Prevent merge messages from being sorted to the top of email chains

Gitea will currrently resend the same message-id for the closed/merged/reopened
messages for issues. This will cause the merged message to leap to the top of an
email chain and become out of sync.

This PR adds specific suffices for these actions.

Fix go-gitea#18560

Signed-off-by: Andrew Thornton <[email protected]>

Author: zeripath

services/mailer/mail.go

@@ -14,6 +14,7 @@ import (
 	"strconv"
 	"strings"
 	texttmpl "text/template"
+	"time"
 
 	"code.gitea.io/gitea/models"
 	repo_model "code.gitea.io/gitea/models/repo"
@@ -298,13 +299,15 @@ func composeIssueCommentMessages(ctx *mailCommentContext, lang string, recipient
 	}
 
 	// Make sure to compose independent messages to avoid leaking user emails
+	msgID := createReference(ctx.Issue, ctx.Comment, ctx.ActionType)
+	reference := createReference(ctx.Issue, nil, models.ActionType(0))
+
 	msgs := make([]*Message, 0, len(recipients))
 	for _, recipient := range recipients {
 		msg := NewMessageFrom([]string{recipient.Email}, ctx.Doer.DisplayName(), setting.MailService.FromEmail, subject, mailBody.String())
 		msg.Info = fmt.Sprintf("Subject: %s, %s", subject, info)
 
-		msg.SetHeader("Message-ID", "<"+createReference(ctx.Issue, ctx.Comment)+">")
-		reference := createReference(ctx.Issue, nil)
+		msg.SetHeader("Message-ID", "<"+msgID+">")
 		msg.SetHeader("In-Reply-To", "<"+reference+">")
 		msg.SetHeader("References", "<"+reference+">")
 
@@ -318,7 +321,7 @@ func composeIssueCommentMessages(ctx *mailCommentContext, lang string, recipient
 	return msgs, nil
 }
 
-func createReference(issue *models.Issue, comment *models.Comment) string {
+func createReference(issue *models.Issue, comment *models.Comment, actionType models.ActionType) string {
 	var path string
 	if issue.IsPull {
 		path = "pulls"
@@ -329,6 +332,17 @@ func createReference(issue *models.Issue, comment *models.Comment) string {
 	var extra string
 	if comment != nil {
 		extra = fmt.Sprintf("/comment/%d", comment.ID)
+	} else {
+		switch actionType {
+		case models.ActionCloseIssue, models.ActionClosePullRequest:
+			extra = fmt.Sprintf("/close/%d", time.Now().UnixNano()/1e6)
+		case models.ActionReopenIssue, models.ActionReopenPullRequest:
+			extra = fmt.Sprintf("/reopen/%d", time.Now().UnixNano()/1e6)
+		case models.ActionMergePullRequest:
+			extra = fmt.Sprintf("/merge/%d", time.Now().UnixNano()/1e6)
+		case models.ActionPullRequestReadyForReview:
+			extra = fmt.Sprintf("/ready/%d", time.Now().UnixNano()/1e6)
+		}
 	}
 
 	return fmt.Sprintf("%s/%s/%d%s@%s", issue.Repo.FullName(), path, issue.Index, extra, setting.Domain)