File Not Found : Meaningful error messages to identify exact issue

[dumindu]

Folder structure

├── Cargo.toml
└── src
   ├── hello.txt
   └── main.rs

main.rs

use std::fs::File;

fn main() {
    let _file = File::open("hello.txt").expect("file not found");
    println!("{}", "Hello World!");
}

Error

Finished dev [unoptimized + debuginfo] target(s) in 0.0 secs
Running `target/debug/read_file`

thread 'main' panicked at 'file not found: Error { repr: Os { code: 2, message: "No such file or directory" } }', src/libcore/result.rs:906:4
stack backtrace:
   0:        0x10c4135f3 - std::sys::imp::backtrace::tracing::imp::unwind_backtrace::h3160619f5df0b429
   1:        0x10c40fe30 - std::sys_common::backtrace::_print::h1120036038320f80
   2:        0x10c4149e3 - std::panicking::default_hook::{{closure}}::hb299632e05329bb5
   3:        0x10c4146e2 - std::panicking::default_hook::h00107bf0a85963b4
   4:        0x10c414e32 - std::panicking::rust_panic_with_hook::hd9c6ad24a775c34c
   5:        0x10c414d14 - std::panicking::begin_panic::h49e0d0a8e06c5478
   6:        0x10c414be2 - std::panicking::begin_panic_fmt::h1694ee0907f92803
   7:        0x10c414b4a - rust_begin_unwind
   8:        0x10c4462c3 - core::panicking::panic_fmt::h2d82c8387bfa11ba
   9:        0x10c407c4c - core::result::unwrap_failed::he129861d908021e0
  10:        0x10c407f28 - <core::result::Result<T, E>>::expect::h1db24ec21ca210c8
  11:        0x10c40841e - read_file::main::hfb1b70fb4d7706fb
  12:        0x10c444edc - __rust_maybe_catch_panic
  13:        0x10c415128 - std::rt::lang_start::h3fa27024f6a74294
  14:        0x10c408509 - main

Process finished with exit code 101

Expected error message

No such file in <absolute path>

[abonander]

This could be expanded to other error messages as well. This will probably need to be done separately for each platform.

[dumindu]

fn main() {
    let content = include_str!("not_existing_file.txt");
    println!("{}", content);
}

gives
error: couldn't read src/not_existing_file.txt: No such file or directory (os error 2).
At least it gives the root directory

[KasMA1990]

Here is some prior discussion of the same issue :)

[ssokolow]

I'd prefer if, rather than "No such file on <absolute path>", it left the message unaltered and appended something like "(With working directory <absolute path)" to the end.

That way, it doesn't disadvantage situations where the greppability of the error string or the requested path are significant to how easy it is to debug.

[dtolnay]

There are a lot of good points for either side in Add filename information to io::Error. I am not confident that we will be able to reach a consensus here, so I would prefer to follow up in an RFC. I think the most likely way to make progress on this would be to do a thorough and balanced writeup of the tradeoffs, survey how libraries are using io::Error in practice, develop a prototype implementation, provide benchmarks and an assessment of how those impact various use cases, and make a concrete recommendation for what approach to pursue in the standard library that balances everybody's needs.