mr create: Allow email addresses

On large new projects users often know each other by their email
addresses and not their GitLab usernames.  GitLab provides functionality
to lookup a UserID from an email address so it is easy to incorporate
this functionality into lab.

Allow email addresses to be used in the --reviewer and --assignee fields
of 'mr create'.

This also allows email addresses to be used in the --assign and --review
fields of 'mr edit'.

Signed-off-by: Prarit Bhargava <prarit@redhat.com>

cmd/util.go

@@ -605,19 +605,31 @@ func same(a, b []string) bool {
 
 // getUser returns the userID for use with other GitLab API calls.
 func getUserID(user string) *int {
+	var (
+		err    error
+		userID int
+	)
+
 	if user == "" {
 		return nil
 	}
+
 	if user[0] == '@' {
 		user = user[1:]
 	}
-	userID, err := lab.UserIDFromUsername(user)
+
+	if strings.Contains(user, "@") {
+		userID, err = lab.UserIDFromEmail(user)
+	} else {
+		userID, err = lab.UserIDFromUsername(user)
+	}
 	if err != nil {
 		return nil
 	}
 	if userID == -1 {
 		return nil
 	}
+
 	return gitlab.Int(userID)
 }
 

internal/gitlab/gitlab.go

@@ -1499,6 +1499,18 @@ func UserIDFromUsername(username string) (int, error) {
 	return us[0].ID, nil
 }
 
+// UserIDFromEmail returns the associated Users ID in GitLab. This is useful
+// for API calls that allow you to reference a user, but only by ID.
+func UserIDFromEmail(email string) (int, error) {
+	us, _, err := lab.Users.ListUsers(&gitlab.ListUsersOptions{
+		Search: gitlab.String(email),
+	})
+	if err != nil || len(us) == 0 {
+		return -1, err
+	}
+	return us[0].ID, nil
+}
+
 // AddMRDiscussionNote adds a note to an existing MR discussion on GitLab
 func AddMRDiscussionNote(project string, mrNum int, discussionID string, body string) (string, error) {
 	p, err := FindProject(project)