Make every not exist error unwrappable to a fs.ErrNotExist (#20891)

A lot of our code is repeatedly testing if individual errors are
specific types of Not Exist errors. This is repetitative and unnecesary.
`Unwrap() error` provides a common way of labelling an error as a
NotExist error and we can/should use this.

This PR has chosen to use the common `io/fs` errors e.g.
`fs.ErrNotExist` for our errors. This is in some ways not completely
correct as these are not filesystem errors but it seems like a
reasonable thing to do and would allow us to simplify a lot of our code
to `errors.Is(err, fs.ErrNotExist)` instead of
`package.IsErr...NotExist(err)`

I am open to suggestions to use a different base error - perhaps
`models/db.ErrNotExist` if that would be felt to be better.


Signed-off-by: Andrew Thornton <art27@cantab.net>
Co-authored-by: delvh <dev.lh@web.de>

models/user/email_address.go

@@ -40,6 +40,10 @@ func (err ErrEmailCharIsNotSupported) Error() string {
 	return fmt.Sprintf("e-mail address contains unsupported character [email: %s]", err.Email)
 }
 
+func (err ErrEmailCharIsNotSupported) Unwrap() error {
+	return util.ErrInvalidArgument
+}
+
 // ErrEmailInvalid represents an error where the email address does not comply with RFC 5322
 // or has a leading '-' character
 type ErrEmailInvalid struct {
@@ -56,6 +60,10 @@ func (err ErrEmailInvalid) Error() string {
 	return fmt.Sprintf("e-mail invalid [email: %s]", err.Email)
 }
 
+func (err ErrEmailInvalid) Unwrap() error {
+	return util.ErrInvalidArgument
+}
+
 // ErrEmailAlreadyUsed represents a "EmailAlreadyUsed" kind of error.
 type ErrEmailAlreadyUsed struct {
 	Email string
@@ -71,6 +79,10 @@ func (err ErrEmailAlreadyUsed) Error() string {
 	return fmt.Sprintf("e-mail already in use [email: %s]", err.Email)
 }
 
+func (err ErrEmailAlreadyUsed) Unwrap() error {
+	return util.ErrAlreadyExist
+}
+
 // ErrEmailAddressNotExist email address not exist
 type ErrEmailAddressNotExist struct {
 	Email string
@@ -86,6 +98,10 @@ func (err ErrEmailAddressNotExist) Error() string {
 	return fmt.Sprintf("Email address does not exist [email: %s]", err.Email)
 }
 
+func (err ErrEmailAddressNotExist) Unwrap() error {
+	return util.ErrNotExist
+}
+
 // ErrPrimaryEmailCannotDelete primary email address cannot be deleted
 type ErrPrimaryEmailCannotDelete struct {
 	Email string
@@ -101,6 +117,10 @@ func (err ErrPrimaryEmailCannotDelete) Error() string {
 	return fmt.Sprintf("Primary email address cannot be deleted [email: %s]", err.Email)
 }
 
+func (err ErrPrimaryEmailCannotDelete) Unwrap() error {
+	return util.ErrInvalidArgument
+}
+
 // EmailAddress is the list of all email addresses of a user. It also contains the
 // primary email address which is saved in user table.
 type EmailAddress struct {

models/user/error.go

@@ -6,6 +6,8 @@ package user
 
 import (
 	"fmt"
+
+	"code.gitea.io/gitea/modules/util"
 )
 
 //  ____ ___
@@ -30,6 +32,11 @@ func (err ErrUserAlreadyExist) Error() string {
 	return fmt.Sprintf("user already exists [name: %s]", err.Name)
 }
 
+// Unwrap unwraps this error as a ErrExist error
+func (err ErrUserAlreadyExist) Unwrap() error {
+	return util.ErrAlreadyExist
+}
+
 // ErrUserNotExist represents a "UserNotExist" kind of error.
 type ErrUserNotExist struct {
 	UID   int64
@@ -47,6 +54,11 @@ func (err ErrUserNotExist) Error() string {
 	return fmt.Sprintf("user does not exist [uid: %d, name: %s, keyid: %d]", err.UID, err.Name, err.KeyID)
 }
 
