Improve error when file cannot be read

[fgsch]

Use the filename in the output.

[cratelyn]

thank you @fgsch! this is an excellent improvement to our error message.

i have a single, teensy quibble about how we convert our path into a string. other than that, this looks great! ✨

[fgsch]

Somewhat related, I'd like to extend this for InvalidFastlyToml error as well.
I was thinking about copying the from_str implementation into from_file and so I can access the path.
Do you have any suggestions?

[cratelyn]

Somewhat related, I'd like to extend this for InvalidFastlyToml error as well.
I was thinking about copying the from_str implementation into from_file and so I can access the path.
Do you have any suggestions?

for this, i might suggest providing this context elsewhere. threading a path through all of the code that isn't otherwise concerned with the file system doesn't feel quite right, so i'd imagine that we'd have better luck logging a warning near the call-site using something like...

let config = match FastlyConfig::from_file(config_path) {
    Ok(config) => config,
    Err(err) => {
        tracing::warn!(path = ?path, err = %err, "error reading configuration file");
        return Err(err);
    }
}

you can also spell this out with res.map_err(|e| { .. })?, or using something like tap, but that's the core idea. 🙂

[cratelyn]

this looks good to me!