facet-args

Crates.io	facet-args
lib.rs	facet-args
version	0.29.0
created_at	2025-04-10 03:39:14.09265+00
updated_at	2025-09-17 18:24:50.719671+00
description	Command-line argument parsing for the facet ecosystem
homepage
repository	https://github.com/facet-rs/facet-args
max_upload_size
id	1627609
size	86,483

Amos Wenger (fasterthanlime)

documentation

https://docs.rs/facet-args

README

facet-args

Provides CLI argument parsing (WIP).

use facet_pretty::FacetPretty;
use facet::Facet;

#[derive(Facet)]
struct Args {
    #[facet(positional)]
    path: String,

    #[facet(named, short = 'v')]
    verbose: bool,

    #[facet(named, short = 'j')]
    concurrency: usize,
}

# fn main() -> Result<(), Box<dyn std::error::Error>> {
let args: Args = facet_args::from_slice(&["--verbose", "-j", "14", "example.rs"])?;
eprintln!("args: {}", args.pretty());
Ok(())
# }

Behavior

The behavior of facet-args is still in flux, but here are the broad strokes:

We're always parsing to a struct (not an enum, vec etc.)
The struct we're parsing to is always owned — no borrowing happening here, it gets too complicated with &'slice [&'text str]
Arguments are either positional or named — fields lacking either annotation are ignored
Accepted syntaxes for short flags are: short = 'v' and short = "v" (where v can be any letter)
positional args of type Vec (or anything that has a Def::List) will soak up all the positional arguments — if followed by positional arguments of type String for example, those will never get filled
After parsing every available argument, uninitialized struct fields are filled with their default value if they have facet(default) set: this includes Vec.