pn.cache(hash_funcs=custom_funcs, ...) are not applied recursively (ie. at all)

[tomascsantos]

ALL software version info

panel==0.14.1

Description of expected behavior and the observed behavior

First, feedback: custom hashing functions is super hard to debug. I'm in deep. Better error messages would be nice bonus to this fix

Complete, minimal, self-contained example code that reproduces the issue

I ran the below code, and pressed the button kicking off the stack trace..

import panel as pn
from sqlalchemy import select, text

import ptvsd
ptvsd.enable_attach(address=('localhost', 5678))
print('Ready to attach the VS Code debugger')
ptvsd.wait_for_attach()  # Only include this line if you always want to attach the debugger

sqlalchemy_select = select(text('hello world'))

# pulling strait from the function that determines matches for custom hash funcs
select_type = pn.io.cache._get_fqn(sqlalchemy_select)
print(select_type)

hash_funcs = {
    select_type: lambda x: 'tmp'.encode(),
}


@pn.cache(hash_funcs=hash_funcs)
def callback(event):
    print('we hit database')
    return 'hello'


btn = pn.widgets.Button(name="test")
btn.on_click(callback)

pn.Column(btn).servable()

Stack traceback

When I click the button, we can see in the Locals view, that args=(<sqlalchemy....>,). Note that it is a tuple

Stepping into compute_hash... and down a few more...
Note that the fqn_type is builtins.tuple... ok fair enough.

So it selected function: _contianer_hash to take it apart.
(Also note we have hash_funcs={my custom funcs} still... but not for long...)

Now we have lost our custom hash_funcs :(

So I have to always match on tuple if I want anything to work. This seems like a bug to me.

Screenshots or screencasts of the bug in action

Finally the not-very-helpful error message:

