add environment variable expansion for environment variables

[rafaelmartins]

Description

This closes #12645.

Checklist - did you ...

• Add a file to the news directory (using the template) for the next release's release notes?
• Add / update necessary tests?
• Add / update outdated documentation?

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[rafaelmartins]

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[jezdez]

As mentioned in #12074 I don't think we should pile on env update like this, this is broadening the scope of the config parsing differences between different parts of conda, which is opposite to what we should be doing.

IOW, this really needs a refactoring.

#12074 (comment) is an important insight:

[..] but unfortunately there exists multiple classes in conda for doing this. In conda, there is both conda and conda_env and both of these modules have their own classes and functions for parsing configuration, specifically YAML files. This is because conda_env used to be its own project and was brought in to the main conda code sometime ago.

#11633 remains true and I feel we're working backwards here basically.

[rafaelmartins]

As mentioned in #12074 I don't think we should pile on env update like this, this is broadening the scope of the config parsing differences between different parts of conda, which is opposite to what we should be doing.

IOW, this really needs a refactoring.

#12074 (comment) is an important insight:

[..] but unfortunately there exists multiple classes in conda for doing this. In conda, there is both conda and conda_env and both of these modules have their own classes and functions for parsing configuration, specifically YAML files. This is because conda_env used to be its own project and was brought in to the main conda code sometime ago.

#11633 remains true and I feel we're working backwards here basically.

do you have a suggestion of proper design for this?

[travishathaway]

@rafaelmartins,

The proper design for this would essentially see us adding conda env abilities (e.g. being about to read directly from an environment file using conda update). Because of that, we might deprecate the usage of conda env commands in the future (this still isn't a sure thing though).

Therefore, we are currently hesitant about adding new features/abilities to anything under conda env. I hope you understand, and I apologize for not communicating that more effectively earlier.