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>

1 files changed, 10 insertions, 0 deletions

diff --git a/models/foreignreference/error.go b/models/foreignreference/error.go
index d783a08730..a1db773cd2 100644
--- a/models/foreignreference/error.go
+++ b/models/foreignreference/error.go
@@ -6,6 +6,8 @@ package foreignreference
 
 import (
 	"fmt"
+
+	"code.gitea.io/gitea/modules/util"
 )
 
 // ErrLocalIndexNotExist represents a "LocalIndexNotExist" kind of error.
@@ -25,6 +27,10 @@ func (err ErrLocalIndexNotExist) Error() string {
 	return fmt.Sprintf("repository %d has no LocalIndex for ForeignIndex %d of type %s", err.RepoID, err.ForeignIndex, err.Type)
 }
 
+func (err ErrLocalIndexNotExist) Unwrap() error {
+	return util.ErrNotExist
+}
+
 // ErrForeignIndexNotExist represents a "ForeignIndexNotExist" kind of error.
 type ErrForeignIndexNotExist struct {
 	RepoID     int64
@@ -41,3 +47,7 @@ func IsErrForeignIndexNotExist(err error) bool {
 func (err ErrForeignIndexNotExist) Error() string {
 	return fmt.Sprintf("repository %d has no ForeignIndex for LocalIndex %d of type %s", err.RepoID, err.LocalIndex, err.Type)
 }
+
+func (err ErrForeignIndexNotExist) Unwrap() error {
+	return util.ErrNotExist
+}