Also consider wrapped errors when checking for file IsNotExist errors

Fixes #10534

2 files changed, 55 insertions, 2 deletions

diff --git a/common/herrors/errors.go b/common/herrors/errors.go
index 6ce908853..822271ef2 100644
--- a/common/herrors/errors.go
+++ b/common/herrors/errors.go
@@ -1,4 +1,4 @@
-// Copyright 2018 The Hugo Authors. All rights reserved.
+// Copyright 2022 The Hugo Authors. All rights reserved.
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
@@ -19,6 +19,7 @@ import (
 	"errors"
 	"fmt"
 	"io"
+	"os"
 	"runtime"
 	"runtime/debug"
 	"strconv"
@@ -38,7 +39,8 @@ type ErrorSender interface {
 
 // Recover is a helper function that can be used to capture panics.
 // Put this at the top of a method/function that crashes in a template:
-//     defer herrors.Recover()
+//
+//	defer herrors.Recover()
 func Recover(args ...any) {
 	if r := recover(); r != nil {
 		fmt.Println("ERR:", r)
@@ -69,3 +71,18 @@ func Must(err error) {
 		panic(err)
 	}
 }
+
+// IsNotExist returns true if the error is a file not found error.
+// Unlike os.IsNotExist, this also considers wrapped errors.
+func IsNotExist(err error) bool {
+	if os.IsNotExist(err) {
+		return true
+	}
+
+	// os.IsNotExist does not consider wrapped errors.
+	if os.IsNotExist(errors.Unwrap(err)) {
+		return true
+	}
+
+	return false
+}
diff --git a/common/herrors/errors_test.go b/common/herrors/errors_test.go
new file mode 100644
index 000000000..1e0730028
--- /dev/null
+++ b/common/herrors/errors_test.go
@@ -0,0 +1,36 @@
+// Copyright 2022 The Hugo Authors. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package herrors
+
+import (
+	"fmt"
+	"testing"
+
+	qt "github.com/frankban/quicktest"
+	"github.com/spf13/afero"
+)
+
+func TestIsNotExist(t *testing.T) {
+	c := qt.New(t)
+
+	c.Assert(IsNotExist(afero.ErrFileNotFound), qt.Equals, true)
+	c.Assert(IsNotExist(afero.ErrFileExists), qt.Equals, false)
+	c.Assert(IsNotExist(afero.ErrDestinationExists), qt.Equals, false)
+	c.Assert(IsNotExist(nil), qt.Equals, false)
+
+	c.Assert(IsNotExist(fmt.Errorf("foo")), qt.Equals, false)
+
+	// os.IsNotExist returns false for wrapped errors.
+	c.Assert(IsNotExist(fmt.Errorf("foo: %w", afero.ErrFileNotFound)), qt.Equals, true)
+}