Backport PR jupyterlab#11427: Handle relative paths to themePath and schemaDir (jupyterlab#11428)

Co-authored-by: Jason Grout <[email protected]>

Author: meeseeksmachine

jupyterlab/commands.py

@@ -2071,10 +2071,10 @@ def _validate_extension(data):
     if mime_extension and mime_extension not in files:
         messages.append('Missing mimeExtension module "%s"' % mime_extension)
 
-    if themePath and not any(f.startswith(themePath) for f in files):
+    if themePath and not any(f.startswith(str(Path(themePath))) for f in files):
         messages.append('themePath is empty: "%s"' % themePath)
 
-    if schemaDir and not any(f.startswith(schemaDir) for f in files):
+    if schemaDir and not any(f.startswith(str(Path(schemaDir))) for f in files):
         messages.append('schemaDir is empty: "%s"' % schemaDir)
 
     return messages