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/auth/oauth2.go

@@ -486,7 +486,7 @@ type ErrOAuthClientIDInvalid struct {
 	ClientID string
 }
 
-// IsErrOauthClientIDInvalid checks if an error is a ErrReviewNotExist.
+// IsErrOauthClientIDInvalid checks if an error is a ErrOAuthClientIDInvalid.
 func IsErrOauthClientIDInvalid(err error) bool {
 	_, ok := err.(ErrOAuthClientIDInvalid)
 	return ok
@@ -497,6 +497,11 @@ func (err ErrOAuthClientIDInvalid) Error() string {
 	return fmt.Sprintf("Client ID invalid [Client ID: %s]", err.ClientID)
 }
 
+// Unwrap unwraps this as a ErrNotExist err
+func (err ErrOAuthClientIDInvalid) Unwrap() error {
+	return util.ErrNotExist
+}
+
 // ErrOAuthApplicationNotFound will be thrown if id cannot be found
 type ErrOAuthApplicationNotFound struct {
 	ID int64
@@ -513,6 +518,11 @@ func (err ErrOAuthApplicationNotFound) Error() string {
 	return fmt.Sprintf("OAuth application not found [ID: %d]", err.ID)
 }
 
+// Unwrap unwraps this as a ErrNotExist err
+func (err ErrOAuthApplicationNotFound) Unwrap() error {
+	return util.ErrNotExist
+}
+
 // GetActiveOAuth2ProviderSources returns all actived LoginOAuth2 sources
 func GetActiveOAuth2ProviderSources() ([]*Source, error) {
 	sources := make([]*Source, 0, 1)

models/auth/source.go

@@ -12,6 +12,7 @@ import (
 	"code.gitea.io/gitea/models/db"
 	"code.gitea.io/gitea/modules/log"
 	"code.gitea.io/gitea/modules/timeutil"
+	"code.gitea.io/gitea/modules/util"
 
 	"xorm.io/xorm"
 	"xorm.io/xorm/convert"
@@ -366,6 +367,11 @@ func (err ErrSourceNotExist) Error() string {
 	return fmt.Sprintf("login source does not exist [id: %d]", err.ID)
 }
 
+// Unwrap unwraps this as a ErrNotExist err
+func (err ErrSourceNotExist) Unwrap() error {
+	return util.ErrNotExist
+}
+
 // ErrSourceAlreadyExist represents a "SourceAlreadyExist" kind of error.
 type ErrSourceAlreadyExist struct {
 	Name string
@@ -381,6 +387,11 @@ func (err ErrSourceAlreadyExist) Error() string {
 	return fmt.Sprintf("login source already exists [name: %s]", err.Name)
 }
 
+// Unwrap unwraps this as a ErrExist err
+func (err ErrSourceAlreadyExist) Unwrap() error {
+	return util.ErrAlreadyExist
+}
+
 // ErrSourceInUse represents a "SourceInUse" kind of error.
 type ErrSourceInUse struct {
 	ID int64

models/auth/token.go

@@ -35,6 +35,10 @@ func (err ErrAccessTokenNotExist) Error() string {
 	return fmt.Sprintf("access token does not exist [sha: %s]", err.Token)
 }
 
+func (err ErrAccessTokenNotExist) Unwrap() error {
+	return util.ErrNotExist
+}
+
 // ErrAccessTokenEmpty represents a "AccessTokenEmpty" kind of error.
 type ErrAccessTokenEmpty struct{}
 
@@ -48,6 +52,10 @@ func (err ErrAccessTokenEmpty) Error() string {
 	return "access token is empty"
 }
 
+func (err ErrAccessTokenEmpty) Unwrap() error {
+	return util.ErrInvalidArgument
+}
+
 var successfulAccessTokenCache *lru.Cache
 
 // AccessToken represents a personal access token.

models/auth/twofactor.go

@@ -41,6 +41,11 @@ func (err ErrTwoFactorNotEnrolled) Error() string {
 	return fmt.Sprintf("user not enrolled in 2FA [uid: %d]", err.UID)
 }
 
+// Unwrap unwraps this as a ErrNotExist err
+func (err ErrTwoFactorNotEnrolled) Unwrap() error {
+	return util.ErrNotExist
+}
+
 // TwoFactor represents a two-factor authentication token.
 type TwoFactor struct {
 	ID               int64 `xorm:"pk autoincr"`

models/auth/webauthn.go

@@ -11,6 +11,7 @@ import (
 
 	"code.gitea.io/gitea/models/db"
 	"code.gitea.io/gitea/modules/timeutil"
+	"code.gitea.io/gitea/modules/util"
 
 	"github.com/duo-labs/webauthn/webauthn"
 	"xorm.io/xorm"
@@ -29,6 +30,11 @@ func (err ErrWebAuthnCredentialNotExist) Error() string {
 	return fmt.Sprintf("WebAuthn credential does not exist [credential_id: %x]", err.CredentialID)
 }
 
+// Unwrap unwraps this as a ErrNotExist err
+func (err ErrWebAuthnCredentialNotExist) Unwrap() error {
+	return util.ErrNotExist
+}
+
 // IsErrWebAuthnCredentialNotExist checks if an error is a ErrWebAuthnCredentialNotExist.
 func IsErrWebAuthnCredentialNotExist(err error) bool {
 	_, ok := err.(ErrWebAuthnCredentialNotExist)