From 963105b0873b8c15ad2cb79025c7ad4066482221 Mon Sep 17 00:00:00 2001
From: Pieter Noordhuis <pieter.noordhuis@databricks.com>
Date: Thu, 18 Dec 2025 10:14:26 +0100
Subject: [PATCH 1/3] Unexport errors returned by the filer package

---
 libs/filer/dbfs_client.go                     |  20 +--
 libs/filer/errors.go                          | 117 ++++++++++++++++++
 libs/filer/errors_test.go                     |  96 ++++++++++++++
 libs/filer/fake_filer.go                      |   2 +-
 libs/filer/filer.go                           |  94 --------------
 libs/filer/files_client.go                    |  30 ++---
 libs/filer/local_client.go                    |  20 +--
 libs/filer/workspace_files_cache.go           |   2 +-
 libs/filer/workspace_files_client.go          |  26 ++--
 .../workspace_files_extensions_client.go      |  12 +-
 10 files changed, 269 insertions(+), 150 deletions(-)
 create mode 100644 libs/filer/errors.go
 create mode 100644 libs/filer/errors_test.go

diff --git a/libs/filer/dbfs_client.go b/libs/filer/dbfs_client.go
index 7f7c4570d9..dfa6a6f7b8 100644
--- a/libs/filer/dbfs_client.go
+++ b/libs/filer/dbfs_client.go
@@ -106,7 +106,7 @@ func (w *DbfsClient) Write(ctx context.Context, name string, reader io.Reader, m
 			// This API returns a 404 if the file doesn't exist.
 			if aerr.StatusCode == http.StatusNotFound {
 				if aerr.ErrorCode == "RESOURCE_DOES_NOT_EXIST" {
-					return NoSuchDirectoryError{path.Dir(absPath)}
+					return noSuchDirectoryError{path.Dir(absPath)}
 				}
 			}
 
@@ -124,7 +124,7 @@ func (w *DbfsClient) Write(ctx context.Context, name string, reader io.Reader, m
 		// This API returns a 400 if the file already exists.
 		if aerr.StatusCode == http.StatusBadRequest {
 			if aerr.ErrorCode == "RESOURCE_ALREADY_EXISTS" {
-				return FileAlreadyExistsError{absPath}
+				return fileAlreadyExistsError{absPath}
 			}
 		}
 
@@ -150,7 +150,7 @@ func (w *DbfsClient) Read(ctx context.Context, name string) (io.ReadCloser, erro
 	if err != nil {
 		// Return error if file is a directory
 		if strings.Contains(err.Error(), "cannot open directory for reading") {
-			return nil, NotAFile{absPath}
+			return nil, notAFile{absPath}
 		}
 
 		var aerr *apierr.APIError
@@ -161,7 +161,7 @@ func (w *DbfsClient) Read(ctx context.Context, name string) (io.ReadCloser, erro
 		// This API returns a 404 if the file doesn't exist.
 		if aerr.StatusCode == http.StatusNotFound {
 			if aerr.ErrorCode == "RESOURCE_DOES_NOT_EXIST" {
-				return nil, FileDoesNotExistError{absPath}
+				return nil, fileDoesNotExistError{absPath}
 			}
 		}
 
@@ -180,7 +180,7 @@ func (w *DbfsClient) Delete(ctx context.Context, name string, mode ...DeleteMode
 
 	// Illegal to delete the root path.
 	if absPath == w.root.rootPath {
-		return CannotDeleteRootError{}
+		return cannotDeleteRootError{}
 	}
 
 	// Issue info call before delete because delete succeeds if the specified path doesn't exist.
@@ -198,7 +198,7 @@ func (w *DbfsClient) Delete(ctx context.Context, name string, mode ...DeleteMode
 		// This API returns a 404 if the file doesn't exist.
 		if aerr.StatusCode == http.StatusNotFound {
 			if aerr.ErrorCode == "RESOURCE_DOES_NOT_EXIST" {
-				return FileDoesNotExistError{absPath}
+				return fileDoesNotExistError{absPath}
 			}
 		}
 
@@ -227,7 +227,7 @@ func (w *DbfsClient) Delete(ctx context.Context, name string, mode ...DeleteMode
 	case http.StatusBadRequest:
 		// Anecdotally, this error is returned when attempting to delete a non-empty directory.
 		if aerr.ErrorCode == "IO_ERROR" {
-			return DirectoryNotEmptyError{absPath}
+			return directoryNotEmptyError{absPath}
 		}
 	}
 
@@ -250,7 +250,7 @@ func (w *DbfsClient) ReadDir(ctx context.Context, name string) ([]fs.DirEntry, e
 		// This API returns a 404 if the file doesn't exist.
 		if aerr.StatusCode == http.StatusNotFound {
 			if aerr.ErrorCode == "RESOURCE_DOES_NOT_EXIST" {
-				return nil, NoSuchDirectoryError{absPath}
+				return nil, noSuchDirectoryError{absPath}
 			}
 		}
 
@@ -258,7 +258,7 @@ func (w *DbfsClient) ReadDir(ctx context.Context, name string) ([]fs.DirEntry, e
 	}
 
 	if len(res.Files) == 1 && res.Files[0].Path == absPath {
-		return nil, NotADirectory{absPath}
+		return nil, notADirectory{absPath}
 	}
 
 	info := make([]fs.DirEntry, len(res.Files))
@@ -296,7 +296,7 @@ func (w *DbfsClient) Stat(ctx context.Context, name string) (fs.FileInfo, error)
 		// This API returns a 404 if the file doesn't exist.
 		if aerr.StatusCode == http.StatusNotFound {
 			if aerr.ErrorCode == "RESOURCE_DOES_NOT_EXIST" {
-				return nil, FileDoesNotExistError{absPath}
+				return nil, fileDoesNotExistError{absPath}
 			}
 		}
 
