FileDownload does not work with fast-design

[hoxbro]

import panel as pn

pn.extension(design="fast")  # Works without this
pn.widgets.FileDownload().servable()

Traceback:

AttributeError: 'FileDownload.param' object has no attribute 'value'

Traceback (most recent call last):
  File "/home/shh/miniconda3/envs/holoviz/lib/python3.12/site-packages/bokeh/application/handlers/code_runner.py", line 229, in run
    exec(self._code, module.__dict__)
  File "/home/shh/Development/holoviz/example_download_widgets.py", line 4, in <module>
    pn.widgets.FileDownload().servable()
  File "/home/shh/projects/holoviz/repos/panel/panel/viewable.py", line 399, in servable
    self.server_doc(title=title, location=location) # type: ignore
    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/shh/projects/holoviz/repos/panel/panel/viewable.py", line 1038, in server_doc
    wrapper = self._design._wrapper(self)
              ^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/shh/projects/holoviz/repos/panel/panel/theme/fast.py", line 261, in _wrapper
    return FastWrapper(design=None, object=model, style=self.theme.style)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/shh/projects/holoviz/repos/panel/panel/reactive.py", line 1610, in __init__
    super().__init__(**params)
  File "/home/shh/projects/holoviz/repos/panel/panel/reactive.py", line 555, in __init__
    super().__init__(**params)
  File "/home/shh/projects/holoviz/repos/panel/panel/reactive.py", line 117, in __init__
    super().__init__(**params)
  File "/home/shh/projects/holoviz/repos/panel/panel/viewable.py", line 704, in __init__
    super().__init__(**params)
  File "/home/shh/projects/holoviz/repos/panel/panel/viewable.py", line 543, in __init__
    super().__init__(**params)
  File "/home/shh/projects/holoviz/repos/panel/panel/viewable.py", line 304, in __init__
    super().__init__(**params)
  File "/home/shh/projects/holoviz/repos/param/param/parameterized.py", line 4177, in __init__
    refs, deps = self.param._setup_params(**params)
                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/shh/projects/holoviz/repos/param/param/parameterized.py", line 1683, in override_initialization
    ret = fn(self_, *args, **kw)
          ^^^^^^^^^^^^^^^^^^^^^^
  File "/home/shh/projects/holoviz/repos/param/param/parameterized.py", line 1967, in _setup_params
    ref, ref_deps, resolved, is_async = self_._resolve_ref(pobj, val)
                                        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/shh/projects/holoviz/repos/param/param/parameterized.py", line 2033, in _resolve_ref
    deps = resolve_ref(value, recursive=pobj.nested_refs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/shh/projects/holoviz/repos/param/param/parameterized.py", line 202, in resolve_ref
    reference = transform_reference(reference)
                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/shh/projects/holoviz/repos/param/param/parameterized.py", line 148, in transform_reference
    arg = transform(arg)
          ^^^^^^^^^^^^^^
  File "/home/shh/projects/holoviz/repos/panel/panel/widgets/base.py", line 255, in _widget_transform
    return obj.param.value if isinstance(obj, Widget) else obj
           ^^^^^^^^^^^^^^^
  File "/home/shh/projects/holoviz/repos/param/param/parameterized.py", line 1890, in __getattr__
    raise AttributeError(f"'{self_.cls.__name__}.param' object has no attribute {attr!r}")
AttributeError: 'FileDownload.param' object has no attribute 'value'. Did you mean: 'values'?

[hoxbro]

Button also break it: pn.widgets.Button(name="Button").servable()

ValueError: ClassSelector parameter 'ReactiveHTMLMetaclass.object' value must be an instance of Viewable, not False.

Traceback (most recent call last):
  File "/home/shh/miniconda3/envs/holoviz/lib/python3.12/site-packages/bokeh/application/handlers/code_runner.py", line 229, in run
    exec(self._code, module.__dict__)
  File "/home/shh/Development/holoviz/example_download_widgets.py", line 16, in <module>
    pn.widgets.Button(name="Button").servable()
  File "/home/shh/projects/holoviz/repos/panel/panel/viewable.py", line 399, in servable
    self.server_doc(title=title, location=location) # type: ignore
    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/shh/projects/holoviz/repos/panel/panel/viewable.py", line 1038, in server_doc
    wrapper = self._design._wrapper(self)
              ^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/shh/projects/holoviz/repos/panel/panel/theme/fast.py", line 261, in _wrapper
    return FastWrapper(design=None, object=model, style=self.theme.style)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/shh/projects/holoviz/repos/panel/panel/reactive.py", line 1610, in __init__
    super().__init__(**params)
  File "/home/shh/projects/holoviz/repos/panel/panel/reactive.py", line 555, in __init__
    super().__init__(**params)
  File "/home/shh/projects/holoviz/repos/panel/panel/reactive.py", line 117, in __init__
    super().__init__(**params)
  File "/home/shh/projects/holoviz/repos/panel/panel/viewable.py", line 704, in __init__
    super().__init__(**params)
  File "/home/shh/projects/holoviz/repos/panel/panel/viewable.py", line 543, in __init__
    super().__init__(**params)
  File "/home/shh/projects/holoviz/repos/panel/panel/viewable.py", line 304, in __init__
    super().__init__(**params)
  File "/home/shh/projects/holoviz/repos/param/param/parameterized.py", line 4177, in __init__
    refs, deps = self.param._setup_params(**params)
                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/shh/projects/holoviz/repos/param/param/parameterized.py", line 1683, in override_initialization
    ret = fn(self_, *args, **kw)
          ^^^^^^^^^^^^^^^^^^^^^^
  File "/home/shh/projects/holoviz/repos/param/param/parameterized.py", line 1972, in _setup_params
    setattr(self, name, resolved)
  File "/home/shh/projects/holoviz/repos/param/param/parameterized.py", line 528, in _f
    return f(self, obj, val)
           ^^^^^^^^^^^^^^^^^
  File "/home/shh/projects/holoviz/repos/param/param/parameterized.py", line 1495, in __set__
    self._validate(val)
  File "/home/shh/projects/holoviz/repos/param/param/parameters.py", line 2182, in _validate
    self._validate_class_(val, self.class_, self.is_instance)
  File "/home/shh/projects/holoviz/repos/param/param/parameters.py", line 2193, in _validate_class_
    raise ValueError(
ValueError: ClassSelector parameter 'ReactiveHTMLMetaclass.object' value must be an instance of Viewable, not False.

[hoxbro]

Did you also test the second case?

[philippjfr]

No, but it works.