Add breaking email restrictions checker in doctor (#19903)

* Add breaking change check in doctor

- This patch introduces a new kind of doctor type, breaking. This file
is made to register checks that helps with detecting when a breaking
change might impact a Gitea instance.
- For now the only check here(and the reason of creating this) is to
check if all users in the database has a valid email address, which
might not be the case after
https://github.com/go-gitea/gitea/pull/17688. This _simply_ uses the
validation function to detect and report these cases.
- Helps admins with detecting #19897.
- I have no clue which priority should be and IsDefault is true, because
when breaking change happen and we have a doctor check for it, we can
say "run `gitea doctor` to help you with this and maybe you find other
errors 😉".

* Makes no sense tbh

* Fix copyright

* Update modules/doctor/breaking.go

Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>

Co-authored-by: techknowlogick <matti@mdranta.net>
Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>
Co-authored-by: techknowlogick <techknowlogick@gitea.io>

modules/doctor/breaking.go

@@ -0,0 +1,69 @@
+// Copyright 2022 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 doctor
+
+import (
+	"context"
+	"fmt"
+
+	"code.gitea.io/gitea/models/db"
+	"code.gitea.io/gitea/models/user"
+	"code.gitea.io/gitea/modules/log"
+
+	"xorm.io/builder"
+)
+
+func iterateUserAccounts(ctx context.Context, each func(*user.User) error) error {
+	err := db.Iterate(
+		ctx,
+		new(user.User),
+		builder.Gt{"id": 0},
+		func(idx int, bean interface{}) error {
+			return each(bean.(*user.User))
+		},
+	)
+	return err
+}
+
+// Since 1.16.4 new restrictions has been set on email addresses. However users with invalid email
+// addresses would be currently facing a error due to their invalid email address.
+// Ref: https://github.com/go-gitea/gitea/pull/19085 & https://github.com/go-gitea/gitea/pull/17688
+func checkUserEmail(ctx context.Context, logger log.Logger, _ bool) error {
+	// We could use quirky SQL to get all users that start without a [a-zA-Z0-9], but that would mean
+	// DB provider-specific SQL and only works _now_. So instead we iterate trough all user accounts and
+	// use the user.ValidateEmail function to be future-proof.
+	var invalidUserCount int64
+	if err := iterateUserAccounts(ctx, func(u *user.User) error {
+		// Only check for users, skip
+		if u.Type != user.UserTypeIndividual {
+			return nil
+		}
+
+		if err := user.ValidateEmail(u.Email); err != nil {
+			invalidUserCount++
+			logger.Warn("User[id=%d name=%q] have not a valid e-mail: %v", u.ID, u.Name, err)
+		}
+		return nil
+	}); err != nil {
+		return fmt.Errorf("iterateUserAccounts: %v", err)
+	}
+
+	if invalidUserCount == 0 {
+		logger.Info("All users have a valid e-mail.")
+	} else {
+		logger.Warn("%d user(s) have a non-valid e-mail.", invalidUserCount)
+	}
+	return nil
+}
+
+func init() {
+	Register(&Check{
+		Title:     "Check if users has an valid email address",
+		Name:      "check-user-email",
+		IsDefault: false,
+		Run:       checkUserEmail,
+		Priority:  9,
+	})
+}