Rewrite delivery of issue and comment mails (#9009)

* Mail issue subscribers, rework the function

* Simplify a little more

* Fix unused variable

* Refactor mail delivery to avoid heavy load on server

* Avoid splitting into too many goroutines

* Fix comments and optimize GetMaileableUsersByIDs()

* Fix return on errors

1 files changed, 13 insertions, 0 deletions

diff --git a/models/issue.go b/models/issue.go
index 1fe9140dad..0113f0a404 100644
--- a/models/issue.go
+++ b/models/issue.go
@@ -1219,6 +1219,19 @@ func Issues(opts *IssuesOptions) ([]*Issue, error) {
 	return issues, nil
 }
 
+// GetParticipantsIDsByIssueID returns the IDs of all users who participated in comments of an issue,
+// but skips joining with `user` for performance reasons.
+// User permissions must be verified elsewhere if required.
+func GetParticipantsIDsByIssueID(issueID int64) ([]int64, error) {
+	userIDs := make([]int64, 0, 5)
+	return userIDs, x.Table("comment").
+		Cols("poster_id").
+		Where("issue_id = ?", issueID).
+		And("type in (?,?,?)", CommentTypeComment, CommentTypeCode, CommentTypeReview).
+		Distinct("poster_id").
+		Find(&userIDs)
+}
+
 // GetParticipantsByIssueID returns all users who are participated in comments of an issue.
 func GetParticipantsByIssueID(issueID int64) ([]*User, error) {
 	return getParticipantsByIssueID(x, issueID)