Warn if user checks is_stored for plugin not always saved

[cfuselli]

What is the problem / what does the code in this PR do

This PR addresses the issue of users potentially being unaware when querying for stored data of a plugin in strax that is configured with save_when < ALWAYS (3). In such cases, even if the is_stored function returns False, it might not reflect a lack of data due to processing or storage issues but rather due to the plugin's configuration. This update aims to improve user awareness by providing a warning in such scenarios.

Tested quickly with some single-output and multi-output plugins and seems to work.

[coveralls]

coverage: 91.504% (+0.002%) from 91.502%
when pulling a7840eb on warning-is-stored-never
into 1ce8401 on master.

[WenzDaniel]

Hej @cfuselli you could add within this if-statement something like:

try:
    components = st.get_components('058518', target)
    targets_plugin_made_from = components.loaders.keys()
    # Warn user:
    print('Can be made from: ', targets_plugin_made_from)
except strax.DataNotAvailable:
    # Warn that data cannot be made
    print('cannot be made')

[cfuselli]

Nice but I think it goes way beyond the scope of is_stored, no?
The warning is just intended to inform user of the existence of plugins that are not stored, so that they won't use these plugins to check if something is stored.

[dachengx]

Hey @WenzDaniel. Shal I still mark this as an unsolved thread?

[WenzDaniel]

For me it is fine to move ahead. I take what I can get.

[dachengx]

I just realized that strax.Context.stored_dependencies is the best function for the task @WenzDaniel mentioned.

Let's keep that in mind and update is_stored later if necessary.

[yuema137]

I also tested with a few plugins and it looks fine to me. Regarding Daniel's comment, I'm thinking that we could probably add a is_makable function to tell the users the nearest stored parents that the plugin could be made of.

[yuema137]

@dachengx should we merge this PR soon? I think it's a good warning message for the users.