Pass system environment variables when executing custom command

[woohyunjin06]

Short description 📝

This PR allows sub process (e.g. Plugin) to have access to system environment variables

How to test the changes locally 🧐

Run custom command that require environment variables, run unit test

Checklist ✅

• The code architecture and patterns are consistent with the rest of the codebase.
• The changes have been tested following the documented guidelines.
• The PR includes the label changelog:added, changelog:fixed, or changelog:changed, whenever it should be included in the “Added”, “Fixed” or “Changed” section of the CHANGELOG. Note: when included in the CHANGELOG, the title of the PR will be used as entry, please make sure it is clear and suitable.
• In case the PR introduces changes that affect users, the documentation has been updated.
• In case the PR introduces changes that affect how the cache artifact is generated starting from the TuistGraph.Target, the Constants.cacheVersion has been updated.

[fortmarek]

I'm not sure about writing so much code to MockSystem for testing a very specific thing. I would rather use E2E tests for this:

• Define a new step here for adding a custom env variable
• Update or create a new plugin inside this example repository. A new release will need to be made (I can do this for you if you ping me)
• Invoke that command here - make sure it would fail if the env variable was not passed.

Given the E2E flow for plugins is not as straightforward as I want it to be, I am personally ok for now to merge this without any additional tests. Or if you could simplify the unit test without introducing too much code in MockSystem. I will leave that up to you, let me know 🙂

[woohyunjin06]

Thanks @fortmarek !

As you suggested, I updated create-file plugin in this repository to retrieve content string from the environment variable. And implemented E2E test cases.

My ExampleTuistPlugin implementation is currently in my forked repository and if there is no problem with this change, I will create PR in tuist organization's repository

[fortmarek]

This is great! Please, create a PR against the tuist's ExampleTuistPlugin repo and I'll do a review there 👍

[danieleformichelli]

@woohyunjin06 I have updated the PR to use the new plugin, could you please have a look that everything is ok?

[woohyunjin06]

Thanks @danyf90

The test scenario currently written cannot be completed successfully without tuist-create-file executable file.
So I changed scenario to execute create-file task in the project directory.

I don't know the exact intension of executing create-file task in the current directory, so could you check if it is ok?