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/repo/attachment.go

@@ -14,6 +14,7 @@ import (
 	"code.gitea.io/gitea/modules/setting"
 	"code.gitea.io/gitea/modules/storage"
 	"code.gitea.io/gitea/modules/timeutil"
+	"code.gitea.io/gitea/modules/util"
 )
 
 // Attachment represent a attachment of issue/comment/release.
@@ -83,6 +84,10 @@ func (err ErrAttachmentNotExist) Error() string {
 	return fmt.Sprintf("attachment does not exist [id: %d, uuid: %s]", err.ID, err.UUID)
 }
 
+func (err ErrAttachmentNotExist) Unwrap() error {
+	return util.ErrNotExist
+}
+
 // GetAttachmentByID returns attachment by given id
 func GetAttachmentByID(ctx context.Context, id int64) (*Attachment, error) {
 	attach := &Attachment{}

models/repo/redirect.go

@@ -10,6 +10,7 @@ import (
 	"strings"
 
 	"code.gitea.io/gitea/models/db"
+	"code.gitea.io/gitea/modules/util"
 )
 
 // ErrRedirectNotExist represents a "RedirectNotExist" kind of error.
@@ -28,6 +29,10 @@ func (err ErrRedirectNotExist) Error() string {
 	return fmt.Sprintf("repository redirect does not exist [uid: %d, name: %s]", err.OwnerID, err.RepoName)
 }
 
+func (err ErrRedirectNotExist) Unwrap() error {
+	return util.ErrNotExist
+}
+
 // Redirect represents that a repo name should be redirected to another
 type Redirect struct {
 	ID             int64  `xorm:"pk autoincr"`

models/repo/release.go

@@ -37,6 +37,10 @@ func (err ErrReleaseAlreadyExist) Error() string {
 	return fmt.Sprintf("release tag already exist [tag_name: %s]", err.TagName)
 }
 
+func (err ErrReleaseAlreadyExist) Unwrap() error {
+	return util.ErrAlreadyExist
+}
+
 // ErrReleaseNotExist represents a "ReleaseNotExist" kind of error.
 type ErrReleaseNotExist struct {
 	ID      int64
@@ -53,6 +57,10 @@ func (err ErrReleaseNotExist) Error() string {
 	return fmt.Sprintf("release tag does not exist [id: %d, tag_name: %s]", err.ID, err.TagName)
 }
 
+func (err ErrReleaseNotExist) Unwrap() error {
+	return util.ErrNotExist
+}
+
 // Release represents a release of repository.
 type Release struct {
 	ID               int64            `xorm:"pk autoincr"`

models/repo/repo.go

@@ -43,6 +43,10 @@ func (err ErrUserDoesNotHaveAccessToRepo) Error() string {
 	return fmt.Sprintf("user doesn't have access to repo [user_id: %d, repo_name: %s]", err.UserID, err.RepoName)
 }
 
+func (err ErrUserDoesNotHaveAccessToRepo) Unwrap() error {
+	return util.ErrPermissionDenied
+}
+
 var (
 	reservedRepoNames    = []string{".", "..", "-"}
 	reservedRepoPatterns = []string{"*.git", "*.wiki", "*.rss", "*.atom"}
@@ -643,6 +647,11 @@ func (err ErrRepoNotExist) Error() string {
 		err.ID, err.UID, err.OwnerName, err.Name)
 }
 
+// Unwrap unwraps this error as a ErrNotExist error
+func (err ErrRepoNotExist) Unwrap() error {
+	return util.ErrNotExist
+}
+
 // GetRepositoryByOwnerAndNameCtx returns the repository by given owner name and repo name
 func GetRepositoryByOwnerAndNameCtx(ctx context.Context, ownerName, repoName string) (*Repository, error) {
 	var repo Repository

models/repo/repo_unit.go

@@ -13,6 +13,7 @@ import (
 	"code.gitea.io/gitea/modules/json"
 	"code.gitea.io/gitea/modules/setting"
 	"code.gitea.io/gitea/modules/timeutil"
+	"code.gitea.io/gitea/modules/util"
 
 	"xorm.io/xorm"
 	"xorm.io/xorm/convert"
@@ -33,6 +34,10 @@ func (err ErrUnitTypeNotExist) Error() string {
 	return fmt.Sprintf("Unit type does not exist: %s", err.UT.String())
 }
 