diff --git a/libs/filer/errors.go b/libs/filer/errors.go
new file mode 100644
index 0000000000..67f15ecb01
--- /dev/null
+++ b/libs/filer/errors.go
@@ -0,0 +1,117 @@
+package filer
+
+import "io/fs"
+
+// fileAlreadyExistsError is returned when attempting to write a file at a path
+// that already exists, without using the OverwriteIfExists WriteMode flag.
+type fileAlreadyExistsError struct {
+	path string
+}
+
+func (err fileAlreadyExistsError) Error() string {
+	return "file already exists: " + err.path
+}
+
+func (err fileAlreadyExistsError) Is(other error) bool {
+	return other == fs.ErrExist
+}
+
+// fileDoesNotExistError is returned when attempting to read, delete, or stat
+// a file that does not exist. It is also returned by the workspace files
+// extensions client when a notebook exists at a path but a file was expected.
+type fileDoesNotExistError struct {
+	path string
+}
+
+func (err fileDoesNotExistError) Is(other error) bool {
+	return other == fs.ErrNotExist
+}
+
+func (err fileDoesNotExistError) Error() string {
+	return "file does not exist: " + err.path
+}
+
+// noSuchDirectoryError is returned when attempting to write a file to a path
+// whose parent directory does not exist (without CreateParentDirectories mode),
+// or when attempting to read a directory that does not exist.
+type noSuchDirectoryError struct {
+	path string
+}
+
+func (err noSuchDirectoryError) Error() string {
+	return "no such directory: " + err.path
+}
+
+func (err noSuchDirectoryError) Is(other error) bool {
+	return other == fs.ErrNotExist
+}
+
+// notADirectory is returned when attempting to read a directory (ReadDir)
+// but the path points to a file instead of a directory.
+type notADirectory struct {
+	path string
+}
+
+func (err notADirectory) Error() string {
+	return "not a directory: " + err.path
+}
+
+func (err notADirectory) Is(other error) bool {
+	return other == fs.ErrInvalid
+}
+
+// notAFile is returned when attempting to read a file but the path points
+// to a directory instead of a file.
+type notAFile struct {
+	path string
+}
+
+func (err notAFile) Error() string {
+	return "not a file: " + err.path
+}
+
+func (err notAFile) Is(other error) bool {
+	return other == fs.ErrInvalid
+}
+
+// directoryNotEmptyError is returned when attempting to delete a directory
+// that contains files or subdirectories, without using the DeleteRecursively
+// DeleteMode flag.
+type directoryNotEmptyError struct {
+	path string
+}
+
+func (err directoryNotEmptyError) Error() string {
+	return "directory not empty: " + err.path
+}
+
+func (err directoryNotEmptyError) Is(other error) bool {
+	return other == fs.ErrInvalid
+}
+
+// cannotDeleteRootError is returned when attempting to delete the root path
+// of the filer. Deleting the root is not allowed as it would break subsequent
+// file operations.
+type cannotDeleteRootError struct{}
+
+func (err cannotDeleteRootError) Error() string {
+	return "unable to delete filer root"
+}
+
+func (err cannotDeleteRootError) Is(other error) bool {
+	return other == fs.ErrInvalid
+}
+
+// permissionError is returned when access is denied to a path, for example
+// when attempting to create a directory but lacking write permissions.
+type permissionError struct {
+	path string
+}
+
+func (err permissionError) Error() string {
+	return "access denied: " + err.path
+}
+
+func (err permissionError) Is(other error) bool {
+	return other == fs.ErrPermission
+}
diff --git a/libs/filer/errors_test.go b/libs/filer/errors_test.go
new file mode 100644
index 0000000000..a1fb066e09
--- /dev/null
+++ b/libs/filer/errors_test.go
@@ -0,0 +1,96 @@
+package filer
+
+import (
+	"io/fs"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestFileAlreadyExistsError_Is(t *testing.T) {
+	err := fileAlreadyExistsError{path: "/test/path"}
+	assert.ErrorIs(t, err, fs.ErrExist)
+	assert.NotErrorIs(t, err, fs.ErrNotExist)
+}
+
+func TestFileAlreadyExistsError_Error(t *testing.T) {
+	err := fileAlreadyExistsError{path: "/test/path"}
+	assert.Equal(t, "file already exists: /test/path", err.Error())
+}
+
+func TestFileDoesNotExistError_Is(t *testing.T) {
+	err := fileDoesNotExistError{path: "/test/path"}
+	assert.ErrorIs(t, err, fs.ErrNotExist)
+	assert.NotErrorIs(t, err, fs.ErrExist)
+}
+
+func TestFileDoesNotExistError_Error(t *testing.T) {
+	err := fileDoesNotExistError{path: "/test/path"}
+	assert.Equal(t, "file does not exist: /test/path", err.Error())
+}
+
+func TestNoSuchDirectoryError_Is(t *testing.T) {
+	err := noSuchDirectoryError{path: "/test/path"}
+	assert.ErrorIs(t, err, fs.ErrNotExist)
+	assert.NotErrorIs(t, err, fs.ErrExist)
+}
+
+func TestNoSuchDirectoryError_Error(t *testing.T) {
+	err := noSuchDirectoryError{path: "/test/path"}
+	assert.Equal(t, "no such directory: /test/path", err.Error())
+}
+
+func TestNotADirectory_Is(t *testing.T) {
+	err := notADirectory{path: "/test/path"}
+	assert.ErrorIs(t, err, fs.ErrInvalid)
+	assert.NotErrorIs(t, err, fs.ErrNotExist)
+}
+
+func TestNotADirectory_Error(t *testing.T) {
+	err := notADirectory{path: "/test/path"}
+	assert.Equal(t, "not a directory: /test/path", err.Error())
+}
+
+func TestNotAFile_Is(t *testing.T) {
+	err := notAFile{path: "/test/path"}
+	assert.ErrorIs(t, err, fs.ErrInvalid)
+	assert.NotErrorIs(t, err, fs.ErrNotExist)
+}
+
+func TestNotAFile_Error(t *testing.T) {
+	err := notAFile{path: "/test/path"}
+	assert.Equal(t, "not a file: /test/path", err.Error())
+}
+
+func TestDirectoryNotEmptyError_Is(t *testing.T) {
+	err := directoryNotEmptyError{path: "/test/path"}
+	assert.ErrorIs(t, err, fs.ErrInvalid)
+	assert.NotErrorIs(t, err, fs.ErrNotExist)
+}
+
+func TestDirectoryNotEmptyError_Error(t *testing.T) {
+	err := directoryNotEmptyError{path: "/test/path"}
+	assert.Equal(t, "directory not empty: /test/path", err.Error())
+}
+
+func TestCannotDeleteRootError_Is(t *testing.T) {
+	err := cannotDeleteRootError{}
+	assert.ErrorIs(t, err, fs.ErrInvalid)
+	assert.NotErrorIs(t, err, fs.ErrNotExist)
+}
+
+func TestCannotDeleteRootError_Error(t *testing.T) {
+	err := cannotDeleteRootError{}
+	assert.Equal(t, "unable to delete filer root", err.Error())
+}
+
+func TestPermissionError_Is(t *testing.T) {
+	err := permissionError{path: "/test/path"}
+	assert.ErrorIs(t, err, fs.ErrPermission)
+	assert.NotErrorIs(t, err, fs.ErrNotExist)
+}
+
+func TestPermissionError_Error(t *testing.T) {
+	err := permissionError{path: "/test/path"}
+	assert.Equal(t, "access denied: /test/path", err.Error())
+}
diff --git a/libs/filer/fake_filer.go b/libs/filer/fake_filer.go
index 1e1cbd9852..f6eb5955ee 100644
--- a/libs/filer/fake_filer.go
+++ b/libs/filer/fake_filer.go
@@ -37,7 +37,7 @@ func (f *FakeFiler) ReadDir(ctx context.Context, p string) ([]fs.DirEntry, error
 	p = strings.TrimSuffix(p, "/")
 	entry, ok := f.entries[p]
 	if !ok {
-		return nil, NoSuchDirectoryError{p}
+		return nil, noSuchDirectoryError{p}
 	}
 
