Ruminating on outputs

[o-smirnov]

Some things to consider about cab/recipe outputs:

• I see some outputs.msouts defined, but this seems redundant if there is an inputs.ms with writable: true, because surely that already implies the ms is both an input and an output?

• Explicit File and MS type outputs need to be validated before running perhaps, at least in the sense of checking for valid output filenames

• Implicit File and MS type outputs are currently treated as globs. An example from wsclean.yaml:

    residual:
      dtype: List[File]
      implicit: "{self.prefix}-????-residual.fits"

  ...will turn into a list of matching files when the output is validated. But what if other (preexisting) files match the glob pattern? Should we maybe check timestamps, to ignore pre-existing files? Seems fiddly and non-robust.

• Can we have an output that is a str? A float? I can see use cases for such things, but I don't see my way to a generic and elegant solution (yet).