Hi!
I have been scratching my head with a weird segfault while using the docopt crate. The code is below (or at https://github.com/rekka/docopt_test). To summarize, when parsing an invalid command line input, the program segfaults instead of printing the error message. But this does not happen when I don't use struct Args from lib.rs but from main.rs, or if I change the order of the struct fields! I have no idea whose bug this is so I am not even sure where to report it.
First my compiler (I'm on a Mac).
$ rustc --version && cargo --version
rustc 1.10.0 (cfcb716cf 2016-07-03)
cargo 0.11.0-nightly (259324c 2016-05-20)
Now the code. Clone from https://github.com/rekka/docopt_test.
File main.rs
extern crate docopt;
extern crate rustc_serialize;
extern crate docopt_test;
const USAGE: &'static str = "
Test
Usage:
test [options] [<test>]
Options:
-n=INT Integer
";
#[derive(Debug, RustcDecodable)]
pub struct Args {
arg_test: Option<String>,
flag_n: Option<usize>,
}
fn main() {
let args: docopt_test::Args = docopt::Docopt::new(USAGE)
.and_then(|d| d.decode())
.unwrap_or_else(|e| e.exit());
println!("{:?}", args.flag_n);
}
file lib.rs
extern crate rustc_serialize;
#[derive(Debug, RustcDecodable)]
pub struct Args {
pub arg_test: Option<String>,
pub flag_n: Option<usize>,
}
Compiling this and running with invalid input segfaults:
$ cargo build && target/debug/docopt_test -nm
[1] 88206 segmentation fault target/debug/docopt_test -nm
Other inputs are reported properly:
$ cargo build && target/debug/docopt_test -n
Expected argument for flag '-n' but reached end of arguments.
Usage:
test [options] [<test>]
$ cargo build && target/debug/docopt_test -n8
Some(8)
But if I use the local struct Args by changing the docopt call to
let args: Args = docopt::Docopt::new(USAGE)
or just reorder the fields in docopt_test::Args like so
pub struct Args {
pub flag_n: Option<usize>,
pub arg_test: Option<String>,
}
the program yields the correct output:
$ cargo build && target/debug/docopt_test -nm
...
Could not decode 'm' to usize for '-n'.
The docopt crate does not seem to have any unsafe code. What is causing this?
Any tips are greatly appreciated!