 	if !entry.FakeDir {
diff --git a/libs/filer/filer.go b/libs/filer/filer.go
index 372c829297..4ad1d97b95 100644
--- a/libs/filer/filer.go
+++ b/libs/filer/filer.go
@@ -30,100 +30,6 @@ const (
 	DeleteRecursively DeleteMode = 1 << iota
 )
 
-type FileAlreadyExistsError struct {
-	path string
-}
-
-func (err FileAlreadyExistsError) Error() string {
-	return "file already exists: " + err.path
-}
-
-func (err FileAlreadyExistsError) Is(other error) bool {
-	return other == fs.ErrExist
-}
-
-type FileDoesNotExistError struct {
-	path string
-}
-
-func (err FileDoesNotExistError) Is(other error) bool {
-	return other == fs.ErrNotExist
-}
-
-func (err FileDoesNotExistError) Error() string {
-	return "file does not exist: " + err.path
-}
-
-type NoSuchDirectoryError struct {
-	path string
-}
-
-func (err NoSuchDirectoryError) Error() string {
-	return "no such directory: " + err.path
-}
-
-func (err NoSuchDirectoryError) Is(other error) bool {
-	return other == fs.ErrNotExist
-}
-
-type NotADirectory struct {
-	path string
-}
-
-func (err NotADirectory) Error() string {
-	return "not a directory: " + err.path
-}
-
-func (err NotADirectory) Is(other error) bool {
-	return other == fs.ErrInvalid
-}
-
-type NotAFile struct {
-	path string
-}
-
-func (err NotAFile) Error() string {
-	return "not a file: " + err.path
-}
-
-func (err NotAFile) Is(other error) bool {
-	return other == fs.ErrInvalid
-}
-
-type DirectoryNotEmptyError struct {
-	path string
-}
-
-func (err DirectoryNotEmptyError) Error() string {
-	return "directory not empty: " + err.path
-}
-
-func (err DirectoryNotEmptyError) Is(other error) bool {
-	return other == fs.ErrInvalid
-}
-
-type CannotDeleteRootError struct{}
-
-func (err CannotDeleteRootError) Error() string {
-	return "unable to delete filer root"
-}
-
-func (err CannotDeleteRootError) Is(other error) bool {
-	return other == fs.ErrInvalid
-}
-
-type PermissionError struct {
-	path string
-}
-
-func (err PermissionError) Error() string {
-	return "access denied: " + err.path
-}
-
-func (err PermissionError) Is(other error) bool {
-	return other == fs.ErrPermission
-}
-
 // Filer is used to access files in a workspace.
 // It has implementations for accessing files in WSFS and in DBFS.
 type Filer interface {
diff --git a/libs/filer/files_client.go b/libs/filer/files_client.go
index 2594d35a39..4160b9b209 100644
--- a/libs/filer/files_client.go
+++ b/libs/filer/files_client.go
@@ -138,7 +138,7 @@ func (w *FilesClient) Write(ctx context.Context, name string, reader io.Reader,
 
 			// This API returns a 404 if the file doesn't exist.
 			if aerr.StatusCode == http.StatusNotFound {
-				return NoSuchDirectoryError{path.Dir(absPath)}
+				return noSuchDirectoryError{path.Dir(absPath)}
 			}
 
 			return err
@@ -163,7 +163,7 @@ func (w *FilesClient) Write(ctx context.Context, name string, reader io.Reader,
 
