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With the ClapSerde procedural macro both clap and serde can be derived from a struct.
Then the struct can be parsed from clap and serde sources as in a layered config: the last
source has the precedence.
Args::from(serde_parsed) .merge_clap();
In the snippet the precedence is:
- Command line from clap;
- Config file from serde;
- Default values.
In this example we define a struct which derives both clap and serde. The struct has various parameter type and also various attributes on its fields.
Finally we parse the structure from a YAML file with serde and then from command line with clap. The arguments from clap will override those from serde; the default value will be used if no source contained the field.
use clap_serde_derive::{ clap::{self, ArgAction}, serde::Serialize, ClapSerde, }; #[derive(ClapSerde, Serialize)] #[derive(Debug)] #[command(author, version, about)] pub struct Args { /// Input files pub input: Vec<std::path::PathBuf>, /// String argument #[arg(short, long)] name: String, /// Skip serde deserialize #[default(13)] #[serde(skip_deserializing)] #[arg(long = "num")] pub clap_num: u32, /// Skip clap #[serde(rename = "number")] #[arg(skip)] pub serde_num: u32, /// Recursive fields #[clap_serde] #[command(flatten)] pub suboptions: SubConfig, } #[derive(ClapSerde, Serialize)] #[derive(Debug)] pub struct SubConfig { #[default(true)] #[arg(long = "no-flag", action = ArgAction::SetFalse)] pub flag: bool, } let args = Args::from(serde_yaml::from_str::<<Args as ClapSerde>::Opt>("number: 12").unwrap()) .merge_clap(); assert_eq!( serde_yaml::to_string(&args).unwrap(), serde_yaml::to_string(&Args { serde_num: 12, clap_num: 13, ..Args::default() }) .unwrap(), );
You can easily take the config file path from command line in this way.
use std::{fs::File, io::BufReader}; use clap_serde_derive::{ clap::{self, Parser}, ClapSerde, }; #[derive(Parser)] #[command(author, version, about)] struct Args { /// Input files input: Vec<std::path::PathBuf>, /// Config file #[arg(short, long = "config", default_value = "config.yml")] config_path: std::path::PathBuf, /// Rest of arguments #[command(flatten)] pub config: <Config as ClapSerde>::Opt, } #[derive(ClapSerde)] struct Config { /// String argument #[arg(short, long)] name: String, } // Parse whole args with clap let mut args = Args::parse(); // Get config file let config = if let Ok(f) = File::open(&args.config_path) { // Parse config with serde match serde_yaml::from_reader::<_, <Config as ClapSerde>::Opt>(BufReader::new(f)) { // merge config already parsed from clap Ok(config) => Config::from(config).merge(&mut args.config), Err(err) => panic!("Error in configuration file:\n{}", err), } } else { // If there is not config file return only config parsed from clap Config::from(&mut args.config) };