Need a way to determine what release of checkout_externals was used in a specific CESM tag

[cacraigucar]

Summary of Issue:

External components which maintain standalone capability need to maintain the checkout_externals version. Typically for CAM's case we take a previously tested CESM tag and duplicate the externals used in it. This is now being extended to needing to also maintain the version of checkout_externals. We want to identify and use the version of checkout_externals that was used in a specific CESM tag. Being able to check this easily, becomes more important as time goes on and checkout_externals is only updated sporadically - we need an easy way to determine that it has been updated.

Expected behavior and actual behavior:

An ideal solution would be for the plans page to have a location somewhere on each tag's page which indicates the checkout_externals which was used. Perhaps this could be populated (automatically?) when checkout_externals is brought into the CESM tag. Currently, there is no good way to determine the checkout_externals tag other than cloning cesm and mining the log.

Steps to reproduce the problem. Include externals description file(s) and link to public repository):

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What is the changeset ID of the code, and the machine you are using:

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have you modified the code? If so, it must be committed and available for testing:

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Screen output or log file showing the error message and context:

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@bjandre suggested that I bring @mvertens , @fischer-ncar , @bertinia and possibly @jedwards4b into this discussion.

[fischer-ncar]

There is an easier way to determine the tag version of checkout_externals. You can go to the tag, https://github.com/ESCOMP/cesm/tree/cesm2_0_alpha10a, and see the comment on the version of manage_externals. But that requires the comments to be correct when a new manage_externals tag is pushed.

We should also have something in the cesm ChangeLog that points out changes to manage_externals and cime_config. That would be easy. It'll be a bit harder to place something on the plans page. Maybe a comment in the "Planned Tag Summary" would be enough?