git-ext: Better handling of "not found" errors

[cloudhead]

Currently I have code like this:

        match repo.reference(remote, sigref) {
            Err(git_ext::Error::Git(e)) if git_ext::is_not_found_err(&e) => None,
            Err(git_ext::Error::NotFound(_)) => None,
            Err(e) => return Err(e.into()),
...
        };

It would be nice if git_ext::Error simply had a is_not_found(&self) -> bool method, so that it could be converted to:

        match repo.reference(remote, sigref) {
            Err(e) if e.is_not_found() => None,
            Err(e) => return Err(e.into()),
...
        };

This is the pattern I've been using with my other error types.

[FintanH]

I'm a bit confused. There's no git_ext::Error?

There's one for blob.rs and one for name.rs. Neither of those pertain to a function called reference.

However, we often do this:

use std_ext::ResultExt as _;
use git_ext as ext;

repo.reference(remote, sigref).or_matches(ext::is_not_found, || None)

[FintanH]

Ok, after the discussion here, I think we should not re-export the Error and NotFound errors from blob.rs because that error is suppose to only pertain to that small API.

[cloudhead]

Yes, it's re-exported from the top-level crate, so I know it as git_ext::Error :D

[cloudhead]

In that case I think we could create our own Git error type inside heartwood, and use that. No need to change anything with git_ext, just not export the errors from the top level, or alias them as eg. BlobError if we do.

[cloudhead]

Actually it would still be useful to have that is_not_found method, for when we use the git_ext blob functions.