[MM-53428] Delete empty drafts on upsert (#24046)

* [MM-53428] Delete empty drafts on upsert

* Add migrations to fix existing drafts

* Fix CI

* Delete empty drafts entirely from the DB

* Fix lint

* Implement batch migration for deleting drafts

* Missing store layers

* Add updated mock

* Remove unnecessary test

* PR feedback

* Add check for cluster migration

* Fix MySQL

* Don't check for len<2

* Bit of PR feedback

* Use query builder for parameters

* PR feedback

* More PR feedback

* Merge'd

* unit test GetLastCreateAtAndUserIdValuesForEmptyDraftsMigration

* simplified builder interface

* fix DeleteEmptyDraftsByCreateAtAndUserId for MySQL

* rework as batch migration worker

* fix typo

* log ip address on version mismatches too

* simplify reset semantics

* remove trace log in favour of low spam

* document parameters for clarity

---------

Co-authored-by: Mattermost Build <build@mattermost.com>
Co-authored-by: Jesse Hallam <jesse.hallam@gmail.com>

server/channels/app/draft.go

@@ -56,6 +56,15 @@ func (a *App) UpsertDraft(c *request.Context, draft *model.Draft, connectionID s
 		return nil, model.NewAppError("CreateDraft", "app.user.get.app_error", nil, nErr.Error(), http.StatusInternalServerError)
 	}
 
+	// If the draft is empty, just delete it
+	if draft.Message == "" {
+		deleteErr := a.Srv().Store().Draft().Delete(draft.UserId, draft.ChannelId, draft.RootId)
+		if deleteErr != nil {
+			return nil, model.NewAppError("CreateDraft", "app.draft.save.app_error", nil, deleteErr.Error(), http.StatusInternalServerError)
+		}
+		return nil, nil
+	}
+
 	dt, nErr := a.Srv().Store().Draft().Upsert(draft)
 	if nErr != nil {
 		return nil, model.NewAppError("CreateDraft", "app.draft.save.app_error", nil, nErr.Error(), http.StatusInternalServerError)