Fix listing notebooks in a subdirectory (#1468)

## Changes

This worked fine if the notebooks are located in the filer's root and
didn't if they are nested in a directory.

This change adds test coverage and fixes the underlying issue.

## Tests

Ran integration test manually.

internal/filer_test.go

@@ -511,6 +511,7 @@ func TestAccFilerWorkspaceFilesExtensionsReadDir(t *testing.T) {
 		content string
 	}{
 		{"dir1/dir2/dir3/file.txt", "file content"},
+		{"dir1/notebook.py", "# Databricks notebook source\nprint('first upload'))"},
 		{"foo.py", "print('foo')"},
 		{"foo.r", "print('foo')"},
 		{"foo.scala", "println('foo')"},
@@ -523,6 +524,16 @@ func TestAccFilerWorkspaceFilesExtensionsReadDir(t *testing.T) {
 		{"sqlNb.sql", "-- Databricks notebook source\n SELECT \"first upload\""},
 	}
 
+	// Assert that every file has a unique basename
+	basenames := map[string]struct{}{}
+	for _, f := range files {
+		basename := path.Base(f.name)
+		if _, ok := basenames[basename]; ok {
+			t.Fatalf("basename %s is not unique", basename)
+		}
+		basenames[basename] = struct{}{}
+	}
+
 	ctx := context.Background()
 	wf, _ := setupWsfsExtensionsFiler(t)
 
@@ -534,7 +545,6 @@ func TestAccFilerWorkspaceFilesExtensionsReadDir(t *testing.T) {
 	// Read entries
 	entries, err := wf.ReadDir(ctx, ".")
 	require.NoError(t, err)
-	assert.Len(t, entries, len(files))
 	names := []string{}
 	for _, e := range entries {
 		names = append(names, e.Name())
@@ -552,6 +562,18 @@ func TestAccFilerWorkspaceFilesExtensionsReadDir(t *testing.T) {
 		"scalaNb.scala",
 		"sqlNb.sql",
 	}, names)
+
+	// Read entries in subdirectory
+	entries, err = wf.ReadDir(ctx, "dir1")
+	require.NoError(t, err)
+	names = []string{}
+	for _, e := range entries {
+		names = append(names, e.Name())
+	}
+	assert.Equal(t, []string{
+		"dir2",
+		"notebook.py",
+	}, names)
 }
 
 func setupFilerWithExtensionsTest(t *testing.T) filer.Filer {

libs/filer/workspace_files_extensions_client.go

@@ -235,7 +235,7 @@ func (w *workspaceFilesExtensionsClient) ReadDir(ctx context.Context, name strin
 
 		// If the object is a notebook, include an extension in the entry.
 		if sysInfo.ObjectType == workspace.ObjectTypeNotebook {
-			stat, err := w.getNotebookStatByNameWithoutExt(ctx, entries[i].Name())
+			stat, err := w.getNotebookStatByNameWithoutExt(ctx, path.Join(name, entries[i].Name()))
 			if err != nil {
 				return nil, err
 			}