[BUG] no_update is not allowed as an output to set_progress for background progress

[lunathanael]

Describe your context
An easy way to replicate te code is using the provided example from Dash Plotly Website. I slightly modified to code by adding a no_update as a return value

• replace the result of pip list | grep dash below

dash                 0.42.0
dash-core-components 0.47.0
dash-html-components 0.16.0
dash-renderer        0.23.0
dash-table           3.6.0

• if frontend related, tell us your Browser, Version and OS

  • OS: [e.g. iOS]
  • Browser [e.g. chrome, safari]
  • Version [e.g. 22]

Describe the bug

Returning dash.no_update as a value in set_progress is not allowed.

Expected behavior

dash.no_update should function as normally intended in callback functions

Screenshots

import time
import os

from dash import Dash, DiskcacheManager, CeleryManager, Input, Output, html, callback, no_update

if 'REDIS_URL' in os.environ:
    # Use Redis & Celery if REDIS_URL set as an env variable
    from celery import Celery
    celery_app = Celery(__name__, broker=os.environ['REDIS_URL'], backend=os.environ['REDIS_URL'])
    background_callback_manager = CeleryManager(celery_app)

else:
    # Diskcache for non-production apps when developing locally
    import diskcache
    cache = diskcache.Cache("./cache")
    background_callback_manager = DiskcacheManager(cache)

app = Dash(__name__, background_callback_manager=background_callback_manager)

app.layout = html.Div(
    [
        html.Div(
            [
                html.P(id="paragraph_id", children=["Button not clicked"]),
                html.Progress(id="progress_bar", value="0"),
            ]
        ),
        html.Button(id="button_id", children="Run Job!"),
        html.Button(id="cancel_button_id", children="Cancel Running Job!"),
    ]
)

@callback(
    output=Output("paragraph_id", "children"),
    inputs=Input("button_id", "n_clicks"),
    background=True,
    running=[
        (Output("button_id", "disabled"), True, False),
        (Output("cancel_button_id", "disabled"), False, True),
        (
            Output("paragraph_id", "style"),
            {"visibility": "hidden"},
            {"visibility": "visible"},
        ),
        (
            Output("progress_bar", "style"),
            {"visibility": "visible"},
            {"visibility": "hidden"},
        ),
    ],
    cancel=Input("cancel_button_id", "n_clicks"),
    progress=[Output("progress_bar", "value"), Output("progress_bar", "max")],
    prevent_initial_call=True
)
def update_progress(set_progress, n_clicks):
    total = 5
    for i in range(total + 1):
        set_progress((no_update, str(total)))
        time.sleep(1)

    return f"Clicked {n_clicks} times"


if __name__ == "__main__":
    app.run(debug=True)