 	// This API returns 409 if the file already exists, when the object type is file
 	if aerr.StatusCode == http.StatusConflict && aerr.ErrorCode == "ALREADY_EXISTS" {
-		return FileAlreadyExistsError{absPath}
+		return fileAlreadyExistsError{absPath}
 	}
 
 	return err
@@ -193,11 +193,11 @@ func (w *FilesClient) Read(ctx context.Context, name string) (io.ReadCloser, err
 	if aerr.StatusCode == http.StatusNotFound {
 		// Check if the path is a directory. If so, return not a file error.
 		if _, err := w.statDir(ctx, name); err == nil {
-			return nil, NotAFile{absPath}
+			return nil, notAFile{absPath}
 		}
 
 		// No file or directory exists at the specified path. Return no such file error.
-		return nil, FileDoesNotExistError{absPath}
+		return nil, fileDoesNotExistError{absPath}
 	}
 
 	return nil, err
@@ -211,7 +211,7 @@ func (w *FilesClient) deleteFile(ctx context.Context, name string) error {
 
 	// Illegal to delete the root path.
 	if absPath == w.root.rootPath {
-		return CannotDeleteRootError{}
+		return cannotDeleteRootError{}
 	}
 
 	err = w.workspaceClient.Files.DeleteByFilePath(ctx, absPath)
@@ -229,7 +229,7 @@ func (w *FilesClient) deleteFile(ctx context.Context, name string) error {
 
 	// This files delete API returns a 404 if the specified path does not exist.
 	if aerr.StatusCode == http.StatusNotFound {
-		return FileDoesNotExistError{absPath}
+		return fileDoesNotExistError{absPath}
 	}
 
 	return err
@@ -243,7 +243,7 @@ func (w *FilesClient) deleteDirectory(ctx context.Context, name string) error {
 
 	// Illegal to delete the root path.
 	if absPath == w.root.rootPath {
-		return CannotDeleteRootError{}
+		return cannotDeleteRootError{}
 	}
 
 	err = w.workspaceClient.Files.DeleteDirectoryByDirectoryPath(ctx, absPath)
@@ -266,7 +266,7 @@ func (w *FilesClient) deleteDirectory(ctx context.Context, name string) error {
 		if !slices.Contains(reasons, "FILES_API_DIRECTORY_IS_NOT_EMPTY") {
 			return err
 		}
-		return DirectoryNotEmptyError{absPath}
+		return directoryNotEmptyError{absPath}
 	}
 
 	return err
@@ -395,11 +395,11 @@ func (w *FilesClient) ReadDir(ctx context.Context, name string) ([]fs.DirEntry,
 	if apierr.StatusCode == http.StatusNotFound {
 		// Check if the path is a file. If so, return not a directory error.
 		if _, err := w.statFile(ctx, name); err == nil {
-			return nil, NotADirectory{absPath}
+			return nil, notADirectory{absPath}
 		}
 
 		// No file or directory exists at the specified path. Return no such directory error.
-		return nil, NoSuchDirectoryError{absPath}
+		return nil, noSuchDirectoryError{absPath}
 	}
 	return nil, err
 }
@@ -417,7 +417,7 @@ func (w *FilesClient) Mkdir(ctx context.Context, name string) error {
 	// Special handling of this error only if it is an API error.
 	var aerr *apierr.APIError
 	if errors.As(err, &aerr) && aerr.StatusCode == http.StatusConflict {
-		return FileAlreadyExistsError{absPath}
+		return fileAlreadyExistsError{absPath}
 	}
 
 	return err
@@ -449,7 +449,7 @@ func (w *FilesClient) statFile(ctx context.Context, name string) (fs.FileInfo, e
 
 	// This API returns a 404 if the specified path does not exist.
 	if aerr.StatusCode == http.StatusNotFound {
-		return nil, FileDoesNotExistError{absPath}
+		return nil, fileDoesNotExistError{absPath}
 	}
 
 	return nil, err
@@ -477,7 +477,7 @@ func (w *FilesClient) statDir(ctx context.Context, name string) (fs.FileInfo, er
 
 	// The directory metadata API returns a 404 if the specified path does not exist.
 	if aerr.StatusCode == http.StatusNotFound {
-		return nil, NoSuchDirectoryError{absPath}
+		return nil, noSuchDirectoryError{absPath}
 	}
 
 	return nil, err
@@ -492,8 +492,8 @@ func (w *FilesClient) Stat(ctx context.Context, name string) (fs.FileInfo, error
 		return dirInfo, nil
 	}
 
-	// Return early if the error is not a NoSuchDirectoryError.
-	if !errors.As(err, &NoSuchDirectoryError{}) {
+	// Return early if the error is not a noSuchDirectoryError.
+	if !errors.Is(err, fs.ErrNotExist) {
 		return nil, err
 	}
 
diff --git a/libs/filer/local_client.go b/libs/filer/local_client.go
index 385aa69247..ded6fc8e2b 100644
--- a/libs/filer/local_client.go
+++ b/libs/filer/local_client.go
@@ -58,9 +58,9 @@ func (w *LocalClient) Write(ctx context.Context, name string, reader io.Reader,
 	if err != nil {
 		switch {
 		case errors.Is(err, fs.ErrNotExist):
-			return NoSuchDirectoryError{path: absPath}
+			return noSuchDirectoryError{path: absPath}
 		case errors.Is(err, fs.ErrExist):
-			return FileAlreadyExistsError{path: absPath}
+			return fileAlreadyExistsError{path: absPath}
 		default:
 			return err
 		}
@@ -87,13 +87,13 @@ func (w *LocalClient) Read(ctx context.Context, name string) (io.ReadCloser, err
 	stat, err := os.Stat(absPath)
 	if err != nil {
 		if errors.Is(err, fs.ErrNotExist) {
-			return nil, FileDoesNotExistError{path: absPath}
+			return nil, fileDoesNotExistError{path: absPath}
 		}
 		return nil, err
 	}
 
 	if stat.IsDir() {
-		return nil, NotAFile{path: absPath}
+		return nil, notAFile{path: absPath}
 	}
 
 	return os.Open(absPath)
@@ -107,7 +107,7 @@ func (w *LocalClient) Delete(ctx context.Context, name string, mode ...DeleteMod
 
