Ensure 'not exist' errors wrap os.ErrNotExist (#3982)

* Ensure 'not exist' errors wrap os.ErrNotExist

* Update go.sum

* Use an error type to avoid changing the error's string

api/filesys/filesystem_test.go

@@ -0,0 +1,40 @@
+package filesys
+
+import (
+	"os"
+	"testing"
+
+	"github.com/pkg/errors"
+	"github.com/stretchr/testify/assert"
+)
+
+var filesysBuilders = map[string]func() FileSystem{
+	"MakeFsInMemory":       MakeFsInMemory,
+	"MakeFsOnDisk":         MakeFsOnDisk,
+	"MakeEmptyDirInMemory": func() FileSystem { return MakeEmptyDirInMemory() },
+}
+
+func TestNotExistErr(t *testing.T) {
+	for name, builder := range filesysBuilders {
+		t.Run(name, func(t *testing.T) {
+			testNotExistErr(t, builder())
+		})
+	}
+}
+
+func testNotExistErr(t *testing.T, fs FileSystem) {
+	const path = "bad-dir/file.txt"
+
+	err := fs.RemoveAll(path)
+	assert.Falsef(t, errors.Is(err, os.ErrNotExist), "RemoveAll should not return ErrNotExist, got %v", err)
+	_, err = fs.Open(path)
+	assert.Truef(t, errors.Is(err, os.ErrNotExist), "Open should return ErrNotExist, got %v", err)
+	_, err = fs.ReadDir(path)
+	assert.Truef(t, errors.Is(err, os.ErrNotExist), "ReadDir should return ErrNotExist, got %v", err)
+	_, _, err = fs.CleanedAbs(path)
+	assert.Truef(t, errors.Is(err, os.ErrNotExist), "CleanedAbs should return ErrNotExist, got %v", err)
+	_, err = fs.ReadFile(path)
+	assert.Truef(t, errors.Is(err, os.ErrNotExist), "ReadFile should return ErrNotExist, got %v", err)
+	err = fs.Walk(path, func(_ string, _ os.FileInfo, err error) error { return err })
+	assert.Truef(t, errors.Is(err, os.ErrNotExist), "Walk should return ErrNotExist, got %v", err)
+}

api/filesys/fsnode.go

@@ -236,7 +236,7 @@ func (n *fsNode) CleanedAbs(path string) (ConfirmedDir, string, error) {
 		return "", "", errors.Wrap(err, "unable to clean")
 	}
 	if node == nil {
-		return "", "", fmt.Errorf("'%s' doesn't exist", path)
+		return "", "", notExistError(path)
 	}
 	if node.isNodeADir() {
 		return ConfirmedDir(node.Path()), "", nil
@@ -309,7 +309,8 @@ func (n *fsNode) RemoveAll(path string) error {
 		return err
 	}
 	if result == nil {
-		return fmt.Errorf("cannot find '%s' to remove it", path)
+		// If the path doesn't exist, no need to remove anything.
+		return nil
 	}
 	return result.Remove()
 }
@@ -351,6 +352,9 @@ func (n *fsNode) IsDir(path string) bool {
 
 // ReadDir implements FileSystem.
 func (n *fsNode) ReadDir(path string) ([]string, error) {
+	if !n.Exists(path) {
+		return nil, notExistError(path)
+	}
 	if !n.IsDir(path) {
 		return nil, fmt.Errorf("%s is not a directory", path)
 	}
@@ -398,7 +402,7 @@ func (n *fsNode) Open(path string) (File, error) {
 		return nil, err
 	}
 	if result == nil {
-		return nil, fmt.Errorf("cannot find '%s' to open it", path)
+		return nil, notExistError(path)
 	}
 	if result.offset != nil {
 		return nil, fmt.Errorf("cannot open previously opened file '%s'", path)
@@ -423,7 +427,7 @@ func (n *fsNode) ReadFile(path string) (c []byte, err error) {
 		return nil, err
 	}
 	if result == nil {
-		return nil, fmt.Errorf("cannot find '%s' to read it", path)
+		return nil, notExistError(path)
 	}
 	if result.isNodeADir() {
 		return nil, fmt.Errorf("cannot read content from non-file '%s'", n.Path())
@@ -490,7 +494,7 @@ func (n *fsNode) Walk(path string, walkFn filepath.WalkFunc) error {
 		return err
 	}
 	if result == nil {
-		return fmt.Errorf("cannot find '%s' to walk it", path)
+		return notExistError(path)
 	}
 	return result.WalkMe(walkFn)
 }
@@ -629,3 +633,10 @@ func (n *fsNode) Glob(pattern string) ([]string, error) {
 	sort.Strings(result)
 	return result, nil
 }
+
+// notExistError indicates that a file or directory does not exist.
+// Unwrapping returns os.ErrNotExist so errors.Is(err, os.ErrNotExist) works correctly.
+type notExistError string
+
+func (err notExistError) Error() string { return fmt.Sprintf("'%s' doesn't exist", string(err)) }
+func (err notExistError) Unwrap() error { return os.ErrNotExist }

api/filesys/fsondisk.go

@@ -57,7 +57,7 @@ func (x fsOnDisk) CleanedAbs(
 	deLinked, err := filepath.EvalSymlinks(absRoot)
 	if err != nil {
 		return "", "", fmt.Errorf(
-			"evalsymlink failure on '%s' : %v", path, err)
+			"evalsymlink failure on '%s' : %w", path, err)
 	}
 	if x.IsDir(deLinked) {
 		return ConfirmedDir(deLinked), "", nil