all: Move away from pkg/errors, easy cases

github.com/pkg/errors is no longer getting updates, because Go 1.13
went with the more flexible errors.{As,Is} function. Use those instead:
errors from pkg/errors already support the Unwrap interface used by 1.13
error handling. Also:

* check for io.EOF with a straight ==. That value should not be wrapped,
  and the chunker (whose error is checked in the cases changed) does not
  wrap it.
* Give custom Error methods pointer receivers, so there's no ambiguity
  when type-switching since the value type will no longer implement error.
* Make restic.ErrAlreadyLocked private, and rename it to
  alreadyLockedError to match the stdlib convention that error type
  names end in Error.
* Same with rest.ErrIsNotExist => rest.notExistError.
* Make s3.Backend.IsAccessDenied a private function.

cmd/restic/cmd_backup.go

@@ -144,7 +144,7 @@ func init() {
 func filterExisting(items []string) (result []string, err error) {
 	for _, item := range items {
 		_, err := fs.Lstat(item)
-		if err != nil && os.IsNotExist(errors.Cause(err)) {
+		if errors.Is(err, os.ErrNotExist) {
 			Warnf("%v does not exist, skipping\n", item)
 			continue
 		}

cmd/restic/cmd_mount.go

@@ -116,7 +116,7 @@ func runMount(opts MountOptions, gopts GlobalOptions, args []string) error {
 
 	mountpoint := args[0]
 
-	if _, err := resticfs.Stat(mountpoint); os.IsNotExist(errors.Cause(err)) {
+	if _, err := resticfs.Stat(mountpoint); errors.Is(err, os.ErrNotExist) {
 		Verbosef("Mountpoint %s doesn't exist\n", mountpoint)
 		return err
 	}

cmd/restic/global.go

@@ -297,7 +297,7 @@ func resolvePassword(opts GlobalOptions, envStr string) (string, error) {
 	}
 	if opts.PasswordFile != "" {
 		s, err := textfile.Read(opts.PasswordFile)
-		if os.IsNotExist(errors.Cause(err)) {
+		if errors.Is(err, os.ErrNotExist) {
 			return "", errors.Fatalf("%s does not exist", opts.PasswordFile)
 		}
 		return strings.TrimSpace(string(s)), errors.Wrap(err, "Readfile")
@@ -398,7 +398,7 @@ func ReadRepo(opts GlobalOptions) (string, error) {
 		}
 
 		s, err := textfile.Read(opts.RepositoryFile)
-		if os.IsNotExist(errors.Cause(err)) {
+		if errors.Is(err, os.ErrNotExist) {
 			return "", errors.Fatalf("%s does not exist", opts.RepositoryFile)
 		}
 		if err != nil {

cmd/restic/main.go

@@ -98,7 +98,7 @@ func main() {
 	err := cmdRoot.Execute()
 
 	switch {
-	case restic.IsAlreadyLocked(errors.Cause(err)):
+	case restic.IsAlreadyLocked(err):
 		fmt.Fprintf(os.Stderr, "%v\nthe `unlock` command can be used to remove stale locks\n", err)
 	case err == ErrInvalidSourceData:
 		fmt.Fprintf(os.Stderr, "Warning: %v\n", err)

internal/archiver/archiver_test.go

@@ -2040,8 +2040,8 @@ func TestArchiverAbortEarlyOnError(t *testing.T) {
 			})
 
 			_, _, err := arch.Snapshot(ctx, []string{"."}, SnapshotOptions{Time: time.Now()})
-			if errors.Cause(err) != test.err {
-				t.Errorf("expected error (%v) not found, got %v", test.err, errors.Cause(err))
+			if !errors.Is(err, test.err) {
+				t.Errorf("expected error (%v) not found, got %v", test.err, err)
 			}
 
 			t.Logf("Snapshot return error: %v", err)

internal/archiver/file_saver.go

@@ -165,7 +165,7 @@ func (s *FileSaver) saveFile(ctx context.Context, chnker *chunker.Chunker, snPat
 	for {
 		buf := s.saveFilePool.Get()
 		chunk, err := chnker.Next(buf.Data)
-		if errors.Cause(err) == io.EOF {
+		if err == io.EOF {
 			buf.Release()
 			break
 		}

internal/backend/layout.go

@@ -152,7 +152,7 @@ func ParseLayout(ctx context.Context, repo Filesystem, layout, defaultLayout, pa
 		l, err = DetectLayout(ctx, repo, path)
 
