Implement `micromamba env update`

[jonashaag]

It would be nice to have a way in Micromamba to update an env from an environment.yml. In Mamba this works by mamba env update -n X -f environment.yml.

[wolfv]

I think we can use the current micromamba update -f myenv.yml for that.

We can add a command line option to --prune-to-specs.

[jonashaag]

micromamba update -f myenv.yml seems to ignore myenv.yml.

[wolfv]

I am realizing that maybe that is the desired behavior and micromamba install is all we should ever need?

Let's picture some scenarios -- assuming we have a created environment. What should the ideal command line look like. We could quite easily add the following flags:

• micromamba install -f env.yml -> installs new packages to specs
• micromamba install -f env.yml --update -> installs & updates new packages according to env.yml
• micromamba install -f env.yml --update --prune-to-specs -> installs & updates new packages to specs, removes packages not in the environment but not in env.yml

[jonashaag]

Yes that sounds reasonable as well. What would be the role of micromamba update in that case? Is it just a shorthand to install --update?

[wolfv]

When using install --update we could use the SOLVER_FLAG_INSTALL_ALSO_UPDATES flag. It would be different from update because update doesn't install any new packages.

#1317

[jonashaag]

We just hit this again. Shall we remove the --file option from `update?

[CDTR-MattConroy]

Is there any intention to add a --prune option to be able to remove packages that are not specified in an environment file?

[shenker]

My understanding is that mamba env update -n myenv -f environment.yml --prune will install new packages, update existing packages, and remove extraneous packages so that myenv ends up in the same state as it would be if you did mamba env remove -n myenv && mamba create -n myenv -f environment.yml.

It would be good for an analogous command to exist in micromamba. It would be especially convenient if this command created the environment if it didn't already exist. (E.g., after you run this command, you're guaranteed to end up with myenv matching the given environment.yml file regardless of the initial state or existence of myenv, and the command would get you there in the most efficient way.)

[goyalyashpal]

--prune-to-specs
- @ wolfv at #1455 (comment)

that is very much needed 😃
the issue with env create is that it doesn't use existing cache and has to download all the packages again.

combining this with #2700 issue, this pruning feature will allow to quickly remove the devt dependencies to get a lean environment back again.

[GitHunter0]

What's the current best alternative to micromamba env update -n X -f environment.yml?