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, 13 insertions, 0 deletions

diff --git a/models/issues/dependency.go b/models/issues/dependency.go
index d664c0758e..4754ed0f5f 100644
--- a/models/issues/dependency.go
+++ b/models/issues/dependency.go
@@ -11,6 +11,7 @@ import (
 	"code.gitea.io/gitea/models/db"
 	user_model "code.gitea.io/gitea/models/user"
 	"code.gitea.io/gitea/modules/timeutil"
+	"code.gitea.io/gitea/modules/util"
 )
 
 // ErrDependencyExists represents a "DependencyAlreadyExists" kind of error.
@@ -29,6 +30,10 @@ func (err ErrDependencyExists) Error() string {
 	return fmt.Sprintf("issue dependency does already exist [issue id: %d, dependency id: %d]", err.IssueID, err.DependencyID)
 }
 
+func (err ErrDependencyExists) Unwrap() error {
+	return util.ErrAlreadyExist
+}
+
 // ErrDependencyNotExists represents a "DependencyAlreadyExists" kind of error.
 type ErrDependencyNotExists struct {
 	IssueID      int64
@@ -45,6 +50,10 @@ func (err ErrDependencyNotExists) Error() string {
 	return fmt.Sprintf("issue dependency does not exist [issue id: %d, dependency id: %d]", err.IssueID, err.DependencyID)
 }
 
+func (err ErrDependencyNotExists) Unwrap() error {
+	return util.ErrNotExist
+}
+
 // ErrCircularDependency represents a "DependencyCircular" kind of error.
 type ErrCircularDependency struct {
 	IssueID      int64
@@ -91,6 +100,10 @@ func (err ErrUnknownDependencyType) Error() string {
 	return fmt.Sprintf("unknown dependency type [type: %d]", err.Type)
 }
 
+func (err ErrUnknownDependencyType) Unwrap() error {
+	return util.ErrInvalidArgument
+}
+
 // IssueDependency represents an issue dependency
 type IssueDependency struct {
 	ID           int64              `xorm:"pk autoincr"`