 		// use the default layout if auto detection failed
-		if errors.Cause(err) == ErrLayoutDetectionFailed && defaultLayout != "" {
+		if errors.Is(err, ErrLayoutDetectionFailed) && defaultLayout != "" {
 			debug.Log("error: %v, use default layout %v", err, defaultLayout)
 			return ParseLayout(ctx, repo, defaultLayout, "", path)
 		}

internal/backend/mem/mem_backend.go

@@ -71,7 +71,7 @@ func (be *MemoryBackend) Test(ctx context.Context, h restic.Handle) (bool, error
 
 // IsNotExist returns true if the file does not exist.
 func (be *MemoryBackend) IsNotExist(err error) bool {
-	return errors.Cause(err) == errNotFound
+	return errors.Is(err, errNotFound)
 }
 
 // Save adds new Data to the backend.

internal/backend/rclone/backend_test.go

@@ -29,7 +29,8 @@ func newTestSuite(t testing.TB) *test.Suite {
 			t.Logf("Create()")
 			cfg := config.(rclone.Config)
 			be, err := rclone.Create(context.TODO(), cfg)
-			if e, ok := errors.Cause(err).(*exec.Error); ok && e.Err == exec.ErrNotFound {
+			var e *exec.Error
+			if errors.As(err, &e) && e.Err == exec.ErrNotFound {
 				t.Skipf("program %q not found", e.Name)
 				return nil, nil
 			}

internal/backend/rclone/internal_test.go

@@ -18,7 +18,8 @@ func TestRcloneExit(t *testing.T) {
 	cfg := NewConfig()
 	cfg.Remote = dir
 	be, err := Open(cfg, nil)
-	if e, ok := errors.Cause(err).(*exec.Error); ok && e.Err == exec.ErrNotFound {
+	var e *exec.Error
+	if errors.As(err, &e) && e.Err == exec.ErrNotFound {
 		t.Skipf("program %q not found", e.Name)
 		return
 	}

internal/backend/rest/rest.go

@@ -169,21 +169,20 @@ func (b *Backend) Save(ctx context.Context, h restic.Handle, rd restic.RewindRea
 	return errors.Wrap(cerr, "Close")
 }
 
-// ErrIsNotExist is returned whenever the requested file does not exist on the
+// notExistError is returned whenever the requested file does not exist on the
 // server.
-type ErrIsNotExist struct {
+type notExistError struct {
 	restic.Handle
 }
 
-func (e ErrIsNotExist) Error() string {
+func (e *notExistError) Error() string {
 	return fmt.Sprintf("%v does not exist", e.Handle)
 }
 
 // IsNotExist returns true if the error was caused by a non-existing file.
 func (b *Backend) IsNotExist(err error) bool {
-	err = errors.Cause(err)
-	_, ok := err.(ErrIsNotExist)
-	return ok
+	var e *notExistError
+	return errors.As(err, &e)
 }
 
 // Load runs fn with a reader that yields the contents of the file at h at the
@@ -296,7 +295,7 @@ func (b *Backend) openReader(ctx context.Context, h restic.Handle, length int, o
 
 	if resp.StatusCode == http.StatusNotFound {
 		_ = resp.Body.Close()
-		return nil, ErrIsNotExist{h}
+		return nil, &notExistError{h}
 	}
 
 	if resp.StatusCode != 200 && resp.StatusCode != 206 {
@@ -341,7 +340,7 @@ func (b *Backend) Stat(ctx context.Context, h restic.Handle) (restic.FileInfo, e
 
 	if resp.StatusCode == http.StatusNotFound {
 		_ = resp.Body.Close()
-		return restic.FileInfo{}, ErrIsNotExist{h}
+		return restic.FileInfo{}, &notExistError{h}
 	}
 
 	if resp.StatusCode != 200 {
@@ -392,7 +391,7 @@ func (b *Backend) Remove(ctx context.Context, h restic.Handle) error {
 
 	if resp.StatusCode == http.StatusNotFound {
 		_ = resp.Body.Close()
-		return ErrIsNotExist{h}
+		return &notExistError{h}
 	}
 
 	if resp.StatusCode != 200 {

internal/backend/s3/s3.go

@@ -137,7 +137,7 @@ func Create(ctx context.Context, cfg Config, rt http.RoundTripper) (restic.Backe
 	}
 	found, err := be.client.BucketExists(ctx, cfg.Bucket)
 