 	// Illegal to delete the root path.
 	if absPath == w.root.rootPath {
-		return CannotDeleteRootError{}
+		return cannotDeleteRootError{}
 	}
 
 	err = os.Remove(absPath)
@@ -118,14 +118,14 @@ func (w *LocalClient) Delete(ctx context.Context, name string, mode ...DeleteMod
 	}
 
 	if errors.Is(err, fs.ErrNotExist) {
-		return FileDoesNotExistError{path: absPath}
+		return fileDoesNotExistError{path: absPath}
 	}
 
 	if errors.Is(err, fs.ErrExist) {
 		if slices.Contains(mode, DeleteRecursively) {
 			return os.RemoveAll(absPath)
 		}
-		return DirectoryNotEmptyError{path: absPath}
+		return directoryNotEmptyError{path: absPath}
 	}
 
 	return err
@@ -140,13 +140,13 @@ func (w *LocalClient) ReadDir(ctx context.Context, name string) ([]fs.DirEntry,
 	stat, err := os.Stat(absPath)
 	if err != nil {
 		if errors.Is(err, fs.ErrNotExist) {
-			return nil, NoSuchDirectoryError{path: absPath}
+			return nil, noSuchDirectoryError{path: absPath}
 		}
 		return nil, err
 	}
 
 	if !stat.IsDir() {
-		return nil, NotADirectory{path: absPath}
+		return nil, notADirectory{path: absPath}
 	}
 
 	return os.ReadDir(absPath)
@@ -169,7 +169,7 @@ func (w *LocalClient) Stat(ctx context.Context, name string) (fs.FileInfo, error
 
 	stat, err := os.Stat(absPath)
 	if errors.Is(err, fs.ErrNotExist) {
-		return nil, FileDoesNotExistError{path: absPath}
+		return nil, fileDoesNotExistError{path: absPath}
 	}
 	return stat, err
 }
diff --git a/libs/filer/workspace_files_cache.go b/libs/filer/workspace_files_cache.go
index 5837ad27dc..7b822d5feb 100644
--- a/libs/filer/workspace_files_cache.go
+++ b/libs/filer/workspace_files_cache.go
@@ -385,7 +385,7 @@ func (c *cache) statFromReadDir(ctx context.Context, name string, entry *readDir
 		return e.wait(ctx)
 	}
 
-	return nil, FileDoesNotExistError{name}
+	return nil, fileDoesNotExistError{name}
 }
 
 // Stat returns the file info for a file or directory.
diff --git a/libs/filer/workspace_files_client.go b/libs/filer/workspace_files_client.go
index 6acd066808..eb09d532e3 100644
--- a/libs/filer/workspace_files_client.go
+++ b/libs/filer/workspace_files_client.go
@@ -172,14 +172,14 @@ func (w *WorkspaceFilesClient) Write(ctx context.Context, name string, reader io
 	// This API returns a 404 if the parent directory does not exist.
 	if aerr.StatusCode == http.StatusNotFound {
 		if !slices.Contains(mode, CreateParentDirectories) {
-			return NoSuchDirectoryError{path.Dir(absPath)}
+			return noSuchDirectoryError{path.Dir(absPath)}
 		}
 
 		// Create parent directory.
 		err = w.workspaceClient.Workspace.MkdirsByPath(ctx, path.Dir(absPath))
 		if err != nil {
 			if errors.As(err, &aerr) && aerr.StatusCode == http.StatusForbidden {
-				return PermissionError{absPath}
+				return permissionError{absPath}
 			}
 			return fmt.Errorf("unable to mkdir to write file %s: %w", absPath, err)
 		}
@@ -190,7 +190,7 @@ func (w *WorkspaceFilesClient) Write(ctx context.Context, name string, reader io
 
 	// This API returns 409 if the file already exists, when the object type is file
 	if aerr.StatusCode == http.StatusConflict {
-		return FileAlreadyExistsError{absPath}
+		return fileAlreadyExistsError{absPath}
 	}
 
 	// This API returns 400 if the file already exists, when the object type is notebook
@@ -199,16 +199,16 @@ func (w *WorkspaceFilesClient) Write(ctx context.Context, name string, reader io
 		// Parse file path from regex capture group
 		matches := regex.FindStringSubmatch(aerr.Message)
 		if len(matches) == 2 {
-			return FileAlreadyExistsError{matches[1]}
+			return fileAlreadyExistsError{matches[1]}
 		}
 
 		// Default to path specified to filer.Write if regex capture fails
-		return FileAlreadyExistsError{absPath}
+		return fileAlreadyExistsError{absPath}
 	}
 
 	// This API returns StatusForbidden when you have read access but don't have write access to a file
 	if aerr.StatusCode == http.StatusForbidden {
-		return PermissionError{absPath}
+		return permissionError{absPath}
 	}
 
 	return err
@@ -230,7 +230,7 @@ func (w *WorkspaceFilesClient) Read(ctx context.Context, name string) (io.ReadCl
 		return nil, err
 	}
 	if stat.IsDir() {
-		return nil, NotAFile{absPath}
+		return nil, notAFile{absPath}
 	}
 
 	// Export file contents. Note the /workspace/export API has a limit of 10MBs
@@ -246,7 +246,7 @@ func (w *WorkspaceFilesClient) Delete(ctx context.Context, name string, mode ...
 
