Would appreciate this change as well

Thanks for the PR!

The regex used in this library matches the one used by GitHub, so while it's not ideal, I think I'd rather keep the default aligned with the validation GitHub uses.

If we can make the parsing configurable, I would be open to making this available as an option (either a flag for the more permissive regex, or the ability to provide a custom email regex). The same applies to supporting GitLab syntax (#13) — while I think the default should align to GitHub's implementation as it's the most widespread, I'd be up for supporting more variants.

Hey, I added a Matcher interface to make the parsing extendable. There are no breaking changes to the API and the Matchers are totally optional. The extended API would look something like this:

var lessRestrictiveEmailRegexp = regexp.MustCompile("^[a-zA-Z0-9.!#$%&'*+\\/=?^_`{|}~-]+@[a-zA-Z0-9](?:[a-zA-Z0-9-]{0,61}[a-zA-Z0-9])?(?:\\.[a-zA-Z0-9](?:[a-zA-Z0-9-]{0,61}[a-zA-Z0-9])?)*$")

func MatchLessRestrictiveEmail(s string) (codeowners.Owner, error) {
	match := lessRestrictiveEmailRegexp.FindStringSubmatch(s)
	if match == nil {
		return codeowners.Owner{}, codeowners.ErrNoMatch
	}

	return codeowners.Owner{
		Value: match[0],
		Type:  codeowners.EmailOwner,
	}, nil
}

var lessRestrictiveEmailMatcher = codeowners.MatcherFunc(MatchLessRestrictiveEmail)

func main() {
	f, err := os.Open("CODEOWNERS")
	if err != nil {
		log.Fatal(err)
	}

	_, err = codeowners.ParseFile(f, lessRestrictiveEmailMatcher)
	if err != nil {
		log.Fatal(err)
	}
}

You could also just extend the default matcher:

func main() {
	f, err := os.Open("CODEOWNERS")
	if err != nil {
		log.Fatal(err)
	}

	_, err = codeowners.ParseFile(f, append(codeowners.DefaultMatchers, lessRestrictiveEmailMatcher)...)
	if err != nil {
		log.Fatal(err)
	}
}

Hey, could this please get another round of review. I'm looking forward to it being merged. If something doesn't meet project standards, just let me know.

@hmarr I would highly appreciate it if you could take a look at this PR

Hey @haveachin, sorry for taking so long to look at this. Thanks for the work on this—overall it looks great!

I pushed a follow-up commit in #23 — have a quick look at let me know what you think.

@haveachin my latest commit is included in this PR now—would you mind having a look and checking it meets your needs before I merge?

LGTM

Would be great if this could be merged 😄 Thanks to everyone involved for their work 😄

Sorry for taking so long to merge this, thanks for the contribution @haveachin!