What's the best way to give SwerveDriveKinematics module headings?

[Gold856]

Currently, SwerveDriveKinematics maintains its own internal module states used solely for maintaining module headings when a ChassisSpeeds is all zero in toSwerveModuleStates. There's issues and discussion about this at #5029, #5123, and #5167. There's been a little discussion on whether or not to keep the internal module states. There are a few ways to deal with this:

1. Keep the internal states and allow the user to modify them. This would break the fewest things.
2. Remove the internal states and let the user handle an all zero ChassisSpeeds. The thing is, every team will have to deal with this, so maybe we should just deal with it for them. toSwerveModuleStates currently deals with it for teams.
3. Remove the internal states and the user pass all the module headings to toSwerveModuleStates to use for an all zero ChassisSpeeds. The API would look kind of weird (why am I passing in headings to get module states back?) but getting module headings into an array is debatably easier than checking ChassisSpeeds and then also getting module headings and placing them inside a SwerveModuleStates array.

Thoughts?

[calcmogul]

Merging #5123 and fixing #5167 is the ideal way forward, in my opinion.

[Gold856]

Do we need users to pass in whole module states, or just headings? Obviously, only headings are needed, but maybe it's easier for teams if we take module states?

[calcmogul]

Is it easier though? Making intermediate SwerveModuleState objects for just heading seems like more work than passing headings directly to reset().

[Gold856]

Yeah, you're right, I was thinking teams might create SwerveModuleState objects for something else, but there's not a use case for that. So that means SwerveDriveKinematics can just store an array of Rotation2d objects and they can be provided through the constructor or reset().

[auscompgeek]

FWIW there are a few teams out there that turn the modules into an X pattern (pointing towards the centre) to stop and prevent the robot sliding in any particular direction.