Collect code from `ssp_dev` branches in private repos

[khaeru]

Two branches are used heavily in the ScenarioMIP/SSP projects. These contain code and data that should eventually move to message-ix-models as the initial/base/reference implementation of MESSAGEix-GLOBIOM versions and scenarios that will be central in future work. This issue is to collect information and discussion about this work.

The branches are:

message_data branch ssp_dev.

• As of today, this branch is 288 commits ahead of the main branch from which it started.

message_single_country branch SSP_Dev_2023.

• As of today, this branch is 127 commits ahead of the master branch from which it started.

Click here for a table listing some of the items to be collected. (See #276 to update the table.)

Further information

• There is currently no single definitive source of documentation on how these branches are used.

• In some cases, functions or modules in message_data have been replaced with functions or modules in message_single_country, and the former are no longer used/obsolete.

• Migrating these may involve multiple PRs using a variety of approaches.

• The general strategy will be:

  1. Identify atomic pieces of code that can be moved.
  2. Migrate these to message-ix-models.
  3. Adjust usage in message_data and elsewhere to import these from message-ix-models.
  4. Delete the existing code in message_data and/or message_single_country.

  Through (4), the amount of code and data remaining on the two source branches will shrink, and this will make (1) easier for subsequent pieces.

Ways to contribute

• Comment here or on particular lines of the Track migration work #276 diff with details of how code is used (by you or others you know); opinions about which versions of particular code should be preferred; or any other information which may help us make these decisions.