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//! Demonstrates usage of `Error::caused` method. This method enables chaining errors
//! like `ResultExt::chain_err` but doesn't require the presence of a `Result` wrapper.
#[macro_use]
extern crate error_chain;
use std::fs::File;
mod errors {
use super::LaunchStage;
use std::io;
error_chain! {
foreign_links {
Io(io::Error) #[doc = "Error during IO"];
}
errors {
Launch(phase: LaunchStage) {
description("An error occurred during startup")
display("Startup aborted: {:?} did not complete successfully", phase)
}
ConfigLoad(path: String) {
description("Config file not found")
display("Unable to read file `{}`", path)
}
}
}
impl From<LaunchStage> for ErrorKind {
fn from(v: LaunchStage) -> Self {
ErrorKind::Launch(v)
}
}
}
pub use errors::*;
#[derive(Debug, Clone, PartialEq, Eq)]
pub enum LaunchStage {
ConfigLoad,
ConfigParse,
ConfigResolve,
}
/// Read the service config from the file specified.
fn load_config(rel_path: &str) -> Result<()> {
File::open(rel_path)
.map(|_| ())
.chain_err(|| ErrorKind::ConfigLoad(rel_path.to_string()))
}
/// Launch the service.
fn launch(rel_path: &str) -> Result<()> {
load_config(rel_path).map_err(|e| match e {
e @ Error(ErrorKind::ConfigLoad(_), _) => e.chain_err(|| LaunchStage::ConfigLoad),
e => e.chain_err(|| "Unknown failure"),
})
}
fn main() {
let chain = launch("does_not_exist.json").unwrap_err();
for err in chain.iter() {
println!("{}", err);
}
}