No default_value_os for reliably specifying filesystem paths as default arguments

[ssokolow]

Affected Version of clap

2.20.3

Expected Behavior Summary

Functions like validator_os and value_of_os should be complemented with a default_value_os.

Actual Behavior Summary

Only default_value and its variants are provided... which means that it's not possible to specify all valid paths as default values.

Sample Code or Link to Sample Code

// env::current_dir is fallible and default_value can't take a callback for lazy eval, so
// resort to "." but future-proof it in case of esoteric platforms.
// (Not perfect, but to_string_lossy() is necessary without a `default_value_os`)
let lazy_currdir = &Component::CurDir.as_os_str().to_string_lossy();

let matches = App::new(env!("CARGO_PKG_NAME"))
    .version(crate_version!())
    // .about("Description text here")
    // TODO: Add args to control slog logging level
    .arg(arg::with_name("inpath")
        .help("file(s) to use as input")
        .multiple(true)
        .empty_values(false)
        .default_value(lazy_currdir)
        // .validator_os(validators::path_readable)
        .required(true))
    .get_matches();

(It's an excerpt from the "new project" boilerplate I'm putting together)

[kbknapp]

While I agree there could be a default_value_os and I'm not opposed to adding it, do you actually need to add a path with invalid UTF-8? I know it's possible, but that doesn't mean it's practical. I'm asking for my own curiosity 😉

[ssokolow]

At the moment, it's more a matter of wanting correctness in how I glue the "get me the current directory" APIs to clap and wanting the APIs I deal with to be complete.

However, there is actually a set of situations where I expect this to be a problem. Some of the projects I have on hold (currently partially prototyped in old Python code using optparse) embed a shell in a way where default values can get very dynamic... and I intend to use them on folders where round-tripping through different distros over the years has not been kind.

(ie. Folders full of files with Japanese filenames names so mojibake'd that they're not even valid UTF-8)

As-is, to play it safe in those projects, I'll be setting a dummy default value (probably \0) and then reinventing defaulting using match if I don't have default_value_os.

[ssokolow]

I finally got around to looking at this and it seems you implemented default_value_if_os and default_value_ifs_os but, despite the commit message saying it should be there, you neglected to implement default_value_os.

I can't find any evidence of it in the diff and here are the search results from locally-built docs for clap 2.23.1:

[kbknapp]

Oh wow!

[kbknapp]

Thanks for letting me know, I'll get this added shortly!