+func (err ErrUnitTypeNotExist) Unwrap() error {
+	return util.ErrNotExist
+}
+
 // RepoUnit describes all units of a repository
 type RepoUnit struct { //revive:disable-line:exported
 	ID          int64

models/repo/topic.go

@@ -13,6 +13,7 @@ import (
 	"code.gitea.io/gitea/models/db"
 	"code.gitea.io/gitea/modules/container"
 	"code.gitea.io/gitea/modules/timeutil"
+	"code.gitea.io/gitea/modules/util"
 
 	"xorm.io/builder"
 )
@@ -55,6 +56,10 @@ func (err ErrTopicNotExist) Error() string {
 	return fmt.Sprintf("topic is not exist [name: %s]", err.Name)
 }
 
+func (err ErrTopicNotExist) Unwrap() error {
+	return util.ErrNotExist
+}
+
 // ValidateTopic checks a topic by length and match pattern rules
 func ValidateTopic(topic string) bool {
 	return len(topic) <= 35 && topicPattern.MatchString(topic)

models/repo/update.go

@@ -63,6 +63,10 @@ func (err ErrReachLimitOfRepo) Error() string {
 	return fmt.Sprintf("user has reached maximum limit of repositories [limit: %d]", err.Limit)
 }
 
+func (err ErrReachLimitOfRepo) Unwrap() error {
+	return util.ErrPermissionDenied
+}
+
 // ErrRepoAlreadyExist represents a "RepoAlreadyExist" kind of error.
 type ErrRepoAlreadyExist struct {
 	Uname string
@@ -79,6 +83,10 @@ func (err ErrRepoAlreadyExist) Error() string {
 	return fmt.Sprintf("repository already exists [uname: %s, name: %s]", err.Uname, err.Name)
 }
 
+func (err ErrRepoAlreadyExist) Unwrap() error {
+	return util.ErrAlreadyExist
+}
+
 // ErrRepoFilesAlreadyExist represents a "RepoFilesAlreadyExist" kind of error.
 type ErrRepoFilesAlreadyExist struct {
 	Uname string
@@ -95,6 +103,10 @@ func (err ErrRepoFilesAlreadyExist) Error() string {
 	return fmt.Sprintf("repository files already exist [uname: %s, name: %s]", err.Uname, err.Name)
 }
 
+func (err ErrRepoFilesAlreadyExist) Unwrap() error {
+	return util.ErrAlreadyExist
+}
+
 // CheckCreateRepository check if could created a repository
 func CheckCreateRepository(doer, u *user_model.User, name string, overwriteOrAdopt bool) error {
 	if !doer.CanCreateRepo() {

models/repo/upload.go

@@ -36,6 +36,10 @@ func (err ErrUploadNotExist) Error() string {
 	return fmt.Sprintf("attachment does not exist [id: %d, uuid: %s]", err.ID, err.UUID)
 }
 
+func (err ErrUploadNotExist) Unwrap() error {
+	return util.ErrNotExist
+}
+
 // Upload represent a uploaded file to a repo to be deleted when moved
 type Upload struct {
 	ID   int64  `xorm:"pk autoincr"`

models/repo/wiki.go

@@ -30,6 +30,10 @@ func (err ErrWikiAlreadyExist) Error() string {
 	return fmt.Sprintf("wiki page already exists [title: %s]", err.Title)
 }
 
+func (err ErrWikiAlreadyExist) Unwrap() error {
+	return util.ErrAlreadyExist
+}
+
 // ErrWikiReservedName represents a reserved name error.
 type ErrWikiReservedName struct {
 	Title string
@@ -45,6 +49,10 @@ func (err ErrWikiReservedName) Error() string {
 	return fmt.Sprintf("wiki title is reserved: %s", err.Title)
 }
 
+func (err ErrWikiReservedName) Unwrap() error {
+	return util.ErrInvalidArgument
+}
+
 // ErrWikiInvalidFileName represents an invalid wiki file name.
 type ErrWikiInvalidFileName struct {
 	FileName string
@@ -60,6 +68,10 @@ func (err ErrWikiInvalidFileName) Error() string {
 	return fmt.Sprintf("Invalid wiki filename: %s", err.FileName)
 }
 
+func (err ErrWikiInvalidFileName) Unwrap() error {
+	return util.ErrInvalidArgument
+}
+
 // WikiCloneLink returns clone URLs of repository wiki.
 func (repo *Repository) WikiCloneLink() *CloneLink {
 	return repo.cloneLink(true)