit());
    println!("{:?}", args);
}

[andrew@Liger play] cargo build
[andrew@Liger play] ./target/scratch 
-a => Switch(false)
[andrew@Liger play] ./target/scratch -a
-a => Switch(true)
[andrew@Liger play] ./target/scratch -b
Unknown flag: '-b'

Usage: mycmd [-a]

I looked around in the Cargo source, but I couldn't see any obvious places where the error gets diced up. Or maybe the error is dropped and only the usage is printed?

[huonw]

(Pie-in-the-sky extension: "did you mean --release?")

[BurntSushi]

@huonw Issue added. :-)

[alexcrichton]

Cargo's transformation of docopt errors happens here:

cargo/src/cargo/lib.rs

Lines 212 to 218 in 13f32f9

	let code = if e.fatal() {1} else {0};
	let desc = match e {
	docopt::Error::WithProgramUsage(_, s) => s,
	ref e if e.fatal() => e.description().to_string(),
	e => e.to_string(),
	};
	CliError::from_error(human(desc), code)

.

It looks pretty fishy to me, so I'll look into it soon and see if we're just doing something wrong. Thanks anyway @BurntSushi!