README.md

try_io_result

What it does

Checks for ? operators applied to values of type std::io::Result.

Why is this bad?

Returning a std::io::Result could mean relevant context (e.g., files or paths involved) is lost. The problem is discussed under "Verbose IO errors" in Yoshua Wuyts' Error Handling Survey.

Known problems

No interprocedural analysis is done. So if context is added by the caller, it will go unnoticed.

Example

fn foo() -> std::io::Result<()> {
    let _ = File::open("/dev/null")?;
    Ok(())
}

Use instead:

use anyhow::Context;
fn foo() -> anyhow::Result<()> {
    let _ = File::open("/dev/null").with_context(|| "could not open `/dev/null`")?;
    Ok(())
}