Slack webhook channel name cannot be empty or just contain an hashtag (#4786)

modules/auth/repo_form.go

@@ -10,6 +10,8 @@ import (
 	"strings"
 
 	"code.gitea.io/gitea/models"
+	"code.gitea.io/gitea/routers/utils"
+
 	"github.com/Unknwon/com"
 	"github.com/go-macaron/binding"
 	"gopkg.in/macaron.v1"
@@ -225,6 +227,11 @@ func (f *NewSlackHookForm) Validate(ctx *macaron.Context, errs binding.Errors) b
 	return validate(errs, ctx.Data, f, ctx.Locale)
 }
 
+// HasInvalidChannel validates the channel name is in the right format
+func (f NewSlackHookForm) HasInvalidChannel() bool {
+	return !utils.IsValidSlackChannel(f.Channel)
+}
+
 // NewDiscordHookForm form for creating discord hook
 type NewDiscordHookForm struct {
 	PayloadURL string `binding:"Required;ValidUrl"`