Run terraform plan on package

[ndellosa95]

Is your feature request related to a problem? Please describe.
I created a bug issue here related to pants check not running terraform init before terraform validate. IMO, check should also run terraform plan.

Describe the solution you'd like
pants check runs terraform plan after running init and validate.

Describe alternatives you've considered
Check feels like the right goal to me but I'm fairly ambivalent about what the actual goal is called so long as some mechanism to call terraform plan is in place.

[lilatomic]

I think that the check goal is the wrong place for terraform plan. check is described as "Run type checking or the lightest variant of compilation available for a language." In that way, terraform validate is the command that fits under that goal. terraform plan needs to interact with state, which is a reason against including it under check.
I agree that we should have a way of running terraform plan that isn't just "type 'no' at the prompt for apply". Pants wasn't designed with managing infrastructure in mind, so it doesn't have a gamut of goals to map 1:1 to every Terraform command. (at the extreme, Pants having a workspace goal wouldn't really fit). So there isn't really a goal that terraform plan maps to. Given that plan is essentially a dry-run, we could make a "dry run" flag which will toggle between plan and apply (invocation like pants experimental-deploy --dry-run src/tf/my_deployment:stg). That would let you set it as an environment variable as well.
An alternative would be to use the export goal (not yet implemented for Terraform) to do the equivalent of terraform init so you can work out of there with all the commands (that's probably what you'd need to do to run the Terraform-specific commands like import). But given that plan is just a dry-run, I think it would be a bit of a shame to have to break out.
For comparison, Helm allows this by allowing --dry-run to be passed through to the underlying processes.

[agoblet]

Hello there, I would like to implement this feature. I added a draft PR highlighting my approach so far. I'm still figuring out the test suite, so it's not done yet. But I wanted to get in touch already for some early feedback. How do you feel about this change?

[agoblet]

added a unit test as well and removed the Draft from the PR, looking forward to your feedback.

[agoblet]

ping @alonsodomin @lilatomic