+// Unwrap unwraps this error as a ErrNotExist error
+func (err ErrUserNotExist) Unwrap() error {
+	return util.ErrNotExist
+}
+
 // ErrUserProhibitLogin represents a "ErrUserProhibitLogin" kind of error.
 type ErrUserProhibitLogin struct {
 	UID  int64
@@ -63,6 +75,11 @@ func (err ErrUserProhibitLogin) Error() string {
 	return fmt.Sprintf("user is not allowed login [uid: %d, name: %s]", err.UID, err.Name)
 }
 
+// Unwrap unwraps this error as a ErrPermission error
+func (err ErrUserProhibitLogin) Unwrap() error {
+	return util.ErrPermissionDenied
+}
+
 // ErrUserInactive represents a "ErrUserInactive" kind of error.
 type ErrUserInactive struct {
 	UID  int64
@@ -78,3 +95,8 @@ func IsErrUserInactive(err error) bool {
 func (err ErrUserInactive) Error() string {
 	return fmt.Sprintf("user is inactive [uid: %d, name: %s]", err.UID, err.Name)
 }
+
+// Unwrap unwraps this error as a ErrPermission error
+func (err ErrUserInactive) Unwrap() error {
+	return util.ErrPermissionDenied
+}

models/user/external_login_user.go

@@ -10,6 +10,7 @@ import (
 	"time"
 
 	"code.gitea.io/gitea/models/db"
+	"code.gitea.io/gitea/modules/util"
 
 	"xorm.io/builder"
 )
@@ -31,6 +32,10 @@ func (err ErrExternalLoginUserAlreadyExist) Error() string {
 	return fmt.Sprintf("external login user already exists [externalID: %s, userID: %d, loginSourceID: %d]", err.ExternalID, err.UserID, err.LoginSourceID)
 }
 
+func (err ErrExternalLoginUserAlreadyExist) Unwrap() error {
+	return util.ErrAlreadyExist
+}
+
 // ErrExternalLoginUserNotExist represents a "ExternalLoginUserNotExist" kind of error.
 type ErrExternalLoginUserNotExist struct {
 	UserID        int64
@@ -47,6 +52,10 @@ func (err ErrExternalLoginUserNotExist) Error() string {
 	return fmt.Sprintf("external login user link does not exists [userID: %d, loginSourceID: %d]", err.UserID, err.LoginSourceID)
 }
 
+func (err ErrExternalLoginUserNotExist) Unwrap() error {
+	return util.ErrNotExist
+}
+
 // ExternalLoginUser makes the connecting between some existing user and additional external login sources
 type ExternalLoginUser struct {
 	ExternalID        string                 `xorm:"pk NOT NULL"`

models/user/openid.go

@@ -10,6 +10,7 @@ import (
 	"fmt"
 
 	"code.gitea.io/gitea/models/db"
+	"code.gitea.io/gitea/modules/util"
 )
 
 // ErrOpenIDNotExist openid is not known
@@ -65,6 +66,10 @@ func (err ErrOpenIDAlreadyUsed) Error() string {
 	return fmt.Sprintf("OpenID already in use [oid: %s]", err.OpenID)
 }
 
+func (err ErrOpenIDAlreadyUsed) Unwrap() error {
+	return util.ErrAlreadyExist
+}
+
 // AddUserOpenID adds an pre-verified/normalized OpenID URI to given user.
 // NOTE: make sure openid.URI is normalized already
 func AddUserOpenID(ctx context.Context, openid *UserOpenID) error {

models/user/redirect.go

@@ -10,6 +10,7 @@ import (
 	"strings"
 
 	"code.gitea.io/gitea/models/db"
+	"code.gitea.io/gitea/modules/util"
 )
 
 // ErrUserRedirectNotExist represents a "UserRedirectNotExist" kind of error.
@@ -27,6 +28,10 @@ func (err ErrUserRedirectNotExist) Error() string {
 	return fmt.Sprintf("user redirect does not exist [name: %s]", err.Name)
 }
 
+func (err ErrUserRedirectNotExist) Unwrap() error {
+	return util.ErrNotExist
+}
+
 // Redirect represents that a user name should be redirected to another
 type Redirect struct {
 	ID             int64  `xorm:"pk autoincr"`