 	// Illegal to delete the root path.
 	if absPath == w.root.rootPath {
-		return CannotDeleteRootError{}
+		return cannotDeleteRootError{}
 	}
 
 	recursive := slices.Contains(mode, DeleteRecursively)
@@ -270,10 +270,10 @@ func (w *WorkspaceFilesClient) Delete(ctx context.Context, name string, mode ...
 	switch aerr.StatusCode {
 	case http.StatusBadRequest:
 		if aerr.ErrorCode == "DIRECTORY_NOT_EMPTY" {
-			return DirectoryNotEmptyError{absPath}
+			return directoryNotEmptyError{absPath}
 		}
 	case http.StatusNotFound:
-		return FileDoesNotExistError{absPath}
+		return fileDoesNotExistError{absPath}
 	}
 
 	return err
@@ -290,7 +290,7 @@ func (w *WorkspaceFilesClient) ReadDir(ctx context.Context, name string) ([]fs.D
 	})
 
 	if len(objects) == 1 && objects[0].Path == absPath {
-		return nil, NotADirectory{absPath}
+		return nil, notADirectory{absPath}
 	}
 
 	if err != nil {
@@ -303,7 +303,7 @@ func (w *WorkspaceFilesClient) ReadDir(ctx context.Context, name string) ([]fs.D
 		// NOTE: This API returns a 404 if the specified path does not exist,
 		// but can also do so if we don't have read access.
 		if aerr.StatusCode == http.StatusNotFound {
-			return nil, NoSuchDirectoryError{path.Dir(absPath)}
+			return nil, noSuchDirectoryError{path.Dir(absPath)}
 		}
 		return nil, err
 	}
@@ -354,7 +354,7 @@ func (w *WorkspaceFilesClient) Stat(ctx context.Context, name string) (fs.FileIn
 
 		// This API returns a 404 if the specified path does not exist.
 		if aerr.StatusCode == http.StatusNotFound {
-			return nil, FileDoesNotExistError{absPath}
+			return nil, fileDoesNotExistError{absPath}
 		}
 	}
 
diff --git a/libs/filer/workspace_files_extensions_client.go b/libs/filer/workspace_files_extensions_client.go
index 0127d180c6..debc8582eb 100644
--- a/libs/filer/workspace_files_extensions_client.go
+++ b/libs/filer/workspace_files_extensions_client.go
@@ -61,7 +61,7 @@ func (w *WorkspaceFilesExtensionsClient) getNotebookStatByNameWithExt(ctx contex
 	stat, err := w.stat(ctx, nameWithoutExt)
 	if err != nil {
 		// If the file does not exist, return early.
-		if errors.As(err, &FileDoesNotExistError{}) {
+		if errors.Is(err, fs.ErrNotExist) {
 			return nil, nil
 		}
 		log.Debugf(ctx, "attempting to determine if %s could be a notebook. Failed to fetch the status of object at %s: %s", name, path.Join(w.root, nameWithoutExt), err)
@@ -259,7 +259,7 @@ func (w *WorkspaceFilesExtensionsClient) Read(ctx context.Context, name string)
 	r, err := w.wsfs.Read(ctx, name)
 
 	// If the file is not found, it might be a notebook.
-	if errors.As(err, &FileDoesNotExistError{}) {
+	if errors.Is(err, fs.ErrNotExist) {
 		stat, serr := w.getNotebookStatByNameWithExt(ctx, name)
 		if serr != nil {
 			// Unable to stat. Return the stat error.
@@ -302,7 +302,7 @@ func (w *WorkspaceFilesExtensionsClient) Delete(ctx context.Context, name string
 	err = w.wsfs.Delete(ctx, name, mode...)
 
 	// If the file is not found, it might be a notebook.
-	if errors.As(err, &FileDoesNotExistError{}) {
+	if errors.Is(err, fs.ErrNotExist) {
 		stat, serr := w.getNotebookStatByNameWithExt(ctx, name)
 		if serr != nil {
 			// Unable to stat. Return the stat error.
@@ -324,7 +324,7 @@ func (w *WorkspaceFilesExtensionsClient) Stat(ctx context.Context, name string)
 	info, err := w.wsfs.Stat(ctx, name)
 
 	// If the file is not found, it might be a notebook.
-	if errors.As(err, &FileDoesNotExistError{}) {
+	if errors.Is(err, fs.ErrNotExist) {
 		stat, serr := w.getNotebookStatByNameWithExt(ctx, name)
 		if serr != nil {
 			// Unable to stat. Return the stat error.
@@ -342,7 +342,7 @@ func (w *WorkspaceFilesExtensionsClient) Stat(ctx context.Context, name string)
 		return nil, err
 	}
 
-	// If an object is found and it is a notebook, return a FileDoesNotExistError.
+	// If an object is found and it is a notebook, return a fileDoesNotExistError.
 	// If a notebook is found by the workspace files client, without having stripped
 	// the extension, this implies that no file with the same name exists.
 	//
@@ -352,7 +352,7 @@ func (w *WorkspaceFilesExtensionsClient) Stat(ctx context.Context, name string)
 	// To stat the metadata of a notebook called `foo` in the workspace the user
 	// should use the name with the extension included like `foo.ipynb` or `foo.sql`.
 	if info.Sys().(workspace.ObjectInfo).ObjectType == workspace.ObjectTypeNotebook {
-		return nil, FileDoesNotExistError{name}
+		return nil, fileDoesNotExistError{name}
 	}
 
 	return info, nil

From 7fb4c9d1e46efebba11fae5c3b71d89dff14aeab Mon Sep 17 00:00:00 2001
From: Pieter Noordhuis <pieter.noordhuis@databricks.com>
Date: Thu, 18 Dec 2025 10:20:00 +0100
Subject: [PATCH 2/3] Missing diffs