Traceback (most recent call last):
  File "/opt/anaconda3/envs/holoviz/lib/python3.9/site-packages/bokeh/server/protocol_handler.py", line 97, in handle
    work = await handler(message, connection)
  File "/opt/anaconda3/envs/holoviz/lib/python3.9/site-packages/bokeh/server/session.py", line 95, in _needs_document_lock_wrapper
    result = func(self, *args, **kwargs)
  File "/opt/anaconda3/envs/holoviz/lib/python3.9/site-packages/bokeh/server/session.py", line 289, in _handle_patch
    message.apply_to_document(self.document, self)
  File "/opt/anaconda3/envs/holoviz/lib/python3.9/site-packages/bokeh/protocol/messages/patch_doc.py", line 115, in apply_to_document
    invoke_with_curdoc(doc, lambda: doc.apply_json_patch(self.content, setter))
  File "/opt/anaconda3/envs/holoviz/lib/python3.9/site-packages/bokeh/document/callbacks.py", line 408, in invoke_with_curdoc
    return f()
  File "/opt/anaconda3/envs/holoviz/lib/python3.9/site-packages/bokeh/protocol/messages/patch_doc.py", line 115, in <lambda>
    invoke_with_curdoc(doc, lambda: doc.apply_json_patch(self.content, setter))
  File "/opt/anaconda3/envs/holoviz/lib/python3.9/site-packages/bokeh/document/document.py", line 391, in apply_json_patch
    DocumentPatchedEvent.handle_json(self, event_json, references, setter)
  File "/opt/anaconda3/envs/holoviz/lib/python3.9/site-packages/bokeh/document/events.py", line 259, in handle_json
    handler(doc, event_json, references, setter)
  File "/opt/anaconda3/envs/holoviz/lib/python3.9/site-packages/bokeh/document/events.py", line 300, in _handle_json
    cb(event_json["msg_data"])
  File "/opt/anaconda3/envs/holoviz/lib/python3.9/site-packages/bokeh/document/callbacks.py", line 355, in trigger_json_event
    model._trigger_event(event)
  File "/opt/anaconda3/envs/holoviz/lib/python3.9/site-packages/bokeh/util/callback_manager.py", line 119, in _trigger_event
    self.document.callbacks.notify_event(cast(Model, self), event, invoke)
  File "/opt/anaconda3/envs/holoviz/lib/python3.9/site-packages/bokeh/document/callbacks.py", line 247, in notify_event
    invoke_with_curdoc(doc, callback_invoker)
  File "/opt/anaconda3/envs/holoviz/lib/python3.9/site-packages/bokeh/document/callbacks.py", line 408, in invoke_with_curdoc
    return f()
  File "/opt/anaconda3/envs/holoviz/lib/python3.9/site-packages/bokeh/util/callback_manager.py", line 115, in invoke
    cast(EventCallbackWithEvent, callback)(event)
  File "/opt/anaconda3/envs/holoviz/lib/python3.9/site-packages/panel/reactive.py", line 428, in _server_event
    self._comm_event(doc, event)
  File "/opt/anaconda3/envs/holoviz/lib/python3.9/site-packages/panel/reactive.py", line 415, in _comm_event
    state._handle_exception(e)
  File "/opt/anaconda3/envs/holoviz/lib/python3.9/site-packages/panel/io/state.py", line 399, in _handle_exception
    raise exception
  File "/opt/anaconda3/envs/holoviz/lib/python3.9/site-packages/panel/reactive.py", line 413, in _comm_event
    self._process_bokeh_event(doc, event)
  File "/opt/anaconda3/envs/holoviz/lib/python3.9/site-packages/panel/reactive.py", line 350, in _process_bokeh_event
    self._process_event(event)
  File "/opt/anaconda3/envs/holoviz/lib/python3.9/site-packages/panel/widgets/button.py", line 184, in _process_event
    self.clicks += 1
  File "/opt/anaconda3/envs/holoviz/lib/python3.9/site-packages/param/parameterized.py", line 367, in _f
    instance_param.__set__(obj, val)
  File "/opt/anaconda3/envs/holoviz/lib/python3.9/site-packages/param/parameterized.py", line 369, in _f
    return f(self, obj, val)
  File "/opt/anaconda3/envs/holoviz/lib/python3.9/site-packages/param/__init__.py", line 625, in __set__
    super(Dynamic,self).__set__(obj,val)
  File "/opt/anaconda3/envs/holoviz/lib/python3.9/site-packages/param/parameterized.py", line 369, in _f
    return f(self, obj, val)
  File "/opt/anaconda3/envs/holoviz/lib/python3.9/site-packages/param/parameterized.py", line 1248, in __set__
    obj.param._call_watcher(watcher, event)
  File "/opt/anaconda3/envs/holoviz/lib/python3.9/site-packages/param/parameterized.py", line 2039, in _call_watcher
    self_._execute_watcher(watcher, (event,))
  File "/opt/anaconda3/envs/holoviz/lib/python3.9/site-packages/param/parameterized.py", line 2021, in _execute_watcher
    watcher.fn(*args, **kwargs)
  File "/Users/tcastrosantos/Documents/dashboard-portal/dashboards/bms-developers/cycle-explorer/mvp.py", line 27, in callback
    return fetch_from_db(sqlalchemy_select)
  File "/opt/anaconda3/envs/holoviz/lib/python3.9/site-packages/panel/io/cache.py", line 337, in wrapped_func
    hash_value = compute_hash(func, hash_funcs, hash_args, hash_kwargs)
  File "/opt/anaconda3/envs/holoviz/lib/python3.9/site-packages/panel/io/cache.py", line 270, in compute_hash
    hasher.update(_generate_hash(args, hash_funcs))
  File "/opt/anaconda3/envs/holoviz/lib/python3.9/site-packages/panel/io/cache.py", line 200, in _generate_hash
    hash_value = _generate_hash_inner(obj, hash_funcs)
  File "/opt/anaconda3/envs/holoviz/lib/python3.9/site-packages/panel/io/cache.py", line 177, in _generate_hash_inner
    raise ValueError(
ValueError: User hash function <function _container_hash at 0x7f9050cccee0> failed for input (<sqlalchemy.sql.selectable.Select object at 0x7f90517cc940>,) with following error: ValueError("Could not hash object of type function").