Add option to change mail from user display name (#31528)

Make it posible to let mails show e.g.:

`Max Musternam (via gitea.kithara.com) <gitea@kithara.com>`

Docs: https://gitea.com/gitea/docs/pulls/23

---
*Sponsored by Kithara Software GmbH*

services/mailer/mail.go

@@ -314,7 +314,7 @@ func composeIssueCommentMessages(ctx *mailCommentContext, lang string, recipient
 	for _, recipient := range recipients {
 		msg := NewMessageFrom(
 			recipient.Email,
-			ctx.Doer.GetCompleteName(),
+			fromDisplayName(ctx.Doer),
 			setting.MailService.FromEmail,
 			subject,
 			mailBody.String(),
@@ -536,3 +536,19 @@ func actionToTemplate(issue *issues_model.Issue, actionType activities_model.Act
 	}
 	return typeName, name, template
 }
+
+func fromDisplayName(u *user_model.User) string {
+	if setting.MailService.FromDisplayNameFormatTemplate != nil {
+		var ctx bytes.Buffer
+		err := setting.MailService.FromDisplayNameFormatTemplate.Execute(&ctx, map[string]any{
+			"DisplayName": u.DisplayName(),
+			"AppName":     setting.AppName,
+			"Domain":      setting.Domain,
+		})
+		if err == nil {
+			return mime.QEncoding.Encode("utf-8", ctx.String())
+		}
+		log.Error("fromDisplayName: %w", err)
+	}
+	return u.GetCompleteName()
+}

services/mailer/mail_release.go

@@ -86,7 +86,7 @@ func mailNewRelease(ctx context.Context, lang string, tos []*user_model.User, re
 	}
 
 	msgs := make([]*Message, 0, len(tos))
-	publisherName := rel.Publisher.DisplayName()
+	publisherName := fromDisplayName(rel.Publisher)
 	msgID := generateMessageIDForRelease(rel)
 	for _, to := range tos {
 		msg := NewMessageFrom(to.EmailTo(), publisherName, setting.MailService.FromEmail, subject, mailBody.String())

services/mailer/mail_repo.go

@@ -79,7 +79,7 @@ func sendRepoTransferNotifyMailPerLang(lang string, newOwner, doer *user_model.U
 	}
 
 	for _, to := range emailTos {
-		msg := NewMessage(to.EmailTo(), subject, content.String())
+		msg := NewMessageFrom(to.EmailTo(), fromDisplayName(doer), setting.MailService.FromEmail, subject, content.String())
 		msg.Info = fmt.Sprintf("UID: %d, repository pending transfer notification", newOwner.ID)
 
 		SendAsync(msg)

services/mailer/mail_test.go

@@ -403,3 +403,51 @@ func TestGenerateMessageIDForRelease(t *testing.T) {
 	})
 	assert.Equal(t, "<owner/repo/releases/1@localhost>", msgID)
 }
+
+func TestFromDisplayName(t *testing.T) {
+	template, err := texttmpl.New("mailFrom").Parse("{{ .DisplayName }}")
+	assert.NoError(t, err)
+	setting.MailService = &setting.Mailer{FromDisplayNameFormatTemplate: template}
+	defer func() { setting.MailService = nil }()
+
+	tests := []struct {
+		userDisplayName string
+		fromDisplayName string
+	}{{
+		userDisplayName: "test",
+		fromDisplayName: "test",
+	}, {
+		userDisplayName: "Hi Its <Mee>",
+		fromDisplayName: "Hi Its <Mee>",
+	}, {
+		userDisplayName: "Æsir",
+		fromDisplayName: "=?utf-8?q?=C3=86sir?=",
+	}, {
+		userDisplayName: "new😀user",
+		fromDisplayName: "=?utf-8?q?new=F0=9F=98=80user?=",
+	}}
+
+	for _, tc := range tests {
+		t.Run(tc.userDisplayName, func(t *testing.T) {
+			user := &user_model.User{FullName: tc.userDisplayName, Name: "tmp"}
+			got := fromDisplayName(user)
+			assert.EqualValues(t, tc.fromDisplayName, got)
+		})
+	}
+
+	t.Run("template with all available vars", func(t *testing.T) {
+		template, err = texttmpl.New("mailFrom").Parse("{{ .DisplayName }} (by {{ .AppName }} on [{{ .Domain }}])")
+		assert.NoError(t, err)
+		setting.MailService = &setting.Mailer{FromDisplayNameFormatTemplate: template}
+		oldAppName := setting.AppName
+		setting.AppName = "Code IT"
+		oldDomain := setting.Domain
+		setting.Domain = "code.it"
+		defer func() {
+			setting.AppName = oldAppName
+			setting.Domain = oldDomain
+		}()
+
+		assert.EqualValues(t, "Mister X (by Code IT on [code.it])", fromDisplayName(&user_model.User{FullName: "Mister X", Name: "tmp"}))
+	})
+}