---
 bundle/deploy/lock/acquire.go                |  4 +---
 experimental/ssh/internal/client/releases.go |  3 ++-
 integration/cmd/fs/cat_test.go               |  2 +-
 integration/cmd/fs/ls_test.go                |  2 +-
 integration/cmd/fs/mkdir_test.go             |  4 ++--
 integration/cmd/fs/rm_test.go                |  1 -
 integration/libs/filer/filer_test.go         | 12 ++----------
 libs/locker/locker.go                        |  2 +-
 8 files changed, 10 insertions(+), 20 deletions(-)

diff --git a/bundle/deploy/lock/acquire.go b/bundle/deploy/lock/acquire.go
index ab1f1cba16..d4f788c3ca 100644
--- a/bundle/deploy/lock/acquire.go
+++ b/bundle/deploy/lock/acquire.go
@@ -8,7 +8,6 @@ import (
 	"github.com/databricks/cli/bundle"
 	"github.com/databricks/cli/bundle/permissions"
 	"github.com/databricks/cli/libs/diag"
-	"github.com/databricks/cli/libs/filer"
 	"github.com/databricks/cli/libs/locker"
 	"github.com/databricks/cli/libs/log"
 )
@@ -57,8 +56,7 @@ func (m *acquire) Apply(ctx context.Context, b *bundle.Bundle) diag.Diagnostics
 			return permissions.ReportPossiblePermissionDenied(ctx, b, b.Config.Workspace.StatePath)
 		}
 
-		notExistsError := filer.NoSuchDirectoryError{}
-		if errors.As(err, &notExistsError) {
+		if errors.Is(err, fs.ErrNotExist) {
 			// If we get a "doesn't exist" error from the API this indicates
 			// we either don't have permissions or the path is invalid.
 			return permissions.ReportPossiblePermissionDenied(ctx, b, b.Config.Workspace.StatePath)
diff --git a/experimental/ssh/internal/client/releases.go b/experimental/ssh/internal/client/releases.go
index 89f64e742f..f147244e9e 100644
--- a/experimental/ssh/internal/client/releases.go
+++ b/experimental/ssh/internal/client/releases.go
@@ -5,6 +5,7 @@ import (
 	"errors"
 	"fmt"
 	"io"
+	"io/fs"
 	"net/http"
 	"os"
 	"path/filepath"
@@ -49,7 +50,7 @@ func uploadReleases(ctx context.Context, workspaceFiler filer.Filer, getRelease
 		if err == nil {
 			cmdio.LogString(ctx, fmt.Sprintf("File %s already exists in the workspace, skipping upload", remoteBinaryPath))
 			continue
-		} else if !errors.As(err, &filer.FileDoesNotExistError{}) {
+		} else if !errors.Is(err, fs.ErrNotExist) {
 			return fmt.Errorf("failed to check if file %s exists in workspace: %w", remoteBinaryPath, err)
 		}
 
diff --git a/integration/cmd/fs/cat_test.go b/integration/cmd/fs/cat_test.go
index 14ec8140e2..6f5ea4ded3 100644
--- a/integration/cmd/fs/cat_test.go
+++ b/integration/cmd/fs/cat_test.go
@@ -48,7 +48,7 @@ func TestFsCatOnADir(t *testing.T) {
 			require.NoError(t, err)
 
 			_, _, err = testcli.RequireErrorRun(t, ctx, "fs", "cat", path.Join(tmpDir, "dir1"))
-			assert.ErrorAs(t, err, &filer.NotAFile{})
+			assert.ErrorIs(t, err, fs.ErrInvalid)
 		})
 	}
 }
diff --git a/integration/cmd/fs/ls_test.go b/integration/cmd/fs/ls_test.go
index 0f53193bf9..d4d7cedef7 100644
--- a/integration/cmd/fs/ls_test.go
+++ b/integration/cmd/fs/ls_test.go
@@ -116,7 +116,7 @@ func TestFsLsOnFile(t *testing.T) {
 
 			_, _, err := testcli.RequireErrorRun(t, ctx, "fs", "ls", path.Join(tmpDir, "a", "hello.txt"), "--output=json")
 			assert.Regexp(t, "not a directory: .*/a/hello.txt", err.Error())
-			assert.ErrorAs(t, err, &filer.NotADirectory{})
+			assert.ErrorIs(t, err, fs.ErrInvalid)
 		})
 	}
 }
diff --git a/integration/cmd/fs/mkdir_test.go b/integration/cmd/fs/mkdir_test.go
index 5cea0599c6..9b78748570 100644
--- a/integration/cmd/fs/mkdir_test.go
+++ b/integration/cmd/fs/mkdir_test.go
@@ -2,13 +2,13 @@ package fs_test
 
 import (
 	"context"
+	"io/fs"
 	"path"
 	"regexp"
 	"strings"
 	"testing"
 
 	"github.com/databricks/cli/internal/testcli"
-	"github.com/databricks/cli/libs/filer"
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
 )
@@ -129,6 +129,6 @@ func TestFsMkdirWhenFileExistsAtPath(t *testing.T) {
 		// assert mkdir fails
 		_, _, err = testcli.RequireErrorRun(t, ctx, "fs", "mkdir", path.Join(tmpDir, "hello"))
 
-		assert.ErrorAs(t, err, &filer.FileAlreadyExistsError{})
+		assert.ErrorIs(t, err, fs.ErrExist)
 	})
 }
diff --git a/integration/cmd/fs/rm_test.go b/integration/cmd/fs/rm_test.go
index fc19bb5b53..736172f94b 100644
--- a/integration/cmd/fs/rm_test.go
+++ b/integration/cmd/fs/rm_test.go
@@ -95,7 +95,6 @@ func TestFsRmNonEmptyDirectory(t *testing.T) {
 			// Run rm command
 			_, _, err = testcli.RequireErrorRun(t, ctx, "fs", "rm", path.Join(tmpDir, "a"))
 			assert.ErrorIs(t, err, fs.ErrInvalid)
-			assert.ErrorAs(t, err, &filer.DirectoryNotEmptyError{})
 		})
 	}
 }
diff --git a/integration/libs/filer/filer_test.go b/integration/libs/filer/filer_test.go
index e67495e2de..2222e4b56c 100644
--- a/integration/libs/filer/filer_test.go
+++ b/integration/libs/filer/filer_test.go
@@ -107,12 +107,12 @@ func commonFilerRecursiveDeleteTest(t *testing.T, ctx context.Context, f filer.F
 	assert.Equal(t, []string{"file1", "file2", "subdir1", "subdir2"}, names)
 
 	err = f.Delete(ctx, "dir")
-	assert.ErrorAs(t, err, &filer.DirectoryNotEmptyError{})
+	assert.ErrorIs(t, err, fs.ErrInvalid)
 
 	err = f.Delete(ctx, "dir", filer.DeleteRecursively)
 	assert.NoError(t, err)
 	_, err = f.ReadDir(ctx, "dir")
-	assert.ErrorAs(t, err, &filer.NoSuchDirectoryError{})
+	assert.ErrorIs(t, err, fs.ErrNotExist)
 }
 
 func TestFilerRecursiveDelete(t *testing.T) {
@@ -145,12 +145,10 @@ func commonFilerReadWriteTests(t *testing.T, ctx context.Context, f filer.Filer)
 