-	if err != nil && be.IsAccessDenied(err) {
+	if err != nil && isAccessDenied(err) {
 		err = nil
 		found = true
 	}
@@ -158,29 +158,23 @@ func Create(ctx context.Context, cfg Config, rt http.RoundTripper) (restic.Backe
 	return be, nil
 }
 
-// IsAccessDenied returns true if the error is caused by Access Denied.
-func (be *Backend) IsAccessDenied(err error) bool {
-	debug.Log("IsAccessDenied(%T, %#v)", err, err)
+// isAccessDenied returns true if the error is caused by Access Denied.
+func isAccessDenied(err error) bool {
+	debug.Log("isAccessDenied(%T, %#v)", err, err)
 
-	if e, ok := errors.Cause(err).(minio.ErrorResponse); ok && e.Code == "AccessDenied" {
-		return true
-	}
-
-	return false
+	var e minio.ErrorResponse
+	return errors.As(err, &e) && e.Code == "Access Denied"
 }
 
 // IsNotExist returns true if the error is caused by a not existing file.
 func (be *Backend) IsNotExist(err error) bool {
 	debug.Log("IsNotExist(%T, %#v)", err, err)
-	if os.IsNotExist(errors.Cause(err)) {
+	if errors.Is(err, os.ErrNotExist) {
 		return true
 	}
 
-	if e, ok := errors.Cause(err).(minio.ErrorResponse); ok && e.Code == "NoSuchKey" {
-		return true
-	}
-
-	return false
+	var e minio.ErrorResponse
+	return errors.As(err, &e) && e.Code == "NoSuchKey"
 }
 
 // Join combines path components with slashes.

internal/backend/sftp/sftp.go

@@ -183,7 +183,6 @@ func (r *SFTP) ReadDir(ctx context.Context, dir string) ([]os.FileInfo, error) {
 
 // IsNotExist returns true if the error is caused by a not existing file.
 func (r *SFTP) IsNotExist(err error) bool {
-	err = errors.Cause(err)
 	return errors.Is(err, os.ErrNotExist)
 }
 
@@ -496,7 +495,7 @@ func (r *SFTP) Test(ctx context.Context, h restic.Handle) (bool, error) {
 	defer r.sem.ReleaseToken()
 
 	_, err := r.c.Lstat(r.Filename(h))
-	if os.IsNotExist(errors.Cause(err)) {
+	if errors.Is(err, os.ErrNotExist) {
 		return false, nil
 	}
 

internal/backend/sftp/sftp_test.go

@@ -20,7 +20,7 @@ func findSFTPServerBinary() string {
 	for _, dir := range strings.Split(rtest.TestSFTPPath, ":") {
 		testpath := filepath.Join(dir, "sftp-server")
 		_, err := os.Stat(testpath)
-		if !os.IsNotExist(errors.Cause(err)) {
+		if !errors.Is(err, os.ErrNotExist) {
 			return testpath
 		}
 	}

internal/backend/swift/swift.go

@@ -311,11 +311,8 @@ func (be *beSwift) removeKeys(ctx context.Context, t restic.FileType) error {
 
 // IsNotExist returns true if the error is caused by a not existing file.
 func (be *beSwift) IsNotExist(err error) bool {
-	if e, ok := errors.Cause(err).(*swift.Error); ok {
-		return e.StatusCode == http.StatusNotFound
-	}
-
-	return false
+	var e *swift.Error
+	return errors.As(err, &e) && e.StatusCode == http.StatusNotFound
 }
 
 // Delete removes all restic objects in the container.

internal/backend/test/tests.go

@@ -361,8 +361,8 @@ func (s *Suite) TestListCancel(t *testing.T) {
 			return nil
 		})
 
-		if errors.Cause(err) != context.Canceled {
-			t.Fatalf("expected error not found, want %v, got %v", context.Canceled, errors.Cause(err))
+		if !errors.Is(err, context.Canceled) {
+			t.Fatalf("expected error not found, want %v, got %v", context.Canceled, err)
 		}
 	})
 
