Using CESM_share code from CMEPS and CDEPS?

[billsacks]

For the water tracer work, the design @mvertens and I came up with to coordinate water tracer information across CESM components is to have a module in CESM_share that stores this information and can provide it to other components as needed. (This information includes the number of tracers, the names of the tracers, their initial ratio, their identity – e.g., as a particular water isotope – and other, similar information.)

There are a few places where I'd like to use this module from both CMEPS and CDEPS. I'm not clear, though, on what is or isn't allowed in terms of including CESM_share code (shr_) modules within CMEPS and CDEPS.

• In CDEPS: I see usage of shr_ modules, which presumably come from the copies of the CESM_share code that exist in the CDEPS repository
• In CMEPS: I see that there is a small amount of usage of shr_ modules; it's not clear to me where those come from with UFS; is this using the same modules as are present in CDEPS??

Is it acceptable for me to introduce uses of my new shr_wtracers_mod in various places in CMEPS and CDEPS? If, so, would I need to provide either a working copy or a stub of this somewhere for UFS? Note that, in a run without water tracers, any uses of this new module will be a no-op because there won't be any water tracer fields to operate on (num_tracers = 0), so it should be easy to provide a stub version of this if that's an acceptable path.

@mvertens and @DeniseWorthen - I'd especially like to hear your input here. (I welcome input from anyone else, too.)