Allow passing on_change_callback for CustomComponents

[raethlein]

Describe your changes

In the past, some custom components have used a patch to register an on_change callback. Recently, we have done some refactoring that broke this workaround. This PR is a suggestion to extend our official API to make the patch redundant.

Note that we only want to pass the on_change_callback and not the args and kwargs.
The register_widget function today uses args and kwargs as keywords to pass to the on_change callback. Besides the unfortunate naming - these are special keywords meant for functions themselves and not for pass-through arguments - we are thinking about deprecating them entirely, since you can wrap the callback easily to pass the arguments.

The way you can use it then looks like the following:

from functools import partial

import streamlit.components.v1 as components

_custom_component = components.declare_component("example", path=build_dir)

callback = partial(lambda x: f"On Change called with {x}", "some-value-for-x")

value = _custom_component("some-arg", other_arg="some-other-arg", on_change=callback)

Without the partial-function

import streamlit.components.v1 as components

_custom_component = components.declare_component("example", path=build_dir)

def create_callback(x):
  return lambda: f"On Change called with {x}"
callback = create_callback("some-value-for-x")

value = _custom_component("some-arg", other_arg="some-other-arg", on_change=callback)

GitHub Issue Link (if applicable)

Closes #3977
Related to victoryhb/streamlit-option-menu#70

Testing Plan

• Explanation of why no additional tests are needed
• Unit Tests (JS and/or Python)
  • A new unit test is added to make sure the on_change callback is called when the value changes during a ScriptRun
• E2E Tests
  • prepare on_change callback test in the option_menu function
• Any manual testing needed?
  • I manually tested it on the example of streamlit-option-menu

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[raethlein]

this is an unrelated drive-by change since the linter complained about wrong typing

[raethlein]

This has to be added if you want to run the tests here standalone like pytest lib/tests/streamlit/components_test.py. In the CI it does not fail due to pure luck as apparently the order of execution of the tests ensures that a runtime exists 🫠

[whitphx]

Hi, this PR looks great,
and as @raethlein suggested in #3977 (comment), I would like to test this patch in my use case.
Is it possible to get a wheel file including this somehow?

[raethlein]

@whitphx great, thanks for trying it out! Each PR generates a wheel file in the CI pipeline, here is the one for this 😊: https://core-previews.s3-us-west-2.amazonaws.com/pr-8633/streamlit-1.34.0-py2.py3-none-any.whl

[whitphx]

Thanks!
I tested it and confirmed my use case was totally covered :D

[raethlein]

@sfc-gh-jcarroll @jrieke Lukas' point makes sense to me. Could you have a quick look and confirm this, please?

[LukasMasuch]

LGTM 👍 But I think we probably want to call this on_change and not on_change_handler to better align with APIs of other commands.

[LukasMasuch]

LGTM 👍 Another way to test it could be to update our component-template tests and update a component to use this callback.