Feature flags being set by a file is dangerous

[julianstirling]

I think feature flags being set by import in any file is confusing and will cause problems in the future. It means that adding a new Thing to a configuration can change the behaviour of other base things. For example if someone turned a feature flag on in a custom extension in the microscope it changes the base microscope behaviour. I didn't see that this was the mechanism before it was merged as part of an unrelated MR, but I think it is likely to cause problems.

I would be in favour of changing this before any release

I would suggest rather than using

lt.FEATURE_FLAGS.validate_properties_on_set = True

to turn on a feature flag instead. I would only turn them on and off in the configuration, however any file that requires a flag to be on or off could do:

lt.feature_flags.require = {"validate_properties_on_set", True}

This way, it is very clear what to do if two things require something incompatible. It will also allow a Thing to do:

lt.feature_flags.require = {"feature_from_future_version", False}

And as it is a string LabThings could warn that this feature doesn't exits rather than error. Allowing code to run on old versions as long as the feature flag was required not to exists.