Prevent merge messages from being sorted to the top of email chains (#18566) (#18588)

Backport #18566

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 #18560

Signed-off-by: Andrew Thornton <art27@cantab.net>

services/mailer/mail_test.go

@@ -6,7 +6,9 @@ package mailer
 
 import (
 	"bytes"
+	"fmt"
 	"html/template"
+	"strings"
 	"testing"
 	texttmpl "text/template"
 
@@ -15,7 +17,6 @@ import (
 	"code.gitea.io/gitea/models/unittest"
 	user_model "code.gitea.io/gitea/models/user"
 	"code.gitea.io/gitea/modules/setting"
-
 	"github.com/stretchr/testify/assert"
 )
 
@@ -236,3 +237,115 @@ func TestGenerateAdditionalHeaders(t *testing.T) {
 		}
 	}
 }
+
+func Test_createReference(t *testing.T) {
+	_, _, issue, comment := prepareMailerTest(t)
+	_, _, pullIssue, _ := prepareMailerTest(t)
+	pullIssue.IsPull = true
+
+	type args struct {
+		issue      *models.Issue
+		comment    *models.Comment
+		actionType models.ActionType
+	}
+	tests := []struct {
+		name   string
+		args   args
+		prefix string
+		suffix string
+	}{
+		{
+			name: "Open Issue",
+			args: args{
+				issue:      issue,
+				actionType: models.ActionCreateIssue,
+			},
+			prefix: fmt.Sprintf("%s/issues/%d@%s", issue.Repo.FullName(), issue.Index, setting.Domain),
+		},
+		{
+			name: "Open Pull",
+			args: args{
+				issue:      pullIssue,
+				actionType: models.ActionCreatePullRequest,
+			},
+			prefix: fmt.Sprintf("%s/pulls/%d@%s", issue.Repo.FullName(), issue.Index, setting.Domain),
+		},
+		{
+			name: "Comment Issue",
+			args: args{
+				issue:      issue,
+				comment:    comment,
+				actionType: models.ActionCommentIssue,
+			},
+			prefix: fmt.Sprintf("%s/issues/%d/comment/%d@%s", issue.Repo.FullName(), issue.Index, comment.ID, setting.Domain),
+		},
+		{
+			name: "Comment Pull",
+			args: args{
+				issue:      pullIssue,
+				comment:    comment,
+				actionType: models.ActionCommentPull,
+			},
+			prefix: fmt.Sprintf("%s/pulls/%d/comment/%d@%s", issue.Repo.FullName(), issue.Index, comment.ID, setting.Domain),
+		},
+		{
+			name: "Close Issue",
+			args: args{
+				issue:      issue,
+				actionType: models.ActionCloseIssue,
+			},
+			prefix: fmt.Sprintf("%s/issues/%d/close/", issue.Repo.FullName(), issue.Index),
+		},
+		{
+			name: "Close Pull",
+			args: args{
+				issue:      pullIssue,
+				actionType: models.ActionClosePullRequest,
+			},
+			prefix: fmt.Sprintf("%s/pulls/%d/close/", issue.Repo.FullName(), issue.Index),
+		},
+		{
+			name: "Reopen Issue",
+			args: args{
+				issue:      issue,
+				actionType: models.ActionReopenIssue,
+			},
+			prefix: fmt.Sprintf("%s/issues/%d/reopen/", issue.Repo.FullName(), issue.Index),
+		},
+		{
+			name: "Reopen Pull",
+			args: args{
+				issue:      pullIssue,
+				actionType: models.ActionReopenPullRequest,
+			},
+			prefix: fmt.Sprintf("%s/pulls/%d/reopen/", issue.Repo.FullName(), issue.Index),
+		},
+		{
+			name: "Merge Pull",
+			args: args{
+				issue:      pullIssue,
+				actionType: models.ActionMergePullRequest,
+			},
+			prefix: fmt.Sprintf("%s/pulls/%d/merge/", issue.Repo.FullName(), issue.Index),
+		},
+		{
+			name: "Ready Pull",
+			args: args{
+				issue:      pullIssue,
+				actionType: models.ActionPullRequestReadyForReview,
+			},
+			prefix: fmt.Sprintf("%s/pulls/%d/ready/", issue.Repo.FullName(), issue.Index),
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got := createReference(tt.args.issue, tt.args.comment, tt.args.actionType)
+			if !strings.HasPrefix(got, tt.prefix) {
+				t.Errorf("createReference() = %v, want %v", got, tt.prefix)
+			}
+			if !strings.HasSuffix(got, tt.suffix) {
+				t.Errorf("createReference() = %v, want %v", got, tt.prefix)
+			}
+		})
+	}
+}