default begin-time dependency format in `flux jobs` about flux-core HOT 2 CLOSED

Valid request! However, this is going to be slightly tricky because of the way dependencies work and how outstanding dependencies are transmitted back to flux jobs from the job-list service.

Dependencies are represented as strings, added by a dependency-add event, then removed by a dependency-remove event. Internally, the outstanding dependencies (holding a job in the DEPEND state) are thus represented as a set of strings. For the begin-time dependency, the string is just begin-time=T, where T is floating-point seconds since the epoch, i.e. the UNIX time. When flux jobs gets the list of current dependencies, it just gets the current set of dependency strings and prints them as is. This is partially done because these dependency strings or descriptions are considered somewhat opaque and extensible.

Given these limitations, there are a couple approaches we could take:

• Have the begin-time dependency plugin represent the time as something more human readable. This would be simplest but has the drawback that any such representation would have to pick a timezone (likely the timezone of the broker process) and use that for the representation. This may not match the user's actual timezone, so this could be confusing (but could be mitigated by appending the timezone to the description)
• Add some special handling for begin-time dependencies in flux jobs or the underlying JobInfo class. The code would need to walk the set of dependencies looking for begin-time=. Since it is known that the remainder of the string is a timestamp, it could parse this and replace with a datetime rendered in the current timezone. This method could be extended to handle other known dependencies in the future if needed.

from flux-core.

Well patching something into JobInfo was pretty easy as a prototype.

For instance, we could show the simple begin time if the job is scheduled to run today, the date otherwise:

flux jobs
       JOBID USER     NAME       ST NTASKS NNODES     TIME INFO
   ƒ6DBbeYzK grondo   hostname    D      1      -        - depends:begin=17:11:55
   ƒ6FuQt6sH grondo   hostname    D      1      -        - depends:begin=Sep23-17:01:55

from flux-core.