[ENH] Implicit "defaults" channel

[AlbertDeFusco]

Starting in version 0.11.0 condarc "channels:" list is ignored.

• If a project yaml does not have any "channels:" listed it is now unusable.
• Some project yaml files have "channels:" but would implicitly rely on "defaults"
  • in an unspecified/tested/studied order

Proposal:

• always use "defaults" with and without explicit channel lists
• implement Conda env create's "nodefaults": https://github.dev/conda/conda/blob/9bf4c1721da4d44739546109a78fb2edb40af95b/conda_env/installers/conda.py#L19
• if "defaults" is not listed in the ordered-list of channels it will go ????

Goal:

• ensure some backward compatibility while still not relying on condarc state

[AlbertDeFusco]

@jbednar and @jlstevens where should defaults go when not supplied in channels and when nodefaults is not also specified? First or last?

Conda env support for implicit utilization of ~/.condarc is to extend the channels listed in the environment.yml file. Meaning that "defaults" (and other channels) as added at the END. https://github.dev/conda/conda/blob/9bf4c1721da4d44739546109a78fb2edb40af95b/conda_env/installers/conda.py#L25

[jbednar]

I vote for implementingnodefaults and for otherwise assuming defaults is in the list.

@jbednar and @jlstevens where should defaults go when not supplied in channels and when nodefaults is not also specified? First or last?

Wherever anaconda-project behaves as it did before. Did it previously act like it was implicitly first, or implicitly last?

[jlstevens]

I will confirm it for myself but I believe it was implicitly last (as Albert mentioned above).

[AlbertDeFusco]

merged and released in 0.11.1