Support rust-cross

[epage]

From assert-rs/assert_cmd#139

It would be nice to mention that when running tests in cross, one needs to prepend their command with the value contained in CARGO_TARGET_*_RUNNER i.e qemu-aarch64 xh

fn find_runner() -> Option<String> {
    for (key, value) in std::env::vars() {
        if key.starts_with("CARGO_TARGET_") && key.ends_with("_RUNNER") && value.contains("qemu") {
            return Some(value);
        }
    }
    None
}

fn get_base_command() -> Command {
    let mut cmd;
    let path = assert_cmd::cargo::cargo_bin("xh");
    if let Some(runner) = find_runner() {
        cmd = Command::new(runner);
        cmd.arg(path);
    } else {
        cmd = Command::new(path);
    }
    cmd
}

Also, see ducaale/xh#190 (comment)

[tmatilai]

How could this be used with TestCases? There is default_bin_path(), but no way to push args, as far as I see.

[epage]

I've fixed the title to better reflect the situation. I don't use cross, so I don't have test cases or have a feel for what all the needs are.

[tmatilai]

So when running with cross, the tested command should be in the form like :

/linux-runner armv7 /target/armv7-unknown-linux-gnueabihf/debug/command --some args

The "wrapper" prefix is taken from the CARGO_TARGET_ARMV7_UNKNOWN_LINUX_GNUEABIHF_RUNNER env variable.

I'm not very experienced with Rust, and not familiar with the trycmd code base, so I might have hard times figuring out a way to add ability to optionally prepend commands. But I can take a look later if you give some hints. 🙂