Improve variable alias managament

[jvegreg]

Porting the changes from ESMValGroup/ESMValTool#950 and fixing the issue with the data finder described in ESMValGroup/ESMValTool#1593 and ESMValGroup/ESMValTool#1605

Tasks

• Create an issue to discuss what you are going to do, if you haven't done so already (and add the link at the bottom)
• This pull request has a descriptive title that can be used in a changelog
• Add unit tests
• Public functions should have a numpy-style docstring so they appear properly in the API documentation. For all other functions a one line docstring is sufficient.
• If writing a new/modified preprocessor function, please update the documentation
• Circle/CI tests pass. Status can be seen below your pull request. If the tests are failing, click the link to find out why.
• Codacy code quality checks pass. Status can be seen below your pull request. If there is an error, click the link to find out why. If you suspect Codacy may be wrong, please ask by commenting.
• Please use yamllint to check that your YAML files do not contain mistakes
• If you make backward incompatible changes to the recipe format, make a new pull request in the ESMValTool repository and add the link below

If you need help with any of the tasks above, please do not hesitate to ask by commenting in the issue or pull request.

---

Closes ESMValGroup/ESMValTool#1605

[valeriupredoi]

cheers muchly @jvegasbsc 🍺 in principle am OK with this and I trust there is no other viable way going around these types of variables; but as @bouweandela points out - another layer of complexity for the user to figure out and set? BTW I don't see the documentation entry for it?

[valeriupredoi]

if you resolve los conflictos then it's good from my side, amigo! cool stuff 🍺

[bouweandela]

It would be great if you could add documentation for the new feature

[jvegreg]

Doc added, I also rebased it

[bouweandela]

Looks good to me, but someone would need to test this. @sloosvel or @schlunma would one of you have time to run one or more recipes to test the new and old functionality?

[schlunma]

I can run a recipe in the background. What changes are to be expected?

[bouweandela]

Great! The following variables have changed names between cmip5 and cmip6:

- ['sic', 'siconc']
- ['sit', 'sithick']
- ['tro3', 'o3']
- ['usi', 'siu']
- ['vsi', 'siv'] 

The expected outcome from this pull request is that it works if you use one of these variables with

1. the cmip5 name and cmip5 datasets (as currently already works)
2. the cmip6 name and cmip6 datasets (as currently already works)
3. the cmip5 name and a mix of cmip5 and cmip6 datasets (currently broken)
4. the cmip6 name and a mix of cmip5 and cmip6 datasets (currently broken)

[schlunma]

Tested successfully with this recipe:

documentation:
  description: |
    Recipe that demonstrates various uses of the preprocessor derive functionality.

  authors:
    - andela_bouwe

  maintainer:
    - righi_mattia

  projects:
    - c3s-magic

TEST: &alb_cmip5
  mip: Amon
  exp: historical
  start_year: 2004
  end_year: 2005
  additional_datasets:
    - {dataset: GFDL-CM3,     project: CMIP5, ensemble: r1i1p1}
    - {dataset: IPSL-CM6A-LR, project: CMIP6, ensemble: r1i1p1f1, grid: gr}


diagnostics:

  cmip5:
    description: Test variable derivation for CMIP5 models.
    variables:
      usi:
        <<: *alb_cmip5
        start_year: 1979
        end_year: 1979
        additional_datasets:
          - {dataset: GFDL-CM3,     project: CMIP5, ensemble: r1i1p1, mip: day}
          - {dataset: MPI-ESM1-2-HR,project: CMIP6, ensemble: r1i1p1f1, grid: gn, mip: SImon}
      vsi:
        <<: *alb_cmip5
        start_year: 1979
        end_year: 1979
        additional_datasets:
          - {dataset: GFDL-CM3,     project: CMIP5, ensemble: r1i1p1, mip: day}
          - {dataset: MPI-ESM1-2-HR,project: CMIP6, ensemble: r1i1p1f1, grid: gn, mip: SImon}
      siu:
        <<: *alb_cmip5
        start_year: 1979
        end_year: 1979
        additional_datasets:
          - {dataset: GFDL-CM3,     project: CMIP5, ensemble: r1i1p1, mip: day}
          - {dataset: MPI-ESM1-2-HR,project: CMIP6, ensemble: r1i1p1f1, grid: gn, mip: SImon}
      siv:
        <<: *alb_cmip5
        start_year: 1979
        end_year: 1979
        additional_datasets:
          - {dataset: GFDL-CM3,     project: CMIP5, ensemble: r1i1p1, mip: day}
          - {dataset: MPI-ESM1-2-HR,project: CMIP6, ensemble: r1i1p1f1, grid: gn, mip: SImon}
      sic:
        <<: *alb_cmip5
        start_year: 1979
        end_year: 1979
        additional_datasets:
          - {dataset: GFDL-CM3,     project: CMIP5, ensemble: r1i1p1, mip: day}
          - {dataset: MPI-ESM1-2-HR,project: CMIP6, ensemble: r1i1p1f1, grid: gn, mip: SImon}
      sit:
        <<: *alb_cmip5
        start_year: 1979
        end_year: 1979
        additional_datasets:
          - {dataset: GFDL-CM3,     project: CMIP5, ensemble: r1i1p1, mip: day}
          - {dataset: MPI-ESM1-2-HR,project: CMIP6, ensemble: r1i1p1f1, grid: gn, mip: SImon}
      siconc:
        <<: *alb_cmip5
        start_year: 1979
        end_year: 1979
        additional_datasets:
          - {dataset: GFDL-CM3,     project: CMIP5, ensemble: r1i1p1, mip: day}
          - {dataset: MPI-ESM1-2-HR,project: CMIP6, ensemble: r1i1p1f1, grid: gn, mip: SImon}
      sithick:
        <<: *alb_cmip5
        start_year: 1979
        end_year: 1979
        additional_datasets:
          - {dataset: GFDL-CM3,     project: CMIP5, ensemble: r1i1p1, mip: day}
          - {dataset: MPI-ESM1-2-HR,project: CMIP6, ensemble: r1i1p1f1, grid: gn, mip: SImon}
      tro3:
        <<: *alb_cmip5
      o3:
        <<: *alb_cmip5
    scripts: null