feat: add env to activation table

[ruben-arts]

Note

I'm not a 100% happy with the fact that this doesn't work with environment variables that already exist. For example:
I would expect it to expand variables if you would do:

[activation.env]
PATH = "bla/bli/blu:$PATH"
PATH_TO_XACRO = "$PIXI_PROJECT_ROOT/.pixi/envs/default/share/ros/bla/bli/xacro.xacro

But like the scripts, this also isn't cross platform/shell.

That said we made the decision to clean this up and release it as a first version so users that can use it will benefit from it and it would give us more time to come up with a good solution.

[ruben-arts]

@wolfv What do you think? Merge this already (after adding docs) or figuring out a better parsing solution for the variables?

[ruben-arts]

After merging #972 This feature is to simple and will cause confusion

[ruben-arts]

@baszalmstra Do you have some smart ideas on how to easily and in a cross-platform way, add these env vars?
Specifically reusing existing variables:

[activation]
env = { PATH = "$PIXI_PROJECT_ROOT/extra/path:$PATH", MODEL_LOCATION = "$PIXI_PROJECT_ROOT/models"}

One of my ideas would be parsing the strings ourself and use rusts std::env::var(), what do you think about that?

[baszalmstra]

@baszalmstra Do you have some smart ideas on how to easily and in a cross-platform way, add these env vars? Specifically reusing existing variables:

Yeah that could work but its a little bit more tricky because on Windows the separator for the PATH variable is not :' but ;` so you'd have to normalize that too. How do other task executors do this? Did you check taskfile?

[ruben-arts]

Will have to try it out as they seem to just use the direct naming but they do support taskfiles per OS.

[beenje]

After merging #972 This feature is to simple and will cause confusion

Sometimes you really want some variables per environment.
It can be done with activation script, but I personally don't like having to add 2 extra scripts (.sh and .bat) to the repo just for that. Could also need more scripts in case of multi-environments. It's much nicer to be able to keep that in the pixi.toml file.

I currently use the variables per task but when you have several tasks using the same variable(s), it becomes quite verbose. And you might want a variable to be set without defining a specific task.
I think having the same feature as variable per task but per env would be a nice addition. I also really like that those are default you can overwrite from the shell.

[ruben-arts]

He @beenje, Thanks for the input. I completely agree with you. Still need to get back to this PR to test the above discussed change.