@@ -380,7 +380,7 @@ func (s *Suite) TestListCancel(t *testing.T) {
 			return nil
 		})
 
-		if errors.Cause(err) != context.Canceled {
+		if !errors.Is(err, context.Canceled) {
 			t.Fatalf("expected error not found, want %v, got %v", context.Canceled, err)
 		}
 
@@ -403,7 +403,7 @@ func (s *Suite) TestListCancel(t *testing.T) {
 			return nil
 		})
 
-		if errors.Cause(err) != context.Canceled {
+		if !errors.Is(err, context.Canceled) {
 			t.Fatalf("expected error not found, want %v, got %v", context.Canceled, err)
 		}
 
@@ -429,7 +429,7 @@ func (s *Suite) TestListCancel(t *testing.T) {
 			return nil
 		})
 
-		if errors.Cause(err) != context.DeadlineExceeded {
+		if !errors.Is(err, context.DeadlineExceeded) {
 			t.Fatalf("expected error not found, want %#v, got %#v", context.DeadlineExceeded, err)
 		}
 

internal/checker/checker.go

@@ -160,18 +160,15 @@ type PackError struct {
 	Err      error
 }
 
-func (e PackError) Error() string {
+func (e *PackError) Error() string {
 	return "pack " + e.ID.Str() + ": " + e.Err.Error()
 }
 
 // IsOrphanedPack returns true if the error describes a pack which is not
 // contained in any index.
 func IsOrphanedPack(err error) bool {
-	if e, ok := errors.Cause(err).(PackError); ok && e.Orphaned {
-		return true
-	}
-
-	return false
+	var e *PackError
+	return errors.As(err, &e) && e.Orphaned
 }
 
 // Packs checks that all packs referenced in the index are still available and
@@ -204,7 +201,7 @@ func (c *Checker) Packs(ctx context.Context, errChan chan<- error) {
 			select {
 			case <-ctx.Done():
 				return
-			case errChan <- PackError{ID: id, Err: errors.New("does not exist")}:
+			case errChan <- &PackError{ID: id, Err: errors.New("does not exist")}:
 			}
 			continue
 		}
@@ -214,7 +211,7 @@ func (c *Checker) Packs(ctx context.Context, errChan chan<- error) {
 			select {
 			case <-ctx.Done():
 				return
-			case errChan <- PackError{ID: id, Err: errors.Errorf("unexpected file size: got %d, expected %d", reposize, size)}:
+			case errChan <- &PackError{ID: id, Err: errors.Errorf("unexpected file size: got %d, expected %d", reposize, size)}:
 			}
 		}
 	}
@@ -224,7 +221,7 @@ func (c *Checker) Packs(ctx context.Context, errChan chan<- error) {
 		select {
 		case <-ctx.Done():
 			return
-		case errChan <- PackError{ID: orphanID, Orphaned: true, Err: errors.New("not referenced in any index")}:
+		case errChan <- &PackError{ID: orphanID, Orphaned: true, Err: errors.New("not referenced in any index")}:
 		}
 	}
 }

internal/checker/checker_test.go

@@ -109,7 +109,7 @@ func TestMissingPack(t *testing.T) {
 	test.Assert(t, len(errs) == 1,
 		"expected exactly one error, got %v", len(errs))
 
-	if err, ok := errs[0].(checker.PackError); ok {
+	if err, ok := errs[0].(*checker.PackError); ok {
 		test.Equals(t, packHandle.Name, err.ID.String())
 	} else {
 		t.Errorf("expected error returned by checker.Packs() to be PackError, got %v", err)
@@ -145,7 +145,7 @@ func TestUnreferencedPack(t *testing.T) {
 	test.Assert(t, len(errs) == 1,
 		"expected exactly one error, got %v", len(errs))
 
-	if err, ok := errs[0].(checker.PackError); ok {
+	if err, ok := errs[0].(*checker.PackError); ok {
 		test.Equals(t, packID, err.ID.String())
 	} else {
 		t.Errorf("expected error returned by checker.Packs() to be PackError, got %v", err)

internal/errors/errors.go

@@ -52,4 +52,6 @@ func Cause(err error) error {
 
 // Go 1.13-style error handling.
 
