`FMSControlData` field data missing in DataLog capture

[jwbonner]

We've had multiple bug reports on AdvantageScope (Mechanical-Advantage/AdvantageScope#365 and Mechanical-Advantage/AdvantageScope#346) which are triggered by logs where the FMSControlData field never updates while the DS:enabled field is valid (example below). AdvantageScope currently assumes that all fields containing the enabled state are equivalent, so this causes significant issues by making it look like the robot was never enabled (of course, the temporary workaround is for AdvantageScope to simply prioritize the DS:enabled field when available).

Log files with this behavior are attached to the issues linked above. It's unclear whether the FMSControlData topic is being updated on NT in the first place, or if this is specifically an issue with capturing the updates to DataLog.

[jwbonner]

Per this comment, it seems like the issue occurs when starting DataLogManager before disabling NT logging. The WPILOG includes the start and finish records appropriately, which is technically correct but causes the unintuitive behavior of making the NT topics appear as valid fields in both AdvantageScope and the DataLog tool (since they existed very briefly).

Theoretically it would be possible to detect these kinds of meaningless fields when parsing the log (a finish record that appears very soon after a start record), but it also seems like this behavior from DataLogManager is less than ideal given the common use case of configuring and starting the logger at program startup (potentially in the "wrong" order). Maybe one potential solution would be to wait to start NT capture until after the Robot constructor exits?