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use std::error::Error;
fn main() {
if let Err(e) = fallible_main() {
eprintln!("ERROR: {}", e);
let mut err = e.source();
while let Some(underlying) = err {
eprintln!("caused by: {}", underlying);
err = underlying.source();
}
}
}
fn fallible_main() -> Result<(), HelloError> {
let args = Args::parse();
println!("hello, {}", args.whom()?);
Ok(())
}
use clap::Parser;
use std::fs::read;
use std::path::PathBuf;
#[derive(Parser)]
struct Args {
#[clap(default_value = "world")]
whom: String,
#[clap(short, long)]
filename: Option<PathBuf>,
}
impl Args {
fn whom(&self) -> Result<String, HelloError> {
if let Some(filename) = &self.filename {
let data = read(&filename)
.map_err(|e| {
HelloError::Read(filename.clone(), e)
})?;
let whom = String::from_utf8(data)
.map_err(|e| {
HelloError::Utf8(filename.clone(), e)
})?;
Ok(whom.trim().to_string())
} else {
Ok(self.whom.clone())
}
}
}
#[derive(Debug, thiserror::Error)]
enum HelloError {
#[error("failed to read file {0}")]
Read(PathBuf, #[source] std::io::Error),
#[error("failed to parse file {0} as UTF-8")]
Utf8(PathBuf, #[source] std::string::FromUtf8Error),
}
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