Support setting the --environment flag via env var

[mariusvniekerk]

Problem description

When running a pixi task in an config that has >1 environment and the task is defined in default env pixi will ask you to specify the environment

$ pixi run test_sdk
  × the task 'install_sdk' is ambiguous
  help: These environments provide the task 'install_sdk': default, engine
        
        Specify the '--environment' flag to run the task in a specific environment, e.g:.
        
                pixi run --environment default install_sdk

It would be a nice ux improvement to allow setting the environment flag by means of the PIXI_ENVIRONMENT_NAME env var

$ PIXI_ENVIRONMENT_NAME=default pixi run test_sdk

That will allow a bunch of associated tasks to be more easily coordinated from a higher order place (or using the env var as a matrix in things like github actions)

[ruben-arts]

I'm trying to understand the use-case, as I think it would be more transparent in GitHub actions if you do:

pixi run -e $PIXI_ENVIRONMENT_NAME install_sdk

The problem I see is that people unexpectedly start running with different environments than they expect, thus we would need to add more logging or other logic to make sure that doesn't happen.

[baszalmstra]

Note that once #900 is merged this will work out of the box.

[pavelzw]

I like this approach since this ensures that you are running the proper commands when you are in pixi shell or you did the activation with eval "$(pixi shell-hook)" and direnv.

Maybe also add the behavior that you don't activate again if the env var is already set? But this might be a bit too much magic...

[baszalmstra]

I think there are two cases:

1. You already activated the environment through shell-hook or shell, in that case, I also think it makes sense that we default the environment to the currently activated environment.
2. You have not yet activated an environment. This is the case that @ruben-arts is talking about I think.

We could also look at the PIXI_PROJECT_MANIFEST variable and only if that points to the same path as the current project use PIXI_ENVIRONMENT_NAME as the default. We could also short-circuit activation if the environment is already activated based on that environment variable.

WDYT?

[mariusvniekerk]

I think as long as we print something when this env var is actually set the "magic" behavior that may exist goes away

[ruben-arts]

We've decided that we want to implement as @baszalmstra describes. Adding the warning as @mariusvniekerk describes is a nice to have.

[ruben-arts]

Fixed in: #1080