Redirect on changed user and org name (#11649)

* Add redirect for user

* Add redirect for orgs

* Add user redirect test

* Appease linter

* Add comment to DeleteUserRedirect function

* Fix locale changes

* Fix GetUserByParams

* Fix orgAssignment

* Remove debug logging

* Add redirect prompt

* Dont Export DeleteUserRedirect & only use it within a session

* Unexport newUserRedirect

* cleanup

* Fix & Dedub API code

* Format Template

* Add Migration & rm dublicat

* Refactor: unexport newRepoRedirect() & rm dedub del exec

* if this fails we'll need to re-rename the user directory

Co-authored-by: 6543 <6543@obermui.de>
Co-authored-by: zeripath <art27@cantab.net>
Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>

models/user_redirect.go

@@ -0,0 +1,52 @@
+// Copyright 2020 The Gitea Authors. All rights reserved.
+// Use of this source code is governed by a MIT-style
+// license that can be found in the LICENSE file.
+
+package models
+
+import "strings"
+
+// UserRedirect represents that a user name should be redirected to another
+type UserRedirect struct {
+	ID             int64  `xorm:"pk autoincr"`
+	LowerName      string `xorm:"UNIQUE(s) INDEX NOT NULL"`
+	RedirectUserID int64  // userID to redirect to
+}
+
+// LookupUserRedirect look up userID if a user has a redirect name
+func LookupUserRedirect(userName string) (int64, error) {
+	userName = strings.ToLower(userName)
+	redirect := &UserRedirect{LowerName: userName}
+	if has, err := x.Get(redirect); err != nil {
+		return 0, err
+	} else if !has {
+		return 0, ErrUserRedirectNotExist{Name: userName}
+	}
+	return redirect.RedirectUserID, nil
+}
+
+// newUserRedirect create a new user redirect
+func newUserRedirect(e Engine, ID int64, oldUserName, newUserName string) error {
+	oldUserName = strings.ToLower(oldUserName)
+	newUserName = strings.ToLower(newUserName)
+
+	if err := deleteUserRedirect(e, newUserName); err != nil {
+		return err
+	}
+
+	if _, err := e.Insert(&UserRedirect{
+		LowerName:      oldUserName,
+		RedirectUserID: ID,
+	}); err != nil {
+		return err
+	}
+	return nil
+}
+
+// deleteUserRedirect delete any redirect from the specified user name to
+// anything else
+func deleteUserRedirect(e Engine, userName string) error {
+	userName = strings.ToLower(userName)
+	_, err := e.Delete(&UserRedirect{LowerName: userName})
+	return err
+}