 	// Write should fail because the intermediate directory doesn't exist.
 	err = f.Write(ctx, "/foo/bar", strings.NewReader(`hello world`))
-	assert.ErrorAs(t, err, &filer.NoSuchDirectoryError{})
 	assert.ErrorIs(t, err, fs.ErrNotExist)
 
 	// Read should fail because the intermediate directory doesn't yet exist.
 	_, err = f.Read(ctx, "/foo/bar")
-	assert.ErrorAs(t, err, &filer.FileDoesNotExistError{})
 	assert.ErrorIs(t, err, fs.ErrNotExist)
 
 	// Read should fail because the path points to a directory
@@ -166,7 +164,6 @@ func commonFilerReadWriteTests(t *testing.T, ctx context.Context, f filer.Filer)
 
 	// Write should fail because there is an existing file at the specified path.
 	err = f.Write(ctx, "/foo/bar", strings.NewReader(`hello universe`))
-	assert.ErrorAs(t, err, &filer.FileAlreadyExistsError{})
 	assert.ErrorIs(t, err, fs.ErrExist)
 
 	// Write with OverwriteIfExists should succeed.
@@ -196,12 +193,10 @@ func commonFilerReadWriteTests(t *testing.T, ctx context.Context, f filer.Filer)
 
 	// Delete should fail if the file doesn't exist.
 	err = f.Delete(ctx, "/doesnt_exist")
-	assert.ErrorAs(t, err, &filer.FileDoesNotExistError{})
 	assert.ErrorIs(t, err, fs.ErrNotExist)
 
 	// Stat should fail if the file doesn't exist.
 	_, err = f.Stat(ctx, "/doesnt_exist")
-	assert.ErrorAs(t, err, &filer.FileDoesNotExistError{})
 	assert.ErrorIs(t, err, fs.ErrNotExist)
 
 	// Delete should succeed for file that does exist.
@@ -210,7 +205,6 @@ func commonFilerReadWriteTests(t *testing.T, ctx context.Context, f filer.Filer)
 
 	// Delete should fail for a non-empty directory.
 	err = f.Delete(ctx, "/foo")
-	assert.ErrorAs(t, err, &filer.DirectoryNotEmptyError{})
 	assert.ErrorIs(t, err, fs.ErrInvalid)
 
 	// Delete should succeed for a non-empty directory if the DeleteRecursively flag is set.
@@ -220,7 +214,6 @@ func commonFilerReadWriteTests(t *testing.T, ctx context.Context, f filer.Filer)
 	// Delete of the filer root should ALWAYS fail, otherwise subsequent writes would fail.
 	// It is not in the filer's purview to delete its root directory.
 	err = f.Delete(ctx, "/")
-	assert.ErrorAs(t, err, &filer.CannotDeleteRootError{})
 	assert.ErrorIs(t, err, fs.ErrInvalid)
 }
 
@@ -276,7 +269,6 @@ func commonFilerReadDirTest(t *testing.T, ctx context.Context, f filer.Filer) {
 
 	// Expect an error if the path doesn't exist.
 	_, err = f.ReadDir(ctx, "/dir/a/b/c/d/e")
-	assert.ErrorAs(t, err, &filer.NoSuchDirectoryError{}, err)
 	assert.ErrorIs(t, err, fs.ErrNotExist)
 
 	// Expect two entries in the root.
diff --git a/libs/locker/locker.go b/libs/locker/locker.go
index aadc50b587..003f169cd3 100644
--- a/libs/locker/locker.go
+++ b/libs/locker/locker.go
@@ -156,7 +156,7 @@ func (locker *Locker) Lock(ctx context.Context, isForced bool) error {
 		// the error and instead fall through to [assertLockHeld] below.
 		// This function will return a more descriptive error message that includes
 		// details about the current holder of the lock.
-		if !errors.As(err, &filer.FileAlreadyExistsError{}) {
+		if !errors.Is(err, fs.ErrExist) {
 			return err
 		}
 	}

From fb496110406a7aa259a037330064ce7a862f4266 Mon Sep 17 00:00:00 2001
From: Pieter Noordhuis <pieter.noordhuis@databricks.com>
Date: Thu, 18 Dec 2025 11:11:11 +0100
Subject: [PATCH 3/3] Fix

---
 libs/filer/dbfs_client.go | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/libs/filer/dbfs_client.go b/libs/filer/dbfs_client.go
index 1ae1119901..d7d79207fd 100644
--- a/libs/filer/dbfs_client.go
+++ b/libs/filer/dbfs_client.go
@@ -233,7 +233,7 @@ func (w *DbfsClient) Delete(ctx context.Context, name string, mode ...DeleteMode
 		// Since 17th december we are observing the backend return an error_code of BAD_REQUEST
 		// instead of IO_ERROR. Doing direct comparison on the error string instead.
 		if strings.Contains(aerr.Message, "Directory is not empty. Use recursive delete or remove contents first.") {
-			return DirectoryNotEmptyError{absPath}
+			return directoryNotEmptyError{absPath}
 		}
 	}