Ditch pkg/errors, use native error (un)wrapping

Compatibility notes:

1. ErrSymlinkLoop is removed in favor of wrapping syscall.ELOOP into
   &os.PathError{}; users should use e.g. errors.Is(err, syscall.ELOOP)
   to check for this particular error.

2. IsNotExist now does not use pkg/errors.Cause but native go error
   unwrapping; it could breaks a use case when it is used for some
   third-party errors wrapped using pkg/errors.Wrap[f].

I was not able to find any users of either feature.

Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>

Author: kolyshkin

join.go

@@ -12,39 +12,20 @@ package securejoin
 
 import (
 	"bytes"
+	"errors"
 	"os"
 	"path/filepath"
 	"strings"
 	"syscall"
-
-	"github.com/pkg/errors"
 )
 
-// ErrSymlinkLoop is returned by SecureJoinVFS when too many symlinks have been
-// evaluated in attempting to securely join the two given paths.
-var ErrSymlinkLoop = errors.Wrap(syscall.ELOOP, "secure join")
-
 // IsNotExist tells you if err is an error that implies that either the path
 // accessed does not exist (or path components don't exist). This is
 // effectively a more broad version of os.IsNotExist.
 func IsNotExist(err error) bool {
-	// If it's a bone-fide ENOENT just bail.
-	if os.IsNotExist(errors.Cause(err)) {
-		return true
-	}
-
 	// Check that it's not actually an ENOTDIR, which in some cases is a more
 	// convoluted case of ENOENT (usually involving weird paths).
-	var errno error
-	switch err := errors.Cause(err).(type) {
-	case *os.PathError:
-		errno = err.Err
-	case *os.LinkError:
-		errno = err.Err
-	case *os.SyscallError:
-		errno = err.Err
-	}
-	return errno == syscall.ENOTDIR || errno == syscall.ENOENT
+	return errors.Is(err, os.ErrNotExist) || errors.Is(err, syscall.ENOTDIR) || errors.Is(err, syscall.ENOENT)
 }
 
 // SecureJoinVFS joins the two given path components (similar to Join) except
@@ -68,7 +49,7 @@ func SecureJoinVFS(root, unsafePath string, vfs VFS) (string, error) {
 	n := 0
 	for unsafePath != "" {
 		if n > 255 {
-			return "", ErrSymlinkLoop
+			return "", &os.PathError{Op: "SecureJoin", Path: root + "/" + unsafePath, Err: syscall.ELOOP}
 		}
 
 		// Next path component, p.

join_test.go

@@ -187,7 +187,7 @@ func TestSymlinkLoop(t *testing.T) {
 		{dir, "/self/././.."},
 	} {
 		got, err := SecureJoin(test.root, test.unsafe)
-		if err != ErrSymlinkLoop {
+		if !errors.Is(err, syscall.ELOOP) {
 			t.Errorf("securejoin(%q, %q): expected ELOOP, got %v & %q", test.root, test.unsafe, err, got)
 			continue
 		}

vendor.conf

@@ -1 +0,0 @@
-github.com/pkg/errors v0.8.0