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, 5 insertions, 0 deletions

diff --git a/models/issues/content_history.go b/models/issues/content_history.go
index 3e321784bd..f5cfa65b8f 100644
--- a/models/issues/content_history.go
+++ b/models/issues/content_history.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/builder"
 )
@@ -201,6 +202,10 @@ func (err ErrIssueContentHistoryNotExist) Error() string {
 	return fmt.Sprintf("issue content history does not exist [id: %d]", err.ID)
 }
 
+func (err ErrIssueContentHistoryNotExist) Unwrap() error {
+	return util.ErrNotExist
+}
+
 // GetIssueContentHistoryByID get issue content history
 func GetIssueContentHistoryByID(dbCtx context.Context, id int64) (*ContentHistory, error) {
 	h := &ContentHistory{}