+func As(err error, tgt interface{}) bool { return errors.As(err, tgt) }
+
 func Is(x, y error) bool { return errors.Is(x, y) }

internal/repository/key.go

@@ -153,7 +153,7 @@ func SearchKey(ctx context.Context, s *Repository, password string, maxKeys int,
 			debug.Log("key %v returned error %v", fi.Name, err)
 
 			// ErrUnauthenticated means the password is wrong, try the next key
-			if errors.Cause(err) == crypto.ErrUnauthenticated {
+			if errors.Is(err, crypto.ErrUnauthenticated) {
 				return nil
 			}
 

internal/restic/lock.go

@@ -38,13 +38,13 @@ type Lock struct {
 	lockID *ID
 }
 
-// ErrAlreadyLocked is returned when NewLock or NewExclusiveLock are unable to
+// alreadyLockedError is returned when NewLock or NewExclusiveLock are unable to
 // acquire the desired lock.
-type ErrAlreadyLocked struct {
+type alreadyLockedError struct {
 	otherLock *Lock
 }
 
-func (e ErrAlreadyLocked) Error() string {
+func (e *alreadyLockedError) Error() string {
 	s := ""
 	if e.otherLock.Exclusive {
 		s = "exclusively "
@@ -52,25 +52,23 @@ func (e ErrAlreadyLocked) Error() string {
 	return fmt.Sprintf("repository is already locked %sby %v", s, e.otherLock)
 }
 
-// IsAlreadyLocked returns true iff err is an instance of ErrAlreadyLocked.
+// IsAlreadyLocked returns true iff err indicates that a repository is
+// already locked.
 func IsAlreadyLocked(err error) bool {
-	if _, ok := errors.Cause(err).(ErrAlreadyLocked); ok {
-		return true
-	}
-
-	return false
+	var e *alreadyLockedError
+	return errors.As(err, &e)
 }
 
 // NewLock returns a new, non-exclusive lock for the repository. If an
-// exclusive lock is already held by another process, ErrAlreadyLocked is
-// returned.
+// exclusive lock is already held by another process, it returns an error
+// that satisfies IsAlreadyLocked.
 func NewLock(ctx context.Context, repo Repository) (*Lock, error) {
 	return newLock(ctx, repo, false)
 }
 
 // NewExclusiveLock returns a new, exclusive lock for the repository. If
 // another lock (normal and exclusive) is already held by another process,
-// ErrAlreadyLocked is returned.
+// it returns an error that satisfies IsAlreadyLocked.
 func NewExclusiveLock(ctx context.Context, repo Repository) (*Lock, error) {
 	return newLock(ctx, repo, true)
 }
@@ -147,11 +145,11 @@ func (l *Lock) checkForOtherLocks(ctx context.Context) error {
 		}
 
 		if l.Exclusive {
-			return ErrAlreadyLocked{otherLock: lock}
+			return &alreadyLockedError{otherLock: lock}
 		}
 
 		if !l.Exclusive && lock.Exclusive {
-			return ErrAlreadyLocked{otherLock: lock}
+			return &alreadyLockedError{otherLock: lock}
 		}
 
 		return nil

internal/restic/testing.go

@@ -9,8 +9,6 @@ import (
 	"testing"
 	"time"
 
-	"github.com/restic/restic/internal/errors"
-
 	"github.com/restic/chunker"
 )
 
@@ -44,7 +42,7 @@ func (fs *fakeFileSystem) saveFile(ctx context.Context, rd io.Reader) (blobs IDs
 	blobs = IDs{}
 	for {
 		chunk, err := fs.chunker.Next(fs.buf)
-		if errors.Cause(err) == io.EOF {
+		if err == io.EOF {
 			break
 		}
 

internal/test/helpers.go

@@ -175,7 +175,7 @@ func ResetReadOnly(t testing.TB, dir string) {
 
 		return nil
 	})
-	if os.IsNotExist(errors.Cause(err)) {
+	if errors.Is(err, os.ErrNotExist) {
 		err = nil
 	}
 	OK(t, err)
@@ -186,7 +186,7 @@ func ResetReadOnly(t testing.TB, dir string) {
 func RemoveAll(t testing.TB, path string) {
 	ResetReadOnly(t, path)
 	err := os.RemoveAll(path)
-	if os.IsNotExist(errors.Cause(err)) {
+	if errors.Is(err, os.ErrNotExist) {
 		err = nil
 	}
 	OK(t, err)